In the Linux environment, JAR (Java ARchive) files are a common way to package and distribute Java applications. Understanding how to create and run JAR files is essential for Java developers and system administrators working in a Linux environment. This article will guide you through the process of creating a JAR file from Java source code and running it via the command line on a Linux system.

Examples:

1. Creating a JAR File:

   To create a JAR file, you first need to compile your Java source code into bytecode using the javac command. Then, you use the jar command to package the compiled classes into a JAR file.

   • Step 1: Compile Java Source Code

     javac MyProgram.java

     This command compiles MyProgram.java into MyProgram.class.

   • Step 2: Create the JAR File

     jar cvf MyProgram.jar MyProgram.class

     This command creates a JAR file named MyProgram.jar containing the MyProgram.class file. The options used are:

     • c: Create a new JAR file.
     • v: Generate verbose output.
     • f: Specify the JAR file name.

2. Running a JAR File:

   Once you have created the JAR file, you can run it using the java command with the -jar option.

   • Step 1: Run the JAR File

     java -jar MyProgram.jar

     This command runs the MyProgram.jar file.

3. Creating an Executable JAR File:

   If your Java program has a main method, you can create an executable JAR file by specifying the Main-Class attribute in a manifest file.

   • Step 1: Create a Manifest File Create a file named manifest.txt with the following content:

     Main-Class: MyProgram

     Ensure there is a newline at the end of the file.

   • Step 2: Create the Executable JAR File

     jar cvfm MyProgram.jar manifest.txt MyProgram.class

     This command creates an executable JAR file named MyProgram.jar with the specified manifest file.

   • Step 3: Run the Executable JAR File

     java -jar MyProgram.jar

     This command runs the executable JAR file.

4. Automating the Process with a Script:

   You can automate the process of compiling and creating JAR files using a shell script.

   • Step 1: Create a Shell Script Create a file named build.sh with the following content:

     #!/bin/bash
     javac MyProgram.java
     jar cvfm MyProgram.jar manifest.txt MyProgram.class

   • Step 2: Make the Script Executable

     chmod +x build.sh

   • Step 3: Run the Script

     ./build.sh