From 86a996c3efddb1c03c1e011ed1298101e63b0ef9 Mon Sep 17 00:00:00 2001
From: Xi Liu <xiliuant@gmail.com>
Date: Mon, 12 Dec 2016 09:19:49 -0800
Subject: [PATCH 1/2] Enable checkstyle plugin for distributedlog-protocol
 module

---
 distributedlog-build-tools/pom.xml            |  30 ++
 .../resources/distributedlog/checkstyle.xml   | 443 ++++++++++++++++++
 .../resources/distributedlog/suppressions.xml |  29 ++
 distributedlog-protocol/pom.xml               |  33 ++
 .../java/com/twitter/distributedlog/DLSN.java |  67 +--
 .../EnvelopedRecordSetReader.java             |  14 +-
 .../EnvelopedRecordSetWriter.java             |  25 +-
 .../com/twitter/distributedlog/LogRecord.java |  75 +--
 .../twitter/distributedlog/LogRecordSet.java  |  23 +-
 .../distributedlog/LogRecordWithDLSN.java     |  26 +-
 .../twitter/distributedlog/RecordStream.java  |   6 +-
 .../DistributedLogAnnotations.java            |   3 +
 .../annotations/package-info.java             |  21 +
 .../exceptions/AlreadyClosedException.java    |   6 +-
 .../AlreadyTruncatedTransactionException.java |   4 +-
 .../exceptions/BKTransmitException.java       |   6 +-
 .../exceptions/ChecksumFailedException.java   |   3 +
 .../exceptions/DLClientClosedException.java   |   3 +
 .../exceptions/DLException.java               |   4 +-
 .../exceptions/DLIllegalStateException.java   |   3 +
 .../exceptions/EndOfStreamException.java      |   3 +
 .../exceptions/FlushException.java            |   4 +-
 .../exceptions/IdleReaderException.java       |   5 +
 .../exceptions/InternalServerException.java   |   3 +
 .../InvalidEnvelopedEntryException.java       |   2 +-
 .../InvalidStreamNameException.java           |   3 +
 .../exceptions/LockCancelledException.java    |   3 +
 .../exceptions/LockingException.java          |   4 +-
 .../exceptions/LogEmptyException.java         |   4 +-
 .../exceptions/LogExistsException.java        |   2 +-
 .../exceptions/LogNotFoundException.java      |   4 +-
 .../exceptions/LogReadException.java          |   1 -
 .../exceptions/LogRecordTooLongException.java |   5 +
 .../exceptions/MetadataException.java         |   3 +
 .../NotYetImplementedException.java           |   3 +
 .../exceptions/OverCapacityException.java     |   6 +
 .../OwnershipAcquireFailedException.java      |   5 +
 .../exceptions/ReadCancelledException.java    |   3 +
 .../RegionUnavailableException.java           |   5 +
 .../exceptions/RequestDeniedException.java    |   3 +
 .../exceptions/RetryableReadException.java    |   3 +
 .../ServiceUnavailableException.java          |   3 +
 .../exceptions/StreamNotReadyException.java   |   3 +
 .../StreamUnavailableException.java           |   3 +
 .../exceptions/TooManyStreamsException.java   |   3 +
 .../TransactionIdOutOfOrderException.java     |   3 +
 .../exceptions/UnexpectedException.java       |   3 +
 .../UnsupportedMetadataVersionException.java  |   3 +
 .../exceptions/WriteCancelledException.java   |  11 +-
 .../exceptions/WriteException.java            |   6 +-
 .../exceptions/package-info.java              |  21 +
 .../distributedlog/io/CompressionCodec.java   |   5 +-
 .../distributedlog/io/CompressionUtils.java   |  15 +-
 .../io/IdentityCompressionCodec.java          |  15 +-
 .../io/LZ4CompressionCodec.java               |  37 +-
 .../distributedlog/io/package-info.java       |  21 +
 .../twitter/distributedlog/package-info.java  |  21 +
 .../distributedlog/util/BitMaskUtils.java     |  13 +-
 .../distributedlog/util/ProtocolUtils.java    |   5 +-
 .../distributedlog/util/package-info.java     |  21 +
 .../com/twitter/distributedlog/TestDLSN.java  |   7 +-
 .../distributedlog/TestLogRecordSet.java      |  17 +-
 pom.xml                                       |   1 +
 63 files changed, 957 insertions(+), 178 deletions(-)
 create mode 100644 distributedlog-build-tools/pom.xml
 create mode 100644 distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
 create mode 100644 distributedlog-build-tools/src/main/resources/distributedlog/suppressions.xml
 create mode 100644 distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/package-info.java
 create mode 100644 distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/package-info.java
 create mode 100644 distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/package-info.java
 create mode 100644 distributedlog-protocol/src/main/java/com/twitter/distributedlog/package-info.java
 create mode 100644 distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/package-info.java

