[Java] Jars inside Jar

Jar that contains multiple jars inside is not support directly by Java. There are some workarounds on this.

• Put jars in to jar as ordinary files then load them with your own customized classloader. There is a tool such as One-JAR™ but some people told that it causes performance problem (I have not try this).
  
• Extract jars to .class and pack them together to a single jar. You can archive this easily with Ant's Zip Task
  

For me, I choose the second approach. There are more workarounds in reference links below.

Java: Easiest way to merge a release into one jar-file
Is it possible to package all the jar dependencies in one big jar ?