如何从不同的罐子加载相同的类 [英] how to load same class from different jars

问题描述

我在两个不同的jar jar1&中有一个Client.java类。 jar2
现在在运行时我想决定加载哪个Client.class如

I have a class Client.java in two different jars jar1 & jar2 Now at run time i want to decide which Client.class loaded like

if (country==india){
         // load Client class of jar1
) else{
        load client class from jar2 
}

我可以这么做......

can i do that...

推荐答案

如果2个班级有相同的包名称，即com.mycompany.Client，然后您最终会在某种情况下加载哪个版本的Client。它归结为首先在类路径上。这是一个JAR地狱的情况 http://en.wikipedia.org/wiki/Java_Classloader#JAR_hell。

If the 2 classes have the same package name, i.e. com.mycompany.Client, then you end up in a situation where it is somewhat arbitrary which version of Client is loaded. It comes down to which is on the classpath first. This is a JAR hell situation http://en.wikipedia.org/wiki/Java_Classloader#JAR_hell.

这是一个要避免的好情况，但如果你绝对必须拥有相同类的不同版本，那么有办法做到这一点。一种方法是使用自定义类加载器，类加载器将知道您需要执行哪个版本。这不是一件容易的事情，也很难管理。 OSGi框架是一种帮助管理它的替代方案（它使用自定义类加载器），但如果你只有一个类的实例，我就不会使用它，因为它是另一个需要时间和维护的框架。

This is a good situation to avoid but if you absolutely must have different versions of the same class, there are ways to do it. One way is to use a custom classloader and the classloader will know which version you need to do. This is not a trivial thing to do and can be difficult to manage. The OSGi framework is an alternative to help manage this (it uses custom classloaders under the hood), but I wouldn't use that if you just have one instance of a class as it is another framework that takes time and maintenance.

底线：如果可以，请避开这种情况，如果不能，请采取阻力最小的路径。

Bottom line: avoid the situation if you can and take the path of least resistance if you cannot.

如果是班级确实有不同的包名，@ Casidiablo提供了一个很好的答案。

If the classes do have different package names, @Casidiablo has provided a good answer.

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