Groovy和Java程序之间通过套接字进行通信

Question

I am trying to write a small socket program with client side in groovy and the server side in Java. Below is the code I wrote

client:

def s = new Socket("localhost", 4444);
s << "Server before withStreams\n";
s.withStreams { input, output ->
  println"Sending message1" 
  output << "server message1\n"
}
s.close();

server:

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

public class Logger{
  ServerSocket providerSocket;
  Socket connection = null;
  BufferedReader in;
  String message="InitialMessage";
  Logger(){}

  void run()
  {
    try{
      providerSocket = new ServerSocket(4444, 10);
      try{
        Thread.sleep(1000);
      }
      catch(InterruptedException ie)
      {
        System.out.println("Sleep Interrupted");
      }
      System.out.println("Waiting for connection");
      connection = providerSocket.accept();
      System.out.println("Connection received from " + connection.getInetAddress().getHostName());

      in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
      do{
        if(in.ready())
        {
          try{
            System.out.println(in.read());
            message = in.readLine();
            System.out.println("client>" + message);
          }
          catch(IOException e)
          {
            System.out.println(e);
            e.printStackTrace();
            break;
          }
        }
      } while(!message.equals("bye"));
    }
    catch(IOException ioException){
      ioException.printStackTrace();
    }
    finally{
      //4: Closing connection
      try{
        in.close();
        providerSocket.close();
      }
      catch(IOException ioException){
        ioException.printStackTrace();
      }
    }
  }

  public static void main(String args[])
  {
    Logger server = new Logger();
    while(true){
      server.run();
    }
  }
}

When I execute both programs, Socket communication is established. But I get a IOException in server code when it reads from the socket ( message = in.readLine(); )

I guess there is some format problem in writing into socket in client. But not able to figure out the exact problem. Can anybody help?

Answer 1

You generally don't want to close your ServetSocket for each client connection. You want to do this once (or every time you start the server) then on each accept() handle the client connection and close the socket for that connection but keep the ServerSocket open until you want to stop the server.

Here's a rewritten version of your example server that also creates a new Thread for each client request to handle multiple concurrent requests. Note that since the test client doesn't send the terminating string "bye" the connection and socket stays open.

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

public class Logger {
    private ServerSocket providerSocket;

    Logger() {

    }

    public void start() {
        try {
            providerSocket = new ServerSocket(4444, 10);
            while (true) {
                System.out.println("Waiting for connection");
                Socket connection = providerSocket.accept();
                new Thread(new Job(connection)).start();
            }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (providerSocket != null) {
            System.out.println("Stopping server");
            try {
                providerSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    }

    static class Job implements Runnable {
        final Socket connection;
        private static int id;
        private int clientId = ++id;

        public Job(Socket connection) {
            this.connection = connection;
        }

        public void run() {
            BufferedReader in = null;
            try {
                System.out.println("Connection " + clientId + " received from " + connection.getInetAddress().getHostName());
                in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String message = "InitialMessage";
                do {
                    if (in.ready()) {
                        try {
                            // not sure why want to read one character then read the line
                            //int ch = in.read();
                            //System.out.println(ch);
                            // -1 if the end of the stream has been reached
                            //if (ch == -1) break;
                            message = in.readLine();
                            // null if the end of the stream has been reached
                            if (message == null) break;
                            System.out.println("client>" + message);
                        } catch (IOException e) {
                            System.out.println(e);
                            e.printStackTrace();
                            break;
                        }
                    }
                } while (!message.equals("bye"));
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                //4: Closing connection
                System.out.println("Close connection " + clientId);
                if (in != null)
                    try {
                        in.close();
                    } catch (IOException ioException) {
                        ioException.printStackTrace();
                    }
                try {
                    connection.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String args[]) {
        Logger server = new Logger();
        server.start();
    }
}