五、文件传输基础-序列化

1、对象的序列化和反序列化

• 对象序列化，就是将Object转换成byte序列，反之叫对象的反序列化
• 序列化流（ObjectOutputStream），是字节过滤流---writerObject
• 反序列化流（ObjectInPutStream），---readObject
• 序列化接口（ Serializable)
• 对象必须实现序列化接口，才能进行序列化，否则将出现异常，这个接口没有任何方法，只是一个标准。

2、对象序列化，代码示例：

package com.lord.quick;

import java.io.Serializable;

public class Student implements Serializable {

    private static final long serialVersionUID = 6780974907389412343L;

    private String number;
    private String username;
    private int age;

    public Student() {
    }

    public Student(String number, String username, int age) {
        super();
        this.number = number;
        this.username = username;
        this.age = age;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [number=" + number + ", username=" + username + ", age=" + age + "]";
    }

}

public static void main(String[] args) throws Exception {
    String file = "demo/obj.dat";
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file));
    Student stu = new Student("10001", "张三", 20);
    oos.writeObject(stu);
    oos.flush();
    oos.close();
}

3、对象反序列化，代码示例：

public static void main(String[] args) throws Exception {
    String file = "demo/obj.dat";      
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));
    Student stu = (Student)ois.readObject();
    System.out.println(stu);
    ois.close();
}

4、transient关键字

• transient表示类的属性不被序列化

package com.lord.quick;

import java.io.Serializable;

public class Student implements Serializable {

    private static final long serialVersionUID = 6780974907389412343L;

    private String number;
    private String username;
    private transient int age; // 该元素不会进行jvm默认的序列化，也可以自己完成序列化

    public Student() {
    }

    public Student(String number, String username, int age) {
        super();
        this.number = number;
        this.username = username;
        this.age = age;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [number=" + number + ", username=" + username + ", age=" + age + "]";
    }

}

5、自主完成序列化，代码示例

• 此处参考ArrayList类源码序列化和反序列化的实现
• 自主实现序列化和反序列化可提供程序性能

package com.lord.quick;

import java.io.Serializable;

public class Student implements Serializable {

    private static final long serialVersionUID = 6780974907389412343L;

    private String number;
    private String username;
    private transient int age;

    public Student() {
    }

    public Student(String number, String username, int age) {
        super();
        this.number = number;
        this.username = username;
        this.age = age;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [number=" + number + ", username=" + username + ", age=" + age + "]";
    }

    // 序列化
    private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
        s.defaultWriteObject();// 把jvm能默认序列化的元素进行序列化

        s.writeInt(age);
    }

    // 反序列化
    private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();// 把jvm能默认反序列化的元素进行反序列化

        this.age = s.readInt();
    }

}

6、序列化中子父类构造函数问题

• 一个类实现了序列化接口，其子类都可以进行序列化
• 创建对象时，递归调用父类的构造函数
• 对子类对象进行反序列化操作时，如果其父类没有实现序列化接口，那么其父类的构造函数会被显示调用