Add comments on “application-toolkit” module.

skywalking-application-toolkit/skywalking-toolkit-log4j-1.x/src/main/java/com/a/eye/skywalking/toolkit/log/log4j/v1/x/TraceIdPatternConverter.java

@@ -4,6 +4,9 @@ import org.apache.log4j.helpers.PatternConverter;
 import org.apache.log4j.spi.LoggingEvent;
 
 /**
+ * Default implementation outputs "TID: N/A".
+ * But, if in sky-walking agent active mode, output will become the real TraceId.
+ * <p>
  * Created by wusheng on 2016/12/7.
  */
 

skywalking-application-toolkit/skywalking-toolkit-log4j-1.x/src/main/java/com/a/eye/skywalking/toolkit/log/log4j/v1/x/TraceIdPatternLayout.java

@@ -3,8 +3,12 @@ package com.a.eye.skywalking.toolkit.log.log4j.v1.x;
 
 import org.apache.log4j.PatternLayout;
 import org.apache.log4j.helpers.PatternParser;
+import org.apache.log4j.spi.LoggingEvent;
 
 /**
+ * The log4j extend pattern.
+ * By using this pattern, if sky-walking agent is also active, {@link PatternParser#finalizeConverter(char)} method will be override dynamic.
+ * <p>
  * Created by wusheng on 2016/12/7.
  */
 public class TraceIdPatternLayout extends PatternLayout {

skywalking-application-toolkit/skywalking-toolkit-log4j-1.x/src/main/java/com/a/eye/skywalking/toolkit/log/log4j/v1/x/TraceIdPatternParser.java

@@ -3,9 +3,10 @@ package com.a.eye.skywalking.toolkit.log.log4j.v1.x;
 import org.apache.log4j.helpers.PatternParser;
 
 /**
+ * Base on '%T', use {@link TraceIdPatternConverter} to convert the '%t' to traceId.
+ * <p>
  * Created by wusheng on 2016/12/7.
  */
-
 public class TraceIdPatternParser extends PatternParser {
     public TraceIdPatternParser(String pattern) {
         super(pattern);