Mobila applikationer med Android: Lektion 10

• Grunderna om nätverkskommunikation med Android
• Programmet Bouncer (en server som tar emot "PING" från klienten och svarar med "PONG")
• Apparna OnePinger och Pinger (klienter som skickar "PING"-meddelanden till servern)
• Appen AndroidBouncer (servern Bouncer men för Android)
• TCP och UDP

Några viktiga saker som skiljer:

• Man måste ge appen tillåtelse att använda nätet, genom att ange android.permission.INTERNET i AndroidManifest.xml.
• I Android behöver man tänka lite mer på trådar och det grafiska användargränssnittet.
• Nätet kan fungera sämre än på en skrivbordsdator eller server:
  • lägre bandbredd
  • längre latens (fördröjning)
  • korta och långa avbrott
  • begränsningar
  • brandväggar
  • kostar pengar
  • drar batteri

• Bouncer är inte en Android-app, utan ett program för skrivbords-Java (Java SE). Den fungerar som en server. Klienter kan koppla upp sig mot Bouncer och skicka PING, och då svarar Bouncer med PONG. Bouncer kan hantera flera olika klienter samtidigt.
• OnePinger är en Android-app som kopplar upp sig mot Bouncer, skickar ett PING, väntar på Bouncers PONG, och sen är den klar och kopplar ner sig.
• Pinger är en Android-app som kopplar upp sig mot Bouncer, men här kan man skicka mer än ett PING. Appen har tre knappar: Connect, Ping och Disconnect. De gör vad man kan förvänta sig.
• AndroidBouncer är servern Bouncer, men nu i form av en Android-app, så att man kan köra den på en Android-telefon.

• UDPSender är en Android-app som skickar en text till en mottagare, men den här appen arbetar med datagram i stället för uppkopplade socketar. Alla de fyra programmen ovan använder TCP (Transmission Control Protocol), som betyder att man upprättar en uppkoppling, en så kallad socket, och sen ser systemet till att allt som skickas kommer fram, och i rätt ordning. Om något behöver sändas om, sköts det automatiskt. Med UDP (User Datagram Protocol) skickar man datapaket, så kallade datagram, och det finns inga garantier för att de kommer fram, vare sig i rätt ordning eller överhuvudtaget.
• UDPReceiver är en Android-app som tar emot meddelanden, men med datapaket i stället för uppkopplade socketar.

Bouncer 2013-11-05 11:12:16.657 +0100: Öppnar server-socketen...
Bouncer 2013-11-05 11:12:16.661 +0100: Server-socketen: ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=2003]
Bouncer 2013-11-05 11:12:16.661 +0100: Servern lyssnar...
Bouncer 2013-11-05 11:12:16.661 +0100: Väntar på uppkoppling från klient...

Bouncer 2013-11-05 11:12:35.261 +0100: Uppkoppling från klient accepterad.
Bouncer 2013-11-05 11:12:35.261 +0100: Den nya socketen: Socket[addr=/127.0.0.1,port=42196,localport=2003]
Bouncer 2013-11-05 11:12:35.265 +0100: Väntar på uppkoppling från klient...

ClientTalkerThread 1 2013-11-05 11:13:44.940 +0100: Fick ett PING från klienten

Bouncer 2013-11-05 11:14:08.897 +0100: Uppkoppling från klient accepterad.
Bouncer 2013-11-05 11:14:08.897 +0100: Den nya socketen: Socket[addr=/127.0.0.1,port=42231,localport=2003]
Bouncer 2013-11-05 11:14:08.898 +0100: Väntar på uppkoppling från klient...