diff --git a/distributedlog-build-tools/pom.xml b/distributedlog-build-tools/pom.xml
new file mode 100644
index 000000000..45b0b8105
--- /dev/null
+++ b/distributedlog-build-tools/pom.xml
@@ -0,0 +1,30 @@
+<?xml version="1.0"?>
+<!--
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You under the Apache License, Version 2.0
+   (the "License"); you may not use this file except in compliance with
+   the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.twitter</groupId>
+    <artifactId>distributedlog</artifactId>
+    <version>0.4.0-incubating-SNAPSHOT</version>
+    <relativePath>../pom.xml</relativePath>
+  </parent>
+  <artifactId>distributedlog-build-tools</artifactId>
+  <name>Apache DistributedLog :: Build Tools</name>
+  <version>0.4.0-incubating-SNAPSHOT</version>
+</project>
diff --git a/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml b/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
new file mode 100644
index 000000000..45be45e16
--- /dev/null
+++ b/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
@@ -0,0 +1,443 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+    Licensed to the Apache Software Foundation (ASF) under one or more
+    contributor license agreements.  See the NOTICE file distributed with
+    this work for additional information regarding copyright ownership.
+    The ASF licenses this file to You under the Apache License, Version 2.0
+    (the "License"); you may not use this file except in compliance with
+    the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+<!DOCTYPE module PUBLIC
+    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
+    "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+
+<!-- This is a checkstyle configuration file. For descriptions of
+what the following rules do, please see the checkstyle configuration
+page at http://checkstyle.sourceforge.net/config.html -->
+
+<module name="Checker">
+
+  <module name="FileTabCharacter">
+    <!-- Checks that there are no tab characters in the file. -->
+  </module>
+
+  <module name="RegexpSingleline">
+    <!-- Checks that TODOs don't have stuff in parenthesis, e.g., username. -->
+    <property name="format" value="((//.*)|(\*.*))TODO\(" />
+    <property name="message" value="TODO comments must not include usernames." />
+    <property name="severity" value="error" />
+  </module>
+
+  <module name="RegexpSingleline">
+    <property name="format" value="\s+$"/>
+    <property name="message" value="Trailing whitespace"/>
+    <property name="severity" value="error"/>
+  </module>
+
+  <module name="RegexpSingleline">
+    <property name="format" value="Throwables.propagate\("/>
+    <property name="message" value="Throwables.propagate is deprecated"/>
+    <property name="severity" value="error"/>
+  </module>
+
+  <!-- Prevent *Tests.java as tools may not pick them up -->
+  <module name="RegexpOnFilename">
+    <property name="fileNamePattern" value=".*Tests\.java$" />
+  </module>
+
+  <!-- Allow use of comment to suppress javadocstyle -->
+  <module name="SuppressionCommentFilter">
+    <property name="offCommentFormat" value="CHECKSTYLE.OFF\: ([\w\|]+)"/>
+    <property name="onCommentFormat" value="CHECKSTYLE.ON\: ([\w\|]+)"/>
+    <property name="checkFormat" value="$1"/>
+  </module>
+  <module name="SuppressionFilter">
+    <property name="file" value="${checkstyle.suppressions.file}" default="suppressions.xml" />
+  </module>
+
+  <!-- Check that every module has a package-info.java -->
+  <module name="JavadocPackage"/>
+
+  <!-- All Java AST specific tests live under TreeWalker module. -->
+  <module name="TreeWalker">
+
+    <module name="TodoComment">
+      <!-- Checks that disallowed strings are not used in comments.  -->
+      <property name="format" value="(FIXME)|(XXX)|(@author)" />
+    </module>
+
+    <!--
+
+    IMPORT CHECKS
+
+    -->
+
+    <module name="RedundantImport">
+      <!-- Checks for redundant import statements. -->
+      <property name="severity" value="error"/>
+      <message key="import.redundancy"
+               value="Redundant import {0}."/>
+    </module>
+
+    <module name="ImportOrder">
+      <!-- Checks for out of order import statements. -->
+      <property name="severity" value="error"/>
+      <!-- This ensures that static imports go first. -->
+      <property name="option" value="top"/>
+      <property name="sortStaticImportsAlphabetically" value="true"/>
+      <property name="tokens" value="STATIC_IMPORT, IMPORT"/>
+      <message key="import.ordering"
+               value="Import {0} appears after other imports that it should precede"/>
+    </module>
+
+    <module name="AvoidStarImport">
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="IllegalImport">
+      <property name="illegalPkgs" value="autovalue.shaded, avro.shaded, com.google.api.client.repackaged, com.google.appengine.repackaged, io.netty.util.internal"/>
+    </module>
+
+    <module name="RedundantModifier">
+      <!-- Checks for redundant modifiers on various symbol definitions.
+        See: http://checkstyle.sourceforge.net/config_modifier.html#RedundantModifier
+      -->
+      <property name="tokens" value="METHOD_DEF, VARIABLE_DEF, ANNOTATION_FIELD_DEF, INTERFACE_DEF, CLASS_DEF, ENUM_DEF"/>
+    </module>
+
+    <!--
+        IllegalImport cannot blacklist classes, and c.g.api.client.util is used for some shaded
+        code and some useful code. So we need to fall back to Regexp.
+    -->
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="com\.google\.api\.client\.util\.(ByteStreams|Charsets|Collections2|Joiner|Lists|Maps|Objects|Preconditions|Sets|Strings|Throwables)"/>
+    </module>
+
+    <!--
+         Require static importing from Preconditions.
+    -->
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="^import com.google.common.base.Preconditions;$"/>
+      <property name="message" value="Static import functions from Guava Preconditions"/>
+    </module>
+
+    <module name="UnusedImports">
+      <property name="severity" value="error"/>
+      <property name="processJavadoc" value="true"/>
+      <message key="import.unused"
+               value="Unused import: {0}."/>
+    </module>
+
+    <!--
+
+    JAVADOC CHECKS
+
+    -->
+
+    <!-- Checks for Javadoc comments.                     -->
+    <!-- See http://checkstyle.sf.net/config_javadoc.html -->
+    <module name="JavadocMethod">
+      <property name="scope" value="protected"/>
+      <property name="severity" value="error"/>
+      <property name="allowMissingJavadoc" value="true"/>
+      <property name="allowMissingParamTags" value="true"/>
+      <property name="allowMissingReturnTag" value="true"/>
+      <property name="allowMissingThrowsTags" value="true"/>
+      <property name="allowThrowsTagsForSubclasses" value="true"/>
+      <property name="allowUndeclaredRTE" value="true"/>
+    </module>
+
+    <!-- Check that paragraph tags are used correctly in Javadoc. -->
+    <module name="JavadocParagraph"/>
+
+    <module name="JavadocType">
+      <property name="scope" value="protected"/>
+      <property name="severity" value="error"/>
+      <property name="allowMissingParamTags" value="true"/>
+    </module>
+
+    <module name="JavadocStyle">
+      <property name="severity" value="error"/>
+      <property name="checkHtml" value="true"/>
+    </module>
+
+    <!--
+
+    NAMING CHECKS
+
+    -->
+
+    <!-- Item 38 - Adhere to generally accepted naming conventions -->
+
+    <module name="PackageName">
+      <!-- Validates identifiers for package names against the
+        supplied expression. -->
+      <!-- Here the default checkstyle rule restricts package name parts to
+        seven characters, this is not in line with common practice at Google.
+      -->
+      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]{1,})*$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="TypeNameCheck">
+      <!-- Validates static, final fields against the
+      expression "^[A-Z][a-zA-Z0-9]*$". -->
+      <metadata name="altname" value="TypeName"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="ConstantNameCheck">
+      <!-- Validates non-private, static, final fields against the supplied
+      public/package final fields "^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$". -->
+      <metadata name="altname" value="ConstantName"/>
+      <property name="applyToPublic" value="true"/>
+      <property name="applyToProtected" value="true"/>
+      <property name="applyToPackage" value="true"/>
+      <property name="applyToPrivate" value="false"/>
+      <property name="format" value="^([A-Z][A-Za-z0-9_]*|FLAG_.*)$"/>
+      <message key="name.invalidPattern"
+               value="Variable ''{0}'' should be in ALL_CAPS (if it is a constant) or be private (otherwise)."/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="StaticVariableNameCheck">
+      <!-- Validates static, non-final fields against the supplied
+      expression "^[a-z][a-zA-Z0-9]*_?$". -->
+      <metadata name="altname" value="StaticVariableName"/>
+      <property name="applyToPublic" value="true"/>
+      <property name="applyToProtected" value="true"/>
+      <property name="applyToPackage" value="true"/>
+      <property name="applyToPrivate" value="true"/>
+      <property name="format" value="^[a-z][a-zA-Z0-9]*_?$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="MemberNameCheck">
+      <!-- Validates non-static members against the supplied expression. -->
+      <metadata name="altname" value="MemberName"/>
+      <property name="applyToPublic" value="true"/>
+      <property name="applyToProtected" value="true"/>
+      <property name="applyToPackage" value="true"/>
+      <property name="applyToPrivate" value="true"/>
+      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="MethodNameCheck">
+      <!-- Validates identifiers for method names. -->
+      <metadata name="altname" value="MethodName"/>
+      <property name="format" value="^[a-z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="ParameterName">
+      <!-- Validates identifiers for method parameters against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="LocalFinalVariableName">
+      <!-- Validates identifiers for local final variables against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="LocalVariableName">
+      <!-- Validates identifiers for local variables against the
+        expression "^[a-z][a-zA-Z0-9]*$". -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Type parameters must be either one of the four blessed letters
+    T, K, V, W, X or else be capital-case terminated with a T,
+    such as MyGenericParameterT -->
+    <module name="ClassTypeParameterName">
+      <property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="MethodTypeParameterName">
+      <property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="InterfaceTypeParameterName">
+      <property name="format" value="^(((T|K|V|W|X)[0-9]*)|([A-Z][a-z][a-zA-Z]*T))$"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!--
+
+    LENGTH and CODING CHECKS
+
+    -->
+
+    <module name="LineLength">
+      <!-- Checks if a line is too long. -->
+      <property name="max" value="120"/>
+      <property name="severity" value="error"/>
+
+      <!--
+        The default ignore pattern exempts the following elements:
+          - import statements
+          - long URLs inside comments
+      -->
+
+      <property name="ignorePattern"
+          value="^(package .*;\s*)|(import .*;\s*)|( *\* .*https?://.*)$"/>
+    </module>
+
+    <module name="LeftCurly">
+      <!-- Checks for placement of the left curly brace ('{'). -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="RightCurly">
+      <!-- Checks right curlies on CATCH, ELSE, and TRY blocks are on
+      the same line. e.g., the following example is fine:
+      <pre>
+        if {
+          ...
+        } else
+      </pre>
+      -->
+      <!-- This next example is not fine:
+      <pre>
+        if {
+          ...
+        }
+        else
+      </pre>
+      -->
+      <property name="option" value="same"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Checks for braces around if and else blocks -->
+    <module name="NeedBraces">
+      <property name="severity" value="error"/>
+      <property name="tokens" value="LITERAL_IF, LITERAL_ELSE, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO"/>
+    </module>
+
+    <module name="UpperEll">
+      <!-- Checks that long constants are defined with an upper ell.-->
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="FallThrough">
+      <!-- Warn about falling through to the next case statement.  Similar to
+      javac -Xlint:fallthrough, but the check is suppressed if a single-line comment
+      on the last non-blank line preceding the fallen-into case contains 'fall through' (or
+      some other variants that we don't publicized to promote consistency).
+      -->
+      <property name="reliefPattern"
+       value="fall through|Fall through|fallthru|Fallthru|falls through|Falls through|fallthrough|Fallthrough|No break|NO break|no break|continue on"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Checks for over-complicated boolean expressions. -->
+    <module name="SimplifyBooleanExpression"/>
+
+    <!-- Detects empty statements (standalone ";" semicolon). -->
+    <module name="EmptyStatement"/>
+
+    <!--
+
+    MODIFIERS CHECKS
+
+    -->
+
+    <module name="ModifierOrder">
+      <!-- Warn if modifier order is inconsistent with JLS3 8.1.1, 8.3.1, and
+           8.4.3.  The prescribed order is:
+           public, protected, private, abstract, static, final, transient, volatile,
+           synchronized, native, strictfp
+        -->
+      <property name="severity" value="error"/>
+    </module>
+
+
+    <!--
+
+    WHITESPACE CHECKS
+
+    -->
+
+    <module name="WhitespaceAround">
+      <!-- Checks that various tokens are surrounded by whitespace.
+           This includes most binary operators and keywords followed
+           by regular or curly braces.
+      -->
+      <property name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR,
+        BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN,
+        EQUAL, GE, GT, LAND, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE,
+        LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN,
+        LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS,
+        MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION,
+        SL, SL_ASSIGN, SR_ASSIGN, STAR, STAR_ASSIGN"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="WhitespaceAfter">
+      <!-- Checks that commas, semicolons and typecasts are followed by
+           whitespace.
+      -->
+      <property name="tokens" value="COMMA, SEMI, TYPECAST"/>
+    </module>
+
+    <module name="NoWhitespaceAfter">
+      <!-- Checks that there is no whitespace after various unary operators.
+           Linebreaks are allowed.
+      -->
+      <property name="tokens" value="BNOT, DEC, DOT, INC, LNOT, UNARY_MINUS,
+        UNARY_PLUS"/>
+      <property name="allowLineBreaks" value="true"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="NoWhitespaceBefore">
+      <!-- Checks that there is no whitespace before various unary operators.
+           Linebreaks are allowed.
+      -->
+      <property name="tokens" value="SEMI, DOT, POST_DEC, POST_INC"/>
+      <property name="allowLineBreaks" value="true"/>
+      <property name="severity" value="error"/>
+    </module>
+
+    <module name="OperatorWrap">
+      <!-- Checks that operators like + and ? appear at newlines rather than
+           at the end of the previous line.
+      -->
+      <property name="option" value="NL"/>
+      <property name="tokens" value="BAND, BOR, BSR, BXOR, DIV, EQUAL,
+        GE, GT, LAND, LE, LITERAL_INSTANCEOF, LOR, LT, MINUS, MOD,
+        NOT_EQUAL, PLUS, QUESTION, SL, SR, STAR "/>
+    </module>
+
+    <module name="OperatorWrap">
+      <!-- Checks that assignment operators are at the end of the line. -->
+      <property name="option" value="eol"/>
+      <property name="tokens" value="ASSIGN"/>
+    </module>
+
+    <module name="ParenPad">
+      <!-- Checks that there is no whitespace before close parens or after
+           open parens.
+      -->
+      <property name="severity" value="error"/>
+    </module>
+
+    <!-- Required to support SuppressWarningsComment -->
+    <module name="FileContentsHolder"/>
+
+  </module>
+</module>
+
diff --git a/distributedlog-build-tools/src/main/resources/distributedlog/suppressions.xml b/distributedlog-build-tools/src/main/resources/distributedlog/suppressions.xml
new file mode 100644
index 000000000..9f60c2549
--- /dev/null
+++ b/distributedlog-build-tools/src/main/resources/distributedlog/suppressions.xml
@@ -0,0 +1,29 @@
+<?xml version="1.0"?>
+<!--
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License. See accompanying LICENSE file.
+-->
+<!DOCTYPE suppressions PUBLIC
+"-//Puppy Crawl//DTD Suppressions 1.1//EN"
+"http://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
+
+<suppressions>
+  <suppress checks="JavadocPackage" files=".*[\\/]src[\\/]test[\\/].*"/>
+  <suppress checks="JavadocPackage" files=".*[\\/]maven-archetypes[\\/].*"/>
+  <suppress checks="JavadocPackage" files=".*[\\/]examples[\\/].*"/>
+  
+  <!-- suppress all checks in the generated directories -->
+  <suppress checks=".*" files=".+[\\/]generated[\\/].+\.java" />
+  <suppress checks=".*" files=".+[\\/]generated-sources[\\/].+\.java" />
+  <suppress checks=".*" files=".+[\\/]generated-test-sources[\\/].+\.java" />
+</suppressions>
+
diff --git a/distributedlog-protocol/pom.xml b/distributedlog-protocol/pom.xml
index 48b749ae3..ae9cb4677 100644
--- a/distributedlog-protocol/pom.xml
+++ b/distributedlog-protocol/pom.xml
@@ -107,6 +107,39 @@
           <excludeFilterFile>${basedir}/src/main/resources/findbugsExclude.xml</excludeFilterFile>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-checkstyle-plugin</artifactId>
+        <version>2.17</version>
+        <dependencies>
+          <dependency>
+            <groupId>com.puppycrawl.tools</groupId>
+            <artifactId>checkstyle</artifactId>
+            <version>6.19</version>
+          </dependency>
+          <dependency>
+            <groupId>com.twitter</groupId>
+            <artifactId>distributedlog-build-tools</artifactId>
+            <version>${project.version}</version>
+          </dependency>
+        </dependencies>
+        <configuration>
+          <configLocation>distributedlog/checkstyle.xml</configLocation>
+          <suppressionsLocation>distributedlog/suppressions.xml</suppressionsLocation>
+          <consoleOutput>true</consoleOutput>
+          <failOnViolation>true</failOnViolation>
+          <includeResources>false</includeResources>
+          <includeTestSourceDirectory>true</includeTestSourceDirectory>
+        </configuration>
+        <executions>
+          <execution>
+            <phase>test-compile</phase>
+            <goals>
+              <goal>check</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 </project>
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/DLSN.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/DLSN.java
index 9e3b76c1a..57cc0ef36 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/DLSN.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/DLSN.java
@@ -17,12 +17,13 @@
  */
 package com.twitter.distributedlog;
 
+import static com.google.common.base.Preconditions.checkArgument;
+
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.Preconditions;
+import java.nio.ByteBuffer;
 import org.apache.commons.codec.binary.Base64;
 import org.apache.commons.codec.binary.Hex;
 
-import java.nio.ByteBuffer;
 
 /**
  * DistributedLog Sequence Number (DLSN) is the system generated sequence number for log record.
@@ -46,7 +47,7 @@ public class DLSN implements Comparable<DLSN> {
     // The non-inclusive lower bound DLSN
     public static final DLSN NonInclusiveLowerBound = new DLSN(1, 0 , -1);
     // Invalid DLSN
-    public static final DLSN InvalidDLSN = new DLSN(0,-1,-1);
+    public static final DLSN InvalidDLSN = new DLSN(0, -1, -1);
 
     static final byte CUR_VERSION = VERSION1;
     static final int VERSION0_LEN = Long.SIZE * 3 + Byte.SIZE;
@@ -71,14 +72,6 @@ public long getLogSegmentSequenceNo() {
         return logSegmentSequenceNo;
     }
 
-    /**
-     * use {@link #getLogSegmentSequenceNo()} instead
-     */
-    @Deprecated
-    long getLedgerSequenceNo() {
-        return logSegmentSequenceNo;
-    }
-
     /**
      * Return the entry id of the batch that the record is written to.
      *
@@ -100,11 +93,11 @@ public long getSlotId() {
     @Override
     public int compareTo(DLSN that) {
         if (this.logSegmentSequenceNo != that.logSegmentSequenceNo) {
-            return (this.logSegmentSequenceNo < that.logSegmentSequenceNo)? -1 : 1;
+            return (this.logSegmentSequenceNo < that.logSegmentSequenceNo) ? -1 : 1;
         } else if (this.entryId != that.entryId) {
-            return (this.entryId < that.entryId)? -1 : 1;
+            return (this.entryId < that.entryId) ? -1 : 1;
         } else {
-            return (this.slotId < that.slotId)? -1 : (this.slotId == that.slotId)? 0 : 1;
+            return (this.slotId < that.slotId) ? -1 : (this.slotId == that.slotId) ? 0 : 1;
         }
     }
 
@@ -125,7 +118,7 @@ public byte[] serializeBytes() {
      * @return the serialized bytes
      */
     public byte[] serializeBytes(byte version) {
-        Preconditions.checkArgument(version <= CUR_VERSION && version >= VERSION0);
+        checkArgument(version <= CUR_VERSION && version >= VERSION0);
         byte[] data = new byte[CUR_VERSION == version ? VERSION1_LEN : VERSION0_LEN];
         ByteBuffer bb = ByteBuffer.wrap(data);
         bb.put(version);
@@ -208,23 +201,33 @@ static DLSN deserialize0(String dlsn) {
 
     @Override
     public String toString() {
-        return "DLSN{" +
-            "logSegmentSequenceNo=" + logSegmentSequenceNo +
-            ", entryId=" + entryId +
-            ", slotId=" + slotId +
-            '}';
+        return "DLSN{"
+            + "logSegmentSequenceNo=" + logSegmentSequenceNo
+            + ", entryId=" + entryId
+            + ", slotId=" + slotId
+            + '}';
     }
 
     @Override
     public boolean equals(Object o) {
-        if (this == o) return true;
-        if (!(o instanceof DLSN)) return false;
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof DLSN)) {
+            return false;
+        }
 
         DLSN dlsn = (DLSN) o;
 
-        if (entryId != dlsn.entryId) return false;
-        if (logSegmentSequenceNo != dlsn.logSegmentSequenceNo) return false;
-        if (slotId != dlsn.slotId) return false;
+        if (entryId != dlsn.entryId) {
+            return false;
+        }
+        if (logSegmentSequenceNo != dlsn.logSegmentSequenceNo) {
+            return false;
+        }
+        if (slotId != dlsn.slotId) {
+            return false;
+        }
 
         return true;
     }
@@ -238,9 +241,10 @@ public int hashCode() {
     }
 
     /**
-     * Positions to a DLSN greater than the current value - this may not
-     * correspond to an actual LogRecord, its just used by the positioning logic
-     * to position the reader
+     * Positions to a DLSN greater than the current value.
+     *
+     * <p>This may not correspond to an actual LogRecord, its just used by the positioning logic
+     * to position the reader.
      *
      * @return the next DLSN
      */
@@ -249,9 +253,10 @@ public DLSN getNextDLSN() {
     }
 
     /**
-     * Positions to a DLSN greater than the current value - this may not
-     * correspond to an actual LogRecord, its just used by the positioning logic
-     * to position the reader
+     * Positions to next log segment than the current value.
+     *
+     * <p>this may not correspond to an actual LogRecord, its just used by the positioning logic
+     * to position the reader.
      *
      * @return the next DLSN
      */
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetReader.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetReader.java
index d3f7a99e4..dae8403a8 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetReader.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetReader.java
@@ -17,15 +17,19 @@
  */
 package com.twitter.distributedlog;
 
+import static com.twitter.distributedlog.LogRecordSet.COMPRESSION_CODEC_LZ4;
+import static com.twitter.distributedlog.LogRecordSet.METADATA_COMPRESSION_MASK;
+import static com.twitter.distributedlog.LogRecordSet.METADATA_VERSION_MASK;
+import static com.twitter.distributedlog.LogRecordSet.NULL_OP_STATS_LOGGER;
+import static com.twitter.distributedlog.LogRecordSet.VERSION;
+
 import com.twitter.distributedlog.io.CompressionCodec;
 import com.twitter.distributedlog.io.CompressionUtils;
-
 import java.io.DataInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.ByteBuffer;
 
-import static com.twitter.distributedlog.LogRecordSet.*;
 
 /**
  * Record reader to read records from an enveloped entry buffer.
@@ -63,8 +67,8 @@ class EnvelopedRecordSetReader implements LogRecordSet.Reader {
         int metadata = src.readInt();
         int version = metadata & METADATA_VERSION_MASK;
         if (version != VERSION) {
-            throw new IOException(String.format("Version mismatch while reading. Received: %d," +
-                    " Required: %d", version, VERSION));
+            throw new IOException(String.format("Version mismatch while reading. Received: %d,"
+                + " Required: %d", version, VERSION));
         }
         int codecCode = metadata & METADATA_COMPRESSION_MASK;
         this.numRecords = src.readInt();
@@ -76,7 +80,7 @@ class EnvelopedRecordSetReader implements LogRecordSet.Reader {
         if (COMPRESSION_CODEC_LZ4 == codecCode) {
             CompressionCodec codec = CompressionUtils.getCompressionCodec(CompressionCodec.Type.LZ4);
             byte[] decompressedData = codec.decompress(compressedData, 0, actualDataLen,
-                    originDataLen, NullOpStatsLogger);
+                    originDataLen, NULL_OP_STATS_LOGGER);
             this.reader = ByteBuffer.wrap(decompressedData);
         } else {
             if (originDataLen != actualDataLen) {
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetWriter.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetWriter.java
index 32b3cf4fa..7f64a6d52 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetWriter.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/EnvelopedRecordSetWriter.java
@@ -17,15 +17,21 @@
  */
 package com.twitter.distributedlog;
 
