Classpath including JAR within a JAR

Question

If you're trying to create a single jar that contains your application and its required libraries, there are two ways (that I know of) to do that. The first is One-Jar, which uses a special classloader to allow the nesting of jars. The second is UberJar, (or Shade), which explodes the included libraries and puts all the classes in the top-level jar.

I should also mention that UberJar and Shade are plugins for Maven1 and Maven2 respectively. As mentioned below, you can also use the assembly plugin (which in reality is much more powerful, but much harder to properly configure).

You do NOT want to use those "explode JAR contents" solutions. They definitely make it harder to see stuff (since everything is exploded at the same level). Furthermore, there could be naming conflicts (should not happen if people use proper packages, but you cannot always control this).

The feature that you want is one of the top 25 Sun RFEs: RFE 4648386, which Sun, in their infinite wisdom, has designated as being of low priority. We can only hope that Sun wakes up...

In the meanwhile, the best solution that I have come across (which I wish that Sun would copy in the JDK) is to use the custom class loader JarClassLoader.

After some research I have found method that doesn't require maven or any 3rd party extension/program.

You can use "Class-Path" in your manifest file.

For example:

Create manifest file MANIFEST.MF

Manifest-Version: 1.0
Created-By: Bundle
Class-Path: ./custom_lib.jar
Main-Class: YourMainClass

Compile all your classes and run jar cfm Testing.jar MANIFEST.MF *.class custom_lib.jar

c stands for create archive f indicates that you want to specify file v is for verbose input m means that we will pass custom manifest file

Be sure that you included lib in jar package. You should be able to run jar in the normal way.

based on: http://www.ibm.com/developerworks/library/j-5things6/

all other information you need about the class-path do you find here

Use the zipgroupfileset tag (uses same attributes as a fileset tag); it will unzip all files in the directory and add to your new archive file. More information: http://ant.apache.org/manual/Tasks/zip.html

This is a very useful way to get around the jar-in-a-jar problem -- I know because I have googled this exact StackOverflow question while trying to figure out what to do. If you want to package a jar or a folder of jars into your one built jar with Ant, then forget about all this classpath or third-party plugin stuff, all you gotta do is this (in Ant):

<jar destfile="your.jar" basedir="java/dir">
  ...
  <zipgroupfileset dir="dir/of/jars" />
</jar>

If you are building with ant (I am using ant from eclipse), you can just add the extra jar files by saying to ant to add them... Not necessarily the best method if you have a project maintained by multiple people but it works for one person project and is easy.

for example my target that was building the .jar file was:

<jar destfile="${plugin.jar}" basedir="${plugin.build.dir}">
    <manifest>
        <attribute name="Author" value="ntg"/>
        ................................
        <attribute name="Plugin-Version" value="${version.entry.commit.revision}"/>
    </manifest>
</jar>

I just added one line to make it:

<jar ....">
    <zipgroupfileset dir="${external-lib-dir}" includes="*.jar"/>
    <manifest>
        ................................
    </manifest>
</jar>

where

<property name="external-lib-dir" 
          value="C:\...\eclipseWorkspace\Filter\external\...\lib" />

was the dir with the external jars. And that's it...