使用TCP通过套接字发送字符串

Question

I am trying to send a string (and later also an image) from one Android app, to another Android app. I know that I am very close.

The code "SendString" is one Android app on one phone. And the code "AppListener" is on the other phone. "SendString" seems to be working correctly and sending the string because all of my print statements are printing.

"SendString", which is sending a string to "AppListener":

(the string that I am sending "applicationName" is getting passed to "SendString" from a different activity in the project)

I know this code is working because I get all the print statements in "try" and it never gets passed to the catch Exception.

public class SendString extends AsyncTask<String, String, String> {

@Override
protected String doInBackground(String... params) {

    Log.d("tag_name", "Entered AsyncTask");

    String applicationName = params[0];


    // SEND APPLICATION NAME AND ICON TO OTHER APP

    try {

        Log.d("tag_name", "TRY TO SEND STRING");
        Socket socket = new Socket("192.168.0.26", 1755);
        DataOutputStream DOS = new DataOutputStream(socket.getOutputStream());
        DOS.writeUTF(applicationName);
        Log.d("tag_name", "Application Name Sent!");
        socket.close();

    }

    catch (Exception e){

        Log.d("tag_name", "Did not send string");

    }

    return null;
}

}

Here is the other Android app code that is listening for a port connection, and then it should be receiving the string from "SendString".

public class AppListener extends AsyncTask<String, String, String> {



@Override
protected String doInBackground(String... uri) {

    String msg_received = null;

    System.out.println("LISTENING FOR LAST INSTALLED APP");

    try {


        System.out.println("TRY");
        ServerSocket socket = new ServerSocket(1755);
        System.out.println("Connect to Socket and listening");
        Socket clientSocket = socket.accept();       //This is blocking. It will wait.
        System.out.println("This should print after connection");
        DataInputStream DIS = new DataInputStream(clientSocket.getInputStream());
        msg_received = DIS.readUTF();

        System.out.println("Message from server" + msg_received);

        clientSocket.close();
        socket.close();
    } catch (Exception e) {
        System.out.println("Did not connect to SendString");
    }
    System.out.println("Return Statement is Reached");
    return msg_received;
}
}

The problem is that it seems to be getting stuck at the line

Socket clientSocket = socket.accept();       //This is blocking. It will wait.

because I never get the print statement "this should print after connection", but I get all the print statements before that. Does anyone see what the problem is and why my AppListener activity seems to not connect to the port to receive the string, even though I know that the "SendString" app is connecting and sending the string as it should be (because I see all the print statements).

Answer 1

Does anyone see what the problem is and why my Client seems to not connect to the port to receive the string, even though I know that the server side is connecting and sending the string as it should be.

1. You have 'server' and 'client' mixed up. Clients connect: servers accept.
2. Your real server, which you described as your client, isn't accepting a connection.
3. This can only mean that your real client, which you described as your server, isn't creating one.

You must have either not executed your real client at all, or else got a ConnectException you haven't told us about.