+import static com.twitter.distributedlog.LogRecord.MAX_LOGRECORD_SIZE;
+import static com.twitter.distributedlog.LogRecordSet.COMPRESSION_CODEC_LZ4;
+import static com.twitter.distributedlog.LogRecordSet.COMPRESSION_CODEC_NONE;
+import static com.twitter.distributedlog.LogRecordSet.HEADER_LEN;
+import static com.twitter.distributedlog.LogRecordSet.METADATA_COMPRESSION_MASK;
+import static com.twitter.distributedlog.LogRecordSet.METADATA_VERSION_MASK;
+import static com.twitter.distributedlog.LogRecordSet.NULL_OP_STATS_LOGGER;
+import static com.twitter.distributedlog.LogRecordSet.VERSION;
+
+import com.twitter.distributedlog.exceptions.LogRecordTooLongException;
+import com.twitter.distributedlog.exceptions.WriteException;
 import com.twitter.distributedlog.io.Buffer;
 import com.twitter.distributedlog.io.CompressionCodec;
 import com.twitter.distributedlog.io.CompressionUtils;
-import com.twitter.distributedlog.exceptions.LogRecordTooLongException;
-import com.twitter.distributedlog.exceptions.WriteException;
 import com.twitter.util.Promise;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import java.io.DataOutputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
@@ -33,16 +39,15 @@
 import java.nio.channels.WritableByteChannel;
 import java.util.LinkedList;
 import java.util.List;
-
-import static com.twitter.distributedlog.LogRecord.MAX_LOGRECORD_SIZE;
-import static com.twitter.distributedlog.LogRecordSet.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * {@link Buffer} based log record set writer.
  */
 class EnvelopedRecordSetWriter implements LogRecordSet.Writer {
 
-    static final Logger logger = LoggerFactory.getLogger(EnvelopedRecordSetWriter.class);
+    private static final Logger logger = LoggerFactory.getLogger(EnvelopedRecordSetWriter.class);
 
     private final Buffer buffer;
     private final DataOutputStream writer;
@@ -158,7 +163,7 @@ ByteBuffer createBuffer() {
         CompressionCodec compressor =
                     CompressionUtils.getCompressionCodec(codec);
         byte[] compressed =
-                compressor.compress(data, dataOffset, dataLen, NullOpStatsLogger);
+                compressor.compress(data, dataOffset, dataLen, NULL_OP_STATS_LOGGER);
 
         ByteBuffer recordSetBuffer;
         if (compressed.length > dataLen) {
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecord.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecord.java
index c104212f1..74df400c3 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecord.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecord.java
@@ -17,14 +17,13 @@
  */
 package com.twitter.distributedlog;
 
+import com.google.common.annotations.VisibleForTesting;
 import java.io.ByteArrayInputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.EOFException;
 import java.io.IOException;
 import java.io.InputStream;
-
-import com.google.common.annotations.VisibleForTesting;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -41,38 +40,39 @@
  *
  * <h3>User Record</h3>
  *
- * User records are the records written by applications and read by applications. They
+ * <p>User records are the records written by applications and read by applications. They
  * are constructed via {@link #LogRecord(long, byte[])} by applications and appended to
  * logs by writers. And they would be deserialized from bytes by the readers and return
  * to applications.
  *
  * <h3>Control Record</h3>
  *
- * Control records are special records that written by distributedlog. They are invisible
+ * <p>Control records are special records that written by distributedlog. They are invisible
  * to applications. They could be treated as <i>commit requests</i> as what people could find
  * in distributed consensus algorithms, since they are usually written by distributedlog to
  * commit application written records. <i>Commit</i> means making application written records
  * visible to readers to achieve consistent views among them.
- * <p>
- * They are named as 'Control Records' for controlling visibility of application written records.
- * <p>
- * The transaction id of 'Control Records' are assigned by distributedlog by inheriting from last
+ *
+ * <p>They are named as 'Control Records' for controlling visibility of application written records.
+ *
+ * <p>The transaction id of 'Control Records' are assigned by distributedlog by inheriting from last
  * written user records. So we could indicate what user records that a control record is committing
  * by looking at its transaction id.
  *
  * <h4>EndOfStream Record</h4>
  *
- * <code>EoS</code>(EndOfStream) is a special control record that would be written by a writer
+ * <p><code>EoS</code>(EndOfStream) is a special control record that would be written by a writer
  * to seal a log. After a <i>EoS</i> record is written to a log, no writers could append any record
  * after that and readers will get {@link com.twitter.distributedlog.exceptions.EndOfStreamException}
  * when they reach EoS.
+ *
  * <p>TransactionID of EoS is <code>Long.MAX_VALUE</code>.
  *
  * <h3>Serialization & Deserialization</h3>
  *
- * Data type in brackets. Interpretation should be on the basis of data types and not individual
+ * <p>Data type in brackets. Interpretation should be on the basis of data types and not individual
  * bytes to honor Endianness.
- * <p>
+ *
  * <pre>
  * LogRecord structure:
  * -------------------
@@ -98,13 +98,14 @@
  *
  * <h3>Sequence Numbers</h3>
  *
- * A record is associated with three types of sequence numbers. They are generated
+ * <p>A record is associated with three types of sequence numbers. They are generated
  * and used for different purposes. Check {@link LogRecordWithDLSN} for more details.
  *
  * @see LogRecordWithDLSN
  */
 public class LogRecord {
-    static final Logger LOG = LoggerFactory.getLogger(LogRecord.class);
+
+    private static final Logger LOG = LoggerFactory.getLogger(LogRecord.class);
 
     // Allow 4K overhead for metadata within the max transmission size
     public static final int MAX_LOGRECORD_SIZE = 1024 * 1024 - 8 * 1024; //1MB - 8KB
@@ -131,8 +132,8 @@ public class LogRecord {
 
     /**
      * Construct an uninitialized log record.
-     * <p>
-     * NOTE: only deserializer should call this constructor.
+     *
+     * <p>NOTE: only deserializer should call this constructor.
      */
     protected LogRecord() {
         this.txid = 0;
@@ -141,6 +142,7 @@ protected LogRecord() {
 
     /**
      * Construct a log record with <i>TransactionId</i> and payload.
+     *
      * <p>Usually writer would construct the log record for writing.
      *
      * @param txid
@@ -223,8 +225,8 @@ protected long getMetadata() {
      */
     void setPositionWithinLogSegment(int positionWithinLogSegment) {
         assert(positionWithinLogSegment >= 0);
-        metadata = (metadata & LOGRECORD_METADATA_POSITION_UMASK) |
-                (((long) positionWithinLogSegment) << LOGRECORD_METADATA_POSITION_SHIFT);
+        metadata = (metadata & LOGRECORD_METADATA_POSITION_UMASK)
+            | (((long) positionWithinLogSegment) << LOGRECORD_METADATA_POSITION_SHIFT);
     }
 
     /**
@@ -243,6 +245,7 @@ public int getPositionWithinLogSegment() {
 
     /**
      * Get the last position of this record in the log segment.
+     *
      * <p>If the record isn't record set, it would be same as {@link #getPositionWithinLogSegment()},
      * otherwise, it would be {@link #getPositionWithinLogSegment()} + numRecords - 1. If the record set
      * version is unknown, it would be same as {@link #getPositionWithinLogSegment()}.
@@ -264,6 +267,7 @@ int getLastPositionWithinLogSegment() {
 
     /**
      * Set the record to represent a set of records.
+     *
      * <p>The bytes in this record is the serialized format of {@link LogRecordSet}.
      */
     public void setRecordSet() {
@@ -319,6 +323,7 @@ void setEndOfStream() {
 
     /**
      * Check if the record is a <code>EoS</code> mark.
+     *
      * <p><code>EoS</code> mark is a special record that writer would
      * add to seal a log. after <code>Eos</code> mark is written,
      * writers can't write any more records and readers will get
@@ -356,8 +361,9 @@ private void writeToStream(DataOutputStream out) throws IOException {
     }
 
     /**
-     * The size of the serialized log record, this is used to estimate how much will
-     * be be appended to the in-memory buffer
+     * The size of the serialized log record.
+     *
+     * <p>This is used to estimate how much will be be appended to the in-memory buffer.
      *
      * @return serialized size
      */
@@ -367,7 +373,7 @@ int getPersistentSize() {
     }
 
     /**
-     * Class for writing log records
+     * Writer class to write log records into an output {@code stream}.
      */
     public static class Writer {
         private final DataOutputStream buf;
@@ -377,7 +383,7 @@ public Writer(DataOutputStream out) {
         }
 
         /**
-         * Write an operation to the output stream
+         * Write an operation to the output stream.
          *
          * @param record The operation to write
          * @throws IOException if an error occurs during writing.
@@ -392,8 +398,7 @@ public int getPendingBytes() {
     }
 
     /**
-     * This class is a package private class for reading log records
-     * from the persistent
+     * Reader class to read log records from an input {@code stream}.
       */
     public static class Reader {
         private final RecordStream recordStream;
@@ -405,9 +410,11 @@ public static class Reader {
         private LogRecordWithDLSN lastRecordSkipTo = null;
 
