java - 我如何测试有人连接到我的服务器？

Question

我正在创建一个 Android 客户端，我想确保它可以连接到 Java 服务器。

我的服务器是这样的

public static void main(String[] args){

    int portNumber = 5885;
    System.out.println("Starting..");

    // We use a try-with-resources statement to ensure that all sockets and 
    // readers/writers are closed when the program terminates
    try (
            // Set up the server socket on a specified port number
            ServerSocket serverSocket = new ServerSocket(portNumber);

            // Wait until a connection is made by a client and accept its socket
            Socket clientSocket = serverSocket.accept();

            // Set up a writer to the client socket
            PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

            // Set up a reader from the client socket
            BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        ) {

            // Missing Part

        } catch (IOException e) {
            System.out.println("Exception caught when trying to listen on port " + portNumber + " or listening for a connection");
            System.out.println(e.getMessage());
        }
    }
}

客户端正在尝试连接此代码

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.board_layout);

    new Thread(new ClientThread()).start();

 }

class ClientThread implements Runnable {

    @Override
    public void run() {

        try {
            InetAddress serverAddr = InetAddress.getByName(SERVER_IP);

            socket = new Socket(serverAddr, SERVERPORT);

        } catch (UnknownHostException e1) {
            e1.printStackTrace();
        } catch (IOException e1) {
            e1.printStackTrace();
        }

    }

}

如何检查是否有人连接到服务器？用一个

if (clientSocket != null)
     System.out.println("Someone is in");

还是什么？

Answer 1

如果您想知道客户端是否已连接，serverSocket.accept() 将阻塞直到有人连接。这也应该在一个循环中，为每个客户端生成一个专用线程。

如果你想可靠地确认客户端已连接，我会使用心跳(来自客户端的消息的全部目的是确认连接状态):

让每个客户端向服务器发送心跳。例如，客户端有一个线程 hibernate 一段时间(10 秒)，然后醒来发送心跳。这样，如果您在一段时间内没有收到检测信号，您就知道存在连接问题。

只是为了说明这个概念:

服务器:

public void startServer() throws IOException{
        ServerSocket serverSocket = new ServerSocket(9209);
        List<ClientThread> clientThreads = new ArrayList<ClientThread>();
        boolean running = true;
        while(running){
            try {
                Socket clientSocket = serverSocket.accept();
                ClientThread clientThread = new ClientThread(clientSocket);
                clientThread.run();
                clientThreads.add(clientThread);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        for(ClientThread thread : clientThreads){
            thread.shutdown();
        }
}





 public class ClientThread extends Thread{
        private BufferedReader in;
        private volatile boolean running = true;
        private long lastHeartBeat;

        public ClientThread(Socket socket) throws IOException{
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        }

        public void shutdown(){
            running = false;
        }

        @Override
        public void run() {
            while(running){
                try {
                    if(in.readLine().equalsIgnoreCase("HeartBeat")){
                        lastHeartBeat = System.currentTimeMillis();
                    }else{
                        //do something else 
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

每个客户端创建以下之一:

public class HeartBeatThread extends Thread{

    PrintWriter out;
    volatile boolean running = true;

    public HeartBeatThread(Socket socket) throws IOException{
        this.out = new PrintWriter(socket.getOutputStream(), true);
    }

    public void shutdown(){
        running = false;
    }

    @Override
    public void run() {
        while(running){
            try {
                sleep(10000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            out.println("HeartBeat");
        }
    }
}