Develop Reference

Android Socket connects to server but doesn't write anything

I'm currently runing a server on Eclipse(local IP 192.168.1.255, listening to port 4567). A client can connect trought sockets and send messages, that will be printed on the terminal by the server.
Part of the server code is the following:
System.out.println("Client connected: " + clientName);
String line;
while (true){
line = in.nextLine();
System.out.println("STRING RECEIVED: " + line + " FROM " + clientName);
}
where in is the input stream of the client socket.
Part of client code, instead, is:
while(true) {
System.out.print("\nEnter your input: ");
line = stdin.next();
socketOut.println(line);
socketOut.flush();
}
So, in example, a possible output on server terminal with two clients connected is the following:
Client connected: Socket[addr=/192.168.1.225,port=54852,localport=4567]
STRING RECEIVED: Hello FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
STRING RECEIVED: World FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
Client connected: Socket[addr=/192.168.1.225,port=54945,localport=4567]
STRING RECEIVED: Hello2 FROM Socket[addr=/192.168.1.225,port=54945,localport=4567]
Everything works well, so i'm now trying to access server trough sockets on a simple app developed on Android Studio. The code is:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new BackgroundTask().execute();
}
private class BackgroundTask extends AsyncTask {
#Override
protected Object doInBackground(Object[] params) {
try {
Socket socket = new Socket("10.0.2.2", 4567);
PrintWriter out = new PrintWriter(socket.getOutputStream());
out.println(new String("Hi from Android!"));
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
}
But the output is just
Client connected: Socket[addr=/192.168.1.225,port=55001,localport=4567]
and nothing else.
Any advice about the println doesn't send anything? The program works perfectly on Eclipse on both client/server side, so i guess the problem is on Android. Also, i enabled the Android network permissions, so the connection should work.
Thanks in advance to everybody.
EDIT: solved, i just changed Android client code to:
try {
Socket socket = new Socket("10.0.2.2", 4567);
if (socket.isConnected()) {
PrintWriter out = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())), true);
String line = new String("Hi from Android!");
out.println(line);
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

You need to either flush the PrintWriter or construct it to auto-flush. It doesn't by default.

Sending bluetooth data between Android and Hololens

I have created an application to Android and Microsoft Hololens, where it is possible to send some GPS-data with bluetooth from an Android-phone to a Hololens (with Bluetooth LE Advertiser) and that works allright. But when I am trying to send other data from Hololens to Android, I have a problem that Android-phone can't discover Hololens, although these devices are paired. Is it even possible to send data from Hololens with bluetooth, or is there only something wrong in my code? Does Bluetooth LE Advertising support two-way data transfering?

I am guessing you have a BluetoothConnected thread in your android app with an InputStream (mine is mmInStream). Try using this as your 'run' function in the thread:
public void run() {
System.out.println("BT THREAD RUNNING");
mmBuffer = new byte[1024];
int numBytes; // bytes returned from read()
InputStreamReader mmInStreamReader = new InputStreamReader(mmInStream);
BufferedReader mmReader = new BufferedReader(mmInStreamReader);
// Keep listening to the InputStream until an exception occurs.
while (true) {
try {
// Read from the InputStream.
Thread.sleep(100);
String s = mmReader.readLine();
Thread.sleep(100);
//Static class that handles the response
BluetoothCommunications.responseHandler(s);
} catch (IOException e) {
System.out.println("Input stream was disconnected" + e);
main.disconnected();
break;
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}