         /**
-         * Construct the reader
+         * Construct the reader.
          *
+         * @param recordStream the record stream for generating {@code DLSN}s.
          * @param in The stream to read from.
+         * @param startSequenceId the start sequence id.
          */
         public Reader(RecordStream recordStream,
                       DataInputStream in,
@@ -426,9 +433,9 @@ public Reader(RecordStream recordStream,
         }
 
         /**
-         * Read an operation from the input stream.
-         * <p/>
-         * Note that the objects returned from this method may be re-used by future
+         * Read an log record from the input stream.
+         *
+         * <p/> Note that the objects returned from this method may be re-used by future
          * calls to the same method.
          *
          * @return the operation read from the stream, or null at the end of the file
@@ -466,9 +473,11 @@ public LogRecordWithDLSN readOp() throws IOException {
                     nextRecordInStream.readPayload(in);
                     if (LOG.isTraceEnabled()) {
                         if (nextRecordInStream.isControl()) {
-                            LOG.trace("Reading {} Control DLSN {}", recordStream.getName(), nextRecordInStream.getDlsn());
+                            LOG.trace("Reading {} Control DLSN {}",
+                                recordStream.getName(), nextRecordInStream.getDlsn());
                         } else {
-                            LOG.trace("Reading {} Valid DLSN {}", recordStream.getName(), nextRecordInStream.getDlsn());
+                            LOG.trace("Reading {} Valid DLSN {}",
+                                recordStream.getName(), nextRecordInStream.getDlsn());
                         }
                     }
 
@@ -525,7 +534,7 @@ private boolean skipTo(Long txId, DLSN dlsn, boolean skipControl) throws IOExcep
                         currTxId = lastRecordSkipTo.getTransactionId();
                     }
 
-                    if ((null != dlsn) && (recordStream.getCurrentPosition().compareTo(dlsn) >=0)) {
+                    if ((null != dlsn) && (recordStream.getCurrentPosition().compareTo(dlsn) >= 0)) {
                         if (LOG.isTraceEnabled()) {
                             LOG.trace("Found position {} beyond {}", recordStream.getCurrentPosition(), dlsn);
                         }
@@ -556,7 +565,8 @@ private boolean skipTo(Long txId, DLSN dlsn, boolean skipControl) throws IOExcep
                     // get the num of records to skip
                     if (isRecordSet(flags)) {
                         // read record set
-                        LogRecordWithDLSN record = new LogRecordWithDLSN(recordStream.getCurrentPosition(), startSequenceId);
+                        LogRecordWithDLSN record =
+                            new LogRecordWithDLSN(recordStream.getCurrentPosition(), startSequenceId);
                         record.setMetadata(flags);
                         record.setTransactionId(currTxId);
                         record.readPayload(in);
@@ -580,7 +590,8 @@ private boolean skipTo(Long txId, DLSN dlsn, boolean skipControl) throws IOExcep
                             read += bytesToRead;
                         }
                         if (LOG.isTraceEnabled()) {
-                            LOG.trace("Skipped Record with TxId {} DLSN {}", currTxId, recordStream.getCurrentPosition());
+                            LOG.trace("Skipped Record with TxId {} DLSN {}",
+                                currTxId, recordStream.getCurrentPosition());
                         }
                         recordStream.advance(1);
                     }
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordSet.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordSet.java
index dad8e3ece..52970c70b 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordSet.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordSet.java
@@ -17,20 +17,21 @@
  */
 package com.twitter.distributedlog;
 
-import com.google.common.base.Preconditions;
+import static com.google.common.base.Preconditions.checkArgument;
+
 import com.twitter.distributedlog.exceptions.LogRecordTooLongException;
 import com.twitter.distributedlog.exceptions.WriteException;
 import com.twitter.distributedlog.io.CompressionCodec;
 import com.twitter.util.Promise;
-import org.apache.bookkeeper.stats.NullStatsLogger;
-import org.apache.bookkeeper.stats.OpStatsLogger;
-
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import org.apache.bookkeeper.stats.NullStatsLogger;
+import org.apache.bookkeeper.stats.OpStatsLogger;
 
 /**
  * A set of {@link LogRecord}s.
+ *
  * <pre>
  * Structure:
  * Bytes 0  -  4                : Metadata (version + flags)
@@ -56,7 +57,7 @@
  */
 public class LogRecordSet {
 
-    static final OpStatsLogger NullOpStatsLogger =
+    static final OpStatsLogger NULL_OP_STATS_LOGGER =
             NullStatsLogger.INSTANCE.getOpStatsLogger("");
 
     public static final int HEADER_LEN =
@@ -77,7 +78,7 @@ public class LogRecordSet {
     static final int COMPRESSION_CODEC_LZ4 = 0X1;
 
     public static int numRecords(LogRecord record) throws IOException {
-        Preconditions.checkArgument(record.isRecordSet(),
+        checkArgument(record.isRecordSet(),
                 "record is not a recordset");
         byte[] data = record.getPayload();
         return numRecords(data);
@@ -88,8 +89,8 @@ public static int numRecords(byte[] data) throws IOException {
         int metadata = buffer.getInt();
         int version = (metadata & METADATA_VERSION_MASK);
         if (version != VERSION) {
-            throw new IOException(String.format("Version mismatch while reading. Received: %d," +
-                    " Required: %d", version, VERSION));
+            throw new IOException(String.format("Version mismatch while reading. Received: %d,"
+                + " Required: %d", version, VERSION));
         }
         return buffer.getInt();
     }
@@ -100,7 +101,7 @@ public static Writer newWriter(int initialBufferSize,
     }
 
     public static Reader of(LogRecordWithDLSN record) throws IOException {
-        Preconditions.checkArgument(record.isRecordSet(),
+        checkArgument(record.isRecordSet(),
                 "record is not a recordset");
         byte[] data = record.getPayload();
         DLSN dlsn = record.getDlsn();
@@ -120,7 +121,7 @@ public static Reader of(LogRecordWithDLSN record) throws IOException {
     /**
      * Writer to append {@link LogRecord}s to {@link LogRecordSet}.
      */
-    public static interface Writer extends LogRecordSetBuffer {
+    public interface Writer extends LogRecordSetBuffer {
 
         /**
          * Write a {@link LogRecord} to this record set.
@@ -140,7 +141,7 @@ void writeRecord(ByteBuffer record, Promise<DLSN> transmitPromise)
     /**
      * Reader to read {@link LogRecord}s from this record set.
      */
-    public static interface Reader {
+    public interface Reader {
 
         /**
          * Read next log record from this record set.
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordWithDLSN.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordWithDLSN.java
index 521e4520a..14c8e76ea 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordWithDLSN.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/LogRecordWithDLSN.java
@@ -24,7 +24,7 @@
  *
  * <h3>Sequence Numbers</h3>
  *
- * A log record will be assigned with an unique system generated sequence number {@link DLSN} when it is
+ * <p>A log record will be assigned with an unique system generated sequence number {@link DLSN} when it is
  * written to a log. At the mean time, a 64-bits long number is assigned to the record indicates its position
  * within a log, which is called <code>SequenceId</code>. Besides {@link DLSN} and <code>SequenceID</code>,
  * application can assign its own sequence number (called <code>TransactionID</code>) to the log record while
@@ -32,7 +32,7 @@
  *
  * <h4>Transaction ID</h4>
  *
- * Transaction ID is a positive 64-bits long number that is assigned by the application. It is a very helpful
+ * <p>Transaction ID is a positive 64-bits long number that is assigned by the application. It is a very helpful
  * field when application wants to organize the records and position the readers using their own sequencing method.
  * A typical use case of <code>TransactionID</code> is DistributedLog Write Proxy. It assigns the non-decreasing
  * timestamps to log records, which the timestamps could be used as `physical time` to implement `TTL` in a strong
@@ -40,14 +40,14 @@
  *
  * <h4>DLSN</h4>
  *
- * DistributedLog Sequence Number (<i>DLSN</i>) is the sequence number generated during written time. It is comparable
- * and could be used to figure out the order between records. The DLSN is comprised with 3 components. They are
- * <i>Log Segment Sequence Number</i>, <i>Entry Id</i> and <i>Slot Id</i>. (See {@link DLSN} for more details).
+ * <p>DistributedLog Sequence Number (<i>DLSN</i>) is the sequence number generated during written time.
+ * It is comparable and could be used to figure out the order between records. The DLSN is comprised with 3 components.
+ * They are <i>Log Segment Sequence Number</i>, <i>Entry Id</i> and <i>Slot Id</i>. (See {@link DLSN} for more details).
  * The DLSN is usually used for comparison, positioning and truncation.
  *
  * <h4>Sequence ID</h4>
  *
- * Sequence ID is introduced to address the drawback of <code>DLSN</code>, in favor of answering questions like
+ * <p>Sequence ID is introduced to address the drawback of <code>DLSN</code>, in favor of answering questions like
  * `how many records written between two DLSNs`. It is a 64-bits monotonic increasing number (starting from zero).
  * Sequence ids are only accessible by readers. That means writers don't know the sequence ids of records after they
  * wrote them.
@@ -96,12 +96,12 @@ public DLSN getDlsn() {
 
     @Override
     public String toString() {
-        return "LogRecordWithDLSN{" +
-            "dlsn=" + dlsn +
-            ", txid=" + getTransactionId() +
-            ", position=" + getPositionWithinLogSegment() +
-            ", isControl=" + isControl() +
-            ", isEndOfStream=" + isEndOfStream() +
-            '}';
+        return "LogRecordWithDLSN{"
+            + "dlsn=" + dlsn
+            + ", txid=" + getTransactionId()
+            + ", position=" + getPositionWithinLogSegment()
+            + ", isControl=" + isControl()
+            + ", isEndOfStream=" + isEndOfStream()
+            + '}';
     }
 }
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/RecordStream.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/RecordStream.java
index a2b5537ef..d920ea1a1 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/RecordStream.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/RecordStream.java
@@ -18,7 +18,7 @@
 package com.twitter.distributedlog;
 
