I am able to properly send my data through UDP socket , but when I receive data it keeps on waiting at receive command I don't know what is causing this. Please have a look at my code below.
I am able to properly receive data at server side from android device, but when I send data from server side to android device it doesn't receive. but when I send data from server to any other client e.g PC application it receive and displays data properly.
class Task implements Runnable {
@Override
public void run() {
try {
String messageStr = "feed";
int server_port = 8888;
InetAddress local = InetAddress.getByName("10.0.2.2");
int msg_length = messageStr.length();
byte[] message = messageStr.getBytes();
DatagramSocket s = new DatagramSocket();
//
DatagramPacket p = new DatagramPacket(message, msg_length, local, server_port);
s.send(p);//properly able to send data. i receive data to server
for (int i = 0; i <= 20; i++) {
final int value = i;
message = new byte[30000];
p = new DatagramPacket(message,message.length );
s.receive(p); //keeps on waiting here but i am sending data back from server, but it never receives
final byte[] data = p.getData();;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
handler.post(new Runnable() {
@Override
public void run() {
progressBar.setProgress(value);
imageView.setImageBitmap(BitmapFactory.decodeByteArray(data,0,data.length));
}
});
}
}
catch(Exception ex)
{
}
}
}
Tim
Documentation in Eclipse:
Receives a packet from this socket and stores it in the argument pack. All fields of pack must be set according to the data received. If the received data is longer than the packet buffer size it is truncated. This method blocks until a packet is received or a timeout has expired.
The "s.receive(p);" command blocks the thread until it receices data or the timeout set with setSoTimeout(timeout) is over.
I have made 2 classes to make my communication happen. First UDP-Server:
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Build;
public class UDP_Server
{
private AsyncTask<Void, Void, Void> async;
private boolean Server_aktiv = true;
@SuppressLint("NewApi")
public void runUdpServer()
{
async = new AsyncTask<Void, Void, Void>()
{
@Override
protected Void doInBackground(Void... params)
{
byte[] lMsg = new byte[4096];
DatagramPacket dp = new DatagramPacket(lMsg, lMsg.length);
DatagramSocket ds = null;
try
{
ds = new DatagramSocket(Main.SERVER_PORT);
while(Server_aktiv)
{
ds.receive(dp);
Intent i = new Intent();
i.setAction(Main.MESSAGE_RECEIVED);
i.putExtra(Main.MESSAGE_STRING, new String(lMsg, 0, dp.getLength()));
Main.MainContext.getApplicationContext().sendBroadcast(i);
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
if (ds != null)
{
ds.close();
}
}
return null;
}
};
if (Build.VERSION.SDK_INT >= 11) async.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
else async.execute();
}
public void stop_UDP_Server()
{
Server_aktiv = false;
}
}
I send the received data to an BroadcastReceiver and there you can do what ever you want to with the data.
And now my client to send the data. In this code I send a broadcast, but I think it will be no problem to change the code for sending to a direct IP or something.
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import android.annotation.SuppressLint;
import android.os.AsyncTask;
import android.os.Build;
public class UDP_Client
{
private AsyncTask<Void, Void, Void> async_cient;
public String Message;
@SuppressLint("NewApi")
public void NachrichtSenden()
{
async_cient = new AsyncTask<Void, Void, Void>()
{
@Override
protected Void doInBackground(Void... params)
{
DatagramSocket ds = null;
try
{
ds = new DatagramSocket();
DatagramPacket dp;
dp = new DatagramPacket(Message.getBytes(), Message.length(), Main.BroadcastAddress, Main.SERVER_PORT);
ds.setBroadcast(true);
ds.send(dp);
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
if (ds != null)
{
ds.close();
}
}
return null;
}
protected void onPostExecute(Void result)
{
super.onPostExecute(result);
}
};
if (Build.VERSION.SDK_INT >= 11) async_cient.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
else async_cient.execute();
}
And here is how you instantiate the classes from your main class.
//start UDP server
Server = new UDP_Server();
Server.runUdpServer();
//UDP Client erstellen
Client = new UDP_Client();
And here how to send a message with the client.
//Set message
Client.Message = "Your message";
//Send message
Client.NachrichtSenden();
To stop the UDP_Server, just set Server.Server_aktiv to false.
To set the message above u can also write a "setMessage(String message)" methode or something like that.
Here, in this post you will find the detailed code for establishing socket between devices or between two application in the same mobile.
You have to create two application to test below code.
