diff --git a/src/main/java/davidkhala/common/AbstractPropertiesLoader.java b/src/main/java/davidkhala/common/AbstractPropertiesLoader.java
index 4c8316a..3f04dc8 100644
--- a/src/main/java/davidkhala/common/AbstractPropertiesLoader.java
+++ b/src/main/java/davidkhala/common/AbstractPropertiesLoader.java
@@ -4,10 +4,6 @@
 import java.io.InputStream;
 import java.util.Properties;
 
-/**
- * Created by davidliu on 11/4/2016.
- */
-
 public abstract class AbstractPropertiesLoader {
     protected abstract InputStream propertiesProvider() throws IOException;
 
diff --git a/src/main/java/davidkhala/common/CountryTool.java b/src/main/java/davidkhala/common/CountryTool.java
index 13b8db3..0b0a4e4 100644
--- a/src/main/java/davidkhala/common/CountryTool.java
+++ b/src/main/java/davidkhala/common/CountryTool.java
@@ -6,11 +6,6 @@
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-
-/**
- * Created by davidliu on 2/4/2017.
- */
-
 public class CountryTool {
 
     public static ArrayList<String> getNames() {
@@ -18,7 +13,7 @@ public static ArrayList<String> getNames() {
         ArrayList<String> countries = new ArrayList<String>();
         for (Locale locale : locales) {
             String country = locale.getDisplayCountry();
-            if (country.trim().length() > 0 && !countries.contains(country)) {
+            if (!country.trim().isEmpty() && !countries.contains(country)) {
                 countries.add(country);
             }
         }
@@ -54,28 +49,25 @@ public static String trimHKID(String hkid,boolean isStrict){
         if (!m.find()) return null;
         String prefix = m.group(1);
         String serial = m.group(2);
-        String checkdigit = m.group(3);
+        String checkDigit = m.group(3);
         long value = 0;
         if (prefix.length() == 2) {
             value += (prefix.charAt(0) - 55) * 9 + (prefix.charAt(1) - 55) * 8;
         } else if (prefix.length() == 1) {
             value += 36 * 9 + (prefix.charAt(0) - 55) * 8;
         }
-        try {
             for (int i = 0; i < 6; i++) {
-                value += Integer.parseInt(serial.substring(i, i + 1)) * (7 - i);
+                value += (long) Integer.parseInt(serial.substring(i, i + 1)) * (7 - i);
             }
             long reminder = value % 11;
-            long valid_checkdigit = 11 - reminder;
-            if ("A".equalsIgnoreCase(checkdigit) && valid_checkdigit == 10) {
+            long valid_checkDigit = 11 - reminder;
+            if ("A".equalsIgnoreCase(checkDigit) && valid_checkDigit == 10) {
                 return HKID;
             }
-            if (valid_checkdigit == Integer.parseInt(checkdigit)) {
+            if (valid_checkDigit == Integer.parseInt(checkDigit)) {
                 return HKID;
             }
-        } catch (NumberFormatException e) {
-            e.printStackTrace();
-        }
+
         return null;
     }
 
diff --git a/src/main/java/davidkhala/common/FileTool.java b/src/main/java/davidkhala/common/FileTool.java
index f2ded3f..44b24ce 100644
--- a/src/main/java/davidkhala/common/FileTool.java
+++ b/src/main/java/davidkhala/common/FileTool.java
@@ -3,20 +3,11 @@
 
 import java.io.*;
 import java.net.URI;
-import java.nio.file.Files;
-
-
-/**
- * Created by davidliu on 9/29/2016.
- */
+import java.util.Objects;
 
 public class FileTool {
     public static void write(File targetFile, String content) throws IOException {
-        targetFile.createNewFile();
         FileOutputStream fop = new FileOutputStream(targetFile);
-
-
-        // get the content in bytes
         byte[] contentInBytes = content.getBytes();
 
         fop.write(contentInBytes);
@@ -24,43 +15,25 @@ public static void write(File targetFile, String content) throws IOException {
         fop.close();
     }
 
-    public static String read(File targetFile) throws IOException {
-        FileInputStream is = new FileInputStream(targetFile);
-        return read(is);
-    }
+    public static boolean overwrite(File targetFile, String content) throws IOException {
+        boolean noExist = targetFile.createNewFile();
+        if (noExist) {
+            return false;
+        }
 
-    public static String read(InputStream is) throws IOException {
-        int size = is.available();
-        byte[] buffer = new byte[size];
-        is.read(buffer);
-        is.close();
-        return new String(buffer);
+        FileTool.write(targetFile, content);
+        return true;
     }
 
-    public static int copyDir(File from, File to) throws IOException {
-//        Preconditions.checkArgument(from.isDirectory(),"source file should be directory:"+from.getPath());
-//        Preconditions.checkArgument(to.isDirectory(),"target file should be directory:"+to.getPath());
-        File[] files = from.listFiles();
-        if(files==null)return -1;
-        for(File file: files){
-            File targetFile = new File(to,file.getName());
-            if(file.isDirectory()){
-                if(targetFile.mkdir()){
-                    copyDir(file,targetFile);
-                }
-            }else {
-
-//                Files.copy(file.toPath(), targetFile.toPath());
-            }
-        }
-        return files.length;
+    public static String read(File targetFile) throws IOException {
+        FileInputStream is = new FileInputStream(targetFile);
+        return Stream.read(is);
     }
 
     public static boolean deleteDir(File dir) {
 
         boolean result = true;
-        for (File file : dir.listFiles()
-                ) {
+        for (File file : Objects.requireNonNull(dir.listFiles())) {
 
             if (file.isDirectory()) {
                 if (!deleteDir(file)) result = false;
@@ -69,16 +42,14 @@ public static boolean deleteDir(File dir) {
         }
         return result;
     }
+
     public static String getExtensionName(String filename) {
-        if ((filename != null) && (filename.length() > 0)) {
+        if (filename != null && !filename.isEmpty()) {
             int dot = filename.lastIndexOf('.');
-            if ((dot >-1) && (dot < (filename.length() - 1))) {
+            if ((dot > -1) && (dot < (filename.length() - 1))) {
                 return filename.substring(dot + 1);
             }
         }
         return filename;
     }
-    public static File fromURI(URI uri){
-        return new File(uri);
-    }
 }
diff --git a/src/main/java/davidkhala/common/Reflection.java b/src/main/java/davidkhala/common/Reflection.java
index cafa41e..98ab9a3 100644
--- a/src/main/java/davidkhala/common/Reflection.java
+++ b/src/main/java/davidkhala/common/Reflection.java
@@ -6,26 +6,22 @@
 import java.util.HashMap;
 import java.util.Map;
 
-/**
- * Created by davidliu on 2018/1/10.
- */
-
 public class Reflection {
     Object object;
 
-    Class clazz;
+    Class<?> clazz;
     public Reflection(Object object) {
         this.object = object;
         this.clazz = object.getClass();
     }
-    public Reflection asSuperClass(Class clazz){
+    public Reflection asSuperClass(Class<?> clazz){
         if(clazz.isInstance(object)){
             this.clazz = clazz;
         }
         return this;
     }
 
-    private static final Map<Class, Class> WRAPPER_TYPES = new HashMap<>();
+    private static final Map<Class<?>, Class<?>> WRAPPER_TYPES = new HashMap<>();
 
     static {
         WRAPPER_TYPES.put(Boolean.class, Boolean.TYPE);
@@ -44,7 +40,7 @@ public static boolean isWrapperType(Class<?> clazz) {
     }
 