 /**
- * Stream of records
+ * A iterator to iterate records in the stream.
  */
 public interface RecordStream {
     /**
@@ -27,14 +27,14 @@ public interface RecordStream {
     void advance(int numRecords);
 
     /**
-     * Get postion of current record in the stream
+     * Get position of current record in the stream.
      *
      * @return position of current record
      */
     DLSN getCurrentPosition();
 
     /**
-     * Get the name of the stream
+     * Get the name of the stream.
      *
      * @return the name of the stream
      */
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/DistributedLogAnnotations.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/DistributedLogAnnotations.java
index d2d19b235..285900864 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/DistributedLogAnnotations.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/DistributedLogAnnotations.java
@@ -17,6 +17,9 @@
  */
 package com.twitter.distributedlog.annotations;
 
+/**
+ * Common annotation types.
+ */
 public class DistributedLogAnnotations {
     /**
      * Annotation to identify flaky tests in DistributedLog.
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/package-info.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/package-info.java
new file mode 100644
index 000000000..24bb36b20
--- /dev/null
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/annotations/package-info.java
@@ -0,0 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * Defines annotations used across distributedlog project.
+ */
+package com.twitter.distributedlog.annotations;
\ No newline at end of file
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyClosedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyClosedException.java
index f8bb7b834..abbce5f31 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyClosedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyClosedException.java
@@ -17,12 +17,12 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
- * Thrown when the distributed log manager has already been closed
- * (connections have been torn down)
+ * Thrown when any distributedlog resources have already been closed.
+ *
+ * <p>For example, it might be thrown when the connections have been torn down.
  */
 public class AlreadyClosedException extends DLException {
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyTruncatedTransactionException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyTruncatedTransactionException.java
index fa3fb4b97..788b4d8b7 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyTruncatedTransactionException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/AlreadyTruncatedTransactionException.java
@@ -17,12 +17,10 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
- * Thrown when the transaction Id specified in the API is in the range that has already been
- * truncated
+ * Thrown when the transaction Id specified in the API is in the range that has already been truncated.
  */
 public class AlreadyTruncatedTransactionException extends DLException {
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/BKTransmitException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/BKTransmitException.java
index 158ce3146..8f29628f2 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/BKTransmitException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/BKTransmitException.java
@@ -17,12 +17,12 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
- * Thrown when the send to bookkeeper fails
- * This is thrown by the next attempt to write, send or flush
+ * Thrown when the send to bookkeeper fails.
+ *
+ * <p>This is thrown by the next attempt to write, send or flush
  */
 public class BKTransmitException extends DLException {
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ChecksumFailedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ChecksumFailedException.java
index 111dff6c6..4b6729913 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ChecksumFailedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ChecksumFailedException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception thrown when checksum failures occurred.
+ */
 public class ChecksumFailedException extends DLException {
 
     private static final long serialVersionUID = 288438128880378812L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLClientClosedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLClientClosedException.java
index 6c947c26a..2f506ba9d 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLClientClosedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLClientClosedException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exceptions thrown when a distributedlog client is closed.
+ */
 public class DLClientClosedException extends DLException {
 
     private static final long serialVersionUID = -8876218750540927584L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLException.java
index 1e654bfa5..23af0c5d2 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLException.java
@@ -19,9 +19,11 @@
 
 import com.twitter.distributedlog.thrift.service.ResponseHeader;
 import com.twitter.distributedlog.thrift.service.StatusCode;
-
 import java.io.IOException;
 
+/**
+ * The basic exception of all distributedlog exceptions.
+ */
 public class DLException extends IOException {
     private static final long serialVersionUID = -4485775468586114393L;
     protected final StatusCode code;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLIllegalStateException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLIllegalStateException.java
index 78e5e9c8f..c80b9db23 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLIllegalStateException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/DLIllegalStateException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals that a method has been invoked at an illegal or inappropriate time.
+ */
 public class DLIllegalStateException extends DLException {
 
     private static final long serialVersionUID = -6721471104777747420L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/EndOfStreamException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/EndOfStreamException.java
index 663b18bd1..a62e62996 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/EndOfStreamException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/EndOfStreamException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception thrown when a reader reaches end of a sealed log stream.
+ */
 public class EndOfStreamException extends DLException {
 
     private static final long serialVersionUID = -6398949401860680263L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/FlushException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/FlushException.java
index 331de00de..f984b6c79 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/FlushException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/FlushException.java
@@ -17,9 +17,11 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception indicates that errors occurred on flushing data.
+ */
 public class FlushException extends DLException {
 
     private final long lastTxIdWritten;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/IdleReaderException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/IdleReaderException.java
index 475606ffa..1f6923a7e 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/IdleReaderException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/IdleReaderException.java
@@ -19,6 +19,11 @@
 
 import java.io.IOException;
 
+/**
+ * An exception is thrown when a log reader becomes idle.
+ *
+ * <p>A log reader can become idle when there is no records written to the stream.
+ */
 public class IdleReaderException extends IOException {
 
     private static final long serialVersionUID = 4882278671396434834L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InternalServerException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InternalServerException.java
index 4b463963c..2aea1527d 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InternalServerException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InternalServerException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception indicates that there is an internal error at distributedlog service side.
+ */
 public class InternalServerException extends DLException {
 
     private static final long serialVersionUID = 288438028880978802L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidEnvelopedEntryException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidEnvelopedEntryException.java
index fdc50c171..09e146c0c 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidEnvelopedEntryException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidEnvelopedEntryException.java
@@ -20,7 +20,7 @@
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
- * Exception thrown when encounter invalid enveloped entry
+ * Exception thrown when encounter invalid enveloped entry.
  */
 public class InvalidEnvelopedEntryException extends DLException {
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidStreamNameException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidStreamNameException.java
index a7d92023d..1e8f44597 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidStreamNameException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/InvalidStreamNameException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when encountered invalid log stream.
+ */
 public class InvalidStreamNameException extends DLException {
 
     private static final long serialVersionUID = 6393315766140568100L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockCancelledException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockCancelledException.java
index 65e869208..98131ee97 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockCancelledException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockCancelledException.java
@@ -17,6 +17,9 @@
  */
 package com.twitter.distributedlog.exceptions;
 
+/**
+ * A lock is cancelled when waiting for locking a stream.
+ */
 public class LockCancelledException extends LockingException {
 
     private static final long serialVersionUID = -148795017092861106L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockingException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockingException.java
index 92ff8d6d4..326a1cd50 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockingException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LockingException.java
@@ -17,9 +17,11 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception when a log writer attempts to acquire a lock to write data to the stream.
+ */
 public class LockingException extends DLException {
 
     private static final long serialVersionUID = -4960278188448464473L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogEmptyException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogEmptyException.java
index 84813c1e6..7dcd644db 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogEmptyException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogEmptyException.java
@@ -17,9 +17,11 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exceptions are thrown when attempt to read a log stream that doesn't have any records.
+ */
 public class LogEmptyException extends DLException {
 
     private static final long serialVersionUID = -1106184127178002282L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogExistsException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogExistsException.java
index 84ac10ece..e7a0d6d0e 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogExistsException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogExistsException.java
@@ -20,7 +20,7 @@
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
- * Log Already Exists
+ * Exception thrown on creating a log stream but the log stream already exists.
  */
 public class LogExistsException extends DLException {
     private static final long serialVersionUID = 1794053581673506784L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogNotFoundException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogNotFoundException.java
index 5fc843869..e2c93e8be 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogNotFoundException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogNotFoundException.java
@@ -17,9 +17,11 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when a reader attempts to read a log stream that doesn't exist.
+ */
 public class LogNotFoundException extends DLException {
 
     private static final long serialVersionUID = 871435700699403164L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogReadException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogReadException.java
index a4c346b79..6b08f53f1 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogReadException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogReadException.java
@@ -17,7 +17,6 @@
  */
 package com.twitter.distributedlog.exceptions;
 
-import com.twitter.distributedlog.exceptions.DLException;
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
 /**
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogRecordTooLongException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogRecordTooLongException.java
index 0521133a4..76a1aa268 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogRecordTooLongException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/LogRecordTooLongException.java
@@ -19,6 +19,11 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when attempting to write a record whose size is too larger.
+ *
+ * <p>The size limit of a log record is {@link com.twitter.distributedlog.LogRecord#MAX_LOGRECORD_SIZE}.
+ */
 public class LogRecordTooLongException extends DLException {
 
     private static final long serialVersionUID = 2788274084603111386L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/MetadataException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/MetadataException.java
index 76ab57315..cb62e7c9a 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/MetadataException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/MetadataException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when encountering metadata errors.
+ */
 public class MetadataException extends DLException {
 
     private static final long serialVersionUID = 6683578078046016125L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/NotYetImplementedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/NotYetImplementedException.java
index 7c703e412..04edb01e8 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/NotYetImplementedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/NotYetImplementedException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when a method is not implemented yet.
+ */
 public class NotYetImplementedException extends DLException {
 
     private static final long serialVersionUID = -6002036746792556106L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OverCapacityException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OverCapacityException.java
index ab46f6466..d564758c7 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OverCapacityException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OverCapacityException.java
@@ -19,6 +19,12 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when the system is over capacity.
+ *
+ * <p>When this exception is received, the client (either writer or reader) should take actions to not
+ * overwhelm the system. For example, backoff sending any requests.
+ */
 public class OverCapacityException extends DLException {
 
