Java Simple EchoServer 无法工作

Question

我通读了很多，发现很多例子都在做我想做的事情。但是我根本找不到我的代码中的问题。可能我只是需要一双全新的眼睛来审视我的代码。 因此，这里有被标记为重复线程的风险。我有一个简单的 Java 代码。它打开一个端口。将套接字连接到它。获取输入流和输出流。将一些文本放入输出流，输入流尝试读取文本。当执行 readLine 的方法时，它不会返回代码。它只是继续运行，永远不会回到 main 方法。

import java.net.*;
import java.io.*;
import java.io.ObjectInputStream.GetField;

public class echoserver {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    String hostName = "127.0.0.1";
    //      InetAddress.getLocalHost()
    int portNumber = 5000;
    ServerSocket ss = null;
    Socket echoSocket = null;


    try {
        ss = new ServerSocket(portNumber);
        echoSocket = new Socket(hostName, portNumber);
//          echoSocket = ss.accept();
        System.out.println("open");
        System.out.println(echoSocket.isBound());

        PrintWriter writer = new PrintWriter(echoSocket.getOutputStream());
        for (int i = 0; i < 100; i++) {
            writer.print("test String");    
        }

        writer.flush();
//          writer.close();

        System.out.println("inputstream read");
       DataInputStream is = new DataInputStream(echoSocket.getInputStream());
       String fromStream = is.readLine();
       System.out.println(fromStream);

       System.out.println("bufferreader read");

        BufferedReader reader = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
        String fromReader = reader.readLine();

        System.out.println(fromReader);

    } catch (UnknownHostException  ex1) {
        // TODO Auto-generated catch block
        System.out.println("EX1");
        ex1.printStackTrace();
    }

    catch (IOException ex2) {
        // TODO: handle exception
        System.out.println("EX2");
        ex2.printStackTrace();
    }

    finally {
        try {
            echoSocket.close();
            ss.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }



}

}

编辑:更新了下面的代码...此代码中的唯一问题是 Server.Run 中的 while 循环永远不会结束。我寻找了一些其他属性(我记得类似 isTextAvailable 的东西)但找不到。代码背后的想法是将其转换为聊天客户端。不用说这是一场斗争!

编辑 2:我发现了问题所在。我从来没有从编写器端关闭套接字，所以监听器一直在听!感谢大家的帮助!

clientsocket.close();

加了一行就成功了!

import java.net.*;
import java.io.*;
import java.io.ObjectInputStream.GetField;
import java.util.*;

public class echoserver {



static echoserver echo;

public static class Client implements Runnable {

    Socket clientsocket;
    String hostName = "127.0.0.1";
    int portNumber = 5000;
    static int onesleep = 0;

    public void run(){ 


        System.out.println("Client Run  " + new Date());

        try {
            clientsocket = new Socket(hostName,portNumber);
            PrintWriter writer = new PrintWriter(clientsocket.getOutputStream());

            for (int i = 0; i < 10; i++) {
                writer.println("test String   " + i );  
            }

            writer.flush();
                            clientsocket.close();
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }



    }
}

public class Server implements Runnable {

    public void run(){

        System.out.println("Server Run" + new Date());
        int portNumber = 5000;
        ServerSocket ss = null;
        Socket serversocket = null;
        InputStreamReader streamReader; 

        try {
            ss = new ServerSocket(portNumber);
            serversocket = ss.accept();

            System.out.println("bufferreader read  " + new Date());

            streamReader = new InputStreamReader(serversocket.getInputStream());
            BufferedReader reader = new BufferedReader(streamReader);
            String fromReader;

            System.out.println(reader.ready());
            System.out.println(reader.readLine());



            while ((fromReader = reader.readLine()) != null) {
                System.out.println(fromReader);

            }

            System.out.println("After While in Server Run");


        } catch (IOException ex_server) {
            // TODO Auto-generated catch block
            System.out.println("Server Run Error    " + new Date());
            ex_server.printStackTrace();

        }
          finally {
              try {
                serversocket.close();
                  ss.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

          }
        System.out.println("open" + new Date());
        System.out.println(serversocket.isBound());


    }
}


public void go(){

    Server server = new Server();
    Thread serverThread = new Thread(server);
    serverThread.start();

    Client client = new Client();
    Thread clientThread = new Thread(client);
    clientThread.start();

}

public static void main(String[] args) {
    // TODO Auto-generated method stub

    echo = new echoserver();
    echo.go();





}

}

Answer 1

我之前准备了这篇文章的一个版本，但根据你在另一个答案中的最后评论，你似乎已经明白了。无论如何我都会发布这个，以防它有任何帮助。

广泛的答案是，您的类，正如您目前拥有的那样，有效地代表了同一线程/进程中的客户端和服务器端部分。如您所见，您可以将数据写入出站(或客户端)套接字，但服务器端组件永远没有机会监听传入连接。

因此，当您尝试从入站(或服务器端)套接字的输入流中读取数据时，没有任何内容存在，因为没有收到任何内容。 readline() 方法最终会阻塞，直到数据可用，这就是为什么您的程序似乎在那个时候保持不变。此外，如 haifzhan 所说，使用 new Socket(...) 创建新套接字不会建立连接，您所拥有的只是一个套接字，流中没有任何内容。

ServerSocket#accept方法你需要使用什么来监听连接。此方法将为您创建套接字，您可以尝试从中读取其流。正如 haifzhan 所说，该方法会阻塞，直到建立连接，这最终是它无法在单线程环境中正常运行的原因。

要在同一个应用程序中执行此操作，您只需将组件分开并在单独的线程中运行它们。尝试如下操作:

public class EchoClient {

    public static void main(String[] args) throws InterruptedException {
        new Thread(new EchoServer()).start(); // start up the server thread

        String hostName = "localhost";
        int portNumber = 5000;

        try {
            Socket outboundSocket = new Socket(hostName, portNumber);

            System.out.println("Echo client is about to send data to the server...");

            PrintWriter writer = new PrintWriter(outboundSocket.getOutputStream());
            for (int i = 0; i < 100; i++) {
                writer.print("test String");
            }

            System.out.println("Data has been sent");

            writer.flush();
            outboundSocket.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

还有作为单独线程运行的服务器组件:

public class EchoServer implements Runnable {

    public void run(){
        try {
            ServerSocket ss = new ServerSocket(5000);
            System.out.println("Waiting for connection...");
            Socket inboundSocket = ss.accept();

            System.out.println("inputstream read");
            DataInputStream is = new DataInputStream(inboundSocket.getInputStream());

            BufferedReader reader = new BufferedReader(new InputStreamReader(is));

            String fromStream = reader.readLine();
            System.out.println(fromStream);

            System.out.println("bufferreader read");
            ss.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}