Java - 使用一台计算机测试两个 TCP 客户端

Question

对于类(class)，我需要使用 TCP 连接构建一个程序。

我们获得了下面的示例代码来使用并了解如何建立连接。当我只有一个客户端运行时，服务器和客户端可以正常通信。当我尝试启动客户端的新实例来模拟两个人使用该客户端与一台服务器时，第二个客户端无法发送或接收，并且永远不会显示消息“获得 I/O 连接”。这是为什么？

这是示例代码。

// Fig. 27.5: Server.java
// Server portion of a client/server stream-socket connection. 
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class Server extends JFrame 
{
   private JTextField enterField; // inputs message from user
   private JTextArea displayArea; // display information to user
   private ObjectOutputStream output; // output stream to client
   private ObjectInputStream input; // input stream from client
   private ServerSocket server; // server socket
   private Socket connection; // connection to client
   private int counter = 1; // counter of number of connections

   // set up GUI
   public Server()
   {
      super( "Server" );

      enterField = new JTextField(); // create enterField
      enterField.setEditable( false );
      enterField.addActionListener(
         new ActionListener() 
         {
            // send message to client
            public void actionPerformed( ActionEvent event )
            {
               sendData( event.getActionCommand() );
               enterField.setText( "" );
            } // end method actionPerformed
         } // end anonymous inner class
      ); // end call to addActionListener

      add( enterField, BorderLayout.NORTH );

      displayArea = new JTextArea(); // create displayArea
      add( new JScrollPane( displayArea ), BorderLayout.CENTER );

      setSize( 300, 150 ); // set size of window
      setVisible( true ); // show window
   } // end Server constructor

   // set up and run server 
   public void runServer()
   {
      try // set up server to receive connections; process connections
      {
         server = new ServerSocket( 12345, 100 ); // create ServerSocket

         while ( true ) 
         {
            try 
            {
               waitForConnection(); // wait for a connection
               getStreams(); // get input & output streams
               processConnection(); // process connection
            } // end try
            catch ( EOFException eofException ) 
            {
               displayMessage( "\nServer terminated connection" );
            } // end catch
            finally 
            {
               closeConnection(); //  close connection
               ++counter;
            } // end finally
         } // end while
      } // end try
      catch ( IOException ioException ) 
      {
         ioException.printStackTrace();
      } // end catch
   } // end method runServer

   // wait for connection to arrive, then display connection info
   private void waitForConnection() throws IOException
   {
      displayMessage( "Waiting for connection\n" );
      connection = server.accept(); // allow server to accept connection            
      displayMessage( "Connection " + counter + " received from: " +
         connection.getInetAddress().getHostName() );
   } // end method waitForConnection

   // get streams to send and receive data
   private void getStreams() throws IOException
   {
      // set up output stream for objects
      output = new ObjectOutputStream( connection.getOutputStream() );
      output.flush(); // flush output buffer to send header information

      // set up input stream for objects
      input = new ObjectInputStream( connection.getInputStream() );

      displayMessage( "\nGot I/O streams\n" );
   } // end method getStreams

   // process connection with client
   private void processConnection() throws IOException
   {
      String message = "Connection successful";
      sendData( message ); // send connection successful message

      // enable enterField so server user can send messages
      setTextFieldEditable( true );

      do // process messages sent from client
      { 
         try // read message and display it
         {
            message = ( String ) input.readObject(); // read new message
            displayMessage( "\n" + message ); // display message
         } // end try
         catch ( ClassNotFoundException classNotFoundException ) 
         {
            displayMessage( "\nUnknown object type received" );
         } // end catch

      } while ( !message.equals( "CLIENT>>> TERMINATE" ) );
   } // end method processConnection

   // close streams and socket
   private void closeConnection() 
   {
      displayMessage( "\nTerminating connection\n" );
      setTextFieldEditable( false ); // disable enterField

      try 
      {
         output.close(); // close output stream
         input.close(); // close input stream
         connection.close(); // close socket
      } // end try
      catch ( IOException ioException ) 
      {
         ioException.printStackTrace();
      } // end catch
   } // end method closeConnection

   // send message to client
   private void sendData( String message )
   {
      try // send object to client
      {
         output.writeObject( "SERVER>>> " + message );
         output.flush(); // flush output to client
         displayMessage( "\nSERVER>>> " + message );
      } // end try
      catch ( IOException ioException ) 
      {
         displayArea.append( "\nError writing object" );
      } // end catch
   } // end method sendData

   // manipulates displayArea in the event-dispatch thread
   private void displayMessage( final String messageToDisplay )
   {
      SwingUtilities.invokeLater(
         new Runnable() 
         {
            public void run() // updates displayArea
            {
               displayArea.append( messageToDisplay ); // append message
            } // end method run
         } // end anonymous inner class
      ); // end call to SwingUtilities.invokeLater
   } // end method displayMessage

   // manipulates enterField in the event-dispatch thread
   private void setTextFieldEditable( final boolean editable )
   {
      SwingUtilities.invokeLater(
         new Runnable()
         {
            public void run() // sets enterField's editability
            {
               enterField.setEditable( editable );
            } // end method run
         }  // end inner class
      ); // end call to SwingUtilities.invokeLater
   } // end method setTextFieldEditable
} // end class Server

