自定义类加载器classLoader

Posted 2021-05-27 徒手攀岩

package cn.bdqn.userconsumer;

import java.io.*;

/**
 * 自定义classLoader  类加载器
 */
public class HelloClassLoad extends ClassLoader {

    /**
     * 自定义类加载器
     * 继承classLoader  重写findClass()方法
     * @param name
     * @return
     * @throws ClassNotFoundException
     */
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        File file = new File("F:\\\\test",name.replace(".","\\\\").concat(".class"));
        try {
            FileInputStream inputStream = new FileInputStream(file);
            //FileOutputStream fileoutput = new FileOutputStream(new File("F:/test",name.replace(".","/").concat(".class")));
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            int by=0;
            while((by = inputStream.read()) !=0){
                outputStream.write(by);
            }

            byte[] bytes = outputStream.toByteArray();
            outputStream.close();

            defineClass(name,bytes,0,bytes.length);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return super.findClass(name);
    }


    public static void main(String[] args) {
        try {
            //使用自定义 classLoader
            ClassLoader classLoader = new HelloClassLoad();
            //加载指定目录下的类文件
            Class<?> aClass = classLoader.loadClass("cn.bdqn.userconsumer.HelloJol");
            HelloJol helloJol = (HelloJol) aClass.newInstance();
            helloJol.Str();
            System.out.println(classLoader.getClass().getClassLoader());
            System.out.println(classLoader.getParent());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }







}