【Java基础】序列化与反序列化深入分析（下）-阿里云开发者社区

六、序列化问题

　　6.1 采用默认序列化机制，类的静态字段会被序列化吗？

　　采用默认序列化机制进行序列化时，类的静态字段会被序列化吗，此时类的静态字段不会被序列化，当然，我们可以采用自定义序列化逻辑对静态变量进行序列化。

　　6.2 父类序列化问题

　　采用默认序列化机制序列化子类时，其父类的字段会被序列化吗？可以分为如下情形

　　1. 父类没有实现Serializable接口，没有提供默认构造函数

　　这时，反序列化会出错，提示没有提供正确的构造函数。修改Person类，代码如下

package com.hust.grid.leesf.serializable;
import java.io.Serializable;
class Human {
    private int number;
    public Human(int number) {
        this.number = number;
    }
    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
    public String toString() {
        return "number = " + number;
    }
}
public class Person extends Human implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String name;
    private String gender;
    private int age;
    private transient Person friend;
    public Person(int number, String name) {
        super(number);
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Person getFriend() {
        return friend;
    }
    public void setFriend(Person friend) {
        this.friend = friend;
    }
    @Override
    public String toString() {
        return super.toString() + ", name = " + name + ", gender = " + gender + ", age = " + age
                + ", friend info is [" + friend + "]";
    }    
}

　测试类的的代码如下

复制代码
package com.hust.grid.leesf.serializable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class SerializableDemo {
    public static void main(String[] args) throws Exception {
        Person leesf = new Person(1, "leesf");
        Person dyd = new Person(2, "dyd");
        leesf.setAge(24);
        leesf.setGender("man");
        leesf.setName("leesf");
        dyd.setAge(24);
        dyd.setGender("woman");
        dyd.setName("dyd");    
        leesf.setFriend(dyd);
        dyd.setFriend(null);
        File file = new File("test");
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file));
        oos.writeObject(leesf);
        oos.flush();
        oos.close();
        System.out.println(leesf);
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));
        leesf = (Person) ois.readObject();
        ois.close();    
        System.out.println(leesf);    
    }
}

　　运行结果　

number = 1, name = leesf, gender = man, age = 24, friend info is [number = 2, name = dyd, gender = woman, age = 24, friend info is [null]]
Exception in thread "main" java.io.InvalidClassException: com.hust.grid.leesf.serializable.Person; no valid constructor
    at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(ObjectStreamClass.java:150)
    at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:768)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1775)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at com.hust.grid.leesf.serializable.SerializableDemo.main(SerializableDemo.java:32)

说明：可以看出是没有提供合法的构造函数。

　　2. 父类没有实现Serializable接口，提供默认构造函数

　　第一步中出现了错误，此时，我们修改Person类，代码如下　

package com.hust.grid.leesf.serializable;
import java.io.Serializable;
class Human {
    private int number;
    public Human() {
    }
    public Human(int number) {
        this.number = number;
    }
    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
    public String toString() {
        return "number = " + number;
    }
}
public class Person extends Human implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String name;
    private String gender;
    private int age;
    private transient Person friend;
    public Person() {
        super();
    }
    public Person(int number, String name) {
        super(number);
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Person getFriend() {
        return friend;
    }
    public void setFriend(Person friend) {
        this.friend = friend;
    }
    @Override
    public String toString() {
        return super.toString() + ", name = " + name + ", gender = " + gender + ", age = " + age
                + ", friend info is [" + friend + "]";
    }    
}

　说明：给Human类提供了无参构造函数。测试类代码不变，运行结果如下

number = 1, name = leesf, gender = man, age = 24, friend info is [number = 2, name = dyd, gender = woman, age = 24, friend info is [null]]
number = 0, name = leesf, gender = man, age = 24, friend info is [null]

说明：此时，我们可以看到，可以进行反序列化了，但是父类的number字段被赋值为int的默认值0，Person类的transient字段没有被序列化。

　　3. 父类实现Serializable接口

　　当父类实现Serializable接口时，修改Person类代码如下　

package com.hust.grid.leesf.serializable;
import java.io.Serializable;
class Human implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private int number;
    public Human() {
    }
    public Human(int number) {
        this.number = number;
    }
    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
    public String toString() {
        return "number = " + number;
    }
}
public class Person extends Human implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String name;
    private String gender;
    private int age;
    private transient Person friend;
    public Person() {
        super();
    }
    public Person(int number, String name) {
        super(number);
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Person getFriend() {
        return friend;
    }
    public void setFriend(Person friend) {
        this.friend = friend;
    }
    @Override
    public String toString() {
        return super.toString() + ", name = " + name + ", gender = " + gender + ", age = " + age
                + ", friend info is [" + friend + "]";
    }    
}