ClientTalkerThread 1 2013-11-05 11:14:55.115 +0100: Fick ett PING från klienten
ClientTalkerThread 2 2013-11-05 11:14:59.204 +0100: Fick ett PING från klienten
ClientTalkerThread 1 2013-11-05 11:15:00.699 +0100: Fick ett PING från klienten
ClientTalkerThread 2 2013-11-05 11:15:02.251 +0100: Fick ett PING från klienten
ClientTalkerThread 2 2013-11-05 11:15:03.268 +0100: Fick ett PING från klienten
ClientTalkerThread 1 2013-11-05 11:15:04.219 +0100: Fick ett PING från klienten

    1   package se.nekotronic.onepinger;
    2   
    3   import java.io.BufferedReader;
   ....
   20   
   21   public class MainActivity extends Activity implements OnClickListener {
   22       private TextView output_area;
   23       private EditText address_field;
   24       private Button go_button;
   25       public static final String DEFAULT_HOST = "130.243.124.198";
   26       public String host;
   27       public static final int PORT = 2003;
   28       
   29       @Override
   30       protected void onCreate(Bundle savedInstanceState) {
   31           super.onCreate(savedInstanceState);
   32           setContentView(R.layout.activity_main);
   33           output_area = (TextView)findViewById(R.id.output_area);
   34           address_field = (EditText)findViewById(R.id.address_field);
   35           address_field.setText(DEFAULT_HOST);
   36           go_button = (Button)findViewById(R.id.go_button);
   37           go_button.setOnClickListener(this);
   38   
   39           output_area.setText("");
   40           print("AndroidPinger: Appen startar.");
   41       }
   ....

   43       @Override
   44       public void onClick(View view) {
   45           Log.d("*** OnePinger", "Button clicked: view = " + view.toString() + "\n");
   46           if (view == go_button) {
   47               try {
   48                   host = address_field.getText().toString();
   49                   print("Connecting to " + host + "...");
   50                   Socket socket = new Socket(host, PORT);
   51                   print("Connected.");
   52                   BufferedReader from_server = new BufferedReader(new InputStreamReader(socket.getInputStream()));
   53                   PrintWriter to_server = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
   54                   // true: PrintWriter is line buffered
   55                   print("Sending PING to server...");
   56                   to_server.println("PING");
   57                   Log.d("*** OnePinger", "Waiting for a line from the server...");
   58                   String line_from_server = from_server.readLine();
   59                   if (line_from_server == null) {
   60                       print("Nothing to read from server.");
   61                   }
   62                   else {
   63                       print("Got line from server: '" + line_from_server + "'");
   64                   }
   65                   to_server.close();
   66                   from_server.close();
   67                   socket.close();
   68               } catch (UnknownHostException e) {
   69                   warning("Unknown host: " + e.getMessage());
   70               } catch (IOException e) {
   71                   warning("I/O Exception: " + e.getMessage());
   72               }
   73           }
   74       } // onClick

    1   <?xml version="1.0" encoding="utf-8"?>
    2   <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    3       package="se.nekotronic.onepinger"
    4       android:versionCode="1"
    5       android:versionName="1.0" >
    6   
    7       <uses-sdk
    8           android:minSdkVersion="8"
    9           android:targetSdkVersion="18" />
   10   
   11       <uses-permission android:name="android.permission.INTERNET" />
   12       
   13       <application
   14           android:allowBackup="true"
   15           android:icon="@drawable/ic_launcher"
   16           android:label="@string/app_name"
   17           android:theme="@style/AppTheme" >
   18           <activity
   19               android:name="se.nekotronic.onepinger.MainActivity"
   20               android:label="@string/app_name" >
   21               <intent-filter>
   22                   <action android:name="android.intent.action.MAIN" />
   23   
   24                   <category android:name="android.intent.category.LAUNCHER" />
   25               </intent-filter>
   26           </activity>
   27       </application>
   28   
   29   </manifest>