In both application's manifest file, add below permission
<uses-permission android:name="android.permission.INTERNET" />
1st App code: UDP Client Socket
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TableRow
android:id="@+id/tr_send_message"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_marginTop="11dp">
<EditText
android:id="@+id/edt_send_message"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:hint="Enter message"
android:inputType="text" />
<Button
android:id="@+id/btn_send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginRight="10dp"
android:text="Send" />
</TableRow>
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="@+id/tr_send_message"
android:layout_marginTop="25dp"
android:id="@+id/scrollView2">
<TextView
android:id="@+id/tv_reply_from_server"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" />
</ScrollView>
</RelativeLayout>
UDPClientSocketActivity.java
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
/**
* Created by Girish Bhalerao on 5/4/2017.
*/
public class UDPClientSocketActivity extends AppCompatActivity implements View.OnClickListener {
private TextView mTextViewReplyFromServer;
private EditText mEditTextSendMessage;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button buttonSend = (Button) findViewById(R.id.btn_send);
mEditTextSendMessage = (EditText) findViewById(R.id.edt_send_message);
mTextViewReplyFromServer = (TextView) findViewById(R.id.tv_reply_from_server);
buttonSend.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_send:
sendMessage(mEditTextSendMessage.getText().toString());
break;
}
}
private void sendMessage(final String message) {
final Handler handler = new Handler();
Thread thread = new Thread(new Runnable() {
String stringData;
@Override
public void run() {
DatagramSocket ds = null;
try {
ds = new DatagramSocket();
// IP Address below is the IP address of that Device where server socket is opened.
InetAddress serverAddr = InetAddress.getByName("xxx.xxx.xxx.xxx");
DatagramPacket dp;
dp = new DatagramPacket(message.getBytes(), message.length(), serverAddr, 9001);
ds.send(dp);
byte[] lMsg = new byte[1000];
dp = new DatagramPacket(lMsg, lMsg.length);
ds.receive(dp);
stringData = new String(lMsg, 0, dp.getLength());
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ds != null) {
ds.close();
}
}
handler.post(new Runnable() {
@Override
public void run() {
String s = mTextViewReplyFromServer.getText().toString();
if (stringData.trim().length() != 0)
mTextViewReplyFromServer.setText(s + "\nFrom Server : " + stringData);
}
});
}
});
thread.start();
}
}
2nd App Code - UDP Server Socket
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/btn_stop_receiving"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="STOP Receiving data"
android:layout_alignParentTop="true"
android:enabled="false"
android:layout_centerHorizontal="true"
android:layout_marginTop="89dp" />
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@+id/btn_stop_receiving"
android:layout_marginTop="35dp"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true">
<TextView
android:id="@+id/tv_data_from_client"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" />
</ScrollView>
<Button
android:id="@+id/btn_start_receiving"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="START Receiving data"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="14dp" />
</RelativeLayout>
UDPServerSocketActivity.java
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
/**
* Created by Girish Bhalerao on 5/4/2017.
*/
public class UDPServerSocketActivity extends AppCompatActivity implements View.OnClickListener {
final Handler handler = new Handler();
private Button buttonStartReceiving;
private Button buttonStopReceiving;
private TextView textViewDataFromClient;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonStartReceiving = (Button) findViewById(R.id.btn_start_receiving);
buttonStopReceiving = (Button) findViewById(R.id.btn_stop_receiving);
textViewDataFromClient = (TextView) findViewById(R.id.tv_data_from_client);
buttonStartReceiving.setOnClickListener(this);
buttonStopReceiving.setOnClickListener(this);
}
private void startServerSocket() {
Thread thread = new Thread(new Runnable() {
private String stringData = null;
@Override
public void run() {
byte[] msg = new byte[1000];
DatagramPacket dp = new DatagramPacket(msg, msg.length);
DatagramSocket ds = null;
try {
ds = new DatagramSocket(9001);
//ds.setSoTimeout(50000);
ds.receive(dp);
stringData = new String(msg, 0, dp.getLength());
updateUI(stringData);
String msgToSender = "Bye Bye ";
dp = new DatagramPacket(msgToSender.getBytes(), msgToSender.length(), dp.getAddress(), dp.getPort());
ds.send(dp);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ds != null) {
ds.close();
}
}
}
});
thread.start();
}
private void updateUI(final String stringData) {
handler.post(new Runnable() {
@Override
public void run() {
String s = textViewDataFromClient.getText().toString();
if (stringData.trim().length() != 0)
textViewDataFromClient.setText(s + "\n" + "From Client : " + stringData);
}
});
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_start_receiving:
startServerSocket();
buttonStartReceiving.setEnabled(false);
buttonStopReceiving.setEnabled(true);
break;
case R.id.btn_stop_receiving:
//Add logic to stop server socket yourself
buttonStartReceiving.setEnabled(true);
buttonStopReceiving.setEnabled(false);
break;
}
}
}
来源：https://stackoverflow.com/questions/19540715/send-and-receive-data-on-udp-socket-java-android