【JVM学习笔记】类加载器

package com.test.jvm.common;

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

/**
 * 自定义的类加载器
 */
public class MyClassLoader extends ClassLoader {
    private String name; //加载器的名字
//    private String className; //被加载类的全名
    private String path = "D:/workspace/eclipse-workspace64bit17-forPersonalProject/openbank-parent/openbank-test/src/test/java/"; //加载类的路径
    private final String fileType = ".class"; //class文件的扩展名
    
    public MyClassLoader(String name) {
        super(); //让系统类加载器成为该类加载器的父类
        this.name = name;
    }
    public MyClassLoader(ClassLoader parent,String name) {
        super(parent); //显示指定该类加载器的的父加载器
        this.name = name;
    }
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return this.name;
    }
    
    // TODO Auto-generated method stub
    private byte[] loadClassData(String className) {
        InputStream inputStream = null;
        byte[] data = null;
        ByteArrayOutputStream byteArrayOutputStream  = null;
        try {
            className = className.replace(‘.‘, ‘/‘);
            inputStream = new FileInputStream(new File(path+className+fileType));
            byteArrayOutputStream = new ByteArrayOutputStream();
            int ch = 0;
            while(-1 != (ch = inputStream.read())) {
                byteArrayOutputStream.write(ch);
            }
            data = byteArrayOutputStream.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                inputStream.close();
                byteArrayOutputStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return data;
    }
    @Override
    protected Class<?> findClass(String className) throws ClassNotFoundException {
        byte[] data =this.loadClassData(className);
        //将字节数组转换成Class对象
        return this.defineClass(className, data, 0, data.length);
    }
    public String getPath() {
        return path;
    }
    public void setPath(String path) {
        this.path = path;
    }
    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        System.out.println(System.getProperty("java.class.path"));
        System.out.println("------------------");
        MyClassLoader loader1 = new MyClassLoader("loader1");
//        loader1.setPath("D:/temp/serverlib");
        MyClassLoader loader2 = new MyClassLoader(loader1,"loader2"); //将loader1作为loader2的父加载器
//        loader2.setPath("D:/temp/clientlib");
        MyClassLoader loader3 = new MyClassLoader(null,"loader3"); //将第一个参数设为空表示父加载器为根加载器
//        loader3.setPath("d:/temp/systemlib");
        test(loader2);
        System.out.println("-----------------");
        test(loader3);
    }
    public static void test(ClassLoader loader) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        Class clazz = loader.loadClass("com.test.jvm.common.Sample");
        Object object = clazz.newInstance();
    }
}

public class Sample {
    public int v1 = 1;
    public Sample() {
        System.out.println("Sample is loaded by: "+this.getClass().getClassLoader());
        new Dog();
    }
}

public class Dog {
    public Dog() {
        System.out.println("Dog is loaded by: "+this.getClass().getClassLoader());
    }
}

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------------------
Sample is loaded by: sun.misc.Launcher$AppClassLoader@2d8eef25
Dog is loaded by: sun.misc.Launcher$AppClassLoader@2d8eef25
-----------------
Sample is loaded by: loader3
Dog is loaded by: loader3