java_对象序列化、反序列化

1.概念

序列化：将对象转化为字节序列的过程

反序列化：将字节序列转化为对象的过程

用途：

A：将对象转化为字节序列保存在硬盘上，如文件中，如文本中的例子就是将person对象序列化成字节序列，存在person.txt文件中

B：网络传输中一般都是以对象序列化的形式存在，在网络的发送/接收两端进行对象的序列化/反序列化

输入/输出的使用：

一般都是针对内存而言，内存--硬盘--》outputStream     从硬盘--内存--》inputStream

具体使用要根据场景来确定

2.Serializable-example

2.1 无显式的指定UID,采用编译系统自动生成的

Object:

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Serializable;

public class Person implements Serializable {

    private int age;

    private String name;

    private String sex;

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("Person{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append('}');
        return sb.toString();
    }
}

　object  uid

package com.java.baseinfo.knowledge.code.serializable;

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 TestObjSerializeAndDeserialize {

    public static void main(String[] args) {
        // 序列化
        SerializablePerson();
        // 反序列化
        //Deserialization();
    }

    private static void SerializablePerson() {
        Person person = new Person();
        person.setAge(10);
        person.setName("测试");
        person.setSex("女");

        String path = "src/test/resources/person.txt";

        try {
            FileOutputStream fileOutputStream = new FileOutputStream(new File(path));

            ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);

            objectOutputStream.writeObject(person);

            System.out.println("序列化成功");
            fileOutputStream.close();
            objectOutputStream.close();

        } catch (FileNotFoundException e) {
            System.out.printf("FileNotFoundException====>" + e);
        } catch (IOException e) {
            System.out.printf("IOException====>" + e);
        }
    }

    private static Person Deserialization() {

        try {
            FileInputStream fileInputStream = new FileInputStream(new File("src/test/resources/person.txt"));

            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);

            Person person = (Person) objectInputStream.readObject();

            System.out.printf("Deserialization.person===>"+person);

        } catch (FileNotFoundException e) {
            System.out.printf("FileNotFoundException====>" + e);
        } catch (IOException e) {
            System.out.printf("IOException====>" + e);
        } catch (ClassNotFoundException e) {
            System.out.printf("ClassNotFoundException====>" + e);
        }
        return null;
    }
}

先序列化，才进行反序列化

Deserialization.person===>Person{age=10, name='测试', sex='女'}　

给person增加字段，再用原来的序列化后的结果，进行反序列化；

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Serializable;

public class Person implements Serializable {

    private int age;

    private String name;

    private String sex;

    // 增加字段测试序列化
    private String addText;

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddText() {
        return addText;
    }

    public void setAddText(String addText) {
        this.addText = addText;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("Person{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append(", addText='").append(addText).append('\'');
        sb.append('}');
        return sb.toString();
    }
}

　运行结果

IOException====>java.io.InvalidClassException: com.java.baseinfo.knowledge.code.serializable.Person; local class incompatible: stream classdesc serialVersionUID = 6964452789008335213, local class serialVersionUID = -3534890433624150186
Process finished with exit code 0　　

　原因是：之前代码中未显示的指定UID，当Object中新增字段时，编译器又新生成一个UID，于是出现序列化版本不一致的问题；

2.2 显式指定UID

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Serializable;

public class Person implements Serializable {

    private static final long serialVersionUID = -3534890433624150186L;
    private int age;

    private String name;

    private String sex;

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("Person{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append('}');
        return sb.toString();
    }
}

运行上述main函数, 先进行序列化，然后再对object增加属性,再序列化的结果，进行反序列化

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Serializable;

public class Person implements Serializable {

    private static final long serialVersionUID = -3534890433624150186L;
    private int age;

    private String name;

    private String sex;

    // 增加字段测试序列化
    private String addText;

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddText() {
        return addText;
    }

    public void setAddText(String addText) {
        this.addText = addText;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("Person{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append(", addText='").append(addText).append('\'');
        sb.append('}');
        return sb.toString();
    }
}

反序列化结果，新增的字段为空值

Deserialization.person===>Person{age=10, name='测试', sex='女', addText='null'}
Process finished with exit code 0 

显式的指定UID，目前常用到的场景是：当object增加的字段时候，不希望反序列化出现异常，即希望类的不同版本对序列化兼容；

等用到其他场景的时候，再更新。。

3. Externalizable-example

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

public class PersonExternal implements Externalizable {

    private int age;

    private String name;

    private String sex;

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
     //未实现
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
      //未实现
    }

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("PersonExternal{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append('}');
        return sb.toString();
    }　　

先序列化再反序列化

package com.java.baseinfo.knowledge.code.serializable;

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 TetsExternalizable {

    public static void main(String[] args) {
        //ExternalizableEnCode();

        ExternalizableDecode();
    }

    private static void ExternalizableEnCode() {
        PersonExternal personExternal = new PersonExternal();
        personExternal.setName("测试");
        personExternal.setAge(18);
        personExternal.setSex("女");
        File file = new File("src/test/resources/personExternal.txt");

        try {
            FileOutputStream fileOutputStream = new FileOutputStream(file);
            ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
            outputStream.writeObject(personExternal);
            System.out.printf("ExternalizableEnCode===>序列化完成");

        } catch (FileNotFoundException e) {
            System.out.printf("ExternalizableEnCode.FileNotFoundException===>" + e);
        } catch (IOException e) {
            System.out.printf("ExternalizableEnCode.IOException===>" + e);
        }

    }

    private static void ExternalizableDecode() {
        try {
            File file = new File("src/test/resources/personExternal.txt");
            FileInputStream fileInputStream = new FileInputStream(file);
            ObjectInputStream inputStream = new ObjectInputStream(fileInputStream);

            PersonExternal personExternal = (PersonExternal) inputStream.readObject();
            System.out.println("ExternalizableDecode.personExternal====>" + personExternal);

        } catch (FileNotFoundException e) {
            System.out.printf("ExternalizableDecode.FileNotFoundException===>" + e);
        } catch (IOException e) {
            System.out.printf("ExternalizableDecode.IOException===>" + e);
        } catch (ClassNotFoundException e) {
            System.out.printf("ExternalizableDecode.ClassNotFoundException===>" + e);
        }
    }
}

运行结果

ExternalizableDecode.personExternal====>PersonExternal{age=0, name='null', sex='null'}　　

此时发现，当时序列化的对象值并未持久化，是因为我们没有重写Externalizable的writeExternal和readExternal方法

重写externalizable方法

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

public class PersonExternal implements Externalizable {

    private int age;

    private String name;

    private String sex;

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeInt(age);
        out.writeObject(name);
        out.writeObject(sex);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        age = in.readInt();
        name = (String) in.readObject();
        sex = (String) in.readObject();
    }

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("PersonExternal{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append('}');
        return sb.toString();
    }
}　

 运行结果

ExternalizableEnCode===>序列化完成ExternalizableDecode.personExternal====>PersonExternal{age=18, name='测试', sex='女'}　　

结论：

Externalizable反序列化的时候，会调用被序列化的无参构造函数去创建一个新的对象，然后再将被保存的对象的字段分别填充到新的对象中；所以使用Externalizable时候，除了重写write/read方法外，所需要序列化的对象还需要提供一个无参的构造函数；若没有无参构造函数，则会抛异常：java.io.InvalidClassException

eg:

package com.java.baseinfo.knowledge.code.serializable;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

public class PersonExternal implements Externalizable {

    private int age;

    private String name;

    private String sex;

    //构造函数
    public PersonExternal(int age, String name, String sex) {
        this.age = age;
        this.name = name;
        this.sex = sex;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeInt(age);
        out.writeObject(name);
        out.writeObject(sex);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        age = in.readInt();
        name = (String) in.readObject();
        sex = (String) in.readObject();
    }

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("PersonExternal{");
        sb.append("age=").append(age);
        sb.append(", name='").append(name).append('\'');
        sb.append(", sex='").append(sex).append('\'');
        sb.append('}');
        return sb.toString();
    }
}　　

test main

package com.java.baseinfo.knowledge.code.serializable;

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 TetsExternalizable {

    public static void main(String[] args) {
        ExternalizableEnCode();

        ExternalizableDecode();
    }

    private static void ExternalizableEnCode() {
        PersonExternal personExternal = new PersonExternal(18,"测试","女");
/*        personExternal.setName("测试");
        personExternal.setAge(18);
        personExternal.setSex("女");*/
        File file = new File("src/test/resources/personExternal.txt");

        try {
            FileOutputStream fileOutputStream = new FileOutputStream(file);
            ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
            outputStream.writeObject(personExternal);
            System.out.printf("ExternalizableEnCode===>序列化完成");

        } catch (FileNotFoundException e) {
            System.out.printf("ExternalizableEnCode.FileNotFoundException===>" + e);
        } catch (IOException e) {
            System.out.printf("ExternalizableEnCode.IOException===>" + e);
        }

    }

    private static void ExternalizableDecode() {
        try {
            File file = new File("src/test/resources/personExternal.txt");
            FileInputStream fileInputStream = new FileInputStream(file);
            ObjectInputStream inputStream = new ObjectInputStream(fileInputStream);

            PersonExternal personExternal = (PersonExternal) inputStream.readObject();
            System.out.println("ExternalizableDecode.personExternal====>" + personExternal);

        } catch (FileNotFoundException e) {
            System.out.printf("ExternalizableDecode.FileNotFoundException===>" + e);
        } catch (IOException e) {
            System.out.printf("ExternalizableDecode.IOException===>" + e);
        } catch (ClassNotFoundException e) {
            System.out.printf("ExternalizableDecode.ClassNotFoundException===>" + e);
        }
    }
}　　

运行结果

ExternalizableEnCode===>序列化完成ExternalizableDecode.IOException===>java.io.InvalidClassException: com.java.baseinfo.knowledge.code.serializable.PersonExternal; no valid constructor

4.transient 关键字

如果对象的属性被赋予transient属性，则该对象在序列化的时候，当前字段不会被序列化；那么再反序列化的时候，该字段会被赋予默认值，如int类型会是0，String为null

eg

public class Person implements Serializable {

    private static final long serialVersionUID = -3534890433624150186L;
    private transient int age;

    private transient String name;

    private String sex;

    // 增加字段测试序列化
    private String addText;　　

运行2中的序列化代码，则结果为

序列化成功
反序列化Deserialization.person===>Person{age=0, name='null', sex='女', addText='addText'}
Process finished with exit code 0　　

参考：https://www.cnblogs.com/xdp-gacl/p/3777987.html      

http://www.importnew.com/17964.html