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POHow can I issue commands from a thread-run ServerSocket to a client?
 

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  1. POHow can I issue commands from a thread-run ServerSocket to a client?
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    <p>I am using this guide:</p> <p><a href="http://thinkandroid.wordpress.com/2010/03/27/incorporating-socket-programming-into-your-applications/" rel="nofollow">Incorporating Socket Programming into your Applications</a></p> <p>And in this portion of my code I am trying to make the server send messages in response to UI button presses:</p> <pre><code>public class MusicServerThread implements Runnable { Socket client; public void run() { try { if (SERVERIP != null) { //'Success' case when there is an Internet connection. handler.post(new Runnable() { @Override public void run() { Log.d(WiFiDirectActivity.TAG, "MusicServerThread_run: ServerIP = " + SERVERIP); //TODO serverStatus can't be null. Fix this. //serverStatus.setText("Listening on IP: " + SERVERIP); } }); serverSocket = new ServerSocket(SERVERPORT); Log.d(WiFiDirectActivity.TAG, "MusicServerThread_run: serverSocket created on port " + SERVERPORT); while (true) { // listen for incoming clients client = serverSocket.accept(); Log.d(WiFiDirectActivity.TAG, "MusicServerThread_run: Client connection recieved."); handler.post(new Runnable() { @Override public void run() { //serverStatus.setText("Connected."); } }); try { //This line takes the client commands. BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream())); String line = null; while ((line = in.readLine()) != null) { //TODO Stop endless loop from being a radge. Play music command Log.d(WiFiDirectActivity.TAG, "Command issued " + line); if (line.toLowerCase(Locale.getDefault()).trim().equals("play")){ //if the command is play Log.d(WiFiDirectActivity.TAG, "Server says: client command accepted " + line); //MediaPlayer mediaPlayer = MediaPlayer.create(getActivity(), R.raw.mse5251); //mediaPlayer.start(); // no need to call prepare(); create() does that for you handler.post(new Runnable() { @Override public void run() { // do whatever you want to the front end // this is where you can be creative MediaPlayer mediaPlayer = MediaPlayer.create(getActivity(), R.raw.metallica_guitar); mediaPlayer.start(); // no need to call prepare(); create() does that for you } }); } if (line.toLowerCase(Locale.getDefault()).trim().equals("join")){ //if the command is join Log.d(WiFiDirectActivity.TAG, "Server says: client command accepted " + line); //Just for fun server will play as well. //Todo: add a timer to delay start MediaPlayer mediaPlayer = MediaPlayer.create(getActivity(), R.raw.metallica_guitar); mediaPlayer.start(); // no need to call prepare(); create() does that for you try { PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(client .getOutputStream())), true); // where you issue the commands out.println("play"); } catch (Exception e) { Log.e(WiFiDirectActivity.TAG, "S: Error", e); } handler.post(new Runnable() { @Override public void run() { // do whatever you want to the front end // this is where you can be creative } }); } break;// Play command received, break. } break; } catch (Exception e) { handler.post(new Runnable() { @Override public void run() { //serverStatus.setText("Oops. Connection interrupted. Please reconnect your phones."); } }); e.printStackTrace(); } } } else { handler.post(new Runnable() { @Override public void run() { //serverStatus.setText("Couldn't detect internet connection."); } }); } } catch (Exception e) { handler.post(new Runnable() { @Override public void run() { //serverStatus.setText("Error"); } }); e.printStackTrace(); } } /*Method used by the server to send command strings.*/ public void sendCommand(String command){ Log.d(WiFiDirectActivity.TAG, "MusicServerThread_sendCommand: Method reached."); try { PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(client .getOutputStream())), true); // where you issue the commands out.println("play"); } catch (Exception e) { Log.e(WiFiDirectActivity.TAG, "S: Error", e); } } </code></pre> <p>But I receive a null pointer exception for what I think is the client in my SendCommands method. </p> <p>Is it even possible to have the server thread running, waiting for commands, while I try to use it's SendCommands method for sending commands to the client?</p> <p>UPDATE:</p> <p>Here is the stack trace of the error:</p> <pre><code>03-04 16:35:44.055: E/wifidirectdemo(4202): S: Error 03-04 16:35:44.055: E/wifidirectdemo(4202): java.lang.NullPointerException 03-04 16:35:44.055: E/wifidirectdemo(4202): at com.example.android.wifidirect.DeviceDetailFragment$MusicServerThread.sendCommand(DeviceDetailFragment.java:465) 03-04 16:35:44.055: E/wifidirectdemo(4202): at com.example.android.wifidirect.DeviceDetailFragment$4.onClick(DeviceDetailFragment.java:201) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.view.View.performClick(View.java:3538) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.view.View$PerformClick.run(View.java:14330) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.os.Handler.handleCallback(Handler.java:608) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.os.Handler.dispatchMessage(Handler.java:92) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.os.Looper.loop(Looper.java:156) 03-04 16:35:44.055: E/wifidirectdemo(4202): at android.app.ActivityThread.main(ActivityThread.java:4977) 03-04 16:35:44.055: E/wifidirectdemo(4202): at java.lang.reflect.Method.invokeNative(Native Method) 03-04 16:35:44.055: E/wifidirectdemo(4202): at java.lang.reflect.Method.invoke(Method.java:511) 03-04 16:35:44.055: E/wifidirectdemo(4202): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 03-04 16:35:44.055: E/wifidirectdemo(4202): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 03-04 16:35:44.055: E/wifidirectdemo(4202): at dalvik.system.NativeStart.main(Native Method) </code></pre>
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