Question

我正在尝试为分配编写客户端和时间服务器，但我无法让服务器从客户端接收第二个请求。第一个请求顺利完成。那它只是停滞不前。我实际上已经迷失在整个事情中，而且对java仍感到不安，所以我不知道我错过了什么。任何指针都非常感谢。谢谢！

这是服务器代码：

 import java.io.*;
 import java.util.*;
 import java.net.*;
 import java.text.*;

 public class myServer {

      protected static final int PORT_NUMBER = 55555;

      public static void main( String args[]) {

      try {

           ServerSocket servsock = new ServerSocket(PORT_NUMBER);

           System.out.println("Server running...");

           while(true) {

                Socket sock = servsock.accept();

                System.out.println("Connection from: " + sock.getInetAddress());

                Scanner in = new Scanner(sock.getInputStream());
                PrintWriter out = new PrintWriter(sock.getOutputStream());
                String request = "";

                request = in.next();

                System.out.println("Request: " + request);

                if(request.toUpperCase().equals("TIME")) {
                     out.println(getTime());
                     out.flush();
                } else {
                     out.println("Invalid Request...");
                     out.flush();
                }

            }

        } catch(Exception e) {
           System.out.println(e.toString());
        }

    }

      protected static String getTime() {
           DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
           Date date = new Date();
           return (dateFormat.format(date));
      }

}

这是客户：

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

 public class myClient {

        protected static final String HOST = "127.0.0.1";
        protected static final int PORT = 55555;

        protected static Socket sock;

        public static void main(String args[]) {

        try {

              sock = new Socket(HOST,PORT);

              System.out.println("Connected to " + HOST + " on port " + PORT);

              Scanner response = new Scanner(sock.getInputStream());
              PrintWriter request = new PrintWriter(sock.getOutputStream());
              BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
              String txt = "";

              while(!txt.toUpperCase().equals("EXIT")) {

                    System.out.print("prompt:");
                    txt = in.readLine();

                    request.println(txt);
                    request.flush();

                    System.out.println(response.next());

              }

              request.close();
              response.close();
              in.close();
              sock.close();

           } catch(IOException e) {
              System.out.println(e.toString());
           }
      }

 }

Answer 1

你需要有另一个while循环，像这样，

  while(true) {                
      Socket sock = servsock.accept();                
      System.out.println("Connection from: " + sock.getInetAddress());                
      Scanner in = new Scanner(sock.getInputStream());                
      PrintWriter out = new PrintWriter(sock.getOutputStream());                
      String request = "";                
      while (in.hasNext()) {
          request = in.next();                
          System.out.println("Request: " + request);                
          if(request.toUpperCase().equals("TIME")) {                     
              out.println(getTime());
              out.flush();                
          } else {
               out.println("Invalid Request...");                     
               out.flush();
          }
      }
 }

Answer 2

来自PrintWriter docs：

...如果启用了自动刷新，则只有在调用println，printf或format方法之一时才会执行此操作...

您的服务器正在调用print()并且从不刷新流，因此永远不会发送时间。可以调用println()或显式刷新流。

此外，服务器在发送时间后立即关闭连接，因此客户端的第二个请求总是失败...

编辑：这里有一个有趣的怪癖 - 关闭PrintWriter 应该来刷新它（参见Writer的规范），但是到期而似乎的操作顺序是：

in.close()关闭基础Socket
out.close() 将刷新写入的数据，但不能（因为套接字现已关闭）

不确定这正是发生了什么，但是交换这两个语句的顺序会改变行为，大概会让out.close()有机会冲洗......

Java服务器客户端|服务器不会收到第二个请求

2 个答案: