Presents your 
JAVA E-NEWSLETTER for April 17, 2003

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TAKE ADVANTAGE OF RUNNABLE JARS

Jar files make getting classes into the classpath easy and can also make
your application easier to run. Runnable jars have been around since
Java 1.2, but many developers don't take advantage of them.

A runnable jar is a jar that you can execute with a command such as:

java -jar application.jar

The -jar tells the virtual machine to look at the jar's manifest file to
find the class name that is the starting point of the application. You
indicate the class where execution should begin by including a Main-Class
entry in the jar's manifest file:

Main-Class: com.somecompany.someapp.MainClass

To include your own manifest file while creating a jar, use the jar tool's -m switch:

jar cmf manifest runnable.jar .

For example, runnable jars can turn this:

java -cp application.jar com.somecompany.someapp.MainClass

into this:

java -jar application.jar

Not only is that less typing, but it's also less to remember.

However, if your application runs inside of a container or you have a
lot of other jars you need to put in your classpath, then a runnable 
jar might not be the best fit for your environment.

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