欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

ClassLoader Test 博客分类: java语言相关 JavaIDEACC++C#

程序员文章站 2024-02-22 08:24:52
...

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();
    }
}