How to extract a jar file.
A jar file can be extracted using the jar command that is part of the JDK. It can be found at <JAVA_HOME>binjar.exe on Windows machines and at <JAVA_HOME>/bin/jar on *nix machines (where <JAVA_HOME> is the root installation of your JDK).
In a command window/shell terminal type the jar command followed by the options xf 'jar -xf <filename>' (where <filename> is the jar file you want to extract). This will extract the jar to the present directory/folder.
Follow this link for a full explanation of the capabilities of the jar tool and all available command line switches. http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/jar.html
To extract myApp.jar to it's current directory you would navigate to the directory it's contained in and use: jar -xf myApp.jar