Home Page
>
Deployment
>
Packaging Programs in JAR Files
Using JAR-related APIs
The Java platform contains several classes for use with JAR files. Some of these APIs are:
To give you an idea of the possibilities that are opened up
by these new APIs, this lesson guides you through the inner workings of
a sample application called JarRunner.
An Example - The JarRunner Application
JarRunner enables you to run an application that's bundled in a JAR
file by specifying the JAR file's URL on the command line. For example,
if an application called
TargetApp were bundled in a JAR file at
http://www.example.com/TargetApp.jar, you could run
the application using this command:
java JarRunner http://www.example.com/TargetApp.jar
In order for JarRunner to work, it must be able to perform the following
tasks, all of which are accomplished by using the new APIs:
- Access the remote JAR file and establish a communications
link with it.
- Inspect the JAR file's manifest to see which of the classes in the
archive is the main class.
- Load the classes in the JAR file.
The JarRunner application consists of two classes, JarRunner
and JarClassLoader. JarRunner delegates most of the JAR-handling
tasks to the JarClassLoader class. JarClassLoader extends
the java.net.URLClassLoader class. You can browse the source code for
the JarRunner and JarClassLoader classes
before proceeding with the lesson:
This lesson has two parts:
This section shows you how JarClassLoader uses some of the new APIs
to perform tasks required for the JarRunner application to work.
This section summarizes the JarRunner class that comprises the
JarRunner application.
