反射与序列化破解单例模式及解决方法

class Singleton {
    //饿汉式，立即加载,类加载线程安全
    private Singleton(）{}
    private static Singleton instance=new Singleton();
    public static Singleton getInstance(){
        return instance;
    }
}

Singleton s1=Singleton.getInstance();
        Singleton s2=Singleton.getInstance();
        System.out.println(s1);
        System.out.println(s2);     

      输出：
          sf3.Singleton@1db9742
          sf3.Singleton@1db9742

使用反射破解单例：

Class<Singleton> clazz=(Class<Singleton>) 
        Class.forName("sf3.Singleton");
        Constructor<Singleton> c=clazz.getDeclaredConstructor(null);
        c.setAccessible(true);
        Singleton ss1=c.newInstance();
        System.out.println(ss1);    
    输出：
       sf3.Singleton@106d69c

解决反射破坏单例：

private Singleton(){
        if(instance!=null){
            throw new RuntimeException();
        }
    }

序列化破解：

class Singleton implements Serializable{
          
   
    private Singleton(){}
    private static Singleton instance=new Singleton();  
    public static Singleton getInstance(){
        return instance;
    }
}

FileOutputStream  fos=new FileOutputStream("d:/a.txt");
        ObjectOutputStream oos=new ObjectOutputStream(fos);
        oos.writeObject(s1);
        oos.close();
        fos.close();    
        ObjectInputStream ois=
        new ObjectInputStream(new FileInputStream("d:/a.txt"));
        Singleton s3=(Singleton) ois.readObject();
        System.out.println(s3); 
    输出：
        sf3.Singleton@873330

解决序列化破解反射：

class Singleton implements Serializable{
          
   
        private Singleton(){}
        private static Singleton instance=new Singleton();  
        public static Singleton getInstance(){
            return instance;
        }
        private Object readResolve(){
            return instance;
        }
    }