Pre-requisites:
JRE(any version above 1.2)
JDK (any version above 1.2)
This article demonstrates the creation of an executable jar file. This is a hands-on tutorial, I recommend you to follow the below mentioned steps practically instead of simply reading this tutorial.
Step 1:
Download Source Code (nodalo-src.zip) and Binary Classes (nodalo-bin.zip) of the sample Java Project used in this post. Extract the downloaded archive nodalo-bin.zip to Windows D: Drive (D drive optional, can be extracted to any folder).
The structure of the folder ‘nodalo-bin’ would look like this:
nodalo-bin
|___com
|__A.class
|__B.class
|__C.class
|___foo
|__D.class
There is a root directory ‘nodalo-bin’, which in turn has two directories ‘com’ and ‘foo’. Package com contains classes A.class, B.class, C.class . Package foo contains class D.class .
Class B.class has the main method. Our aim is to create an executable jar file, name it nodalo.jar and run main method in the Java Class B.
Step 2:
Create a jar file nodalo.jar that has the directories com and foo in it.
Browse to the directory named “nodalo-bin” and execute the following command in Command Prompt or Terminal.
D:\nodalo-bin> jar cvf nodalo.jar com foo
This command would create nodalo.jar
To view the contents of this jar file, execute:
D:\nodalo-bin>jar tf nodalo.jar
The following output would be shown:
META-INF/MANIFEST.MF com/ com/A.class com/B.class com/C.class foo/ foo/D.class
Note that META-INF folder and the file MANIFEST.MF were created on their own.
Step 3:
To execute this jar file, run command:
D:\nodalo-bin>java -jar nodalo.jar
An error similar to the one below would result in the output:
Failed to load Main-Class manifest attribute from nodalo.jar
Step 4:
This is because java does not know where to look for the main method. So we need to explicitly add a manifest file that tells JVM about the Class that contains main method in this Java project.
Create a new text file, name it mainClass.txt and put the following line of code in it:
Main-Class: com.B
Save mainClass.txt in the nodalo-bin directory. The above line instructs JVM to look for main method in B.class
To merge this Manifest file with the one already existing in nodalo.jar, execute the command:
D:\nodalo-bin> jar cmf mainClass.txt nodalo.jar com foo
Now, try executing the jar again:
D:\nodalo-bin>java -jar nodalo.jar
The above command should result in output:
Inside Class D Inside Class C Inside Class B Inside Class A
Great! We have successfully created an executable jar file. Please comment below, if this tutorial helped you.
Read more about Manifest File in Java.
About the Author: Sridhar Jammalamadaka is the Editor of Interview Mantra. He's a typically non-typical Software Engineer from Pune, India. He likes entrepreneurship, web technologies and Micro Controller programming. He enjoys playing cricket and piano (but rarely does these activities). Through this website, he wishes to gather a large community of aspiring engineers, entrepreneurs and professionals from all parts of the globe. You can connect with him on Facebook - http://www.facebook.com/sridhar.j