Android Datagram/UDP Server example

I posted "Java Datagram/UDP Server and Client, run on raspberry Pi" on my another blogspot. And last post show "Android Datagram/UDP Client example". This post show a Datagram/UDP Server run on Android.


MainActivity.java

package com.blogspot.android_er.androidudpserver;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.TextView;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Date;
import java.util.Enumeration;

public class MainActivity extends AppCompatActivity {

    private final static String TAG = MainActivity.class.getSimpleName();

    TextView infoIp, infoPort;
    TextView textViewState, textViewPrompt;

    static final int UdpServerPORT = 4445;
    UdpServerThread udpServerThread;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        infoIp = (TextView) findViewById(R.id.infoip);
        infoPort = (TextView) findViewById(R.id.infoport);
        textViewState = (TextView)findViewById(R.id.state);
        textViewPrompt = (TextView)findViewById(R.id.prompt);

        infoIp.setText(getIpAddress());
        infoPort.setText(String.valueOf(UdpServerPORT));
    }

    @Override
    protected void onStart() {
        udpServerThread = new UdpServerThread(UdpServerPORT);
        udpServerThread.start();
        super.onStart();
    }

    @Override
    protected void onStop() {
        if(udpServerThread != null){
            udpServerThread.setRunning(false);
            udpServerThread = null;
        }

        super.onStop();
    }

    private void updateState(final String state){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                textViewState.setText(state);
            }
        });
    }

    private void updatePrompt(final String prompt){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                textViewPrompt.append(prompt);
            }
        });
    }

    private class UdpServerThread extends Thread{

        int serverPort;
        DatagramSocket socket;

        boolean running;

        public UdpServerThread(int serverPort) {
            super();
            this.serverPort = serverPort;
        }

        public void setRunning(boolean running){
            this.running = running;
        }

        @Override
        public void run() {

            running = true;

            try {
                updateState("Starting UDP Server");
                socket = new DatagramSocket(serverPort);

                updateState("UDP Server is running");
                Log.e(TAG, "UDP Server is running");

                while(running){
                    byte[] buf = new byte[256];

                    // receive request
                    DatagramPacket packet = new DatagramPacket(buf, buf.length);
                    socket.receive(packet);     //this code block the program flow

                    // send the response to the client at "address" and "port"
                    InetAddress address = packet.getAddress();
                    int port = packet.getPort();

                    updatePrompt("Request from: " + address + ":" + port + "\n");

                    String dString = new Date().toString() + "\n"
                            + "Your address " + address.toString() + ":" + String.valueOf(port);
                    buf = dString.getBytes();
                    packet = new DatagramPacket(buf, buf.length, address, port);
                    socket.send(packet);

                }

                Log.e(TAG, "UDP Server ended");

            } catch (SocketException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if(socket != null){
                    socket.close();
                    Log.e(TAG, "socket.close()");
                }
            }
        }
    }

    private String getIpAddress() {
        String ip = "";
        try {
            Enumeration<NetworkInterface> enumNetworkInterfaces = NetworkInterface
                    .getNetworkInterfaces();
            while (enumNetworkInterfaces.hasMoreElements()) {
                NetworkInterface networkInterface = enumNetworkInterfaces
                        .nextElement();
                Enumeration<InetAddress> enumInetAddress = networkInterface
                        .getInetAddresses();
                while (enumInetAddress.hasMoreElements()) {
                    InetAddress inetAddress = enumInetAddress.nextElement();

                    if (inetAddress.isSiteLocalAddress()) {
                        ip += "SiteLocalAddress: "
                                + inetAddress.getHostAddress() + "\n";
                    }

                }

            }

        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            ip += "Something Wrong! " + e.toString() + "\n";
        }

        return ip;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    android:orientation="vertical"
    tools:context="com.blogspot.android_er.androidudpserver.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/infoip"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="italic" />

    <TextView
        android:id="@+id/infoport"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="italic" />

    <TextView
        android:id="@+id/state"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="un-initiated"
        android:textSize="20dp"/>

    <TextView
        android:id="@+id/prompt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="18dp"/>
</LinearLayout>

uses-permission of "android.permission.INTERNET" is needed in AndroidManifest.xml

Remark about life-cycle:
In this example, the DatagramSocket server is run in background thread. I haven't handle the life-cycle very well (Actually I don't think any application will have UI like this example). Consider the cases:

Case One:
- Start the app, the activity display on screen and the DatagramSocket opened in associated thread.
- the code socket.receive(packet) block the program flow, so the thread stay here and waiting data request.
- Exit the app. It will set running to false, to request the thread to stop. But the thread is blocked in socket.receive(packet), so it's still running.
- Restart the app, the new thread cannot open the DatagramSocket, because it's still held by old thread.
- Client send a request, the DatagramSocket server response the request and exit socket.receive(packet), and check running and exit.
- In this case, the current activity and associated thread have no DatagramSocket opened!

Case Two:
- Start the app, the activity display on screen and the DatagramSocket opened in associated thread.
- the code socket.receive(packet) block the program flow, so the thread stay here and waiting data request.
- Exit the app. It will set running to false, to request the thread to stop. But the thread is blocked in socket.receive(packet), so it's still running.
- Client send a request, the DatagramSocket server response the request and exit socket.receive(packet), and check running and exit.
- Restart the app, and open the DatagramSocket.
- In this case, the current activity and associated thread can open DatagramSocket and work as expected.


Download the files .