     private static final long serialVersionUID = -6398949404860680263L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OwnershipAcquireFailedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OwnershipAcquireFailedException.java
index 9bdef0eb0..78163336a 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OwnershipAcquireFailedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/OwnershipAcquireFailedException.java
@@ -19,6 +19,11 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when a log writer attempt to acquire a lock.
+ *
+ * <p>It is typically thrown when the lock is already acquired by another writer.
+ */
 public class OwnershipAcquireFailedException extends LockingException {
     private static final long serialVersionUID = 8176056926552748001L;
     private final String currentOwner;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ReadCancelledException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ReadCancelledException.java
index 2876d3f62..84d9271a5 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ReadCancelledException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ReadCancelledException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals that a read request has been cancelled.
+ */
 public class ReadCancelledException extends DLException {
 
     private static final long serialVersionUID = -6273430297547510262L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RegionUnavailableException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RegionUnavailableException.java
index 4158c97b5..440d86e30 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RegionUnavailableException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RegionUnavailableException.java
@@ -19,6 +19,11 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception indicates that the service is not available in one region.
+ *
+ * <p>The client should retry the other regions when encountering this exception.
+ */
 public class RegionUnavailableException extends DLException {
 
     private static final long serialVersionUID = 5727337162533143957L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RequestDeniedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RequestDeniedException.java
index e4b61c44a..0a1e1c575 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RequestDeniedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RequestDeniedException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals that a request has been denied at the server.
+ */
 public class RequestDeniedException extends DLException {
 
     private static final long serialVersionUID = 7338220414584728216L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RetryableReadException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RetryableReadException.java
index d35988c91..5224564d6 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RetryableReadException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/RetryableReadException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals that a read request can be retried..
+ */
 public class RetryableReadException extends DLException {
 
     private static final long serialVersionUID = 2803207702150642330L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ServiceUnavailableException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ServiceUnavailableException.java
index 7851c0b22..29e20d83e 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ServiceUnavailableException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/ServiceUnavailableException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception indicates that the service is unavailable at the server side.
+ */
 public class ServiceUnavailableException extends DLException {
 
     private static final long serialVersionUID = 6317900286881665746L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamNotReadyException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamNotReadyException.java
index e44706ae8..6cac4689a 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamNotReadyException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamNotReadyException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when a log stream is not ready on server side for serving the write requests.
+ */
 public class StreamNotReadyException extends DLException {
 
     private static final long serialVersionUID = 684211282036293028L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamUnavailableException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamUnavailableException.java
index 1e23da00b..9872fdc39 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamUnavailableException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/StreamUnavailableException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception thrown when a stream is not available for serving traffic.
+ */
 public class StreamUnavailableException extends DLException {
 
     private static final long serialVersionUID = 684211282036993028L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TooManyStreamsException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TooManyStreamsException.java
index bbee4e4dc..6ee405d55 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TooManyStreamsException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TooManyStreamsException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals that a server has been serving too many streams.
+ */
 public class TooManyStreamsException extends OverCapacityException {
 
     private static final long serialVersionUID = -6391941401860180163L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TransactionIdOutOfOrderException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TransactionIdOutOfOrderException.java
index 370b83e84..915525c2e 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TransactionIdOutOfOrderException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/TransactionIdOutOfOrderException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * An exception is thrown when a log writer attempts to write a record with out-of-order transaction id.
+ */
 public class TransactionIdOutOfOrderException extends DLException {
 
     private static final long serialVersionUID = -6239322552103630036L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnexpectedException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnexpectedException.java
index ec26ad2c8..4454cd091 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnexpectedException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnexpectedException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * An {@code UnexpectedException} is thrown when encountering unexpected conditions.
+ */
 public class UnexpectedException extends DLException {
 
     private static final long serialVersionUID = 903763128422774055L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnsupportedMetadataVersionException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnsupportedMetadataVersionException.java
index 042c7dbea..47c361a4f 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnsupportedMetadataVersionException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/UnsupportedMetadataVersionException.java
@@ -19,6 +19,9 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Exception is thrown when found unsupported metadata version.
+ */
 public class UnsupportedMetadataVersionException extends DLException {
 
     private static final long serialVersionUID = 4980892659955478446L;
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteCancelledException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteCancelledException.java
index 33f11d40c..f3adac203 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteCancelledException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteCancelledException.java
@@ -19,14 +19,17 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * Signals when a write request is cancelled.
+ */
 public class WriteCancelledException extends DLException {
 
     private static final long serialVersionUID = -1836146493496072122L;
 
     public WriteCancelledException(String stream, Throwable t) {
         super(StatusCode.WRITE_CANCELLED_EXCEPTION,
-            "Write cancelled on stream " +
-            stream + " due to an earlier error", t);
+            "Write cancelled on stream "
+                + stream + " due to an earlier error", t);
     }
 
     public WriteCancelledException(String stream, String reason) {
@@ -36,7 +39,7 @@ public WriteCancelledException(String stream, String reason) {
 
     public WriteCancelledException(String stream) {
         super(StatusCode.WRITE_CANCELLED_EXCEPTION,
-            "Write cancelled on stream " +
-            stream + " due to an earlier error");
+            "Write cancelled on stream "
+                + stream + " due to an earlier error");
     }
 }
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteException.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteException.java
index 64714d7d7..77c18d431 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteException.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/WriteException.java
@@ -19,13 +19,15 @@
 
 import com.twitter.distributedlog.thrift.service.StatusCode;
 
+/**
+ * An exception on writing log records.
+ */
 public class WriteException extends DLException {
 
     private static final long serialVersionUID = -1836146493446072122L;
 
     public WriteException(String stream, String transmitError) {
         super(StatusCode.WRITE_EXCEPTION,
-            "Write rejected because stream " + stream + " has encountered an error : " +
-                transmitError);
+            "Write rejected because stream " + stream + " has encountered an error : " + transmitError);
     }
 }
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/package-info.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/package-info.java
new file mode 100644
index 000000000..ad027d860
--- /dev/null
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/exceptions/package-info.java
@@ -0,0 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * Defines exceptions used across distributedlog project.
+ */
+package com.twitter.distributedlog.exceptions;
\ No newline at end of file
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionCodec.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionCodec.java
index 2637f8756..0f1753a8b 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionCodec.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionCodec.java
@@ -20,14 +20,13 @@
 import org.apache.bookkeeper.stats.OpStatsLogger;
 
 /**
- * Common interface for compression/decompression operations using different
- * compression codecs.
+ * Common interface for compression/decompression operations using different compression codecs.
  */
 public interface CompressionCodec {
     /**
      * Enum specifying the currently supported compression types.
      */
-    public static enum Type {
+    enum Type {
         NONE, LZ4, UNKNOWN
     }
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionUtils.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionUtils.java
index 3acef6277..255278691 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionUtils.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/CompressionUtils.java
@@ -17,13 +17,16 @@
  */
 package com.twitter.distributedlog.io;
 
+/**
+ * Utils for compression related operations.
+ */
 public class CompressionUtils {
 
-    public final static String LZ4 = "lz4";
-    public final static String NONE = "none";
+    public static final String LZ4 = "lz4";
+    public static final String NONE = "none";
 
-    private static CompressionCodec identityCodec = new IdentityCompressionCodec();
-    private static CompressionCodec lz4Codec = new LZ4CompressionCodec();
+    private static final CompressionCodec IDENTITY_CODEC = new IdentityCompressionCodec();
+    private static final CompressionCodec LZ4_CODEC = new LZ4CompressionCodec();
 
     /**
      * Get a cached compression codec instance for the specified type.
@@ -32,10 +35,10 @@ public class CompressionUtils {
      */
     public static CompressionCodec getCompressionCodec(CompressionCodec.Type type) {
         if (type == CompressionCodec.Type.LZ4) {
-            return lz4Codec;
+            return LZ4_CODEC;
         }
         // No Compression
-        return identityCodec;
+        return IDENTITY_CODEC;
     }
 
     /**
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/IdentityCompressionCodec.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/IdentityCompressionCodec.java
index 4cc776284..39952c3a1 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/IdentityCompressionCodec.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/IdentityCompressionCodec.java
@@ -17,23 +17,26 @@
  */
 package com.twitter.distributedlog.io;
 
-import java.util.Arrays;
-
-import com.google.common.base.Preconditions;
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
 
+import java.util.Arrays;
 import org.apache.bookkeeper.stats.OpStatsLogger;
 
+/**
+ * An identity compression codec implementation for {@link CompressionCodec}.
+ */
 public class IdentityCompressionCodec implements CompressionCodec {
     @Override
     public byte[] compress(byte[] data, int offset, int length, OpStatsLogger compressionStat) {
-        Preconditions.checkNotNull(data);
-        Preconditions.checkArgument(length >= 0);
+        checkNotNull(data);
+        checkArgument(length >= 0);
         return Arrays.copyOfRange(data, offset, offset + length);
     }
 
     @Override
     public byte[] decompress(byte[] data, int offset, int length, OpStatsLogger decompressionStat) {
-        Preconditions.checkNotNull(data);
+        checkNotNull(data);
         return Arrays.copyOfRange(data, offset, offset + length);
     }
 
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/LZ4CompressionCodec.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/LZ4CompressionCodec.java
index 2137452a6..12d6ac462 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/LZ4CompressionCodec.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/LZ4CompressionCodec.java
@@ -17,21 +17,22 @@
  */
 package com.twitter.distributedlog.io;
 
-import java.util.concurrent.TimeUnit;
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
 
-import com.google.common.base.Preconditions;
 import com.google.common.base.Stopwatch;
-
+import java.util.concurrent.TimeUnit;
 import net.jpountz.lz4.LZ4Compressor;
 import net.jpountz.lz4.LZ4Exception;
 import net.jpountz.lz4.LZ4Factory;
 import net.jpountz.lz4.LZ4FastDecompressor;
 import net.jpountz.lz4.LZ4SafeDecompressor;
-
 import org.apache.bookkeeper.stats.OpStatsLogger;
 
