在Jar文件中加载类并获取它的路径 [英] Load class within Jar file and get it's path

问题描述

我知道这里已经有很多类似的问题，但我无法让他们更聪明。我想在jar文件中加载一个类，此时这没有问题，但是当我想将路径传递给我自己的ClassLoader时，它会抛出一个无法找到类的异常。是否可以使用绝对路径在jar中加载类？例如，
Class cls = loader.loadClass（/path/MyPlugin.jar/MyPlugin.class）;

I know there are already a lot similar questions here, but I couldn't get any smarter form them. I want to load a class inside a jar file, at this point this is no problem, but when I want to pass the path to my own ClassLoader it throws an exception it cannot find the class. Is it possible to load a class inside a jar using an absolute path? For instance,
Class cls = loader.loadClass(/path/MyPlugin.jar/MyPlugin.class);

但是当我这样做时：

File test = new File("path/plugins/MyPlugin.jar/MyPlugin.class");
System.out.println(test.exists());

打印出false。我尝试使用 MyPlugin.jar！/MyPlugin.class 或 MyPlugin.jar.jar！MyPlugin.class 我是哪个我有时在网上看到过，即使我真的不知道这意味着什么......

It prints out false. I tried using MyPlugin.jar!/MyPlugin.class or MyPlugin.jar.jar!MyPlugin.class which i've seen sometimes on the web, even though i don't really know what it means...

当我这样做时，它找到了班级：

When I do this it finds the class:

URLClassLoader loader = new URLClassLoader(new URL[] { "path/plugins/MyPlugin.jar" });
Class cl = loader.loadClass("MyPlugin");

但是现在，我该如何收到路径？类似 URL url = cl.getResource（MyPlugin）; （返回null）

But now, how can I receive the path? Something like URL url = cl.getResource("MyPlugin"); (which gives back a null)

推荐答案

您可以使用 ClassLoader.getResources 。要查找具有特定类的jar，您可以使用以下

You can obtain URLs to classpath resources using ClassLoader.getResources. To find a jar with specific class, you may use the following

URL url = classLoader.getResource("com/example/SomeClass.class");
JarURLConnection connection = (JarURLConnection) url.openConnection();
JarFile file = connection.getJarFile();
String jarPath = file.getName();

其中 classLoader 是任何能够查找的类加载器要加载的类。如果jar是应用程序类路径的一部分，则可以使用系统类加载器：

where classLoader is any classloader capable of finding the class you want to load. If the jar is a part of your application's classpath, you may use system classloader:

ClassLoader classLoader = ClassLoader.getSystemClassloader();

否则，您需要事先知道jar文件位置，并创建一个<$ c $的实例c> URLClassLoader ，在构造函数中传递jar：

Otherwise, you need to know the jar file location beforehand, and create an instance of URLClassLoader, passing the jar in the constructor:

ClassLoader classLoader = new URLClassLoader(new URL[]{new URL("path/to/the/jar/file.jar")});

然后用它来加载你的课程。

and then use it to load your class.

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