用于发送和接收用户定义对象的套接字程序不起作用

Posted 2023-03-30

【中文标题】用于发送和接收用户定义对象的套接字程序不起作用

【英文标题】：Socket program to send and receive user defined objects not working

【发布时间】：2013-12-13 22:10:50

【问题描述】：

我有一个用户定义的类 Message，我想在客户端和服务器之间传递它的对象。

Message类如下：

import java.io.Serializable;

public class Message implements Serializable

    String CorS;
    int data_id;
    int status_id;
    Integer value;
    boolean withdraw;

    public Message()
    
        CorS = null;
        data_id = 0;
        status_id = 0;
        value = 0;
        withdraw = false;
    

    public Message(String CorS, int data_id, int status_id, Integer value)
    
        this.CorS = CorS;
        this.data_id = data_id;
        this.status_id = status_id;
        this.value = value;
    

    public Message(boolean withdraw)
    
        this.withdraw = withdraw;
    

客户端向服务器发送对象的代码如下：

Socket s = null;
    ObjectInputStream in = null;
    ObjectOutputStream out = null;

    String hostname = null;
    int port_no = 0;

    HashMap<String, Integer> map = null;

    Message m = null;

    map = servers.get("Server" + server);

    for(String key : map.keySet())
    
        hostname = key;
        port_no = map.get(key);
    
    //System.out.println(hostname + " " + port_no);

    s = new Socket(hostname, port_no);
    in = new ObjectInputStream(new BufferedInputStream(s.getInputStream()));
    out = new ObjectOutputStream(new BufferedOutputStream(s.getOutputStream()));

    s_now = s;

    m = new Message(client, data, 0, 0);
    out.writeObject(m);
    out.flush();
    System.out.println("Sent obj");

同理，Server端的代码如下：

while (true)
    
        try 
        
            System.out.println("Waiting for client on port " + serverSocket.getLocalPort() + "...");
            Socket server = serverSocket.accept();
            System.out.println("Just connected to " + server.getRemoteSocketAddress());

            ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(server.getInputStream()));
            //ObjectOutputStream out = new ObjectOutputStream(server.getOutputStream());

            Message m = (Message) in.readObject();

            System.out.println(m.value);
         

        catch (IOException e) 
        
            e.printStackTrace();
            break;
        
        catch (ClassNotFoundException e) 
        
            // TODO Auto-generated catch block
            e.printStackTrace();
        
    

问题是对象没有被打印出来。我得到的输出如下：

Waiting for client on port 1051...
Just connected to /127.0.0.1:59216

在这方面的任何帮助将不胜感激。谢谢:)

【参考方案1】：

您需要在两端的ObjectInputStream 之前创建ObjectOutputStream。

原因是，如 Javadoc 中所述，各个构造函数写入和读取流标头。所以输入流构造函数在对等端的输出流构造函数执行之前不能返回。所以如果你先构造两个输入流，就会出现死锁。

【讨论】：

谢谢。那行得通。但是你能告诉我为什么会这样吗？有什么合理的解释吗？