Add comments in “logging-api” module .

skywalking-commons/skywalking-logging/skywalking-logging-api/src/main/java/com/a/eye/skywalking/logging/api/ILog.java

@@ -1,6 +1,10 @@
 package com.a.eye.skywalking.logging.api;
 
 /**
+ * The Log interface.
+ * It's very easy to understand, like any other log-component.
+ * Do just like log4j or log4j2 does.
+ * <p>
  * Created by xin on 2016/11/10.
  */
 public interface ILog {

skywalking-commons/skywalking-logging/skywalking-logging-api/src/main/java/com/a/eye/skywalking/logging/api/LogManager.java

@@ -1,6 +1,14 @@
 package com.a.eye.skywalking.logging.api;
 
 /**
+ * LogManager is the {@link LogResolver} implementation manager.
+ * By using {@link LogResolver}, {@link LogManager#getLogger(Class)} returns a {@link ILog} implementation.
+ * This module use this class as the main entrance, and block the implementation detail about log-component.
+ * In different modules, like server or sniffer, it will use different implementations.
+ * <p>
+ * If no {@link LogResolver} is registered, return {@link NoopLogger#INSTANCE} to avoid {@link NullPointerException}.
+ * If {@link LogManager#setLogResolver(LogResolver)} is called twice, the second will override the first without any warning or exception.
+ * <p>
  * Created by xin on 2016/11/10.
  */
 public class LogManager {

skywalking-commons/skywalking-logging/skywalking-logging-api/src/main/java/com/a/eye/skywalking/logging/api/LogResolver.java

@@ -1,8 +1,14 @@
 package com.a.eye.skywalking.logging.api;
 
 /**
+ * {@link LogResolver} just do only one thing: return the {@link ILog} implementation.
+ * <p>
  * Created by xin on 2016/11/10.
  */
 public interface LogResolver {
+    /**
+     * @param clazz, the class is showed in log message.
+     * @return {@link ILog} implementation.
+     */
     ILog getLogger(Class<?> clazz);
 }

skywalking-commons/skywalking-logging/skywalking-logging-api/src/main/java/com/a/eye/skywalking/logging/api/NoopLogger.java

@@ -2,9 +2,12 @@ package com.a.eye.skywalking.logging.api;
 
 
 /**
+ * No operation logger implementation.
+ * Just implement {@link ILog} interface, but do nothing.
+ * <p>
  * Created by xin on 2016/11/10.
  */
-public class NoopLogger implements ILog{
+public class NoopLogger implements ILog {
     public static final ILog INSTANCE = new NoopLogger();
 
     @Override