当套接字在java中读取输入时循环失败

Question

所以我在读取来自客户的输入时遇到问题。每当我在服务器类中使用我的 if 语句而不用 while 语句包裹它时，它都可以正常工作。谁能指出我为什么会失败？

服务器类：

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

public class Server {

    public static void main(String[] args) throws Exception
    {
        Server myServer = new Server();
        myServer.run();
    }

    public void run() throws Exception
    {

        //Initializes the port the serverSocket will be on
        ServerSocket serverSocket = new ServerSocket(9999);
        System.out.println("The Server is waiting for a client on port 9999");
        //Accepts the connection for the client socket
        Socket socket = serverSocket.accept();

        InputStreamReader ir = new InputStreamReader(socket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        String message = br.readLine();
        //Confirms that the message was received
        System.out.println(message);

    //When this while is here.  The match fails and it goes to the else statement.
    //Without the while statement it will work and print "Received our hello message." 
    //when the client says HELLO.

     while(message != null)
     {
            if(message.equals("HELLO"))
            {
                PrintStream ps = new PrintStream(socket.getOutputStream());
                ps.println("Received our hello message.");
            }
            else
            {
                PrintStream ps = new PrintStream(socket.getOutputStream());
                ps.println("Did not receive your hello message");
            }
        }
    }
}

客户端类：

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

public class Client {

    public static void main(String[] args) throws Exception
    {
        Client myClient = new Client();
        myClient.run();
    }

    public void run() throws Exception
    {
        Socket clientSocket = new Socket("localhost", 9999);
        //Sends message to the server
        PrintStream ps = new PrintStream(clientSocket.getOutputStream());
        Scanner scan = new Scanner(System.in);
        String cMessage = scan.nextLine();
        ps.println(cMessage);
        //Reads and displays response from server
        InputStreamReader ir = new InputStreamReader(clientSocket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        String message = br.readLine();
        System.out.println(message);        
    }

}

Answer 1

你永远不会在 while 循环中修改消息，所以你有一个无限循环。

试试

while((message = br.readLine()) != null)

Answer 2

您只在服务器端循环，而您忘记在客户端循环，我为您做了快速修复，还帮助您关闭了连接。

服务器.java

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

public class Server {

    public static void main(String[] args) throws Exception
    {
        Server myServer = new Server();
        myServer.run();
    }

    public void run() throws Exception
    {

        //Initializes the port the serverSocket will be on
        ServerSocket serverSocket = new ServerSocket(9999);
        System.out.println("The Server is waiting for a client on port 9999");
        //Accepts the connection for the client socket
        Socket socket = serverSocket.accept();

        InputStreamReader ir = new InputStreamReader(socket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        String message;
        //= br.readLine();
        //Confirms that the message was received

    //When this while is here.  The match fails and it goes to the else statement.
    //Without the while statement it will work and print "Received our hello message." 
    //when the client says HELLO.
        PrintStream ps = new PrintStream(socket.getOutputStream());
        while((message =br.readLine())!=null)
         {
             System.out.println(message);
                if(message.equals("HELLO"))
                {

                    ps.println("Received our hello message.");
                }
                if(message.equals("END"))
                {
                    ps.println("Client ended the connection");
                    break;
                }
                else
                {

                    ps.println("Did not receive your hello message");
                }
        }
        ps.close();
        br.close();
        ir.close();
        serverSocket.close();
    }
}

客户端.java

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

public class Client {

    public static void main(String[] args) throws Exception
    {
        Client myClient = new Client();
        myClient.run();

    }

    public void run() throws Exception
    {
        Socket clientSocket = new Socket("localhost", 9999);
        //Sends message to the server
        PrintStream ps = new PrintStream(clientSocket.getOutputStream());
        Scanner scan = new Scanner(System.in);
        String cMessage ="";
        InputStreamReader ir = new InputStreamReader(clientSocket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        while(!(cMessage.trim().equals("END"))){
        cMessage = scan.nextLine();
        ps.println(cMessage);
        //Reads and displays response from server
        String message = br.readLine().trim();
        System.out.println(message);
        }
        br.close();
        ir.close();
        scan.close();
        ps.close();
        clientSocket.close();
    }

}

Answer 3

您的代码可以正常发送一条“HELLO”消息。 但是，就像 ^Tyler 指出的那样，如果您想继续发送消息，您需要在 while 循环中移动 'while((message = br.readLine()) != null)'。

Answer 4

像你一样使用循环......

String line;
while ((line = in.readLine()) != null) {
    System.out.println(line);
    sleep(in);
    if(!in.ready()){
        break;
    }
}

我想出了一个作弊的方法。

private static void sleep(BufferedReader in) throws IOException {
    long time = System.currentTimeMillis();
    while(System.currentTimeMillis()-time < 1000){
        if(in.ready()){
            break;
        }
    }       
}

这可能有点草率，但是如果您创建一个等待一段时间的睡眠方法，然后继续检查 BufferedReader 是否“准备就绪”。如果是的话，你可以突破，但是当你出来的时候再检查一次。 -- 也许你可以只返回一个布尔值而不是检查两次，但这个概念就在那里。