JVM从入门到入土之JVM的类加载机制（下）

protected synchronized Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
    //1 首先检查类是否被加载
    Class c = findLoadedClass(name);
    if (c == null) {
        try {
            if (parent != null) {
             //2 没有则调用父类加载器的loadClass()方法；
                c = parent.loadClass(name, false);
            } else {
            //3 若父类加载器为空，则默认使用启动类加载器作为父加载器；
                c = findBootstrapClass0(name);
            }
        } catch (ClassNotFoundException e) {
           //4 若父类加载失败，抛出ClassNotFoundException 异常后，这个方法就是加载的核心代码
            c = findClass(name);
        }
    }
    if (resolve) {
        //5 再调用自己的findClass() 方法。
        resolveClass(c);
    }
    return c;
}
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class NetworkClassLoader extends ClassLoader {
 *         String host;
 *         int port;
 *
 *         public Class findClass(String name) {
 *             byte[] b = loadClassData(name);
 *             return defineClass(name, b, 0, b.length);
 *         }
 *
 *         private byte[] loadClassData(String name) {
 *             // load the class data from the connection
 *              . . .
 *         }
 *     }
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// Now create the class loader to use to launch the application    
   try {    
       loader = AppClassLoader.getAppClassLoader(extcl);    
   } catch (IOException e) {    
       throw new InternalError(    
   "Could not create application class loader" );    
   }    
   // Also set the context class loader for the primordial thread.    
  Thread.currentThread().setContextClassLoader(loader);    
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