设计模式课程 设计模式精讲 8-7 单例设计模式-反射攻击解决方案及原理分析

2　　　　代码演练

 

2　　　　代码演练

2.1　　代码演练

package com.geely.design.pattern.creational.singleton;

import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Test {

    /*public static void main(String [] args){
        //这样写异常，因为构造方法私有
//        LazySingleton lazySingleton = new LazySingleton();
       LazySingleton lazySingleton = LazySingleton.getInstance();
       System.out.println(lazySingleton);
    }*/

/*    public static void main(String [] args){
        Thread thread1 = new Thread(new T());
        Thread thread2 = new Thread(new T());
        thread1.start();
        thread2.start();
        System.out.println("结束了！！！");
    }*/

    /**
     * 序列化代码演练
     * 将 HungrySingleton对象放入文件，再从文件读取该对象，还是同一个对象吗？
     * 实际应用：在从文件存入后读取，用equals时需要注意（equals比较的是hash码）
     * @param args
     */
    public static void main(String [] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
/*        try {
            //将singleton对象写入到输出流中
            HangrySingleton instance = HangrySingleton.getInstance();
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("singleton_file"));
            oos.writeObject(instance);

            //从输入流中读取到该对象
            File file = new File("singleton_file");
            ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));
            HangrySingleton instance2 = (HangrySingleton) ois.readObject();
            System.out.println(instance);
            System.out.println(instance2);
            System.out.println(instance==instance2);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    */

//反射攻击
        Class objectClass = HangrySingleton.class;
//        Class.forName(HangrySingleton.class.getName());
        //通过反射拿到构造器
        Constructor constructor = objectClass.getDeclaredConstructor();

        //设置权限为true，不设置的话，私有权限反射报错
        constructor.setAccessible(true);
        //通过单例拿到对象
        HangrySingleton instance = HangrySingleton.getInstance();
        //通过反射拿到对象
        HangrySingleton instance2 = (HangrySingleton)constructor.newInstance();
        System.out.println(instance);
        System.out.println(instance2);
        System.out.println(instance==instance2);
    }
}

打印日志：

"C:\Program Files\Java\jdk1.7.0_79\bin\java.exe" "-javaagent:D:\java\devolopKit\idea\anZh\IntelliJ IDEA Community Edition 2018.1.4\lib\idea_rt.jar=27494:D:\java\devolopKit\idea\anZh\IntelliJ IDEA Community Edition 2018.1.4\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.7.0_79\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\jce.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\jfxrt.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\resources.jar;C:\Program Files\Java\jdk1.7.0_79\jre\lib\rt.jar;F:\xiangmu3\Xin\Idea\design_pattern\target\classes" com.geely.design.pattern.creational.singleton.Test
com.geely.design.pattern.creational.singleton.HangrySingleton@6cff7cd8
com.geely.design.pattern.creational.singleton.HangrySingleton@795d80cf
false

Process finished with exit code 0