自定义类加载器

package com.zkn.newlearn.classloader;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;

/**
 *
 * @author zkn
 *
 */

public class ClassLoaderTest01 extends ClassLoader {

	/**
	 * 路径
	 */
	private String path = "";
	/**
	 * 后缀名
	 */
	private String className = ".class";

	private String name = "";

	private ClassLoader loader = null;

	@Override
	protected Class<?> findClass(String name) {
		byte[] b =loadClassData(name);
		if(b != null && b.length > 0)
			return defineClass(name, b, 0, b.length);

		return this.getClass();
	}

	@SuppressWarnings("null")
	private byte[] loadClassData(String names) {
		names = names.replace(".", "\\");
		String clazzName = path + names + className;
		InputStream is = null;
		ByteArrayOutputStream baos = null;
		byte[] bytes = new byte[0];
		int i = 0;
		try{
			is = new FileInputStream(new File(clazzName));
			baos = new ByteArrayOutputStream();
			while(-1!=(i = is.read())){
				baos.write(i);
			}
			bytes = baos.toByteArray();
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			try{
				if(is != null)
					is.close();
				if(baos != null)
					baos.close();
			}catch(Exception ee){
				ee.printStackTrace();
			}
		}
		return bytes;
	}

	public ClassLoaderTest01(String name) {
		super();
		this.name = name;
	}

	public String getPath() {
		return path;
	}

	public void setPath(String path) {
		this.path = path;
	}

	public String getClassName() {
		return className;
	}

	public void setClassName(String className) {
		this.className = className;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Override
	public String toString() {
		return "   "+name;
	}

	public ClassLoaderTest01(String name, ClassLoader loader) {
		super(loader);
		this.name = name;
		this.loader = loader;
	}

	public static void main(String[] args) throws Exception{
		ClassLoaderTest01 loader1 = new ClassLoaderTest01("loader1");
		loader1.setPath("D:\\log4j\\sys\\");

		ClassLoaderTest01 loader2 = new ClassLoaderTest01("loader2",loader1);
		loader2.setPath("D:\\log4j\\common\\");

		ClassLoaderTest01 loader3 = new ClassLoaderTest01("loader3",null);
		loader3.setPath("D:\\log4j\\common\\");

		try{
			test(loader2,"com.zkn.newlearn.classloader.Parent");
		}catch(Exception e){
			loader2 = new ClassLoaderTest01("loader02");
			loader2.setPath("D:\\log4j\\common\\");
			test(loader2,"com.zkn.newlearn.classloader.Parent");
		}

		test(loader3,"com.zkn.newlearn.classloader.Parent");
	}

	private static void test(ClassLoader loader,String name)
			throws ClassNotFoundException, InstantiationException,
			IllegalAccessException {
		Class clazz = null;
		try{
			clazz = loader.loadClass(name);
		}catch(Exception e){
			e.printStackTrace();
		}
		clazz.newInstance();
	}

}

package com.zkn.newlearn.classloader;

/**
 *
 * @author zkn
 *
 */

public class Parent {

	public static int i = 1;

	public Parent(){

		new Dog();
		System.out.println("Parent类加载器为："+Parent.class.getClassLoader());

	}

}

package com.zkn.newlearn.classloader;

/**
 *
 * @author pc
 *
 */

public class Dog {

	public Dog(){
		System.out.println("Dog 类 ：   类加载器为--"+ Dog.class.getClassLoader());
	}

}

ClassLoaderTest01在sys下面：

1、如果Parent类在common下面，由子类加载，即loader2来加载。

<img src="http://img.blog.csdn.net/20160122230640800?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />

2、如果Parent类在sys下面

由父类加载器加载，即loader1来加载。

<img src="http://img.blog.csdn.net/20160122230703769?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />

如果Parent在系统目录下

<img src="http://img.blog.csdn.net/20160122230726426?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />

对于loader3，无论Parent类在哪目录下，Parent类始终由loader3来加载。