How to Create & Execute Jar File in Linux

A JAR(Java Archive) is a platform-independent file that allows you to easily deploy Java Applications in one place. It can be used to aggregate classes, images, text files into a single file for distribution. It improves application security, allows package versioning and enhances portability. In this article, we will learn how to bundle a Java application into a JAR file and how to execute .jar file from Linux command.

How to Create & Execute Jar File in Linux

We have assumed that you have already installed Java command line tool on your system, and you can use it with -jar option to execute a .jar file.

1. Create .java class

First we will create a simple Java class with main method for a demo app called HelloWorld. Create an empty .java file using a text editor.

$ vim HelloWorld.java

Add the following lines to it. It simply prints ‘Hello World’ upon execution.

public class HelloWorld {
	public static void main(String[] args){
		System.out.println("Hello World");
	}
}

2. Compile & Pack the Class into JAR file

Next you need to compile & pack the class into JAR file using javac & jar commands. Basically we first create a class out of our .java code, using javac command. Then we package the class into a .jar file using jar command.

$ javac -d . HelloWorld.java
$ ls
$ jar cvf helloworld.jar HelloWorld.class
$ ls

3. Create Manifest File

You need to create a separate manifest file, and update the JAR file to include it, in order to execute the JAR file. Create an empty manifest file.

$ vim MANIFEST.MF

Copy and paste the following code in it.

Main-Class:  HelloWorld

Save and close the file. Next add the manifest file to the JAR file using the following command.

$ jar cvmf MANIFEST.MF helloworld.jar HelloWorld.class

4. Execute JAR

Once the .jar file is created you can execute it with the following command.

$ java -jar helloworld.jar

Hello World

Running the above code produces the desired result. It is important to remember to create a manifest file and add it to the JAR file otherwise you will get the following error.

no main manifest attribute, in helloworld.jar

Whenever you run a JAR file the Java Virtual Machine (JVM) looks for its manifest attribute to locate the main class containing main method. So the JAR file must contain a line of the form Main-Class:classname to point to the class with main method, that serves as every application’s starting point.

In this article, we have learnt how to create and execute JAR files.

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