JarSplice is an application that builds a fat jar, with the main difference being that JarSplice will build invocation scripts and include native resources.
The main weaknesses of JarSplice seems to be its lack of build tool integration, its (apparently) unmaintained status, and its lack of source code availability (even though it’s described as being under the BSD license).
A “fat jar” (or a “shaded jar”) is a jar file that has been bundled with a project’s full set of required resources.
To explain, imagine that we have a Java project called “foo“, that depends on an external project, called “bar.”
For foo to run properly, then, our runtime classpath must contain foo.jar:bar.jar (in some order, although the order can be significant); both files must be present for the classloader to read in order for the project to run.
A “fat jar,” however, includes all of the resources from the classpath in a single jar. The build would extract every class from both foo.jar and bar.jar and built a new jar – named, for example, foo-all.jar – and therefore only this file would be required in order to run the project, since it has every resource that the prior classpath held.
However, this only works for Java resources; it doesn’t include native resources, like LWJGL‘s or SQLite‘s binary components. If foo uses SQLite, then the computer that foo is running on has to have SQLite deployed as a system library in order for foo to run.
This is what JarSplice addresses; it does bundle SQLite or LWJGL resources into the fat jar.
Again, the main weakness of JarSplice is that it’s not integrated into a build tool, so invoking it is an external mechanism for deployment. Development seems to have stopped (the home page says the code is BSD-licensed but no reference to the code exists.) Luis Quesada Torres built a command-line tool, JarSplicePlus; there are forks of that project that seem like there’s some promise for the future.
Feel free to participate and comment.