     public Object method(String methodName, Object... args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
-        Class[] argClasses = new Class[args.length];
+        Class<?>[] argClasses = new Class[args.length];
         for (int i = 0; i < args.length; i++) {
             Class<?> argClass = args[i].getClass();
             if (isWrapperType(argClass)) {
diff --git a/src/main/java/davidkhala/common/Stream.java b/src/main/java/davidkhala/common/Stream.java
new file mode 100644
index 0000000..5460462
--- /dev/null
+++ b/src/main/java/davidkhala/common/Stream.java
@@ -0,0 +1,14 @@
+package davidkhala.common;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+public class Stream {
+    public static String read(InputStream is) throws IOException {
+        int size = is.available();
+        byte[] buffer = new byte[size];
+        is.read(buffer);
+        is.close();
+        return new String(buffer);
+    }
+}
diff --git a/src/main/java/davidkhala/common/secure/AES.java b/src/main/java/davidkhala/common/secure/AES.java
index 16c79ab..c9a5fb2 100644
--- a/src/main/java/davidkhala/common/secure/AES.java
+++ b/src/main/java/davidkhala/common/secure/AES.java
@@ -6,7 +6,6 @@
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.security.SecureRandom;
-
 import javax.crypto.BadPaddingException;
 import javax.crypto.Cipher;
 import javax.crypto.IllegalBlockSizeException;
@@ -15,9 +14,6 @@
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 
-/**
- * Created by DavidLiu on 25/8/2016.
- */
 public class AES {
     public static byte[] hash(byte[] data) {
         try {
diff --git a/src/main/java/davidkhala/common/secure/AbstractHTTPS.java b/src/main/java/davidkhala/common/secure/AbstractHTTPS.java
index 67bc67b..d20d601 100644
--- a/src/main/java/davidkhala/common/secure/AbstractHTTPS.java
+++ b/src/main/java/davidkhala/common/secure/AbstractHTTPS.java
@@ -3,10 +3,6 @@
 import javax.net.ssl.*;
 import java.security.*;
 
-/**
- * Created by davidliu on 11/9/2016.
- */
-
 public abstract class AbstractHTTPS {
 	public static SSLSocketFactory getSSLSocketFactory(KeyStore keyStore, String keyStorePwd, KeyStore trustKeyStore) throws KeyStoreException, NoSuchAlgorithmException, UnrecoverableKeyException, KeyManagementException {
 		TrustManager[] trustManagers = new KeyStoreTool(trustKeyStore).genTrustedManagers();
diff --git a/src/main/java/davidkhala/common/secure/CSRTool.java b/src/main/java/davidkhala/common/secure/CSRTool.java
index 4f4671f..8bd1aee 100644
--- a/src/main/java/davidkhala/common/secure/CSRTool.java
+++ b/src/main/java/davidkhala/common/secure/CSRTool.java
@@ -13,10 +13,6 @@
 
 import javax.security.auth.x500.X500Principal;
 
-/**
- * Created by davidliu on 1/23/2017.
- */
-
 public class CSRTool {
 	public static String wrapPublicReq(PKCS10CertificationRequest csr) throws IOException {
 		byte[] CSRder;
diff --git a/src/main/java/davidkhala/common/secure/CertTool.java b/src/main/java/davidkhala/common/secure/CertTool.java
index 78bfada..ca461c1 100644
--- a/src/main/java/davidkhala/common/secure/CertTool.java
+++ b/src/main/java/davidkhala/common/secure/CertTool.java
@@ -6,10 +6,6 @@
 import java.security.cert.CertificateException;
 import java.security.cert.CertificateFactory;
 
-/**
- * Created by davidliu on 1/23/2017.
- */
-
 public class CertTool {
 	static String defaultCertType = "X.509";
 	static String defaultProvider = "BC";
diff --git a/src/main/java/davidkhala/common/secure/KeyStoreTool.java b/src/main/java/davidkhala/common/secure/KeyStoreTool.java
index fd1896e..b25a6c6 100644
--- a/src/main/java/davidkhala/common/secure/KeyStoreTool.java
+++ b/src/main/java/davidkhala/common/secure/KeyStoreTool.java
@@ -9,10 +9,6 @@
 import java.util.HashMap;
 import java.util.Map;
 
-/**
- * Created by davidliu on 11/4/2016.
- */
-
 public class KeyStoreTool {
 
     KeyStore keyStore;
diff --git a/src/main/java/davidkhala/common/secure/RSAKeyPair.java b/src/main/java/davidkhala/common/secure/RSAKeyPair.java
index 1081f80..e13cbf2 100644
--- a/src/main/java/davidkhala/common/secure/RSAKeyPair.java
+++ b/src/main/java/davidkhala/common/secure/RSAKeyPair.java
@@ -9,60 +9,55 @@
 import java.security.spec.RSAPublicKeySpec;
 import java.security.spec.X509EncodedKeySpec;
 
