Running a JAR File that Includes Another JAR From the Command Prompt

Today I got a question from a colleague on how-to run a JAR file that includes another JAR file directly from the command prompt, he couldn't get this to work - it just ended up with java.lang.NoClassDefFoundError exception. At first glance this seemed quite trivial, but it turned out to be more complicated than I first thought. My initial attempts also resulted in java.lang.NoClassDefFoundError, so I started to search around a bit for further information about the topic. This led me to this site http://one-jar.sourceforge.net/, and (as always) it turned out that someone else already solved the problem.


As I use JDeveloper (of course...) it needs to be added a few steps in addition to using one-jar to get the whole process to work, this is documented below.


1. First I created a new Workspace in JDeveloper with 2 projects 'mainproject' and 'subproject'.


2. In the 'subproject' there is a single dummy that have one method that just writes something to the System.out. There is also a JAR deployment profile that includes the mentioned class. The target JAR file I just called sub.jar.


3. Now it's time to create the 'mainproject'. As I am using the One-JAR in the end there are 2 restrictions I need to take into account for this project:

a. The main class needs to be named 'Main'
b. The target JAR file needs to be called 'main.jar'

I created a new class called 'Main' in the 'mainproject', added a dependency in the Project Properties to 'subproject' and created a dummy method in this class that uses the class created under 2. I ran the Main class inside JDeveloper to ensure that it worked before proceeding.

After that I created a JAR deployment profile. I made sure to name the target JAR file to 'main.jar'. Also checked the 'Include Manifest File (META-INF/MANIFEST.MF)' box and pointed the 'Main Class' to my 'Main' class. Next I made sure NOT to include my classes from the 'subproject' into this JAR file. This as they will be provided in a separate JAR file.


4. Next, it was time to download and install One-JAR. One-JAR can be downloaded from http://sourceforge.net/projects/one-jar. I created a new empty folder on my file system and placed the one-jar-boot-0.95.jar file there and renamed this to one-jar.jar. In my newly created folder I also added 2 subfolders 'main' and 'lib'. Once done I deployed my 2 JAR filed from JDeveloper, main.jar and sub.jar and placed them in the respective folders (main.jar in main and sub.jar in lib). The archive now has a structure similar to what is shown below:

5. Now it's time to test this, and if it works correctly then the result should look something like:

D:\home\Demos\OneJARDemo\deploy>java -jar one-jar.jar
Hello from Main
Hello from sub project!