使用自己定义的类加载器 加载类

package cn.itcast.myclassloader;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;/** *  * @author ETHAN *protected synchronized Class<?> loadClass(String name, boolean resolve)throws ClassNotFoundException    {// First, check if the class has already been loadedClass c = findLoadedClass(name);if (c == null) {    try {    //先找父类加载器if (parent != null) {//loadClass()再去找父类加载器    c = parent.loadClass(name, false);} else {//parent=null，说明是根加载器bootstrap    c = findBootstrapClass0(name);}//否则就自己去找    } catch (ClassNotFoundException e) {        // If still not found, then invoke findClass in order        // to find the class.        c = findClass(name);    }}if (resolve) {    resolveClass(c);}return c;    } *//* * loadClass() 还是要去调用 findClass *  * 应用程序可以创建一个网络类加载器，从服务器中下载类文件。示例代码如下所示：    ClassLoader loader = new NetworkClassLoader(host, port);   Object main = loader.loadClass("Main", true).newInstance();网络类加载器子类必须定义方法 findClass 和 loadClassData，以实现从网络加载类。下载组成该类的字节后，它应该使用方法 defineClass 来创建类实例。示例实现如下：      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              . . .              //URLConnection(url).getInputStream()         }     } */public class MyClassloader extends ClassLoader {//查找class文件@Overrideprotected Class<?> findClass(String name) throws ClassNotFoundException {//cn.itacast.myclassloader.Person---->cn\\itacast\\myclassloader\\Person.classString clsName = name.replace(".", "\\")+".class";InputStream in = MyClassloader.class.getClassLoader().getResourceAsStream(clsName);ByteArrayOutputStream bos = new ByteArrayOutputStream();byte[] buf = new byte[1024];int len = 0;try {while((len = in.read(buf))!=-1) {bos.write(buf,0,len);}} catch (IOException e) {e.printStackTrace();} finally {try {in.close();bos.flush();bos.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}//获取字节码文件byte[] classbytes = bos.toByteArray();return this.defineClass(name, classbytes, 0, classbytes.length);}}

package cn.itcast.myclassloader;public class Person {@Overridepublic String toString() {return "person...........";}}

package cn.itcast.myclassloader;public class Test {/** * @param args * @throws ClassNotFoundException  */public static void main(String[] args) throws ClassNotFoundException {MyClassloader mc = new MyClassloader();//Class clazz = mc.findClass("cn.itcast.myclassloader.Person");Class clazz = mc.findClass("cn.itcast.myjunit.HelloJunit");try {System.err.println(clazz.newInstance());} catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}}}