Java设计模式之使用反序列化的方式实现单例模式

package com.sinosoft.test;

import java.io.Serializable;

/**
 * 使用序列化的方式实现单例模式
 */
public class HungrySingleton implements Serializable {
    private static HungrySingleton instance=new HungrySingleton();

    public static HungrySingleton getInstance(){
        return instance;
    }

    private HungrySingleton(){

    }
}

创建测试类；实现序列化到此判断过程

package com.sinosoft.test;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * Created by ZhaoYongqiang on 2020/8/30.
 */
public class SerializableTest {
    public static void main(String[] args) throws FileNotFoundException,IOException,ClassNotFoundException {
        HungrySingleton instance=HungrySingleton.getInstance();

        ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("instance"));
        outputStream.writeObject(instance);
        outputStream.close();
        System.out.println("序列化到磁盘成功");
//
//        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("instance"));
//        HungrySingleton object =(HungrySingleton) objectInputStream.readObject();
//        System.out.println("反序列化成功");

    }
}
运行结果：

可见是能够序列化成功的。

接下来在进行反序列化，代码在上面：

 接下来我们看一下序列化和反序列化是否是同一个实例：

package com.sinosoft.test;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * Created by ZhaoYongqiang on 2020/8/30.
 */
public class SerializableTest {
    public static void main(String[] args) throws FileNotFoundException,IOException,ClassNotFoundException {
        HungrySingleton instance=HungrySingleton.getInstance();

        ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("instance"));
        outputStream.writeObject(instance);
        outputStream.close();
        System.out.println("序列化到磁盘成功");

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("instance"));
        HungrySingleton object =(HungrySingleton) objectInputStream.readObject();
        objectInputStream.close();
        System.out.println(object);
        System.out.println("反序列化成功");

        System.out.println("序列化和反序列化是否是同一个实例:"+(instance==object));
    }
}

运行结果：

序列化到磁盘成功
com.sinosoft.test.HungrySingleton@12edcd21
反序列化成功
序列化和反序列化是否是同一个实例:false

可见，已经不是同一个实例了。

那么怎样解决这种问题呢？指定签名

package com.sinosoft.test;

        import java.io.ObjectStreamException;
        import java.io.Serializable;

/**
 * 使用序列化的方式实现单例模式
 */
public class HungrySingleton implements Serializable {
    private static HungrySingleton instance=new HungrySingleton();

    public static HungrySingleton getInstance(){
        return instance;
    }

    private HungrySingleton(){

    }

    Object readResolve() throws ObjectStreamException{
        return instance;
    }
}

再次运行：

序列化到磁盘成功
com.sinosoft.test.HungrySingleton@4d7e1886
反序列化成功
序列化和反序列化是否是同一个实例:true

这个序列化ID加不加都是可以的。

private final long serialVersionUID=42L;