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Using Java jar files. This tutorial explains the usage and purpose of Java JAR files.

1. Defining and using Java libraries

1.1. What is a Java library?

A Java library contains code which you can access and use in your Java project. The deployment format of a Java library is a JAR file.

1.2. What is a JAR file?

A JAR file is a Java archive based on the pkzip file format. JAR files are the deployment format for Java. A JAR can contain Java classes and other resources (icons, property files, etc.) and can be executable.

You can distribute your program in a jar file or you can use existing java code via jars by putting them into your classpath.

If you add a JAR file to your classpath, you can use its classes in your Java application.

2. Executable JAR

An executable JAR means the end-user can run the Java application without explicitly specifying the Java class which should be started. This is done via a MANIFEST.MF file which tells the JVM among other things which class contains the main() method and the classpath.

The following example shows one possible MANIFEST.MF file.

Manifest-Version: 1.0
Main-Class: com.vogella.example.MyApp
Class-Path:. lib/jcommon-1.0.6.jar lib/itext-1.4.6.jar

An empty line is required at the end of the MANIFEST.MF file.

You can create an executable JAR file via the following command.

jar -cvmf MANIFEST.MF app1.jar *.class

Eclipse provides an export wizard to create a JAR file which can be started via File ▸ Export ▸ Java ▸ JAR file.

Create JAR file with the Eclipse export wizard

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Copyright © 2012-2016 vogella GmbH. Free use of the software examples is granted under the terms of the EPL License. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.

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