-/**
- * Created by davidliu on 11/9/2016.
- */
-
 public class RSAKeyPair {
-	public static KeyPair get() {
-		return get(null);
-	}
+  public static KeyPair get() {
+
+      try {
+          return get(null);
+      } catch (NoSuchAlgorithmException |NoSuchProviderException e) {
+          return null;
+      }
+
+  }
+
+  public static RSAPublicKey recoverPubKey(byte[] pubBytes) throws NoSuchAlgorithmException, InvalidKeySpecException {
+    return (RSAPublicKey)
+        KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(pubBytes));
+  }
+
+  public static RSAPublicKey recoverPubKey(RSAPrivateCrtKey privateCrtKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
+      return (RSAPublicKey)
+          KeyFactory.getInstance("RSA")
+              .generatePublic(
+                  new RSAPublicKeySpec(
+                      privateCrtKey.getModulus(), privateCrtKey.getPublicExponent()));
+  }
+
+  public static KeyPair get(String provider) throws NoSuchAlgorithmException, NoSuchProviderException {
+
+      KeyPairGenerator generator =
+          provider == null
+              ? KeyPairGenerator.getInstance("RSA")
+              : KeyPairGenerator.getInstance("RSA", provider); // "BC", "AndroidOpenSSL"
+      if (provider == null)
+        System.out.println("RSAKeypair generator default provider: " + generator.getProvider());
+      generator.initialize(2048);
+      return generator.generateKeyPair();
 
-	public static RSAPublicKey recoverPubKey(byte[] pubBytes) {
-		try {
-			return (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(pubBytes));
-		} catch (InvalidKeySpecException | NoSuchAlgorithmException e) {
-			e.printStackTrace();
-			return null;
-		}
-	}
+  }
 
-	public static RSAPublicKey recoverPubKey(RSAPrivateCrtKey privateCrtKey) {
-		try {
-			return (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new RSAPublicKeySpec(privateCrtKey.getModulus(), privateCrtKey.getPublicExponent()));
-		} catch (InvalidKeySpecException | NoSuchAlgorithmException e) {
-			e.printStackTrace();
-			return null;
-		}
-	}
+  public static RSAPrivateKey recoverPrivKey(byte[] privateBytes) throws NoSuchAlgorithmException, InvalidKeySpecException {
 
-	public static KeyPair get(String provider) {
-		try {
-			KeyPairGenerator generator = provider == null ? KeyPairGenerator.getInstance("RSA") : KeyPairGenerator.getInstance("RSA", provider);//"BC", "AndroidOpenSSL"
-			if (provider == null)
-				System.out.println("RSAKeypair generator default provider: " + generator.getProvider());
-			generator.initialize(2048);
-			return generator.generateKeyPair();
-		} catch (NoSuchAlgorithmException | NoSuchProviderException e) {
-			e.printStackTrace();
-			return null;
-		}
-	}
+      return (RSAPrivateKey)
+          KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(privateBytes));
 
-	public static RSAPrivateKey recoverPrivKey(byte[] privateBytes) {
-		try {
-			return (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(privateBytes));
-		} catch (InvalidKeySpecException | NoSuchAlgorithmException e) {
-			e.printStackTrace();
-			return null;
-		}
-	}
+  }
 
-	public static KeyPair recover(byte[] privateBytes, byte[] pubBytes) {
+  public static KeyPair recover(byte[] privateBytes, byte[] pubBytes) throws NoSuchAlgorithmException, InvalidKeySpecException {
 
-		RSAPrivateKey privateKey = recoverPrivKey(privateBytes);
-		RSAPublicKey publicKey = recoverPubKey(pubBytes);
+    RSAPrivateKey privateKey = recoverPrivKey(privateBytes);
+    RSAPublicKey publicKey = recoverPubKey(pubBytes);
 
