Java Cookbook

Running a Program from a JAR

Problem

You want to distribute a single large file containing all the classes of your application, and run the main program from within the JAR.

Solution

Create a JAR file with a Main-Class: line in the manifest; run the program with the java -jar option.

Discussion

The java command has a -jar option that tells it to run the main program found within a JAR file. In this case, it will also find classes it needs to load from within the same JAR file. How does it know which class to run? You must tell it. Create a one-line entry like this:

Main-class: HelloWorld

in a file called, say, manifest.stub, and assuming that you want to run the program HelloWorld . Then give the following commands:

C:> jikes HelloWorld.java
C:> jar cvmf manifest.stub hello.jar HelloWorld.class
C:> java -jar hello.jar
Hello, World of Java
C:>

You can now copy the JAR file anywhere and run it the same way. You do not need to add it to your CLASSPATH or list the name of the main class.