　　测试类的代码不变，运行结果如下　

number = 1, name = leesf, gender = man, age = 24, friend info is [number = 2, name = dyd, gender = woman, age = 24, friend info is [null]]
number = 1, name = leesf, gender = man, age = 24, friend info is [null]

　说明：从结果可知，已经可以进行正确的序列化与反序列化了，子类的transient字段没有被序列化。

　　6.3 共享对象序列化问题　　

　　当序列化的两个对象都包含另外一个对象的引用时，在反序列化时，另外一个对象只会出现一次吗？修改Person类代码如下　

package com.hust.grid.leesf.serializable;
import java.io.Serializable;
public class Person implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String name;
    private String gender;
    private int age;
    private transient Person friend;
    public Person() {
    }
    public Person(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Person getFriend() {
        return friend;
    }
    public void setFriend(Person friend) {
        this.friend = friend;
    }
}

　测试类代码如下　

package com.hust.grid.leesf.serializable;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;
public class SerializableDemo {
    @SuppressWarnings("unchecked")
    public static void main(String[] args) throws Exception {
        Person leesf = new Person("leesf");    
        Person dyd = new Person("dyd");
        Person lr = new Person("lr");
        leesf.setAge(24);
        leesf.setGender("man");
        dyd.setAge(24);
        dyd.setGender("woman");
        lr.setAge(25);
        lr.setGender("man");
        leesf.setFriend(dyd);
        lr.setFriend(dyd);
        dyd.setFriend(null);
        List<Person> persons = new ArrayList<Person>();
        persons.add(leesf);
        persons.add(dyd);
        persons.add(lr);
        ByteArrayOutputStream bos1 = new ByteArrayOutputStream();
        ByteArrayOutputStream bos2 = new ByteArrayOutputStream();
        ObjectOutputStream oos1 = new ObjectOutputStream(bos1);
        oos1.writeObject(persons);
        oos1.writeObject(persons);
        ObjectOutputStream oos2 = new ObjectOutputStream(bos2);
        oos2.writeObject(persons);
        ByteArrayInputStream bis1 = new ByteArrayInputStream(bos1.toByteArray());
        ByteArrayInputStream bis2 = new ByteArrayInputStream(bos2.toByteArray());
        ObjectInputStream ois1 = new ObjectInputStream(bis1);
        ObjectInputStream ois2 = new ObjectInputStream(bis2);
        List<Person> persons1 = (List<Person>) ois1.readObject();
        List<Person> persons2 = (List<Person>) ois1.readObject();
        List<Person> persons3 = (List<Person>) ois2.readObject();
        System.out.println(persons1);
        System.out.println(persons2);
        System.out.println(persons3);    
    }
}

　运行结果如下　　

[com.hust.grid.leesf.serializable.Person@7f31245a, com.hust.grid.leesf.serializable.Person@6d6f6e28, com.hust.grid.leesf.serializable.Person@135fbaa4]
[com.hust.grid.leesf.serializable.Person@7f31245a, com.hust.grid.leesf.serializable.Person@6d6f6e28, com.hust.grid.leesf.serializable.Person@135fbaa4]
[com.hust.grid.leesf.serializable.Person@45ee12a7, com.hust.grid.leesf.serializable.Person@330bedb4, com.hust.grid.leesf.serializable.Person@2503dbd3]

　说明：从结果可知，oos1执行的writeObject是向同一个内存空间写了两次，从结果可看出，两次写入的对象的地址空间都是一样的，即进行了浅拷贝。而oos2执行的writeObject是向另外一个内存空间写了一次，从结果可看出，因为对象的地址不同于之前的对象地址，即采用了深拷贝。

七、总结

　　写到这里，关于Java中的序列化与反序列化机制就已经分析完了，经过此次分析，对序列化机制的认识更加深刻。学习一个知识点，就要认认真真，踏踏实实的弄懂一个知识点，写博客就是一个特别好的方式。谢谢各位园友的观看~

【Java基础】序列化与反序列化深入分析（下）

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