Java包内省

Question

如何获得包中的所有类？

Answer 1

你不能.类可以通过许多不同的类加载器进入,包括远程加载器.

Answer 2

根据JG发布的想法,这里有一个更完整的方法来解决这个问题.

/**
 * Scans all classloaders for the current thread for loaded jars, and then scans
 * each jar for the package name in question, listing all classes directly under
 * the package name in question. Assumes directory structure in jar file and class
 * package naming follow java conventions (i.e. com.example.test.MyTest would be in
 * /com/example/test/MyTest.class)
 */
public Collection<Class> getClassesForPackage(String packageName) throws Exception {
  String packagePath = packageName.replace(".", "/");
  ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
  Set<URL> jarUrls = new HashSet<URL>();

  while (classLoader != null) {
    if (classLoader instanceof URLClassLoader)
      for (URL url : ((URLClassLoader) classLoader).getURLs())
        if (url.getFile().endsWith(".jar")  // may want better way to detect jar files
          jarUrls.add(url);

    classLoader = classLoader.getParent();
  }

  Set<Class> classes = new HashSet<Class>();

  for (URL url : jarUrls) {
    JarInputStream stream = new JarInputStream(url.openStream()); // may want better way to open url connections
    JarEntry entry = stream.getNextJarEntry();

    while (entry != null) {
      String name = entry.getName();
      int i = name.lastIndexOf("/");

      if (i > 0 && name.endsWith(".class") && name.substring(0, i).equals(packagePath)) 
        classes.add(Class.forName(name.substring(0, name.length() - 6).replace("/", ".")));

      entry = stream.getNextJarEntry();
    }

    stream.close();
  }

  return classes;
}