Java：库中的库和类路径问题

Question

We are having a discussion at work and an interesting point came up:

Say you are developing a small library, call it somelib . Say that somelib needs to do some logging, but you don't want to reinvent the wheel, so you decide to use a 3rd party logging library.

Additionally, you want to make integration of somelib as painless as possible, so you distribute a single JAR file (somelib.jar), which has the other logging JAR, call it logger.jar, embedded inside of it . Much like what Maven's jar-with-dependencies assembly does.

Now comes the issue. Since your product is a library, what if your customer is using somelib and also happen to be using a different version of the same logging library on their own. Now we have a classpath problem.

This seems to me like it would be a common problem for people that write libraries, so what is the typical solution?

1. Do they avoid using JAR bundling methods altogether? Even if we do that, there is still an issue with a user's code expecting version X of the logging library, and somelib 's code expecting version Y.

2. Do they somehow insert a dummy package prefix so that the logger classes in somelib won't conflict?

3. What about dynamic loading of the logger library? (though this still has versioning problems from 1.)

Answer 1

您可以考虑使用OSGI或等待JDK 8及其Jigsaw项目。