线程“main”中的异常java.net.ConnectException：拒绝连接：连接Socket编程Java

问题描述

我最近了解客户端和服务器之间的套接字编程。所以我想做一个连接客户端和服务器的练习。但是，当我尝试运行代码时遇到此错误消息：
线程main中的异常java.net.ConnectException：连接被拒绝：连接

I recently learn about Socket Programming between client and server. So I thought of doing an exercise of connecting both client and server. However, I have encountered this error message when I try to run the code:Exception in thread "main" java.net.ConnectException: Connection refused: connect

这是我的客户类代码：

public class clientpart {
    public static void main(String[]args) throws UnknownHostException, IOException {
        Scanner input = new Scanner(System.in);
        int port = 8080;
        String host=null;
        String answer; String sendMessage; String receivedMessage;
        InetAddress address = InetAddress.getByName(host);
        Socket socket= new Socket(address,port);

        OutputStream os = socket.getOutputStream();
        OutputStreamWriter osw = new OutputStreamWriter(os);
        BufferedWriter bw = new BufferedWriter(osw);

        System.out.println("Please answered the following question: ");
        System.out.println("What is the subject code for Socket Programming?");
        answer = input.nextLine();

        sendMessage = answer;
        bw.write(sendMessage);
        bw.newLine();
        bw.flush();
        System.out.println("Message sent to server: "+sendMessage);

        InputStream is = socket.getInputStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        receivedMessage = br.readLine();
        System.out.println("Message received from server : " + receivedMessage);
    }
}

这是我的服务器代码：

public class serverpart {
    public static Socket socket;
    public static void main(String[]args) throws IOException {
        int port = 8080;
        String answer; String returnedMessage; String reply;
        ServerSocket server = new ServerSocket(port);
        System.out.println("Server start at port "+port+".");

        while(true)
        {
            socket = server.accept();
            InputStream is = socket.getInputStream();
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            answer = br.readLine();
            System.out.println("Message sent from client: " + answer);

            if("NET 3202".equals(answer) || "net 3202".equals(answer) || "NET3202".equals(answer) || "net3202".equals(answer)){
                reply = "Correct!";
                returnedMessage = reply;
            }
            else{
                reply = "Wrong!";
                returnedMessage = reply;
            }

            OutputStream os = socket.getOutputStream();
            OutputStreamWriter osw = new OutputStreamWriter(os);
            BufferedWriter bw = new BufferedWriter(osw);
            bw.write(returnedMessage);
            bw.newLine();
            System.out.println("Message replied to client: "+returnedMessage);
            bw.flush();
        }
    }
}

完整的错误消息是：

Exception in thread "main" java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:244)
at clientpart.main(clientpart.java:13)
C:\Users\PeiErn\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 1 second)

我希望有人可以帮助我，谢谢。

I hope someone can help me, thanks.

推荐答案

您的计划中有2个问题：

There are 2 issues in your program:

1. 您使用端口 80 这是或系统端口（0到1023），因此您需要使用管理员权限启动服务器或更改它例如， 8080 。


2. 你忘了打电话给每个 bw.write（sendMessage）这样它就等到了你在另一边致电这意味着它在您不发送行尾字符时等待整行。

1. You use the port 80 which is part of the well-known ports or system ports (0 to 1023), so you need to launch your server with the admin rights or change it for 8080 for example.
2. You forgot to call bw.newLine() after each bw.write(sendMessage) such that it waits for ever since on the other side you call br.readLine() which means that it waits for an entire line while you don't send the end of line characters.

更改您的代码：

服务器部分：

public class serverpart {
    public static Socket socket;
    public static void main(String[]args) throws IOException {
        int port = 8080;
        ...
            BufferedWriter bw = new BufferedWriter(osw);
            bw.write(returnedMessage);
            bw.newLine();
            ...

输出：

Server start at port 8080.
Accepted
Message sent from client: net3202
Message replied to client: Correct!

客户端部分：

public class clientpart {
    public static void main(String[]args) throws IOException {
        Scanner input = new Scanner(System.in);
        int port = 8080;
        ...
        bw.write(sendMessage);
        bw.newLine();
        bw.flush();
        ...

输出：

Please answered the following question:
What is the subject code for Socket Programming?
net3202
Message sent to server: net3202
Message received from server : Correct!

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