Question

我对Java和Eclipse IDE还是很陌生，在Windows的命令提示符下运行Java代码时遇到问题。如果我通过Eclipse IDE运行代码，则输出为

Message number 0
Message number 1
Message number 2
Timeout. Client is closing.

但是，如果我通过命令提示符java test.Main运行代码，则命令提示符下的消息之间会出现很多空行。

//Hundreds of empty lines 
Message number 0
//Hundreds of empty lines
Message number 1
//Hundreds of empty lines
Message number 2
//Hundreds of empty lines
Timeout. Client is closing.

我尝试添加简单的检查，以在字符串为NULL或为空但不起作用时不输出任何输出。下面是我的代码。我花了很多时间，但是不知道是什么原因造成的。

Main.java

package test;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

// create 5 processes

public class Main {

    public static void main(String[] args) {
        int port = 50001;
        UdpUnicastServer server = new UdpUnicastServer(port);
        UdpUnicastClient client = new UdpUnicastClient(port);

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.submit(client);
        executorService.submit(server);
    }
}

UdpUnicastClient.java

package test;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * Created by dan.geabunea on 6/3/2016.
 */
public class UdpUnicastClient implements Runnable {
    private final int port;

    public UdpUnicastClient(int port) {
        this.port = port;
    }

    @Override
    public void run() {
        /**
         * Bind the client socket to the port on which you expect to
         * read incoming messages
         */
        try (DatagramSocket clientSocket = new DatagramSocket(port)) {
            /**
             * Create a byte array buffer to store incoming data. If the message length
             * exceeds the length of your buffer, then the message will be truncated. To avoid this,
             * you can simply instantiate the buffer with the maximum UDP packet size, which
             * is 65506
             */

            byte[] buffer = new byte[65507];

            // Set a timeout of 3000 ms for the client.
            clientSocket.setSoTimeout(3000);
            while (true) {
                DatagramPacket datagramPacket = new DatagramPacket(buffer, 0, buffer.length);

                /**
                 * The receive method will wait for 3000 ms for data.
                 * After that, the client will throw a timeout exception.
                 */
                clientSocket.receive(datagramPacket);

                String receivedMessage = new String(datagramPacket.getData());
                if(receivedMessage != null && !receivedMessage.isEmpty()) {
                    System.out.println(receivedMessage);
                }
            }
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("Timeout. Client is closing.");
        }
    }
}

UdpUnicastServer.java

package test;

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

/**
 * Created by dan.geabunea on 6/3/2016.
 */
public class UdpUnicastServer implements Runnable {
    /**
     * The port where the client is listening.
     */
    private final int clientPort;

    public UdpUnicastServer(int clientPort) {
        this.clientPort = clientPort;
    }

    @Override
    public void run() {
        /**
         * Create a new server socket and bind it to a free port. I have chosen
         * one in the 49152 - 65535 range, which are allocated for internal applications
         */
        try (DatagramSocket serverSocket = new DatagramSocket(50000)) {
            // The server will generate 3 messages and send them to the client
            for (int i = 0; i < 3; i++) {
                String message = "Message number " + i;
                DatagramPacket datagramPacket = new DatagramPacket(
                        message.getBytes(),
                        message.length(),
                        InetAddress.getLocalHost(),
                        clientPort
                );
                serverSocket.send(datagramPacket);
            }
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Java Eclipse-从命令提示符运行时的输出与通过IDE不同

0 个答案: