如何在Java中选择从哪个库导入类？

Question

I have two versions of a Java library model.jar , each with the same set of classes (but different implementations). I want to write a Java class that imports some classes from one version, and imports some from the other version.

I know I can include both in compilation by giving them different names:

javac -cp model.jar;model2.jar MyClass.java

But any import statement will import the corresponding class from the first .jar file I specify in the classpath.

Can I specify in my import statement which library to import from, given that the library structure will be the same for both files?

Answer 1

It is not possible (well actually, at least not that simply).

Depending on what you are trying to achieve, if you really have to use two versions of a library, you can try a module system like OSGi , Jboss-Modules , or something like that.

Answer 2

If the classes have the same name (including the package) there is no chance unless you work with different class loaders. Java will always use the first matching class it finds on the class path.

Moreover, nasty problems may arise if you use the same library in different versions. You should really try to resolve this in another way.

Answer 3

You can't like this.

The only thing you can do is to use a script to generate one jar from the two with the classes that you want, and put that jar in the classpath