How to Create And Execute JAR File in Linux

1. How to Create & Execute Jar File in Linux

2. 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"); } }

3. 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

4. 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

5. 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.

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