The socket stop t Socket.accept() in Android for TCP Server

I try to create a Simple TCP Server on Android phone and waiting for client.
I only want to implement the connection between TCPServer and Client , it doesn't need to transmit any data.
I have the another application for client , It use to connect to this TCPServer.
The code of TCPServerthread is like the following.
private class TCPServerThread implements Runnable
{
#Override
public void run() {
// TODO Auto-generated method stub
try {
ServerSocket serverSocket = new ServerSocket(PORT);
//while loop
while (true) {
Log.i(TAG, "TCPServerThread...while loop");
try {
Socket socket = serverSocket.accept();
Log.i(TAG, "TCPServerThread...socket.getInetAddress() = " + socket.getInetAddress());
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
Log.i(TAG, "First IOException");
}
}
//while loop end
} catch (Exception e) {
// TODO: handle exception
//e.printStackTrace();
Log.i(TAG, "Second IOException");
}
}
}
But it seems stop at Socket socket = serverSocket.accept(); and doesn't show the log of TCPServerThread...socket.getInetAddress() = when the client try to connect to this Server.
DO I missing something for TCPServer ?
Is it mean the client doesn't connect to the Server when the code stop at Socket socket = serverSocket.accept(); ??
----------------------------EDIT----------------------------------------
Update the process.
The Server(Android Phone) open the WiFi-Hot-Spot, it also open the TCP-Server like the above code.
After Client connect to WiFi-Hot-Spot , the Client and the Server are in the same network.
The Client will get a IP address of gateway, and the Client try to connect to this IP address of gateway by TCP.
So the connection port and Server address seems correct for Client.

Your code is correct, but it seems that no one is connecting to your TCPserver.
To avoid this blocking situation on
Socket socket = serverSocket.accept();
you have to set the timeout option for your socket when you declare it
serverSocket.setSoTimeout(mTime);
;)

Connecting Bluetooth in Android

I have done a simple app to connect my phone with an Arduino via BT and all goes right. My phone have Android 2.3.6... But, when I try the app on my tablet (with android 4.0.3), I can't connect. I post here the specific piece of code:
try {
BluetoothSocket socket = mydevice.createRfcommSocketToServiceRecord(UUID.fromString(ARDUINO_STANDAR_UUID));
socket.connect();
OutputStream output = socket.getOutputStream();
InputStream input = socket.getInputStream();
Log.d(TAG, "Connected");
}
catch (IOException e) { Log.e(TAG, e.getMessage()); }
}
Using the Log, the problem is at socket.connect(); at that point, I have to enter the PIN of the device, but it don't connect anyway... The error is "Connection refused"...
What can be wrong?

Try something like this to take care of the connection. I just updated an old android-10 app the other day to android-17 and dealt with exactly this.
BluetoothDevice yourDevice;
try {
Method m = yourDevice.getClass().getMethod( "createInsecureRfcommSocket", new Class[] { int.class } );
selectedDeviceSocket = (BluetoothSocket) m.invoke( yourDevice, Integer.valueOf( 1 ) );
selectedDeviceSocket.connect();
}

Android TCP app hanging on inStream.readline()

