以下是Classloader的中最重要的方法，也就是所谓的双亲委派模型。这个模型第一次在周志明的书上看到，当时看了只知道是类加载过程是首先是委托给父加载器，否则父不能加载，则自己加载，整个过程实则是一个很简单的递归过程，本文以实例讲解这个模型到底是咋实现的？

protected Class<?> loadClass(String name, boolean resolve)        throws ClassNotFoundException    {        synchronized (getClassLoadingLock(name)) {            // First, check if the class has already been loaded            Class c = findLoadedClass(name);            if (c == null) {                long t0 = System.nanoTime();                try {                    if (parent != null) {                        c = parent.loadClass(name, false);                    } else {                        c = findBootstrapClassOrNull(name);                    }                } catch (ClassNotFoundException e) {                    // ClassNotFoundException thrown if class not found                    // from the non-null parent class loader                }                if (c == null) {                    // If still not found, then invoke findClass in order                    // to find the class.                    long t1 = System.nanoTime();                    c = findClass(name);                              }            }            if (resolve) {                resolveClass(c);            }            return c;        }    }

public class TestLoaderClass {    public TestLoaderClass()    {        System.out.println("加载器为"+TestLoaderClass.class.getClass());                    }    }

//自定义类加载器
import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.nio.ByteOrder;public class MyClassLoader extends ClassLoader {    //类加载器名称    private String name;    //加载类的路径    private String path = "D:/";    private final String fileType = ".class";    public MyClassLoader(String name){        //让系统类加载器成为该 类加载器的父加载器        super();        this.name = name;    }    //显示设置类加载器的父类加载器    public MyClassLoader(ClassLoader parent, String name){        //显示指定该类加载器的父加载器        super(parent);        this.name = name;    }    public String getPath() {        return path;    }    public void setPath(String path) {        this.path = path;    }    @Override    public String toString() {        return this.name;    }    /**     * 获取.class文件的字节数组     * @param name     * @return     */       /**     * 获取Class对象     * @throws IOException      */    private byte[] getBytes(String name) throws IOException    {        //name=name.replace(".", "/");        File f=new File(path+name+fileType);        InputStream in=new FileInputStream(f);        System.out.println(in.available()+"file");        ByteArrayOutputStream bao=new ByteArrayOutputStream();        int r=in.read();        while(r!=-1)        {            bao.write(r);            r=in.read();                    }        System.out.println(bao.toByteArray().toString());        return bao.toByteArray();                            }    public Class<?> findClass(String name){        byte[] data = http://www.mamicode.com/null;        try {            data = getBytes(name);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        System.out.println();        return this.defineClass(name, data, 0, data.length);    }    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {        //loader1的父加载器为系统类加载器        MyClassLoader loader1 = new MyClassLoader("loader1");        loader1.setPath("D:/lib1/");        //loader2的父加载器为loader1        MyClassLoader loader2 = new MyClassLoader(loader1, "loader2");        loader2.setPath("D:/lib2/");        //loader3的父加载器为根类加载器        MyClassLoader loader3 = new MyClassLoader(loader2, "loader3");        loader3.setPath("D:/lib3/");        Class<?> clazz = loader3.loadClass("TestLoaderClass");        System.out.println(clazz.getClassLoader());        ClassLoader cl=loader3;                   }}