ClassLoader Test

配合这篇文章看http://www.iteye.com/topic/753834

 

 

•       自定义的ClassLoader有自己的上下文，你可以指定从什么地方得到这个文件或者流，本例是C:/classes/

•       调用自定义的ClassLoader的loadClass方法能根据package+className得到这个Class对象

              （怎么从流转化为Class这个不需要我们操心，直接调用父类ClassLoader的defineClass方法）

 

package depeng.classload;

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;

/**
 * Created by IntelliJ IDEA.
 * User: depeng
 * Date: 2010-9-3
 * Time: 15:48:02
 * To change this template use File | Settings | File Templates.
 */
public class MyClassLoader extends ClassLoader {
    private String fileName;

    public MyClassLoader(String fileName) {
        this.fileName = fileName;
    }

    protected Class findClass(String className) throws ClassNotFoundException {
        Class clazz = this.findLoadedClass(className);
        if (null == clazz) {
            try {
                String classFile = getClassFile(className);
                FileInputStream fis = null;
                try {
                    fis = new FileInputStream(classFile);
                } catch (FileNotFoundException e) {
                    System.out.println(e);
                    e.printStackTrace();
                }
                FileChannel fileC = fis.getChannel();
                ByteArrayOutputStream baos = new
                        ByteArrayOutputStream();
                WritableByteChannel outC = Channels.newChannel(baos);
                ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
                while (true) {
                    int i = fileC.read(buffer);
                    if (i == 0 || i == -1) {
                        break;
                    }
                    buffer.flip();
                    outC.write(buffer);
                    buffer.clear();
                }
                fis.close();
                byte[] bytes = baos.toByteArray();
                
//                Converts an array of bytes into an instance of class Class
                clazz = defineClass(className, bytes, 0, bytes.length);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return clazz;
    }

    private byte[] loadClassBytes(String className) throws
            ClassNotFoundException {
        try {
            String classFile = getClassFile(className);
            FileInputStream fis = new FileInputStream(classFile);
            FileChannel fileC = fis.getChannel();
            ByteArrayOutputStream baos = new
                    ByteArrayOutputStream();
            WritableByteChannel outC = Channels.newChannel(baos);
            ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
            while (true) {
                int i = fileC.read(buffer);
                if (i == 0 || i == -1) {
                    break;
                }
                buffer.flip();
                outC.write(buffer);
                buffer.clear();
            }
            fis.close();
            return baos.toByteArray();
        } catch (IOException fnfe) {
            throw new ClassNotFoundException(className);
        }
    }

    private String getClassFile(String name) {
        StringBuffer sb = new StringBuffer(fileName);
        name = name.replace('.', File.separatorChar) + ".class";
        sb.append(File.separator + name);
        return sb.toString();
    }
}

 

 

 

 

 

package depeng.classload;

import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * Created by IntelliJ IDEA.
 * User: depeng
 * Date: 2010-9-3
 * Time: 13:56:40
 * To change this template use File | Settings | File Templates.
 */
public class Worker {

    public static void testInFileSystem() throws Exception {
//        URL[] urls = new URL[]{new URL("file:/C:/java/")};
//        URLClassLoader loader = new URLClassLoader(urls);
//        Class clas = loader.loadClass("depeng.classload.URLClassLoaderTest");
//        Method m = clas.getMethods()[0];
//        Object o = clas.newInstance();
//        m.invoke(o,null);
//
//         System.out.println(loader.getClass());
//         System.out.println(loader.getParent().getClass());
//        System.out.println(loader.getParent().getParent().getClass());
//        System.out.println(loader.getParent().getParent().getParent());
//        System.out.println("cccc  " +Worker.class.getClassLoader().getClass());


        MyClassLoader mc = new MyClassLoader("C:/classes/");
        Class aClass = mc.loadClass("depeng.classload.URLClassLoaderTest");
        Method ma = aClass.getMethods()[0];
        Object oa = aClass.newInstance();
        ma.invoke(oa, null);
        System.out.println(mc.getClass());
        System.out.println(mc.getParent().getClass());
        System.out.println(mc.getParent().getParent().getClass());
        System.out.println(mc.getParent().getParent().getParent());


    }

    public static void main(String[] args) throws Exception {
         testInFileSystem();
    }
}