SimpleLogger4j

A lightweight, dependency-free Java logger that gives you:

• A simple API (logger.info(), logger.error(), etc.)
• A pattern engine for shaping log output
• ANSI colour support for easy visual scanning
• String utilities for alignment, clipping, and formatting
• Clean exception handling

Built and tested against Java 1.8

Installation

Gradle

Add the JitPack repository:

repositories {
    maven { url 'https://jitpack.io' }
}

Then add the dependency:

dependencies {
    implementation 'com.github.lovepigeons:SimpleLogger4j:v1.0.4'
}

Maven

Add the JitPack repository:

<repositories>
    <repository>
        <id>jitpack.io</id>
        <url>https://jitpack.io</url>
    </repository>
</repositories>

Then add the dependency:

<dependencies>
    <dependency>
        <groupId>com.github.lovepigeons</groupId>
        <artifactId>SimpleLogger4j</artifactId>
        <version>v1.0.4</version>
    </dependency>
</dependencies>

API Summary

SimpleLog logger = SimpleLog.of(T.class);

logger.info("Test arguments: {} {} {}", 123, 123.456, "testing");

logger.debug("debug msg");
logger.info("info msg");
logger.success("success msg");
logger.warn("warn msg");
logger.error("error msg");
logger.critical("critical msg");

logger.error("error with stack", throwable);
logger.critical("critical with stack", throwable);

Levels: DEBUG, INFO, SUCCESS, WARN, ERROR, CRITICAL

Configuration

Creating a Logger

// Uses default config (simplelogger4j.xml if exists, else internal defaults)
SimpleLog logger = SimpleLog.of(MyClass.class);

// Or specify a custom XML config file
SimpleLog logger = SimpleLog.of(MyClass.class, "mylog.xml");

XML Configuration

Create a simplelogger4j.xml file in your classpath (or specify a custom filename):

<config>
    <minLevel>DEBUG</minLevel>
    <pattern>[%{timestamp:BRIGHT_BLACK}] [%{level:LEVEL|padRight(8)}] (%{package:CYAN}) #%{sequence:BRIGHT_BLACK} %{message}</pattern>
    <consoleColour>true</consoleColour>
    <appenders>
        <console enabled="true"/>
        <file enabled="true" path="app.log" bufferSize="16384" append="true"/>
    </appenders>
    <levelPalette
        debug="BLUE"
        info=""
        warn="BRIGHT_YELLOW"
        success="GREEN"
        error="RED"
        critical="BG_BRIGHT_RED"
    />
</config>

Configuration options:

• minLevel - Minimum log level to output (DEBUG, INFO, SUCCESS, WARN, ERROR, CRITICAL)
• pattern - Output format pattern using tokens and specs
• consoleColour - Enable/disable ANSI colours for console output
• appenders/console - Console output settings
• appenders/file - File output settings with path, buffer size, and append mode
• levelPalette - Colour mapping for each log level (empty string = no colour)

Configuration priority:

1. Custom XML file (if specified in SimpleLog.of())
2. simplelogger4j.xml (if found in classpath)
3. Internal defaults

Output

2025-09-11T10:11:12 INFO     This is logged at info level
2025-09-11T10:11:12 WARN     This is logged at warn level
2025-09-11T10:11:12 SUCCESS  This is logged at success level
2025-09-11T10:11:12 DEBUG    This is logged at debug level
2025-09-11T10:11:12 ERROR    This is logged at error level
2025-09-11T10:11:12 CRITICAL This is logged at critical level
2025-09-11T10:11:12 ERROR    error
java.lang.RuntimeException: Forced error!
    at ...
2025-09-11T10:11:12 CRITICAL error
java.lang.RuntimeException: Forced critical error!
    at ...

Advanced Formatting with PatternEngine

The PatternEngine is where you take full control of how logs look. Instead of being locked into a rigid format, you describe the output with a pattern string.

1. Tokens

Tokens are placeholders written as %{...}. They pull data from the log event:

• timestamp → when the event happened
• level → log level (INFO, ERROR, etc.)
• message → your log text
• thread → thread name
• class → simple class name
• package → package name
• sequence → monotonic counter

Example:

%{timestamp} %{level} %{message}

Might render as:

2025-09-11T10:20:45 INFO Hello, World!

2. Specs (Format Modifiers)

Specs are added after a :. You can chain multiple with |.

• datetime(pattern[, locale]) → custom date/time
• padRight(width[, char]) → pad to a fixed width
• substring(start[, end]) → clip text

Example:

%{timestamp:datetime('yyyy-MM-dd HH:mm:ss')|padRight(20)} %{level:padRight(5)} %{message:substring(0,30)}

Output:

2025-09-11 10:20:45   INFO  Hello, World ttttttttttttttttt

3. Colouring

Add ANSI colours by name:

• Fixed colours: Use any of the available colour names directly in your pattern
• Palette colouring: Use LEVEL to apply colours based on log level (configured once)

Available Colours:

Regular Colours: BLACK, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN, WHITE

Bright Colours: BRIGHT_BLACK, BRIGHT_RED, BRIGHT_GREEN, BRIGHT_YELLOW, BRIGHT_BLUE, BRIGHT_MAGENTA, BRIGHT_CYAN, BRIGHT_WHITE

Background Colours: BG_BLACK, BG_RED, BG_GREEN, BG_YELLOW, BG_BLUE, BG_MAGENTA, BG_CYAN, BG_WHITE

Bright Background Colours: BG_BRIGHT_BLACK, BG_BRIGHT_RED, BG_BRIGHT_GREEN, BG_BRIGHT_YELLOW, BG_BRIGHT_BLUE, BG_BRIGHT_MAGENTA, BG_BRIGHT_CYAN, BG_BRIGHT_WHITE

All possible colours

Pattern using palette:

%{timestamp:datetime('HH:mm:ss')} %{level:LEVEL} %{message}

Pattern using fixed colours:

%{timestamp:CYAN} %{level:BRIGHT_RED} %{message:GREEN}

4. Walkthrough Examples

Example A: Simple plain text

"%{timestamp} %{level} %{message}"

Output:

2025-09-11T10:21:05 INFO Hello, World!

Example B: Neat columns with padding

"%{timestamp:datetime('HH:mm:ss')|padRight(12)} %{level:padRight(7)} %{message}"

Output:

10:21:05    INFO    Hello, World!
10:21:06    ERROR   Something broke

Example C: Multilingual date + clipped messages

"%{timestamp:datetime('EEEE d MMM yyyy HH:mm', 'fr-FR')|padRight(28)} %{level:padRight(5)} %{message:substring(0,30)|padRight(30,' ')}"

Output:

jeudi 11 sept. 2025 10:21       INFO  Bonjour le monde            

Example D: Colourized layout

"%{timestamp:datetime('HH:mm:ss')|padRight(12)} [%{thread:BRIGHT_BLUE}] %{level:LEVEL|padRight(5)} %{message}"

Output:

10:21:07    [main] INFO  Hello, World!

Here, main is bright blue, INFO is green (from palette).

Example E: Columnar, with package/class dimmed

"%{timestamp:datetime('yyyy-MM-dd')|padRight(12)} %{timestamp:datetime('HH:mm:ss')|padRight(10)} %{level:LEVEL|padRight(5)} %{package:DIM_WHITE}.%{class:BRIGHT_WHITE} - %{message:substring(0,60)|padRight(60,' ')} #%{sequence}"

Output:

2025-09-11   10:21:08   INFO  com.example.Demo - Hello, World! tttt...             #42

Happy logging! 🧩