序列化对象后单例模式被破坏解决方案

package org.ddd.section7.example7_6;import java.io.Serializable;public class Earth implements Serializable{    private static final long serialVersionUID = 1L;    private volatile static Earth instance;    public static Earth getInstance() {          if (instance == null) {                synchronized (Earth.class) {                    if (instance == null) {                        instance = new Earth();                    }                }            }        return instance;    }}

package org.ddd.section7.example7_6;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;public class SerializeTool {    /**     * 将对象序列化，并存在在本地文件中     * @param obj 被序列化的对象     * @param fileName 存储的本地文件名     */    public static void serialize(Object obj, String fileName) throws Exception{        File file = new File(fileName); //新建一个本地文件，用于存储，序列化的对象字节流        FileOutputStream output = new FileOutputStream(file); //文件输出流        ObjectOutputStream oos = new ObjectOutputStream(output); //对象输出流        oos.writeObject(obj); //将对象写入对象输出流中        oos.flush(); //提交对象输入流        oos.close();        output.close();    }    /**     * 从本地文件中，通过反序列化获取对象     * @param fileName 本地存储序列化对象的文件     * @return 反序列化后的对象     */    public static Object deSerialize(String fileName) throws Exception{        File file = new File(fileName); //获取存储对象字节流的本地文件        FileInputStream input = new FileInputStream(file); //定义文件输入流        ObjectInputStream ois = new ObjectInputStream(input); //定义对象输入流        Object obj = ois.readObject(); //从对象输入流中读取对象        ois.close();        input.close();        return obj;    }    /**     * 打印指定文件的文件信息，包括文件名，文件大小等     * @param fileName 本地文件名     */    public static void printFileInfo(String fileName){        File file = new File(fileName); //获取本地文件        System.out.println("-----------------------------");        System.out.println("<FileName>: " + fileName); //打印文件名        System.out.println("<FileSize>: " + file.length() + " bytes"); //打印文件大小        System.out.println("-----------------------------");    }}

package org.ddd.section7.example7_6;public class SerializeTest {    public static void main(String[] args) throws Exception{        Earth p = new Earth();        SerializeTool.serialize(p, "temp");        Earth pp = (Earth) SerializeTool.deSerialize("temp");        System.out.println(p==pp);        System.out.println(p);        System.out.println(pp);    }}

输出结果

[e-mail]7_6.Earth@3d4eac69

简要原因

序列化过程中运用了反射的newInstance创建了对象返回

解决方法

package org.ddd.section7.example7_6;import java.io.Serializable;public class Earth implements Serializable{    private static final long serialVersionUID = 1L;    private volatile static Earth instance;    private Earth() {        // TODO Auto-generated constructor stub    }    public static Earth getInstance() {          if (instance == null) {                synchronized (Earth.class) {                    if (instance == null) {                        instance = new Earth();                    }                }            }        return instance;    }    private Object readResolve() {        System.out.println("被调用了");        return getInstance();    }    private Object writeReplace() {        return getInstance();    }}

输出

[e-mail]7_6.Earth@776ec8df