java双亲委派模型如何递归实现

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;
        }
    }

类加载器用来测试的Class文件对应的类

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 = 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;
 
    }
}