-		return new KeyPair(publicKey, privateKey);
-	}
+    return new KeyPair(publicKey, privateKey);
+  }
 }
diff --git a/src/main/java/davidkhala/common/secure/Utils.java b/src/main/java/davidkhala/common/secure/Utils.java
index 7a7e48d..4f49896 100644
--- a/src/main/java/davidkhala/common/secure/Utils.java
+++ b/src/main/java/davidkhala/common/secure/Utils.java
@@ -5,10 +5,6 @@
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 
-/**
- * Created by davidliu on 2/1/2017.
- */
-
 public class Utils {
     /**
      * Hex encoding used throughout the framework. Use with HEX.encode(byte[]) or HEX.decode(CharSequence).
diff --git a/src/main/java/davidkhala/common/secure/X509CertTool.java b/src/main/java/davidkhala/common/secure/X509CertTool.java
index 6e2bf5e..f7dd9d0 100644
--- a/src/main/java/davidkhala/common/secure/X509CertTool.java
+++ b/src/main/java/davidkhala/common/secure/X509CertTool.java
@@ -15,10 +15,6 @@
 
 import javax.security.auth.x500.X500Principal;
 
-/**
- * Created by davidliu on 11/4/2016.
- */
-
 public class X509CertTool {
 
 	public final static String CN_PATTERN = "CN=%s, OU=%s, O=%s, L=%s, ST=%s, C=%s";
@@ -55,10 +51,6 @@ public static String extractIssuerCN(X509Certificate certificate) {
 		return identity;
 	}
 
-	/**
-	 * Created by davidliu on 11/8/2016.
-	 */
-
 	public static class CsrHelper {
 
 
diff --git a/src/test/java/FileTest.java b/src/test/java/FileTest.java
new file mode 100644
index 0000000..5835af1
--- /dev/null
+++ b/src/test/java/FileTest.java
@@ -0,0 +1,32 @@
+import davidkhala.common.FileTool;
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+import org.junit.Test;
+
+public class FileTest {
+  @Test
+  public void create_delete() throws IOException {
+    String fileName = "dummy.txt";
+    File file = new File(fileName);
+    String extension = FileTool.getExtensionName(fileName);
+    assert extension.equals("txt");
+    FileTool.write(file, "txt");
+    file.deleteOnExit();
+  }
+
+  @Test
+  public void createDir() throws IOException {
+    File file = new File("temp");
+    assert file.mkdirs();
+    file.deleteOnExit();
+  }
+
+  @Test
+  public void fromURITest() throws IOException {
+    String uriStr = "file:/C:/Users/david/Downloads/";
+    URI uri = URI.create(uriStr);
+    File file = new File(uri);
+    assert file.toURI().toString().equals(uriStr);
+  }
+}
diff --git a/src/test/java/jdbc/MySQL.java b/src/test/java/jdbc/MySQL.java
index 8fbdd31..e787997 100644
--- a/src/test/java/jdbc/MySQL.java
+++ b/src/test/java/jdbc/MySQL.java
@@ -5,7 +5,7 @@
 
 
 public class MySQL {
-    public static void main(String args[]) throws Exception {
+    public static void main(String[] args) throws Exception {
 
         Connection conn = DriverManager.getConnection("jdbc:mariadb://168.138.162.164:3306/mysql?" + "user=root&password=password&&serverTimezone=UTC");
 
diff --git a/src/test/java/secure/x509Cert.java b/src/test/java/secure/X509CertTest.java
similarity index 62%
rename from src/test/java/secure/x509Cert.java
rename to src/test/java/secure/X509CertTest.java
index 0dda270..e0fbad5 100644
--- a/src/test/java/secure/x509Cert.java
+++ b/src/test/java/secure/X509CertTest.java
@@ -1,18 +1,17 @@
 package secure;
 
 import davidkhala.common.secure.X509CertTool;
+import javax.security.auth.x500.X500Principal;
 import org.junit.Test;
 import org.spongycastle.asn1.x500.X500Name;
 
-import javax.security.auth.x500.X500Principal;
-import java.io.IOException;
-
-public class x509Cert {
+public class X509CertTest {
 	@Test
-	public void getX500Cert() throws IOException {
+	public void getX500Cert()  {
 		X500Name x500Name = X509CertTool.CsrHelper.getX500Name("david", "mediconcen");
-		System.out.println(x500Name.toString());
+		assert x500Name.toString().equals("CN=david,OU=mediconcen,O=,L=,ST=,C=");
+
 		X500Principal x500Principal = X509CertTool.CsrHelper.getX500Principal("david");
-		System.out.println(x500Principal.toString());
+		assert x500Principal.toString().equals("CN=david, OU=, O=, L=, ST=, C=");
 	}
 }