Java序列化與反序列化實現單例模式

package com.wkcto.sigleton.p4;

import java.io.*;

/**
 * 序列化與反序列化的單例實現
 */
public class Test03 {
    public static void main(String[] args) {
        Singleton obj = Singleton.getInstance();
        System.out.println( obj );

        //對象序列化
        try (
                FileOutputStream fos = new FileOutputStream("singleton.dat");
                ObjectOutputStream oos = new ObjectOutputStream(fos);
        ){
            oos.writeObject(obj);   //單例對象的序列化
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //單例對象反序列化
        try (
                FileInputStream fis = new FileInputStream("singleton.dat");
                ObjectInputStream ois = new ObjectInputStream(fis);
        ){
            obj = (Singleton) ois.readObject();
            //直接打印obj對象的哈希碼,與序列化時單例對象的哈希碼不一樣
            System.out.println( obj );
            //可以在反序列化時, 調用單例對象的readResolve()方法返回原來的單例對象
            Singleton  another = obj.readResolve();
            System.out.println(another);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

package com.wkcto.sigleton.p4;

import java.io.Serializable;

/**
 * 允許序列化的單例實現
 */
public class Singleton implements Serializable {
    private static final long serialVersionUID = 7747765510030536000L;

    private Singleton(){}

    //定義靜態內部類
    private static class SingletonHandler{
        private static Singleton obj = new Singleton();
    }
    public static Singleton getInstance() {
        return SingletonHandler.obj;
    }

    //定義實例方法,返回靜態內部類的靜態對象
    public Singleton readResolve(){
        System.out.println("調用了單例 的實例方法readResolve");
        return SingletonHandler.obj;
    }
}