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how to trigger same event from multiple device from one device

i am building app which will become server and other 3 or 5 phones become client. and from server i will send code for instruction all device click photo at same time. i am confusing how to do that..i have tcp/udp but it only connect 1 device but i want multiple device.
class MyServer implements Runnable
{
ServerSocket serverSocket;
Socket socket;
DataInputStream dataInputStream;
String msg="";
Handler handler=new Handler();
#Override
public void run() {
try {
serverSocket=new ServerSocket(9700);
while (true)
{
socket=serverSocket.accept();
dataInputStream=new DataInputStream(socket.getInputStream());
msg= dataInputStream.readUTF();
handler.post(new Runnable() {
#Override
public void run() {
Toast.makeText(MainActivity.this,msg,Toast.LENGTH_SHORT).show();
}
});
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public class Backgroundtask extends AsyncTask<String,Void,String>
{
Socket socket;
DataOutputStream dataOutputStream;
String ip,msg;
#Override
protected String doInBackground(String... strings) {
ip=strings[0];
msg=strings[1];
try {
socket=new Socket(ip,9700);
dataOutputStream=new DataOutputStream(socket.getOutputStream());
dataOutputStream.writeUTF(msg);
dataOutputStream.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
i want when i am trigger instruction from server all device must follow at same time.

Sending commands from phone to computer via Sockets

I'm trying to send commands from my phone to my computer using Sockets.
I've tryed the answers here:
Android and PC Socket connection
But after some digging i found out that you need to use a Async task so i tryed this:
Using AsyncTask for android network connection
But for some reason my socket times out. Is there a way to find out why? because from the error i can't tell:
The error from Logcat:
And this is the client code:
public class MainActivity extends AppCompatActivity {
private Socket client;
private PrintWriter printwriter;
private EditText textField;
private Button button;
private String message;
private static final int SERVERPORT = ####;
private static final String SERVER_IP = "########";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textField = (EditText) findViewById(R.id.editText1); // reference to the text field
button = (Button) findViewById(R.id.button1); // reference to the send button
}
public void onClick(View view) {
message = textField.getText().toString();
textField.setText(""); // Reset the text field to blank
new AsyncAction().execute();
}
private class AsyncAction extends AsyncTask<String, Void, String> {
protected String doInBackground(String... args) {
try {
System.out.println("background running");
System.out.println(message);
client = new Socket(SERVER_IP, SERVERPORT); // connect to server
System.out.println(client.isConnected());
System.out.println("test");
printwriter = new PrintWriter(client.getOutputStream(), true);
printwriter.write(message); // write the message to output stream
printwriter.flush();
printwriter.close();
client.close(); // closing the connection
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
}

I wrote a Server for this in Java and tested it in the emulator.
I had two things to do :
The server IP is "10.0.2.2" if you are using an Android Emulator. LocalHost is de Emulator Virtual Machine.
Your application needs Permission Internet in manifest
Here is the server Code
/**
*
* #author Jean-Pierre
*/
public class SocketServer {
private static final int portnumber = 4444;
public static void main(String[] args) {
SocketServer socketServer = new SocketServer();
socketServer.run();
}
/**
* Reads a String from the client
* Converts it to Uppercase
* and sends it Back.
*/
private void run() {
try {
ServerSocket serverSocket = new ServerSocket(portnumber);
Socket clientSocket = serverSocket.accept();
System.out.println("connected with :" + clientSocket.getInetAddress());
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
InputStreamReader is =
new InputStreamReader(clientSocket.getInputStream());
BufferedReader in =
new BufferedReader(is);
while (true) {
String line = in.readLine();
if (line != null) {
System.out.println("recieved:" + line);
out.println(line.toUpperCase());
}
}
} catch (IOException ex) {
Logger.getLogger(SocketServer.class.getName()).log(Level.SEVERE, null, ex);
}
}
}