This is a continuation of this question because it my orginal question was answered, but it did not solve the bug.
Question:
How do I fix the code hanging on this line inStream.readline()
My Intent:
This is in a thread that will loop through checking if there is an outMessage, if there is, it will send the message.
Next it will check it if there is anything in the in-stream, if there is, it will send it to the handler in my main activity.
Lastly, it will sleep for 1 second, then check again.
This should allow me to read/write multiple times without needing to close and open the socket.
Problem:
It is reading and writing better, but still not working properly
What is happening now:
If outMessage is initialized with a value, upon connection with the server, the socket:
writes and flushes the value (server receives & responds)
updates value of outMessage (to null or to "x" depending on how i have it hard-coded)
reads and shows the response message from the server
re-enters for the next loop
IF i set outMessage to null, it skips over that if statements correctly then hangs; otherwise, if i set outMessage to a string (lets say "x"), it goes through the whole if statement, then hangs.
The code it hangs on is either of the inStream.readline() calls (I currently have one commented out).
Additional info:
- once connected, I can type in the "send" box, submit (updates the outMessage value), then disconnect. Upon re-connecting, it will read the value and do the sequence again until it get stuck on that same line.
Changes since the referenced question:
- Made outMessage and connectionStatus both 'volatile'
- added end-of-line delimiters in neccesary places.
Code:
public void run() {
while (connectionStatus != TCP_SOCKET_STATUS_CONNECTED) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
while (connectionStatus == TCP_SOCKET_STATUS_CONNECTED) {
try {
if (outMessage != null){
OutStream.writeBytes(outMessage + "\n");
OutStream.flush();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "OUT TO SERVER: " + outMessage);
outMessage = "x";
}
Thread.sleep(100);
// if (InStream.readLine().length() > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
// }
Thread.sleep(1000);
} catch (IOException e) {
connectionLost();
break;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
The thread that makes the socket:
public void run() {
setName("AttemptConnectionThread");
connectionStatus = TCP_SOCKET_STATUS_CONNECTING;
try {
SocketAddress sockaddr = new InetSocketAddress(serverIP, port);
tempSocketClient = new Socket(); // Create an unbound socket
// This method will block no more than timeoutMs. If the timeout occurs, SocketTimeoutException is thrown.
tempSocketClient.connect(sockaddr, timeoutMs);
OutStream = new DataOutputStream(tempSocketClient.getOutputStream());
InStream = new BufferedReader(new InputStreamReader(tempSocketClient.getInputStream()));
socketClient = tempSocketClient;
socketClient.setTcpNoDelay(true);
connected();
} catch (UnknownHostException e) {
connectionFailed();
} catch (SocketTimeoutException e) {
connectionFailed();
} catch (IOException e) {
// Close the socket
try {
tempSocketClient.close();
} catch (IOException e2) {
}
connectionFailed();
return;
}
}
Server:
public static void main(String[] args) throws IOException {
String clientSentence;
String capitalizedSentence;
try {
ServerSocket welcomeSocket = new ServerSocket(8888);
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n Listening on IP: " + SERVERIP +"\n\n");
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
while(true)
{
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
clientSentence = inFromClient.readLine();
System.out.println("clientSentance == " + clientSentence);
String ip = connectionSocket.getInetAddress().toString().substring(1);
if(clientSentence != null)
{
System.out.println("In from client ("+ip+")("+ System.currentTimeMillis() +"): "+clientSentence);
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence + '\n');
System.out.println("Out to client ("+ip+"): "+capitalizedSentence);
}
}
} catch (IOException e) {
//if server is already running, it will not open new port but instead re-print the open ports information
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n");
System.out.println("Listening on IP: " + SERVERIP +"\n\n");
}
}
Thanks in advance!
Edits:
added the server code after updating
I tried messing around with setting the SoTimout for the socket but took that back out

Your server is specifically designed to receive exactly one line from a client and send exactly one line back. Look at the code:
while (true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(
new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(
connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
String ip = connectionSocket.getInetAddress().toString()
.substring(1);
System.out.println("In from client (" + ip + "): "
+ clientSentence);
if (clientSentence != null) {
capitalizedSentence = clientSentence.toUpperCase() + '\n';
System.out.println("Out to client (" + ip + "): "
+ capitalizedSentence);
outToClient.writeBytes(capitalizedSentence + "\n");
}
Notice that inside the loop it accepts a new connection, reads exactly one line, and then writes exactly one line. It doesn't close the connection. It doesn't sanely end the conversation. It just stops reading.
A client that worked with this server would have to connect, send exactly one line, read exactly one line back, and then the client would have to close the connection. Your client doesn't do that. Why? Because you had no idea that's what you had to do. Why? Because you had no design ... no plan.
So that's your specific issue. But please, let me urge you to take a huge step back and totally change your approach. Before you write a single line of code, please actually design and specify a protocol at the byte level. The protocol should say what data is sent, how messages are delimited, who sends when, who closes the connection, and so on.
Otherwise, it's impossible to debug your code. Looking at the server code above, is it correct? Well, who knows. Because it's unclear what it's supposed to do. When you wrote the client, you assumed the server behaved one way. Was that assumption valid? Is the server broken? Who knows, because there's no specification of what the server is supposed to do.

You need to check if there is data available:
if (InStream.available > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
}
But to be honest, even that is not ideal because you have no gurantee that the eond-of-line will have been received. If the server sends a few bytes but never sends the end-of-line then you will still be blocking forever. Production socket code should never rely on readLine but instead read into a buffer and check that buffer for end-of-line (or whatever criteria your protocol needs).
Didn't read closely enough, I thought InStream was an InputStream instance. InputStream has available. InputStreamReader has ready (which in turn calls InputStream.available. As long as you keep a refernce to either of these then you can see if data is available to be read.