如何在运行时从文件夹或JAR加载类？ [英] How to load Classes at runtime from a folder or JAR?

问题描述

我试图创建一个Java工具，它将扫描Java应用程序的结构并提供一些有意义的信息。要做到这一点，我需要能够从项目位置（JAR / WAR或只是一个文件夹）扫描所有的.class文件，并使用反射读取他们的方法。这证明是几乎不可能的。

I am trying to make a Java tool that will scan the structure of a Java application and provide some meaningful information. To do this, I need to be able to scan all of the .class files from the project location (JAR/WAR or just a folder) and use reflection to read about their methods. This is proving to be near impossible.

我可以找到很多基于URLClassloader的解决方案，允许我从目录/存档加载特定的类，但没有一个允许我加载类，而没有关于类名或包结构的任何信息。

I can find a lot of solutions based on URLClassloader that allow me to load specific classes from a directory/archive, but none that will allow me to load classes without having any information about the class name or package structure.

编辑：
我认为我写得很差。我的问题不是我不能得到所有的类文件，我可以做递归等，并找到它们正确。我的问题是获取每个类文件的Class对象。

I think I phrased this poorly. My issue is not that I can't get all of the class files, I can do that with recursion etc. and locate them properly. My issue is obtaining a Class object for each class file.

推荐答案

以下代码从JAR文件加载所有类。它不需要知道关于类的任何东西。这些类的名字是从JarEntry中提取的。

The following code loads all classes from a JAR file. It does not need to know anything about the classes. The names of the classes are extracted from the JarEntry.

JarFile jarFile = new JarFile(pathToJar);
Enumeration<JarEntry> e = jarFile.entries();

URL[] urls = { new URL("jar:file:" + pathToJar+"!/") };
URLClassLoader cl = URLClassLoader.newInstance(urls);

while (e.hasMoreElements()) {
    JarEntry je = e.nextElement();
    if(je.isDirectory() || !je.getName().endsWith(".class")){
        continue;
    }
    // -6 because of .class
    String className = je.getName().substring(0,je.getName().length()-6);
    className = className.replace('/', '.');
    Class c = cl.loadClass(className);

}

编辑：

如上所述，javassist也是一种可能性。
在上面代码的while循环之前的某个地方初始化一个ClassPool，而不是用类加载器加载类，你可以创建一个CtClass对象：

As suggested in the comments above, javassist would also be a possibility. Initialize a ClassPool somewhere before the while loop form the code above, and instead of loading the class with the class loader, you could create a CtClass object:

ClassPool cp = ClassPool.getDefault();
...
CtClass ctClass = cp.get(className);

从ctClass，可以获取所有方法，字段，嵌套类....
查看javassist api：
http ：//www.csg.ci.iu-tokyo.ac.jp/~chiba/javassist/html/index.html

From the ctClass, you can get all methods, fields, nested classes, .... Take a look at the javassist api: http://www.csg.ci.i.u-tokyo.ac.jp/~chiba/javassist/html/index.html

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