creating connection within android device using sockets

I am trying to create a connection between two applications using android. I have tried to use sockets to connect. I have created two application
One which accepts the connection when client wants to connect
and another application that requests to connect.
I have successfully run this code in same manner in pc in java in pc network. Is the way of connecting to android also same?
My server class implementation
public class MainActivity extends AppCompatActivity {
private Button startButton;
private ServerSocket server;
private Socket connection;
private TextView statusText;
private ObjectOutputStream output;
private ObjectInputStream input;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
statusText=(TextView)findViewById(R.id.statusText);
startButton=(Button)findViewById(R.id.startButton);
startButton.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
startRunning();
}
}
);
}
private void startRunning() {
try{
server=new ServerSocket(8080);
while(true)
{
try{
waitForConnection();
setUpStreams();
whileChatting();
}catch(Exception e){}
}
} catch(Exception e){}
}
public void waitForConnection()
{
setMyStatus("Waiting for client to connect...");
try {
connection= server.accept();
setMyStatus("Now connected to "+ connection.getInetAddress().getHostName());
} catch (IOException e) {
e.printStackTrace();
}
}
public void setUpStreams()
{
try {
output= new ObjectOutputStream(connection.getOutputStream());
output.flush();
input= new ObjectInputStream(connection.getInputStream());
setMyStatus("Streams are now setup. Ready to go...");
} catch (IOException e) {
e.printStackTrace();
}
}
public void whileChatting()
{
setMyStatus("You can now start chatting...");
}
public void setMyStatus(String msg) {
statusText.setText(msg);
}
}
I will use the tasks like async task later. But i am just trying to set up connection in these application.
My client implementation goes like this
public class MainActivity extends AppCompatActivity {
private Button startButton;
private Socket connection;
private TextView statusText;
public ObjectOutputStream output;
public ObjectInputStream input;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
statusText=(TextView)findViewById(R.id.statusText);
startButton=(Button)findViewById(R.id.startButton);
startButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startRunning();
}
});
}
private void startRunning() {
connectToServer();
setUpStreams();
whileChatting();
}
public void connectToServer()
{
setMyStatus("Connecting to server. Please wait...");
try {
connection= new Socket(InetAddress.getByName("127.0.0.1"),8080);
setMyStatus("Connected to Server."+ connection.getInetAddress().getHostName());
} catch (IOException e) {
e.printStackTrace();
}
}
public void setUpStreams()
{
try {
output= new ObjectOutputStream(connection.getOutputStream());
output.flush();
input= new ObjectInputStream(connection.getInputStream());
setMyStatus("Streams are now setup. Ready to go...");
} catch (IOException e) {
e.printStackTrace();
}
}
public void whileChatting()
{
setMyStatus("You can now start chatting...");
}
public void setMyStatus(String msg) {
statusText.setText(msg);
}
}
The error I got is in the case of client that tries to connect to server
java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.OutputStream java.net.Socket.getOutputStream()' on a null object reference
at com.myapp.client.clientdemo.MainActivity.setUpStreams(MainActivity.java:71)
at com.myapp.client.clientdemo.MainActivity.startRunning(MainActivity.java:46)
at com.myapp.client.clientdemo.MainActivity.access$000(MainActivity.java:16)
at com.myapp.client.clientdemo.MainActivity$1.onClick(MainActivity.java:33)

It's because "connection" was never created. Probably because it failed to connect or it timed out and it moved on to the next code. If it timed out or didn't connect, then you need to catch that exception and retry to connect before moving on with your later code.
Socket can be tricky if you do not catch all the erroneous states they can get into.
simply wrap your try and catch with a while loop until the condition is met like this:
while(!connected & !closed){
try {
connection= new Socket(InetAddress.getByName("127.0.0.1"),8080);
connected = true;
//now it is connected and will exit the loop and continue with other code
} catch (SocketTimeoutException socketTimeoutException) {
//add this for safety
} catch (IOException e) {
e.printStackTrace();
}
}

How to send and receive multiple data from client to server

I have established a connection between java server and android client using sockets. I can send messages from android to java, but only 1 message at a time.
what if I want to send data of 2 variables from android to java and at the same time receive those data in java in 2 different variables.
How can I achieve this.??
Code for Android Client
public class MessageClient extends Activity implements OnClickListener {
EditText etMessage;
Button bSend;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.messageclient);
bSend = (Button) findViewById(R.id.button1);
etMessage = (EditText) findViewById(R.id.etMessage);
bSend.setOnClickListener(this);
}
#Override
public void onClick(View arg0) {
try {
Socket s = new Socket("192.168.0.100",7000);
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
dos.writeUTF(etMessage.getText().toString());
dos.flush();
dos.close();
s.close();
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Code for java server
public static void main(String arg[]){
Thread t = new Thread(){
public void run() {
// TODO Auto-generated method stub
try {
ServerSocket ss = new ServerSocket(7000);
while(true){
Socket s = ss.accept();
System.out.println("Server is running");
DataInputStream dis = new DataInputStream(s.getInputStream());
System.out.println("Received from client: "+dis.readUTF());
dis.close();
s.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
t.start();
}
Thank you.

You are just sending a String and then closing the socket.You can try to send lists and also can send multiple DataInputStream dis without closing the socket connection.

