通过示例解释序列化和反序列化-Java

序列化和反序列化是Java(以及通常的编程)中涉及将对象转换为字节流,以及反之的过程。当你需要传输或存储对象的状态时特别有用,比如将其通过网络发送或持久化到文件中。

序列化:

  • 定义:序列化是将对象的状态(字段和数据)转换为字节流的过程。
  • 目的:它允许保存对象的状态,以便以后可以重建它。
  • Java接口:Java中的Serializable接口是一个标记接口,表示类可以序列化。

反序列化:

  • 定义:反序列化是从字节流重建对象的过程。
  • 目的:它允许从保存的状态重新创建原始对象。
  • Java 接口:实现的类Serializable应该被反序列化。

用途和实时应用:

  • 网络通讯:

  • 用例:当需要通过网络在不同应用程序或系统之间发送对象时。

  • 示例:客户端-服务器应用程序,其中对象在客户端和服务器之间发送。

import java.io.*;
import java.net.*;

public class User implements Serializable {
    private String username;
    private transient String password; // Transient fields are not serialized

    // Constructors, getters, setters...

    public static void main(String[] args) {
        // Serialization (Client Side)
        try (Socket socket = new Socket("server_address", 12345);
             ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream())) {

            User user = new User("john_doe", "password123");
            out.writeObject(user);
            System.out.println("User object sent to server");

        } catch (IOException e) {
            e.printStackTrace();
        }

        // Deserialization (Server Side)
        try (ServerSocket serverSocket = new ServerSocket(12345);
             Socket clientSocket = serverSocket.accept();
             ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream())) {

            User receivedUser = (User) in.readObject();
            System.out.println("Received User object: " + receivedUser);

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

持久化:

  • 用例:将对象的状态存储在文件或数据库中,以便以后检索。
  • 示例:将用户偏好或游戏状态保存在文件中。
import java.io.*;

public class UserPreferences implements Serializable {
    private String theme;
    private int fontSize;

    // Constructors, getters, setters...

    public static void main(String[] args) {
        // Serialization (Save Preferences)
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("user_preferences.ser"))) {

            UserPreferences preferences = new UserPreferences("dark", 16);
            out.writeObject(preferences);
            System.out.println("User preferences saved to file");

        } catch (IOException e) {
            e.printStackTrace();
        }

        // Deserialization (Load Preferences)
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("user_preferences.ser"))) {

            UserPreferences loadedPreferences = (UserPreferences) in.readObject();
            System.out.println("Loaded User preferences: " + loadedPreferences);

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

缓存:

  • 用例:将对象存储在缓存中,以便快速检索而无需重新创建它们。
  • 示例:缓存频繁使用的数据库查询结果。
import java.io.*;
import java.util.HashMap;
import java.util.Map;

public class CacheManager implements Serializable {
    private Map<String, Object> cache = new HashMap<>();

    // Methods to put, get, and manage the cache...

    public static void main(String[] args) {
        // Serialization (Save Cache)
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("cache.ser"))) {

            CacheManager cacheManager = new CacheManager();
            cacheManager.put("queryResult1", /* database query result */);
            cacheManager.put("queryResult2", /* another query result */);

            out.writeObject(cacheManager);
            System.out.println("Cache saved to file");

        } catch (IOException e) {
            e.printStackTrace();
        }

        // Deserialization (Load Cache)
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("cache.ser"))) {

            CacheManager loadedCacheManager = (CacheManager) in.readObject();
            System.out.println("Loaded Cache: " + loadedCacheManager);

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

消息队列:

  • 用例:在不同组件或微服务之间传递对象。
  • 示例:使用消息队列在分布式系统的不同部分之间发送对象。
import java.io.*;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;

public class MessageQueue implements Serializable {
    private Queue<String> messages = new ArrayBlockingQueue<>(10);

    // Methods to add, retrieve, and manage messages...

    public static void main(String[] args) {
        // Serialization (Save Message Queue)
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("message_queue.ser"))) {

            MessageQueue messageQueue = new MessageQueue();
            messageQueue.addMessage("Message1");
            messageQueue.addMessage("Message2");

            out.writeObject(messageQueue);
            System.out.println("Message Queue saved to file");

        } catch (IOException e) {
            e.printStackTrace();
        }

        // Deserialization (Load Message Queue)
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("message_queue.ser"))) {

            MessageQueue loadedMessageQueue = (MessageQueue) in.readObject();
            System.out.println("Loaded Message Queue: " + loadedMessageQueue);

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

远程方法调用(RMI):

  • 用例:像调用本地方法一样在远程对象上调用方法。
  • 示例:分布式应用程序中,一个机器上的对象需要调用另一个机器上对象的方法。
import java.rmi.*;
import java.rmi.registry.*;

public interface RemoteCalculator extends Remote {
    int add(int a, int b) throws RemoteException;
    // Other remote methods...
}

public class CalculatorImpl implements RemoteCalculator {
    public int add(int a, int b) throws RemoteException {
        return a + b;
    }
    // Other method implementations...
}

public class RmiServer {
    public static void main(String[] args) {
        try {
            RemoteCalculator calculator = new CalculatorImpl();
            Registry registry = LocateRegistry.createRegistry(1099);
            Naming.rebind("CalculatorService", calculator);
            System.out.println("RMI Server is running...");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class RmiClient {
    public static void main(String[] args) {
        try {
            RemoteCalculator calculator = (RemoteCalculator) Naming.lookup("rmi://localhost/CalculatorService");
            int result = calculator.add(5, 10);
            System.out.println("Result from RMI server: " + result);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

总之,在Java中,序列化涉及将对象转换为字节流,从而实现其存储或传输;而反序列化则从字节流重构原始对象。这些过程对于诸如将对象状态保存到文件、通过网络发送对象或将数据持久化到数据库等任务至关重要,确保数据能够轻松存储、传输和随后重建。

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