// Fig. 27.7: Client.java
// Client portion of a stream-socket connection between client and server.
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

--

public class Client extends JFrame 
{
   private JTextField enterField; // enters information from user
   private JTextArea displayArea; // display information to user
   private ObjectOutputStream output; // output stream to server
   private ObjectInputStream input; // input stream from server
   private String message = ""; // message from server
   private String chatServer; // host server for this application
   private Socket client; // socket to communicate with server

   // initialize chatServer and set up GUI
   public Client( String host )
   {
      super( "Client" );

      chatServer = host; // set server to which this client connects

      enterField = new JTextField(); // create enterField
      enterField.setEditable( false );
      enterField.addActionListener(
         new ActionListener() 
         {
            // send message to server
            public void actionPerformed( ActionEvent event )
            {
               sendData( event.getActionCommand() );
               enterField.setText( "" );
            } // end method actionPerformed
         } // end anonymous inner class
      ); // end call to addActionListener

      add( enterField, BorderLayout.NORTH );

      displayArea = new JTextArea(); // create displayArea
      add( new JScrollPane( displayArea ), BorderLayout.CENTER );

      setSize( 300, 150 ); // set size of window
      setVisible( true ); // show window
   } // end Client constructor

   // connect to server and process messages from server
   public void runClient() 
   {
      try // connect to server, get streams, process connection
      {
         connectToServer(); // create a Socket to make connection
         getStreams(); // get the input and output streams
         processConnection(); // process connection
      } // end try
      catch ( EOFException eofException ) 
      {
         displayMessage( "\nClient terminated connection" );
      } // end catch
      catch ( IOException ioException ) 
      {
         ioException.printStackTrace();
      } // end catch
      finally 
      {
         closeConnection(); // close connection
      } // end finally
   } // end method runClient

   // connect to server
   private void connectToServer() throws IOException
   {      
      displayMessage( "Attempting connection\n" );

      // create Socket to make connection to server
      client = new Socket( InetAddress.getByName( chatServer ), 12345 );

      // display connection information
      displayMessage( "Connected to: " + 
         client.getInetAddress().getHostName() );
   } // end method connectToServer

   // get streams to send and receive data
   private void getStreams() throws IOException
   {
      // set up output stream for objects
      output = new ObjectOutputStream( client.getOutputStream() );      
      output.flush(); // flush output buffer to send header information

      // set up input stream for objects
      input = new ObjectInputStream( client.getInputStream() );

      displayMessage( "\nGot I/O streams\n" );
   } // end method getStreams

   // process connection with server
   private void processConnection() throws IOException
   {
      // enable enterField so client user can send messages
      setTextFieldEditable( true );

      do // process messages sent from server
      { 
         try // read message and display it
         {
            message = ( String ) input.readObject(); // read new message
            displayMessage( "\n" + message ); // display message
         } // end try
         catch ( ClassNotFoundException classNotFoundException ) 
         {
            displayMessage( "\nUnknown object type received" );
         } // end catch

      } while ( !message.equals( "SERVER>>> TERMINATE" ) );
   } // end method processConnection

   // close streams and socket
   private void closeConnection() 
   {
      displayMessage( "\nClosing connection" );
      setTextFieldEditable( false ); // disable enterField

      try 
      {
         output.close(); // close output stream
         input.close(); // close input stream
         client.close(); // close socket
      } // end try
      catch ( IOException ioException ) 
      {
         ioException.printStackTrace();
      } // end catch
   } // end method closeConnection

   // send message to server
   private void sendData( String message )
   {
      try // send object to server
      {
         output.writeObject( "CLIENT>>> " + message );
         output.flush(); // flush data to output
         displayMessage( "\nCLIENT>>> " + message );
      } // end try
      catch ( IOException ioException )
      {
         displayArea.append( "\nError writing object" );
      } // end catch
   } // end method sendData

   // manipulates displayArea in the event-dispatch thread
   private void displayMessage( final String messageToDisplay )
   {
      SwingUtilities.invokeLater(
         new Runnable()
         {
            public void run() // updates displayArea
            {
               displayArea.append( messageToDisplay );
            } // end method run
         }  // end anonymous inner class
      ); // end call to SwingUtilities.invokeLater
   } // end method displayMessage

   // manipulates enterField in the event-dispatch thread
   private void setTextFieldEditable( final boolean editable )
   {
      SwingUtilities.invokeLater(
         new Runnable() 
         {
            public void run() // sets enterField's editability
            {
               enterField.setEditable( editable );
            } // end method run
         } // end anonymous inner class
      ); // end call to SwingUtilities.invokeLater
   } // end method setTextFieldEditable
} // end class Client

Answer 1

问题出在服务器类中。该类是单线程的(主线程)。主线程用于接受新连接和从套接字读取。接受连接后的主线程转到 processConnection 方法并阻塞以下调用。

message = ( String ) input.readObject();//读取新消息

此调用是在循环中进行的，仅当您从客户端收到“TERMINATE”时才会终止

   } while ( !message.equals( "CLIENT>>> TERMINATE" ) );

直到上面的循环运行代码才能返回到“runServer”方法，该方法可以使用“waitForConnection”接受连接。

您需要分离线程来接受连接并从连接的套接字读取数据。