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.
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 delegates most of the JAR-handling tasks to the
JarClassLoader extends the
java\.net\.URLClassLoader class. You can browse the source code for the
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.