Socket communication between two apps on Android

I have got huge problem with my Android app and I would like to ask you for help.
I am currently writing Android Clietn-Server app using sockets. I have found lots of tutorils on the Internet and from them I have created basics for my project. However, all tutorials are only for one message send and that's all. I need to send more of them so I've been trying to modify it.
This are code fragments responsible for server and client. The rest is not important at this time.
Server:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
serverStatus = (TextView) findViewById(R.id.server_status);
recivedMsg = (TextView)findViewById(R.id.rec_msg);
SERVERIP = getLocalIpAddress();
Thread fst = new Thread(new ServerThread());
fst.start();
}
public class ServerThread implements Runnable {
public void run() {
try {
if (SERVERIP != null) {
handler.post(new Runnable() {
#Override
public void run() {
serverStatus.setText("Listening on IP: " + SERVERIP);
}
});
serverSocket = new ServerSocket(SERVERPORT);
while (true) {
// listen for incoming clients
Socket client = serverSocket.accept();
handler.post(new Runnable() {
#Override
public void run() {
serverStatus.setText("Connected." + System.getProperty("line.separator"));
}
});
try {
line = null;
while (connected) {
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
if((line = in.readLine())!=null)
{
Log.d("ServerActivity", line);
handler.post(new Runnable() {
#Override
public void run() {
if(recivedMsg.equals("CLOSE"))
{
recivedMsg.append("CLOSE socket");
connected = false;
}
else
{
recivedMsg.append("MSG: " + line + System.getProperty("line.separator"));
}
// do whatever you want to the front end
// this is where you can be creative
}
});
}
else
{
recivedMsg.append("empty" + System.getProperty("line.separator"));
}
}
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();
}
}
}
Client
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
serverIp = (EditText) findViewById(R.id.server_ip);
connectPhones = (Button) findViewById(R.id.connect_phones);
sendField = (EditText) findViewById(R.id.send_field);
sendMsg = (Button) findViewById(R.id.msg_send);
connectPhones.setOnClickListener(connectListener);
sendMsg.setOnClickListener(sendMessage);
}
#Override
protected void onStop() {
super.onStop();
try {
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
//send output msg
String outMsg = "CLOSE";
out.write(outMsg);
out.flush();
// make sure you close the socket upon exiting
s.close();
} catch (IOException e) {
e.printStackTrace();
}
}
private OnClickListener connectListener = new OnClickListener() {
#Override
public void onClick(View v) {
serverIpAddress = serverIp.getText().toString();
runTcpConnection();
sendMessageToServer("Msg");
}
};
private OnClickListener sendMessage = new OnClickListener() {
#Override
public void onClick(View v) {
sendMessageToServer(sendField.getText().toString());
}
};
private void runTcpConnection() {
try {
s = new Socket(serverIpAddress, SERVERPORT);
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
//send output msg
String outMsg = "TCP connecting to " + SERVERPORT + System.getProperty("line.separator");
out.write(outMsg);
out.flush();
Log.i("TcpClient", "sent: " + outMsg);
SystemClock.sleep(10);
s.close();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
};
public void sendMessageToServer(String str) {
try {
s = new Socket(serverIpAddress, SERVERPORT);
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
//send output msg
String outMsg = str + System.getProperty("line.separator");
out.write(outMsg);
out.flush();
Log.i("TcpClient", "sent: " + outMsg);
s.close();
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
Log.d("", "hello222");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
Log.d("", "hello4333");
}
}
For now devices connect correctly. Moreover They are sending the first connection messages (those in OnClickListener connectListener). The problem is that when I am trying to send another message using sendMessageToServer it is impossible. Those messages shows only after client activity is destroyed.
Very interesting is that without SystemClock.sleep(10); listener runTcpConnection() behave strange. Only 'Connected.' displays on server.
Can someone tell me what I have to do to be able to send messages normally?
EDIT:
This are things that I have found:
If I am at the connection sending more messages than all are empty (null) and after the second one connection error shows - please reconnect phones
If I am at the connection sending more messages without s.close line in sendMessageToServer only one message is passing through. No error is displayed after it.
The message form runTcpConnection shows always (except when in this function is no SystemClock.sleep(10))
Hope it will help someone to diagnose my error.

As I see, you create a new socket whenever user click button send, right? I recommend you should init it only one time when user click connect, then you use it in send click event ( because this is TCP, you will disconnect to server if you create new instance of socket)
So, you should remove these lines in sendMessageToServer :
s = new Socket(serverIpAddress, SERVERPORT);
s.close();
and this line in runTcpConnection
s.close();
Socket should close whenever you don't want communicate with the server (onstop is an example, or when change activity...)
Also you should create only one instance of BufferedWriter too.
Hope this help.