线程“主”java.net.ConnectException 中的异常：连接被拒绝：连接套接字编程 Java

Question

我最近学习了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“主”java.net.ConnectException 中的异常：连接被拒绝：连接

这是我的客户端类代码：

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();
        }
    }
}

完整的错误信息是：

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)

希望有人能帮助我，谢谢。

Answer 1

您的程序中有 2 个问题：

1. 您使用的端口80 是well-known ports 或系统端口（0 到1023）的一部分，因此您需要以管理员权限启动服务器或将其更改为@例如 987654325@。
2. 您忘记在每个bw.write(sendMessage) 之后调用bw.newLine()，这样它就会一直等待，因为在另一端您调用br.readLine() 这意味着它会等待整行，而您不发送行尾字符。

为此更改您的代码：

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!