 /**
- * All functions are thread safe.
+ * An {@code lz4} based {@link CompressionCodec} implementation.
+ *
+ * <p>All functions are thread safe.
  */
 public class LZ4CompressionCodec implements CompressionCodec {
 
@@ -50,10 +51,10 @@ public LZ4CompressionCodec() {
 
     @Override
     public byte[] compress(byte[] data, int offset, int length, OpStatsLogger compressionStat) {
-        Preconditions.checkNotNull(data);
-        Preconditions.checkArgument(offset >= 0 && offset < data.length);
-        Preconditions.checkArgument(length >= 0);
-        Preconditions.checkNotNull(compressionStat);
+        checkNotNull(data);
+        checkArgument(offset >= 0 && offset < data.length);
+        checkArgument(length >= 0);
+        checkNotNull(compressionStat);
 
         Stopwatch watch = Stopwatch.createStarted();
         byte[] compressed = compressor.compress(data, offset, length);
@@ -63,10 +64,10 @@ public byte[] compress(byte[] data, int offset, int length, OpStatsLogger compre
 
     @Override
     public byte[] decompress(byte[] data, int offset, int length, OpStatsLogger decompressionStat) {
-        Preconditions.checkNotNull(data);
-        Preconditions.checkArgument(offset >= 0 && offset < data.length);
-        Preconditions.checkArgument(length >= 0);
-        Preconditions.checkNotNull(decompressionStat);
+        checkNotNull(data);
+        checkArgument(offset >= 0 && offset < data.length);
+        checkArgument(length >= 0);
+        checkNotNull(decompressionStat);
 
         Stopwatch watch = Stopwatch.createStarted();
         // Assume that we have a compression ratio of 1/3.
@@ -86,11 +87,11 @@ public byte[] decompress(byte[] data, int offset, int length, OpStatsLogger deco
     // length parameter is ignored here because of the way the fastDecompressor works.
     public byte[] decompress(byte[] data, int offset, int length, int decompressedSize,
                              OpStatsLogger decompressionStat) {
-        Preconditions.checkNotNull(data);
-        Preconditions.checkArgument(offset >= 0 && offset < data.length);
-        Preconditions.checkArgument(length >= 0);
-        Preconditions.checkArgument(decompressedSize >= 0);
-        Preconditions.checkNotNull(decompressionStat);
+        checkNotNull(data);
+        checkArgument(offset >= 0 && offset < data.length);
+        checkArgument(length >= 0);
+        checkArgument(decompressedSize >= 0);
+        checkNotNull(decompressionStat);
 
         Stopwatch watch = Stopwatch.createStarted();
         byte[] decompressed = fastDecompressor.decompress(data, offset, decompressedSize);
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/package-info.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/package-info.java
new file mode 100644
index 000000000..bbd9528e8
--- /dev/null
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/io/package-info.java
@@ -0,0 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * I/O related utilities used across the project.
+ */
+package com.twitter.distributedlog.io;
\ No newline at end of file
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/package-info.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/package-info.java
new file mode 100644
index 000000000..8fc526d0a
--- /dev/null
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/package-info.java
@@ -0,0 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * Provides the core data structures used across multiple modules.
+ */
+package com.twitter.distributedlog;
\ No newline at end of file
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/BitMaskUtils.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/BitMaskUtils.java
index adee084a0..07d9d269c 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/BitMaskUtils.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/BitMaskUtils.java
@@ -17,15 +17,18 @@
  */
 package com.twitter.distributedlog.util;
 
-import com.google.common.base.Preconditions;
+import static com.google.common.base.Preconditions.checkArgument;
 
+/**
+ * Utils for bit mask operations.
+ */
 public class BitMaskUtils {
 
     /**
      * 1) Unset all bits where value in mask is set.
      * 2) Set these bits to value specified by newValue.
      *
-     * e.g.
+     * <p>e.g.
      * if oldValue = 1010, mask = 0011, newValue = 0001
      * 1) 1010 -> 1000
      * 2) 1000 -> 1001
@@ -36,19 +39,19 @@ public class BitMaskUtils {
      * @return updated value
      */
     public static long set(long oldValue, long mask, long newValue) {
-        Preconditions.checkArgument(oldValue >= 0L && mask >= 0L && newValue >= 0L);
+        checkArgument(oldValue >= 0L && mask >= 0L && newValue >= 0L);
         return ((oldValue & (~mask)) | (newValue & mask));
     }
 
     /**
-     * Get the bits where mask is 1
+     * Get the bits where mask is 1.
      *
      * @param value value
      * @param mask mask of the value
      * @return the bit of the mask
      */
     public static long get(long value, long mask) {
-        Preconditions.checkArgument(value >= 0L && mask >= 0L);
+        checkArgument(value >= 0L && mask >= 0L);
         return (value & mask);
     }
 }
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/ProtocolUtils.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/ProtocolUtils.java
index 0b084714f..bac5cdd0e 100644
--- a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/ProtocolUtils.java
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/ProtocolUtils.java
@@ -17,11 +17,10 @@
  */
 package com.twitter.distributedlog.util;
 
-import java.util.zip.CRC32;
+import static com.google.common.base.Charsets.UTF_8;
 
 import com.twitter.distributedlog.DLSN;
-
-import static com.google.common.base.Charsets.UTF_8;
+import java.util.zip.CRC32;
 
 /**
  * With CRC embedded in the application, we have to keep track of per api crc. Ideally this
diff --git a/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/package-info.java b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/package-info.java
new file mode 100644
index 000000000..f95e66619
--- /dev/null
+++ b/distributedlog-protocol/src/main/java/com/twitter/distributedlog/util/package-info.java
@@ -0,0 +1,21 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * defines the utilities used across the project.
+ */
+package com.twitter.distributedlog.util;
\ No newline at end of file
diff --git a/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestDLSN.java b/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestDLSN.java
index 373994b87..551d0ca54 100644
--- a/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestDLSN.java
+++ b/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestDLSN.java
@@ -17,9 +17,14 @@
  */
 package com.twitter.distributedlog;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
 import org.junit.Test;
-import static org.junit.Assert.*;
 
+/**
+ * Test Case for {@link DLSN}.
+ */
 public class TestDLSN {
 
     @Test(timeout = 60000)
diff --git a/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestLogRecordSet.java b/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestLogRecordSet.java
index bc1e6273d..4a5fdacf4 100644
--- a/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestLogRecordSet.java
+++ b/distributedlog-protocol/src/test/java/com/twitter/distributedlog/TestLogRecordSet.java
@@ -17,6 +17,13 @@
  */
 package com.twitter.distributedlog;
 
+import static com.google.common.base.Charsets.UTF_8;
+import static com.twitter.distributedlog.LogRecord.MAX_LOGRECORD_SIZE;
+import static com.twitter.distributedlog.LogRecordSet.HEADER_LEN;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
+
 import com.google.common.collect.Lists;
 import com.twitter.distributedlog.LogRecordSet.Reader;
 import com.twitter.distributedlog.LogRecordSet.Writer;
@@ -25,18 +32,12 @@
 import com.twitter.util.Await;
 import com.twitter.util.Future;
 import com.twitter.util.Promise;
-import org.junit.Test;
-
 import java.nio.ByteBuffer;
 import java.util.List;
-
-import static com.google.common.base.Charsets.UTF_8;
-import static com.twitter.distributedlog.LogRecord.*;
-import static com.twitter.distributedlog.LogRecordSet.*;
-import static org.junit.Assert.*;
+import org.junit.Test;
 
 /**
- * Test Case for {@link LogRecordSet}
+ * Test Case for {@link LogRecordSet}.
  */
 public class TestLogRecordSet {
 
diff --git a/pom.xml b/pom.xml
index 6441a26f5..c2773905f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -76,6 +76,7 @@
     </developer>
   </developers>
   <modules>
+    <module>distributedlog-build-tools</module>
     <module>distributedlog-protocol</module>
     <module>distributedlog-core</module>
     <module>distributedlog-client</module>

From 5dc4067e7fe1759c83ceee0ba6bf67e904b39ec3 Mon Sep 17 00:00:00 2001
From: Xi Liu <xiliuant@gmail.com>
Date: Tue, 20 Dec 2016 00:34:29 -0800
Subject: [PATCH 2/2] addressed comments

---
 .../src/main/resources/distributedlog/checkstyle.xml            | 2 +-
 .../src/main/resources/ide/eclipse}/DL_formatter.xml            | 0
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename {dev-support => distributedlog-build-tools/src/main/resources/ide/eclipse}/DL_formatter.xml (100%)

diff --git a/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml b/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
index 45be45e16..e1117c89c 100644
--- a/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
+++ b/distributedlog-build-tools/src/main/resources/distributedlog/checkstyle.xml
@@ -103,7 +103,7 @@ page at http://checkstyle.sourceforge.net/config.html -->
     </module>
 
     <module name="IllegalImport">
-      <property name="illegalPkgs" value="autovalue.shaded, avro.shaded, com.google.api.client.repackaged, com.google.appengine.repackaged, io.netty.util.internal"/>
+      <property name="illegalPkgs" value="autovalue.shaded, avro.shaded, bk-shade, com.google.api.client.repackaged, com.google.appengine.repackaged, io.netty.util.internal"/>
     </module>
 
     <module name="RedundantModifier">
diff --git a/dev-support/DL_formatter.xml b/distributedlog-build-tools/src/main/resources/ide/eclipse/DL_formatter.xml
similarity index 100%
rename from dev-support/DL_formatter.xml
rename to distributedlog-build-tools/src/main/resources/ide/eclipse/DL_formatter.xml