java序列化和反序列化

概念：

java序列化是指将类对象转化成二进制流，序列化的目的是为了方便信息的传输和存储

java反序列化是指将二进制流转化成类对象。

下面代码实现了序列化和反序列化：

1、首先创建Student.java,它实现了Serializable接口，并给serialVersionUID赋值为1L。

package htRQI;
import java.io.Serializable;

public class Student implements Serializable{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
}

2、测试

package htRQI;

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

public class TestSerialize {
    public static void main(String[] args) {
        Student s=new Student();
        s.setName("Bonnie");
        s.setAge(20);
        try {
            
            serialize(s);
            unserialize();
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    /**
     * 序列化
     * @param s
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void serialize(Student s) throws FileNotFoundException, IOException {
        File file=new File("D:/a.txt");
        ObjectOutputStream out=new ObjectOutputStream(new FileOutputStream(file));
        out.writeObject(s);
        System.out.println("序列化完成");
        out.close();
    }
    /**
     * 反序列化
     * @throws FileNotFoundException
     * @throws IOException
     * @throws ClassNotFoundException
     */
    public static void unserialize() throws FileNotFoundException, IOException, ClassNotFoundException {
        ObjectInputStream in=new ObjectInputStream(new FileInputStream(new File("D:/a.txt")));
        Student s=(Student) in.readObject();
        System.out.println("反序列化完成");
        System.out.println("name:"+s.getName()+" age:"+s.getAge());
        in.close();
    }
}

输出结果：

序列化完成
反序列化完成
name:Bonnie age:20

知识点：（1）Serializable接口中没有定义任何方法，它的作用是标识实现它的类可以被序列化。
（2）实现Serializable接口后需要给serialVersionUID赋值。serialVersionUID的作用是用于判断序列化前的对象和序列化得到的对象是否一致。可以做个测试：
serialVersionUID的值改为2L

package htRQI;
import java.io.Serializable;

public class Student implements Serializable{
    /**
     * 
     */
    private static final long serialVersionUID = 2L;
    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
}

将serialize(s);注释掉

package htRQI;

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

public class TestSerialize {
    public static void main(String[] args) {
        Student s=new Student();
        s.setName("Bonnie");
        s.setAge(20);
        try {
            
            //serialize(s);
            unserialize();
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    /**
     * 序列化
     * @param s
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void serialize(Student s) throws FileNotFoundException, IOException {
        File file=new File("D:/a.txt");
        ObjectOutputStream out=new ObjectOutputStream(new FileOutputStream(file));
        out.writeObject(s);
        System.out.println("序列化完成");
        out.close();
    }
    /**
     * 反序列化
     * @throws FileNotFoundException
     * @throws IOException
     * @throws ClassNotFoundException
     */
    public static void unserialize() throws FileNotFoundException, IOException, ClassNotFoundException {
        ObjectInputStream in=new ObjectInputStream(new FileInputStream(new File("D:/a.txt")));
        Student s=(Student) in.readObject();
        System.out.println("反序列化完成");
        System.out.println("name:"+s.getName()+" age:"+s.getAge());
        in.close();
    }
}

会报错：

java.io.InvalidClassException: htRQI.Student; local class incompatible: stream classdesc serialVersionUID = 1, local class serialVersionUID = 2
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:687)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1876)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1745)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2033)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:427)
    at htRQI.TestSerialize.unserialize(TestSerialize.java:45)
    at htRQI.TestSerialize.main(TestSerialize.java:19)

这是因为序列化的时候serialVersionUID的值为1L，而反序列化的时候值为2L。不一致导致invalidClassException。所以这个serialVersionUID需要显示为其赋值，并设为final