在Client Class中创建ObjectInputStream时为什么会卡住？ （套接字编程）

Question

当我在我的服务器 - 客户端程序中使用DataOutputStream / DataInputStream时一切正常，但在我决定使用ObjectInputStream / ObjectOutputStream之前，我在创建ObjectInputStream / ObjectOutputStream时遇到了问题。我和我的朋友无法看出问题所在。如果有人有任何想法，那将是感恩的。这是我的＆＃34; MyClient＆＃34;和＃34; MultiThreadServer＆＃34;类。

它完全停留在以下行：＆＃34; fromServer = new ObjectInputStream（s.getInputStream（））;＆＃34; MyClient类中的行。

这是我的＆＃34; MyClient＆＃34;类：

public class MyClient extends javax.swing.JFrame {

String name;
public MyClient() {
    initComponents();
    sendButton.addActionListener(new ButtonListener());
    jTextField1.addActionListener(new ButtonListener());

    try{
        Socket s = new Socket("localhost", 8080);               // program reaches to this step
        fromServer = new ObjectInputStream(s.getInputStream()); // and gets stuck in this step. (Understand it with using some Sys.out.print();)
        toServer = new ObjectOutputStream(s.getOutputStream());         
    }
    catch(Exception ex){
        System.out.println("Something happend while socket is creating!");
    }
}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
   name = jTextField2.getText();
}                                        

public static void main(String args[]) {

    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Windows".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(MyClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(MyClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(MyClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(MyClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new MyClient().setVisible(true); 
        }
    });
}

private ObjectOutputStream toServer;
private ObjectInputStream fromServer;

private class ButtonListener implements ActionListener{

    @Override
    public void actionPerformed(ActionEvent ae) {

        // Here there are some activities when the button is clicked. 


    }

}
}

这是我的＆＃34; MutliThreadServer＆＃34;类：

public class MultiThreadServer  {

private String secretWord;
public Socket s;
public ArrayList clients = new ArrayList<ObjectOutputStream>();
ServerSocket serverSocket;

public static void main(String[] args) {  
  new MultiThreadServer();   
}

public MultiThreadServer() {

try {
  serverSocket = new ServerSocket(8080);
  System.out.println("MultiThreadServer started at " + new Date() + '\n');

  int clientNo = 1;

  while (true) {

     s = serverSocket.accept(); 

    System.out.println("Starting thread for client " + clientNo +" at " + new Date() + '\n');

    InetAddress inetAddress = s.getInetAddress();
    System.out.println("Client " + clientNo + "'s host name is "+ inetAddress.getHostName() + "\n");
    System.out.println("Client " + clientNo + "'s IP Address is "+ inetAddress.getHostAddress() +     "\n");

    HandleAClient task = new HandleAClient(s);

    new Thread(task).start();

    clientNo++;
   }
 }
catch(IOException ex) {
  System.err.println(ex);
 }
}

class HandleAClient implements Runnable {
private Socket socket;

public HandleAClient(Socket socket) {
  this.socket = socket;
}

/** Run a thread */
public void run() {

  try {
    ObjectInputStream inputFromClient = new ObjectInputStream(
      socket.getInputStream());
    ObjectOutputStream outputToClient = new ObjectOutputStream(
      socket.getOutputStream());

    clients.add(outputToClient);
    outputToClient.writeObject(arrayToString(secretWordArray));

    // Continuously serve the client
    while (true) {

      // some unnecessary things that server makes
    }
  }

}
}

Answer 1

使用Object Stream的套接字时，这是一个经典的“陷阱”。 Object流格式有一个头，它由ObjectOutputStream的构造函数编写，并由ObjectInputStream的构造函数读取。因此，您的构造函数调用阻止尝试从套接字读取标头（尚未编写，因为另一端同样被阻止。

解决方案（对于连接的两端）：

1. 创建ObjectOutputStream
2. flush() ObjectOutputStream
3. 然后创建ObjectInputStream

这将确保将Object流标头写入套接字并发送到接收方，以便可以成功构建ObjectInputStream。