Java IO流(对象的序列化)

对象的序列化

import java.io.*;
public class Person11 implements Serializable
{
    private String name;
    int age;
    Person11(String name,int age)
    {
        this.name = name;
        this.age = age;
    }
    public String toString()
    {
        return name+":"+age;
    }
}
import java.io.*;

public class ObjectStreamDemo {
    public static void main(String[] args) throws Exception
    {
//        writeObj();
        readObj();
    }
    public static void readObj() throws Exception
    {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));

        Person11 p = (Person11)ois.readObject();

        System.out.println(p);

        ois.close();
    }

    public static void writeObj() throws IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));
        oos.writeObject(new Person11("lisi",39));
        oos.close();;
    }
}
//输出
lisi:39

将Person11中的内容改变，重新读取会报错。

import java.io.*;
public class Person11 implements Serializable
{
    String name;
    int age;
    Person11(String name,int age)
    {
        this.name = name;
        this.age = age;
    }
    public String toString()
    {
        return name+":"+age;
    }
}
import java.io.*;

public class ObjectStreamDemo {
    public static void main(String[] args) throws Exception
    {
//        writeObj();
        readObj();
    }
    public static void readObj() throws Exception
    {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));

        Person11 p = (Person11)ois.readObject();

        System.out.println(p);

        ois.close();
    }

    public static void writeObj() throws IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));
        oos.writeObject(new Person11("lisi",39));
        oos.close();;
    }
}
//输出
Exception in thread "main" java.io.InvalidClassException: Person11; local class incompatible: stream classdesc serialVersionUID = -4826887220003220322, local class serialVersionUID = 958454580975609894
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:699)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1885)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1751)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2042)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
    at ObjectStreamDemo.readObj(ObjectStreamDemo.java:13)
    at ObjectStreamDemo.main(ObjectStreamDemo.java:7)

静态成员不能被序列化

import java.io.*;
public class Person11 implements Serializable
{
    public static final long serialVersionUID = 42L;

    private String name;
    int age;
    static String country = "cn";
    Person11(String name,int age,String country)
    {
        this.name = name;
        this.age = age;
        this.country = country;
    }
    public String toString()
    {
        return name+":"+age+":"+country;
    }
}
import java.io.*;

public class ObjectStreamDemo {
    public static void main(String[] args) throws Exception
    {
//        writeObj();
        readObj();
    }
    public static void readObj() throws Exception
    {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));

        Person11 p = (Person11)ois.readObject();

        System.out.println(p);

        ois.close();
    }

    public static void writeObj() throws IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));
        oos.writeObject(new Person11("lisi0",399,"kr"));
        oos.close();;
    }
}
//输出
lisi0:399:cn

成员变量被transient修饰后，不能被序列化，保证其值在堆内存中存在，不在文本文件中存在。

import java.io.*;
public class Person11 implements Serializable
{
    public static final long serialVersionUID = 42L;

    private String name;
    transient int age;
    static String country = "cn";
    Person11(String name,int age,String country)
    {
        this.name = name;
        this.age = age;
        this.country = country;
    }
    public String toString()
    {
        return name+":"+age+":"+country;
    }
}
import java.io.*;

public class ObjectStreamDemo {
    public static void main(String[] args) throws Exception
    {
//        writeObj();
        readObj();
    }
    public static void readObj() throws Exception
    {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));

        Person11 p = (Person11)ois.readObject();

        System.out.println(p);

        ois.close();
    }

    public static void writeObj() throws IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));
        oos.writeObject(new Person11("lisi0",399,"kr"));
        oos.close();;
    }
}
//输出
lisi0:0:cn

序列化多个对象，每读取一个对象，结束符自动标记到这个对象的末尾。再读取时，是下一个对象。

import java.io.*;
public class Person11 implements Serializable
{
    public static final long serialVersionUID = 42L;

    private String name;
    int age;
    static String country = "cn";
    Person11(String name,int age,String country)
    {
        this.name = name;
        this.age = age;
        this.country = country;
    }
    public String toString()
    {
        return name+":"+age+":"+country;
    }
}
import java.io.*;

public class ObjectStreamDemo {
    public static void main(String[] args) throws Exception
    {
//        writeObj();
        readObj();
    }
    public static void readObj() throws Exception
    {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));

        Person11 p = (Person11)ois.readObject();

        System.out.println(p);

        Person11 p0 = (Person11)ois.readObject();

        System.out.println(p0);
        ois.close();
    }

    public static void writeObj() throws IOException
    {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));
        oos.writeObject(new Person11("lisi0",399,"kr"));
        oos.writeObject(new Person11("lisi0",299,"Am"));
        oos.writeObject(new Person11("lisi0",199,"En"));
        oos.writeObject(new Person11("lisi0",99,"Ge"));
        oos.writeObject(new Person11("lisi0",9,"Fr"));
        oos.close();;
    }
}
//输出
lisi0:399:cn
lisi0:299:cn