首先类加载过程的确是使用双亲委托方式，就是先找parent的classLoader加载，Java有几个固定的classLoader：1、BootstrapClassLoader 2、ExtClassLoader 3、AppClassLoader 这里有篇文章，也讲些了这些classLoader的关系 加载器。

但是网上很多文章说这几个加载器是有继承关系，然后我看到代码它们是没有继承关系的，但是它们都有个getParent（）方法去获取所谓的父加载器，其实这个值的设置就要看Launcher的代码

public class Launcher {
 private static URLStreamHandlerFactory factory = new Factory();
 private static Launcher launcher = new Launcher();

 public static Launcher getLauncher() {
  return launcher;
 }

 private ClassLoader loader;

 // ClassLoader.getSystemClassLoader会调用此方法
 public ClassLoader getClassLoader() {
  return loader;
 }

 public Launcher() {
  // 1. 创建ExtClassLoader
  ClassLoader extcl;
  try {
   extcl = ExtClassLoader.getExtClassLoader();
  } catch (IOException e) {
   throw new InternalError("Could not create extension class loader");
  }

  // 2. 用ExtClassLoader作为parent去创建AppClassLoader
  try {
   loader = AppClassLoader.getAppClassLoader(extcl);
  } catch (IOException e) {
   throw new InternalError("Could not create application class loader");
  }

  // 3. 设置AppClassLoader为ContextClassLoader
  Thread.currentThread().setContextClassLoader(loader);
  // ...
 }

 static class ExtClassLoader extends URLClassLoader {
  private File[] dirs;

  public static ExtClassLoader getExtClassLoader() throws IOException {
   final File[] dirs = getExtDirs();
   return new ExtClassLoader(dirs);
  }

  public ExtClassLoader(File[] dirs) throws IOException {
   super(getExtURLs(dirs), null, factory);
   this.dirs = dirs;
  }

  private static File[] getExtDirs() {
   String s = System.getProperty("java.ext.dirs");
   File[] dirs;
   // ...
   return dirs;
  }
 }

 /**
  * The class loader used for loading from java.class.path. runs in a
  * restricted security context.
  */
 static class AppClassLoader extends URLClassLoader {

  public static ClassLoader getAppClassLoader(final ClassLoader extcl) throws IOException {
   final String s = System.getProperty("java.class.path");
   final File[] path = (s == null) ? new File[0] : getClassPath(s);

   URL[] urls = (s == null) ? new URL[0] : pathToURLs(path);
   return new AppClassLoader(urls, extcl);
  }

  AppClassLoader(URL[] urls, ClassLoader parent) {
   super(urls, parent, factory);
  }

  /**
  * Override loadClass so we can checkPackageAccess.
  * 这个方法似乎没什么必要，因为super.loadClass(name, resolve)时也会checkPackageAccess
  */
  public synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
   int i = name.lastIndexOf('.');
   if (i != -1) {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
     //
     sm.checkPackageAccess(name.substring(0, i));
    }
   }
   return (super.loadClass(name, resolve));
  }

 }
}

1.Launcher源码里定义了static的扩展类加载器ExtClassLoader， static的系统类加载器AppClassLoader。