使用Serializable接口进行JAVA的序列化和反序列化

Posted 2020-10-28 ITRoad

OBJECT STREAMS – SERIALIZATION AND DESERIALIZATION IN JAVA EXAMPLE USING SERIALIZABLE INTERFACE

Hitesh Garg | November 7, 2014 | io | 9 Comments

In the previous java tutorials I have discussed about basic of java streams, byte streams, then a modified version of them character streams which were specially for character data, then data streams to solve the problem of reading and writing java primitives directly but Object Streams are used to save the state to an object by converting it into a stream and storing into a file, database or some other location(known as Serialization) and to use it at a later point of time for retrieving the stored values and restoring the objects old state( known as Deserialization).

序列化：基于对象流，将对象状态（实例变量）转换为流，并存储到文件、数据库或其他地方。

反序列化；将对象流还原，获取存储对象实例和对象状态。

TABLE OF CONTENTS –

1. REAL LIFE CASES

2. MARKER INTERFACE

3. MAIN INTERFACES FOR OBJECT STREAMS

4. MAIN CLASSES FOR OBJECT STREAMS

5. TRANSIENT KEYWORD

6. EXAMPLE OF SERIALIZABLE INTERFACE

This serialization and deserialization helps us in many scenarios like gaming, session state management etc.

序列化和反序列化的一些应用场景：游戏、Session状态管理等。

Have you ever wondered how a game starts from the same point where we have left it? Then this is your answer. All this is done by saving the current state of the object(or game) and reloading the state so that the player could continue from the old state only. Also the checkpoint system in games follow this method by permanently saving the progress up to that state for later use.

Serialization-deserialization in Java – Object Streams

MARKER INTERFACE（四大常用的标记接口）

An interface in Java without any field and method is a Marker interface. It is used to inform compiler that the class implementing it has some special behavior or meaning. Some of the Marker interfaces are-

• java.io.Serializable
• java.rmi.Remote
• java.util.RandomAccess
• java.lang.Cloneable

Although since Java 5 marker interfaces are replaced by annotations and they serve the same purpose as marker interfaces did before but for serializability we still use the interfaces and the transient keyword.

特别指出，标记接口中的RandomAccess的重要应用，可以参考【RandomAccess接口理解】https://blog.csdn.net/stick2it/article/details/53469910。该文章介绍了RandomAccess在Collections类的 public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) 方法中应用。

INTERFACES

Every Object Stream class implements either of the two interfaces-

1. OBJECTINPUT – SUBINTERFACE OF DATAINPUT

2. OBJECTOUTPUT – SUBINTERFACE OF DATAOUTPUT

Note:- Since both the interfaces above are sub interface of interfaces Data streams interfaces, That means that all the primitive data I/O methods covered in Data Streams are also implemented in object streams.

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CLASSES FOR OBJECT STREAMS

Two classes that are used for Object Streams are –

1. OBJECTINPUTSTREAM （用于反序列化）

   • This Java class is responsible for deserializing the previously serialized objects and the primitive data. 可反序列化之前已被序列化的对象、原始类型数据。
   • It reads the object from the graph of objects stored while using FileInputStream.
   • Method readObject() is the main method used to deserialize the object.The class of the object, the signature of the class, and the values of the non-transient and non-static fields of the class and all of its super types are read. 注意非transient和非static字段才可反序列化，另外可以读取对象、类以及超类信息。
   • • public final Object readObject() throws IOException,ClassNotFoundException

2. OBJECTOUTPUTSTREAM

   • This Java class is used to store primitives and a graph of Java object which are available to ObjectInputStream to read data from.
   • This does not care about saving the super class and sub class data but it could be achieved by using the writeObject method or by using the methods for primitive data types supported by DataOutput.
   • Method writeObject() is a main method of this Java class which serializes the object directly.
     • public final void writeObject(Object obj) throws IOException

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TRANSIENT KEYWORD

There are scenarios in which we want to store only a part of the object i.e. we want to omit some specific fields from the stored object just like password field from any user class or an Employee or you can think of any other sensitive information.

In these cases we mark these fields as transient and this keyword protects the field from being saved during the process of serialization.

Example – transient private String password;

transient关键词用于屏蔽那些不想被序列化的字段。

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SERIALIZATION AND DESERIALIZATION EXAMPLE

Now lets take an example and see how to do this using actual Java coding and have a look at some key points that should be remembered while using Serializable interface.

USER.JAVA

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package com.codingeek.serialization;   import java.io.Serializable;   public class User implements Serializable {       /**      * Generated Serial version Id      */     private static final long serialVersionUID = -55857686305273843L;   关于java的Serializable Serializable接口 java类为什么要实现Serializable接口 Java 序列化和反序列化Serializable 源码分析 - 1 Java序列化与反序列化学习：序列化接口说明 Serializable接口的作用；Externalizable自定义序列化和反序列化