JAR

JAR (Java Archive) is a package file format used to aggregate multiple Java class files, associated metadata, and resources (text, images, etc.) into one file for distribution.

What is a JAR file?

A JAR file is essentially a ZIP file with a .jar extension that contains compiled Java classes and resources needed for a Java application or library.

Creating JAR files

The basic syntax for creating a JAR file using the command line:

jar cf jar-file input-files

Where:

• c indicates you want to create a new archive
• f specifies the archive filename
• jar-file is the name you want to give your JAR file
• input-files are the files you want to include

Example:

jar cf myProgram.jar *.class

The Manifest file

JAR files can include a special META-INF/MANIFEST.MF file that contains metadata about the JAR:

Manifest-Version: 1.0
Main-Class: com.example.MainClass

To create a JAR with a manifest:

jar cfm myProgram.jar manifest.txt *.class

Executable JAR files

To create an executable JAR:

1. Create a manifest file with Main-Class specified
2. Include the manifest when creating the JAR

Example manifest (manifest.txt):

Main-Class: com.example.MainClass

Creating the executable JAR:

jar cfm myProgram.jar manifest.txt *.class

Running the JAR:

java -jar myProgram.jar

Viewing JAR Contents

To list the contents of a JAR file:

jar tf myProgram.jar

Extracting JAR Contents

To extract the contents of a JAR file:

jar xf myProgram.jar