Executable .jar, with onejar-maven-plugin

Post published:March 22, 2009
Post Author:Hugo Josefson
Post Category:Java / Tips & Tricks
Post Comments:32 Comments

Onejar-maven-plugin collects your application including dependencies, into one executable jar. It’s both easy and works well!

(UPDATED for version 1.3.0. See below.)

Problem

If you have ever tried doing this before with Maven, you have probably used maven-assembly-plugin, which would leave the door open for classpath problems!

It would extract all your dependency jars in one directory together with all your class files and all other classpath resources. The problem is that everything ended up in a big mix, with classpath resources possibly overwriting each other. For example, if two dependencies each had a log4j.properties file in their jar, one log4j.properties would overwrite the other.

No more of that mess!

Solution

Enter maven-onejar-plugin. It lets all your dependency jars stay jars, and your code is in its own jar. All of those jars are put in a bigger jar, which is made executable.

Configuration

It may sound weird, but it’s quite elegant! Just put this in your pom.xml‘s <plugins> tag to make it work:


    org.dstovall
    onejar-maven-plugin
    
        1.3.0
    
    
        
            
                
                    your.package.YourMainClass
                
            
            
                one-jar

You also need to add this to the pom:


    
        onejar-maven-plugin.googlecode.com
        http://onejar-maven-plugin.googlecode.com/svn/mavenrepo

Please note the new Maven repository URL. Me and onejar-maven-plugin founder Drew Stovall just recently moved the project to Google Code to make it more open and easier for others (like me!) to pitch in. ~~Yesterday, I released version 1.2.3 of onejar-maven-plugin to our new Maven repo at Google Code.~~ UPDATE: Just released version 1.3.0 with optional support for including and autoloading native libraries such as .dll files. (detailed usage instructions.)

Make sure you get the <pluginRepository> URL right so that the latest version will be available to you!

Use

Then do this to build everything:

mvn install

That will build both your normal jar, as well as another jar. You will get these:

Standalone one-jar.jar file, along with the original .jar file.

myApp.one-jar.jar is the big executable that includes both myApp.jar, and all dependency jars.

You can run it standalone without any extra files, like this:

java -jar target/myApp.one-jar.jar

If you found this interesting, you might find my post about winstone-maven-plugin enlightning as well. It shows you how to make an executable .war file.

Credits

Thank you Drew Stovall for creating this Maven plugin in the first place, and thank you to the other contributors who have also submitted patches.

Project homepage: http://onejar-maven-plugin.googlecode.com

Tags: assembly, executable, jar, maven, onejar, open source, programming, tools

This Post Has 32 Comments

Ulrik Sandberg 17 Apr 2009 Reply

If you run into problems when using onejar-maven-plugin in an annotation-based Spring project, chances are that it’s the classpath scanning that is the problem.

I had the following setup:

Class:

package com.example;

@Component("transformer")
public class MyTransformer {

Spring config:

<context:component-scan base-package="com.example" />

Bootstrapping code:

	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		MyTransformer transformer = (MyTransformer) context.getBean("transformer");
		transformer.run();
	}

I got the following exception:

NoSuchBeanDefinitionException: No bean named 'transformer' is defined

I then switched to this config, still using annotation-based dependency autowire, but requiring an explicit bean definition: