java - 扫描 Java 中的类或 jar 文件

Question

我需要扫描实现或扩展特定类的类或 jar 文件。
这与 Eclipse 用于扫描插件存在的机制相同。有办法做到这一点吗？

Answer 1

来自exmaple depot: How to load a Class that is not on the classpath :

// Create a File object on the root of the directory 
// containing the class file
File file = new File("c:\\class\\");

try {
    // Convert File to a URL
    URL url = file.toURL();          // file:/c:/class/
    URL[] urls = new URL[]{url};

    // Create a new class loader with the directory
    ClassLoader loader = new URLClassLoader(urls);

    // Load in the class; Class.childclass should be located in
    // the directory file:/c:/class/user/information
    Class cls = loader.loadClass("user.informatin.Class");
} catch (MalformedURLException e) {
} catch (ClassNotFoundException e) {
}

如有必要，使用File.list()列出目录中的文件。

当类被加载时，您可以通过执行clazz.isInstance来检查它是否实现了特定的接口(interface)。来自文档:

Determines if the specified Object is assignment-compatible with the object represented by this Class. This method is the dynamic equivalent of the Java language instanceof operator.

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从 jar 文件加载类:

How to load a jar file at runtime

列出 jar 文件中的文件:JarFile.entries()。