Java distribuion as jar file containg config, libs and deps

Question

Hi folks,

I am developing a framework that needs a lot of stuff to get working. I have several folders inside of my Eclipse project that are needed

[root]
- config
- src
- lib
- serialized

Also there are important files like the log4j.properties and the META-INF dir inside the src directory.

I wonder if there is a way to distribute one JAR containing all essential files so my gui will just have to import one jar. I guess that I have to exclude the config folder in order to make the framework configurable.

I also wonder, if there is a way to move for example the log4j.properties to the config dir so that I have one config folder containg all needed configurations?

Thanks for help and advise on this matter!

Marco

Answer 1

Yes, but not really. You can take all your dependencies, unpack them and simply merge them into a bigger jar. This is what the maven jar plugin does if you make a jar with dependencies. The only problem is that this might result in conflicting files (suppose two of your dependencies contain a log4j.properties). This is one of the problems when doing the above with some of the spring libraries for instance.

I think someone actually wrote a classloader that allows you to bundle the whole jar inside of your jar and use it as is. I'm not sure how mature that is though and can't at the moment recall the name.

I think you're better off distributing all your dependencies separately. Setting up the classpath is a bit of a pain but surely java programmers are used to it by now. You can add dependencies to the Class-Path header in your manifest file, in simple cases. Bigger libraries have to rely on the classpath being set up for them though.

As to the second part of your question, probably dropping the conf/ directory under META-INF is enough for its contents to be picked up. I'm not sure about this. I'm fairly sure it will always be picked up if you put its contents at the top level of the jar. In any case, this is a distribution problem. You can easily have a conf/ directory inside your source tree and have your build scripts (whatever you might be using) copy the files in it to wherever is most convenient.

As to your users configuring. Try to establish some conventions so they have to configure as little as possible. For things that must be configured, it's best to have a basic default configuration and then allow the user to override and add options through his/her own configuration file.

Answer 2

In terms of the resources, it is possible except that if you do that you are not going to be able to load resources (non class files) from the filesystem (via a file path).

It's likely that you're currently loading these resources from the file system. Once in the jar you need to load them as class path resources via the class.getResourceAsStream or similar.

As for the dependent jars you may have, it's common practice for these to be placed as extra jars on the classpath. I know it's complicates things but developers are used to doing this. The nature of the java landscape is that this is inevitable. What the spring framework for example does is supply a bundled zip file with the core jar and the jar dependencies included.

Is your library going to be used in an EE context or an SE context? If it is an EE context then you really don't have to worry about configuration and class path issues as the container takes care of that. In an SE context it is a lot more tricky as that work has to be done manually.