Reference Jars Inside a Jar

Reference jars inside a jar

You will need a custom class loader for this, have a look at One Jar.

One-JAR lets you package a Java application together with its dependency Jars into a single executable Jar file.

It has an ant task which can simplify the building of it as well.

REFERENCE (from background)

Most developers reasonably assume that putting a dependency Jar file into their own Jar file, and adding a Class-Path attribute to the META-INF/MANIFEST will do the trick:

jarname.jar
| /META-INF
| |  MANIFEST.MF
| |    Main-Class: com.mydomain.mypackage.Main
| |    Class-Path: commons-logging.jar
| /com/mydomain/mypackage
| |  Main.class
| commons-logging.jar

Unfortunately this is does not work. The Java Launcher$AppClassLoader does not know how to load classes from a Jar inside a Jar with this kind of Class-Path. Trying to use jar:file:jarname.jar!/commons-logging.jar also leads down a dead-end. This approach will only work if you install (i.e. scatter) the supporting Jar files into the directory where the jarname.jar file is installed.

Classpath including JAR within a JAR

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).

Referencing jars from other projects in the build path in eclipse

You are not referencing the jars in JARS-Project from ProjectX, you are referencing JARS-Project from ProjectX, which is different.

To reference the jars in JARS-Project from ProjectX, you have to reference each jar individually. So go to your build path for ProjectX, then go to Libraries tab, then press "Add Jars", then find each jar you need from the JARS-Project project and add individually.

Note, for this to work the jar files themselves must be in the JARS-Project project. If JARS-Project only references the jars from elsewhere in the file system this will not work.

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