[填坑篇]Java序列化与反序列化注意事项与细节探究

九转成圣

发布于 2024-04-10 16:57:53

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代码可运行

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代码可运行

序列化:(方便在磁盘上存储或者在网络上传输)把对象转换为字节序列的过程称为对象的序列化。

反序列化:把字节序列恢复为对象的过程称为对象的反序列化。
利用ObjectOutputStream和ObjectInputStream序列化和反序列化时一定要实现Serializable接口,否则会报NotSerializableException异常
利用fastjson序列化字符串时不实现Serializable不会报异常(fastjson使用的是反射,通过get方法获取属性,如果没有get方法就直接访问属性,如果属性的访问修饰符为private就拿不到,在fastjson将对象转为字符串的过程中不会修改属性的访问修饰符,transient修饰的字段也不会参数转字符串)

@Data
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    public static int id;
    private String name;
    private int age;
    // 参与序列化的类也必须能序列化,否则会报 NotSerializableException
    private Pet pet;
    private transient Car car;
    private int height;

    public static void main(String[] args) {
        serializePerson();
        deserializePerson();
    }

    private static void serializePerson() {
        Person person = new Person();
        person.setName("张三三");
        person.setAge(18);
        person.setPet(new Pet("大黄"));
        person.setCar(new Car("奥迪"));
        Person.id = 1;
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("person.txt"))) {
            out.writeObject(person);
            System.out.println("序列化完成");
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("JSON.toJSONString(person):"+JSON.toJSONString(person));

    }

    private static void deserializePerson() {
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("person.txt"))) {
            Person readObject = (Person) in.readObject();
            System.out.println("readObject = " + readObject);
            System.out.println(Person.id);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

@Data
public class Car {
    private String name;

    public Car(String name) {
        this.name = name;
    }
}

@Data
public class Pet implements Serializable {
    private String name;

    public Pet(String name) {
        this.name = name;
    }
}

序列化完成
JSON.toJSONString(person):{"age":18,"height":0,"name":"张三三","pet":{"name":"大黄"}}
readObject = Person(name=张三三, age=18, height=0, pet=Pet(name=大黄), car=null)
1

说明:

静态成员变量不能序列化(序列化)

transient修饰的成员变量不参与序列化

参与序列化的引用类型也必须实现Serializable接口,否则会报NotSerializableException异常

@Data
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private Pet pet;

    public static void main(String[] args) throws CloneNotSupportedException, FileNotFoundException {
        Person person = new Person();
        person.setName("张三");
        Pet pet = new Pet();
        pet.setName("大黄");
        person.setPet(pet);
        try (ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("person.txt"))) {
            outputStream.writeObject(person);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@Data
public class Pet {
    private String name;
}

java.io.NotSerializableException: com.example.hello.mianshi.Pet
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
	at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
	at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
	at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
	at com.example.hello.mianshi.Person.main(Person.java:23)

最好显示提供serialVersionUID

实现 Serializable 接口的类不显式地声明 serialVersionUID 字段时，Java 会自动生成一个 serialVersionUID，这种方式的缺点是它会基于类的结构自动生成一个 serialVersionUID，可能会因为类的修改而改变。当serialVersionUID不一致时就会报InvalidClassException异常

序列化时有name和age

@Data
public class Person implements Serializable {
    private String name;
    private int age;

    public static void main(String[] args) throws CloneNotSupportedException, FileNotFoundException {
        serialize();
    }

    private static void serialize() {
        Person person = new Person();
        person.setName("张三");
        person.setAge(18);
        try (ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("person.txt"))) {
            outputStream.writeObject(person);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

反序列化时少了age,多了gender

@Data
public class Person implements Serializable {
    private String name;
    private String gender;

    public static void main(String[] args) throws CloneNotSupportedException, FileNotFoundException {
        deserialize();
    }

    private static void deserialize() {
        try (ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream("person.txt"))) {
            Object o = inputStream.readObject();
            System.out.println("o = " + o);
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

报错

java.io.InvalidClassException: com.example.hello.mianshi.Person; local class incompatible: stream classdesc serialVersionUID = 1, local class serialVersionUID = 1518472723010370216
	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)

加上serialVersionUID

@Data
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private int age;

    public static void main(String[] args) throws CloneNotSupportedException, FileNotFoundException {
        serialize();
    }

    private static void serialize() {
        Person person = new Person();
        person.setName("张三");
        person.setAge(18);
        try (ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("person.txt"))) {
            outputStream.writeObject(person);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@Data
public class Person implements Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    private String gender;

    public static void main(String[] args) throws CloneNotSupportedException, FileNotFoundException {
        deserialize();
    }

    private static void deserialize() {
        try (ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream("person.txt"))) {
            Object o = inputStream.readObject();
            System.out.println("o = " + o);
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}