自定义类加载器

目录结构：

 

 

代码示例：

package com.fxf.jvm;

import java.io.*;

public class MyTest16 extends ClassLoader{

    private String classLoaderName;

    private final String fileExtension = ".class";

    public MyTest16(String classLoaderName) {
        super();// 将系统类加载当做该类加载器的父加载器
        this.classLoaderName = classLoaderName;
    }

    public MyTest16(ClassLoader parent, String classLoaderName) {
        super(parent);
        this.classLoaderName = classLoaderName;
    }

    @Override
    public String toString() {
        return "[" + this.classLoaderName + "]";
    }

    @Override
    protected Class<?> findClass(String className) throws ClassNotFoundException {
        byte[] data = this.loadClassData(className);
        return this.defineClass(classLoaderName, data, 0, data.length);
    }

    private byte[] loadClassData(String name) {
        InputStream is = null;
        byte[] data = null;
        ByteArrayOutputStream baos = null;

        try {
            this.classLoaderName = this.classLoaderName.replace(".", "/");

            is = new FileInputStream(new File(name + this.fileExtension));
            baos = new ByteArrayOutputStream();

            int ch = 0;
            while (-1 != (ch = is.read())) {
                baos.write(ch);
            }
            data = baos.toByteArray();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
                baos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return data;
    }

    public static void main(String[] args) throws IllegalAccessException, InstantiationException, ClassNotFoundException {
        MyTest16 loader1 = new MyTest16("loader1");
        test(loader1);
    }

    public static void test(ClassLoader classLoader) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        Class<?> clazz = classLoader.loadClass("com.fxf.jvm.MyTest1");
        Object object = clazz.newInstance();

        System.out.println(object);
    }
}

运行结果：com.fxf.jvm.MyTest1@1540e19d