Java 在 Jar 文件中加载类并获取它的路径
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Load class within Jar file and get it's path
提问by domizai
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);
我知道这里已经有很多类似的问题，但我无法从它们中得到任何更聪明的答案。我想在 jar 文件中加载一个类，此时这没问题，但是当我想将路径传递给我自己的 ClassLoader 时，它会抛出一个异常，它找不到该类。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);
But when I do this:
但是当我这样做时：
File test = new File("path/plugins/MyPlugin.jar/MyPlugin.class");
System.out.println(test.exists());
It prints out false. I tried using MyPlugin.jar!/MyPlugin.classor MyPlugin.jar.jar!MyPlugin.classwhich i've seen sometimes on the web, even though i don't really know what it means...
它打印出错误。我尝试使用MyPlugin.jar!/MyPlugin.class或MyPlugin.jar.jar!MyPlugin.class有时在网上看到的，即使我真的不知道它意味着什么......
When I do this it finds the class:
当我这样做时，它会找到类：
URLClassLoader loader = new URLClassLoader(new URL[] { "path/plugins/MyPlugin.jar" });
Class cl = loader.loadClass("MyPlugin");
But now, how can I receive the path? Something like URL url = cl.getResource("MyPlugin");(which gives back a null)
但是现在，我怎样才能接收到路径呢？类似的东西URL url = cl.getResource("MyPlugin");（返回一个空值）
采纳答案by Marcin ?o?
You can obtain URLs to classpath resources using ClassLoader.getResources. To find a jar with specific class, you may use the following
您可以使用ClassLoader.getResources获取类路径资源的 URL 。要查找具有特定类的 jar，您可以使用以下命令
URL url = classLoader.getResource("com/example/SomeClass.class");
JarURLConnection connection = (JarURLConnection) url.openConnection();
JarFile file = connection.getJarFile();
String jarPath = file.getName();
where classLoaderis 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任何能够找到您想要加载的类的类加载器在哪里。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：
ClassLoader classLoader = ClassLoader.getSystemClassloader();
Otherwise, you need to know the jar file location beforehand, and create an instance of URLClassLoader, passing the jar in the constructor:
否则，您需要事先知道 jar 文件位置，并创建 的实例URLClassLoader，将 jar 传递到构造函数中：
ClassLoader classLoader = new URLClassLoader(new URL[]{new URL("path/to/the/jar/file.jar")});
and then use it to load your class.
然后用它来加载你的类。
回答by schaeferpp
If you want to access a file in your jar file you have to put it in the same directory as the class files are.
如果要访问 jar 文件中的文件，则必须将其放在与类文件相同的目录中。
For example if Main.class is in bin/my/pkg/Main.class you can store your MyPlugin.class in the same directory (bin/my/pkg/MyPlugin.class) and then, if you want to access that file use
例如，如果 Main.class 在 bin/my/pkg/Main.class 中，您可以将 MyPlugin.class 存储在同一目录 (bin/my/pkg/MyPlugin.class) 中，然后，如果您想访问该文件，请使用
URL url = Main.getResource("MyPlugin.class");
Which uses the location of Main.class in your project as root.
它使用项目中 Main.class 的位置作为根。
Hope it helps!
希望能帮助到你！
