java.net.BindException：地址已在使用中：JVM_Bind但没有端口在使用它

Question

I have java proxy for which I have attached the full code below.

I am constantly getting the following error when starting it.

java.net.BindException: Address already in use: JVM_Bind

I have used tcpview and done searches with netstat but nothing is using the port 9339...

My code is as follows:

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

public class proxy {
  public static void main(String[] args) throws IOException {
    try {
      String host = "gamea.clashofclans.com";
      int remoteport = 9339;
      ServerSocket s = new ServerSocket(0);
      int localport = s.getLocalPort();
      // Print a start-up message
      System.out.println("Starting proxy for " + host + ":" + remoteport
          + " on port " + localport);
      // And start running the server
      runServer(host, remoteport, localport); // never returns
    } catch (Exception e) {
      System.err.println(e);
    }
  }

  /**
   * runs a single-threaded proxy server on
   * the specified local port. It never returns.
   */
  public static void runServer(String host, int remoteport, int localport)
      throws IOException {
    // Create a ServerSocket to listen for connections with
    ServerSocket ss = new ServerSocket(localport);

    final byte[] request = new byte[2048];
    byte[] reply = new byte[4096];

    while (true) {
      Socket client = null, server = null;
      try {
        // Wait for a connection on the local port
        client = ss.accept();

        final InputStream streamFromClient = client.getInputStream();
        final OutputStream streamToClient = client.getOutputStream();

        // Make a connection to the real server.
        // If we cannot connect to the server, send an error to the
        // client, disconnect, and continue waiting for connections.
        try {
          server = new Socket(host, remoteport);
          System.out.println("Client connected to server.");
        } catch (IOException e) {
          PrintWriter out = new PrintWriter(streamToClient);
          out.print("Proxy server cannot connect to " + host + ":"
              + remoteport + ":\n" + e + "\n");
          out.flush();
          client.close();
          continue;
        }

        // Get server streams.
        final InputStream streamFromServer = server.getInputStream();
        final OutputStream streamToServer = server.getOutputStream();

        // a thread to read the client's requests and pass them
        // to the server. A separate thread for asynchronous.
        Thread t = new Thread() {
          public void run() {
            int bytesRead;
            try {
              while ((bytesRead = streamFromClient.read(request)) != -1) {
                streamToServer.write(request, 0, bytesRead);
                streamToServer.flush();
              }
            } catch (IOException e) {
            }

            // the client closed the connection to us, so close our
            // connection to the server.
            try {
              streamToServer.close();
            } catch (IOException e) {
            }
          }
        };

        // Start the client-to-server request thread running
        t.start();

        // Read the server's responses
        // and pass them back to the client.
        int bytesRead;
        try {
          while ((bytesRead = streamFromServer.read(reply)) != -1) {
            streamToClient.write(reply, 0, bytesRead);
            streamToClient.flush();
          }
        } catch (IOException e) {
        }

        // The server closed its connection to us, so we close our
        // connection to our client.
        streamToClient.close();
      } catch (IOException e) {
        System.err.println(e);
      } finally {
        try {
          if (server != null)
            server.close();
          if (client != null)
            client.close();
        } catch (IOException e) {
        }
      }
    }
  }
}

As you can see, the remote port is 9339 and the local port is auto assigned.

I have no idea where I am going wrong, I would greatly appreciate some assistance.

New problem - Original Fixed.

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

public class proxy {
  public static void main(String[] args) throws IOException {
    try {
      String host = "gamea.clashofclans.com";
      int remoteport = 9339;
      ServerSocket ss = new ServerSocket(0);
      int localport = ss.getLocalPort();
      ss.setReuseAddress(true);
      // Print a start-up message
      System.out.println("Starting proxy for " + host + ":" + remoteport
          + " on port " + localport);
      // And start running the server
      runServer(host, remoteport, localport,ss); // never returns
    } catch (Exception e) {
      System.err.println(e);
    }
  }

  /**
   * runs a single-threaded proxy server on
   * the specified local port. It never returns.
   */
  public static void runServer(String host, int remoteport, int localport, ServerSocket ss)
      throws IOException {
    // Create a ServerSocket to listen for connections with

    final byte[] request = new byte[2048];
    byte[] reply = new byte[4096];

    while (true) {
      Socket client = null, server = null;
      try {
        // Wait for a connection on the local port
        client = ss.accept();

        final InputStream streamFromClient = client.getInputStream();
        final OutputStream streamToClient = client.getOutputStream();

        // Make a connection to the real server.
        // If we cannot connect to the server, send an error to the
        // client, disconnect, and continue waiting for connections.
        try {
          server = new Socket(host, remoteport);
          System.out.println("Client connected to server.");
        } catch (IOException e) {
          PrintWriter out = new PrintWriter(streamToClient);
          out.print("Proxy server cannot connect to " + host + ":"
              + remoteport + ":\n" + e + "\n");
          out.flush();
          client.close();
          continue;
        }

        // Get server streams.
        final InputStream streamFromServer = server.getInputStream();
        final OutputStream streamToServer = server.getOutputStream();

        // a thread to read the client's requests and pass them
        // to the server. A separate thread for asynchronous.
        Thread t = new Thread() {
          public void run() {
            int bytesRead;
            try {
              while ((bytesRead = streamFromClient.read(request)) != -1) {
                streamToServer.write(request, 0, bytesRead);
                streamToServer.flush();
              }
            } catch (IOException e) {
            }

            // the client closed the connection to us, so close our
            // connection to the server.
            try {
              streamToServer.close();
            } catch (IOException e) {
            }
          }
        };

        // Start the client-to-server request thread running
        t.start();

        // Read the server's responses
        // and pass them back to the client.
        int bytesRead;
        try {
          while ((bytesRead = streamFromServer.read(reply)) != -1) {
            streamToClient.write(reply, 0, bytesRead);
            streamToClient.flush();
          }
        } catch (IOException e) {
        }

        // The server closed its connection to us, so we close our
        // connection to our client.
        streamToClient.close();
      } catch (IOException e) {
        System.err.println(e);
      } finally {
        try {
          if (server != null)
            server.close();
          if (client != null)
            client.close();
        } catch (IOException e) {
        }
      }
    }
  }
}

The code will run and all but nothing prints out except the starting proxy text.

Answer 1

Your program is creating 2 sockets that tries to listen on the same port:

 ServerSocket s = new ServerSocket(0);

in your main() method, and then you have

ServerSocket ss = new ServerSocket(localport);

in your runServer() method, which you pass in the same port as the socket created in main(). Use only one of these sockets, eg pass in the ServerSocket you create in main() to the runServer() method.