Selectively include dependencies in JAR_问答_开发者

I have a library that I wrote in Scala that uses Bouncy Castle and has a whole bunch of dependencies. When I roll a jar, I can either roll a "fat" jar that has all the dependencies (including scala), which weighs in around 19 MB, or I can roll a skinny jar, which doesn't have dependencies, but is only a few hundred KB.

The problem is that I need to include the Bouncy Castle classes/jar with my library, because if its not on the classpath at runtime, all kinds of开发者_Go百科 exceptions get thrown.

So, I think the ideal situation is if there is some way that I can get either Maven or SBT to include some but not all dependencies in the jar that gets rolled. Some dependencies are needed at compile-time, but not at run time, such as the Scala standard libraries. Is there some way to get that to happen?

Thanks!

I would try out the sbt proguard plugin from https://github.com/nuttycom/sbt-proguard-plugin . It should be able to weed out the classes that are not in use.

If it is sufficient to explicitly define which dependencies should be added (one the artifact-level, i.e., single JARs), you can define an assembly (in case of a single project) or an additional assembly project (in case of a multi-module project). Assembly descriptors can explicitly exclude/include artifacts from the dependencies.

Here is some good documentation on this topic (section 8.5.4), here is the official documentation.

Note that you can include all artifacts that belong to one group by using the wildcard notation in dependecySets, e.g. hibernate:*:jar would include all JAR files belonging to the hibernate group.

Covering maven...

Because you declare your project to be dependent upon bouncy castle in your maven pom, anybody using maven to depend upon your library will by default pull in bouncy castle as a transitive dependency.

You should set the appropriate scope on your dependencies, e.g. compile for stuff needed at compile and runtime, test for dependencies only needed in testing and provided for stuff you expect to be provided by the environment.

Whether your library's dependencies are packaged into dependent projects when they are built is a question of how those are projects configured and setting the scopes will influence the default behaviour.

For example, jar type packaging by default does not include dependencies, whereas war will include those in compile scope (but not test or provided). The design aim here was to have packaging plugins behave in the most commonly required way without needing configuration, but of course packaging plugins in maven can be configured to have different behaviour if needed. The plugins themselves which do packaging are well documented at the apache maven site.

If users of your library are unlikely to be using maven to build their projects, an option is to use the shade plugin which will allow you to produce an "uber-jar" which contains all the dependencies you wish. You can configure particular includes or excludes.

This can be a problematic way to deliver, for example where your library includes dependencies which version clash with the direct dependencies of projects using it, i.e. they use a different version of the same libraries yours does.

However if you can it is best that you leave this to maven to manage so that projects using your library can decide whether they want your dependencies or to specify particular versions giving them more flexibility. This is the idiomatic approach.

For more information on dependencies and scopes in maven, see the reference guide published by Sonatype.

I'm not a scala guy, but I have played around with assembling stuff in Java + Maven.

Have you tried looking into creating your own assembly descriptor for the assembly plugin? https://maven.apache.org/plugins/maven-assembly-plugin/assembly.html

You can copy / paste the jar-with-dependencies descriptor then just add some excludes to your < dependencySet >. I'm not a Maven expert, but you should be able to configure it so different profiles kick off different assembly builds.

EDIT: Ack, didn't see my HTML got hidden