W/dalvikvm(18424): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
E/AndroidRuntime(18424): FATAL EXCEPTION: main
E/AndroidRuntime(18424): android.os.NetworkOnMainThreadException
E/AndroidRuntime(18424):        at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)
E/AndroidRuntime(18424):        at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
E/AndroidRuntime(18424):        at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
E/AndroidRuntime(18424):        at libcore.io.IoBridge.connect(IoBridge.java:112)
E/AndroidRuntime(18424):        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
E/AndroidRuntime(18424):        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
E/AndroidRuntime(18424):        at java.net.Socket.startupSocket(Socket.java:566)
E/AndroidRuntime(18424):        at java.net.Socket.tryAllAddresses(Socket.java:127)
E/AndroidRuntime(18424):        at java.net.Socket.(Socket.java:177)
E/AndroidRuntime(18424):        at java.net.Socket.(Socket.java:149)
E/AndroidRuntime(18424):        at se.nekotronic.onepinger.MainActivity.onClick(MainActivity.java:50)
E/AndroidRuntime(18424):        at android.view.View.performClick(View.java:4204)
E/AndroidRuntime(18424):        at android.view.View$PerformClick.run(View.java:17355)
E/AndroidRuntime(18424):        at android.os.Handler.handleCallback(Handler.java:725)
E/AndroidRuntime(18424):        at android.os.Handler.dispatchMessage(Handler.java:92)
E/AndroidRuntime(18424):        at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(18424):        at android.app.ActivityThread.main(ActivityThread.java:5041)
E/AndroidRuntime(18424):        at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(18424):        at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(18424):        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
E/AndroidRuntime(18424):        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
E/AndroidRuntime(18424):        at dalvik.system.NativeStart.main(Native Method)
W/ActivityManager(  277):   Force finishing activity se.nekotronic.onepinger/.MainActivity

   35       @Override
   36       public void onClick(View view) {
   37           Log.d("*** OnePinger", "Button clicked: view = " + view.toString() + "\n");
   38           if (view == go_button) {
   39               host = address_field.getText().toString();
   40               OnePingThread t = new OnePingThread(this, host, PORT);
   41               t.start();
   42           }
   43       } // onClick

    1   package se.nekotronic.onepinger;
    2   
    3   import java.io.BufferedReader;
    4   import java.io.BufferedWriter;
    5   import java.io.IOException;
    6   import java.io.InputStreamReader;
    7   import java.io.OutputStreamWriter;
    8   import java.io.PrintWriter;
    9   import java.net.Socket;
   10   import java.net.UnknownHostException;
   11   import android.util.Log;
   12   
   13   public class OnePingThread extends Thread {
   14       private MainActivity parent;
   15       private String host;
   16       private int port;
   17       Socket socket;
   18       BufferedReader from_server;
   19       PrintWriter to_server;
   20       
   21       public OnePingThread(MainActivity parent, String host, int port) {
   22           this.parent = parent;
   23           this.host = host;
   24           this.port = port;
   25       }
   26   
   27       public void run() {
   28           try {
   29               parent.print("Connecting to " + host + "...");
   30               Socket socket = new Socket(host, port);
   31               parent.print("Connected.");
   32               BufferedReader from_server = new BufferedReader(new InputStreamReader(socket.getInputStream()));
   33               PrintWriter to_server = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
   34               // true: PrintWriter is line buffered
   35               parent.print("Sending PING to server...");
   36               to_server.println("PING");
   37               Log.d("*** OnePinger", "Waiting for a line from the server...");
   38               String line_from_server = from_server.readLine();
   39               if (line_from_server == null) {
   40                   parent.print("Nothing to read from server.");
   41               }
   42               else {
   43                   parent.print("Got line from server: '" + line_from_server + "'");
   44               }
   45               to_server.close();
   46               from_server.close();
   47               socket.close();
   48           } catch (UnknownHostException e) {
   49               parent.warning("Unknown host: " + e.getMessage());
   50           } catch (IOException e) {
   51               parent.warning("I/O Exception: " + e.getMessage());
   52           }
   53       } // run
   54   } // OnePingThread

   45       public void print(String message) {
   46           Log.d("*** OnePinger", "message: " + message);
   47           Time now = new Time();
   48           now.setToNow();
   49           String timeString = now.format("%H:%M:%S");
   50           final String line = timeString + ": " + message + "\n";
   51           output_area.post(new Runnable() {
   52               @Override
   53               public void run() {
   54                   // output_area.setText(line + output_area.getText());
   55                   output_area.setText(output_area.getText() + line);
   56                   output_area.invalidate();
   57               }
   58           });
   59       } // print

• AsyncTask
• Painless threading
• Sökning på Stack Overflow

    1	package se.nekotronic.onepinger;
    2	
    3	import java.io.BufferedReader;
    4	import java.io.IOException;
    5	import java.io.InputStreamReader;
    6	import java.io.OutputStreamWriter;
    7	import java.io.PrintWriter;
    8	import java.net.Socket;
    9	import java.io.BufferedWriter;
   10	import java.net.UnknownHostException;
   11	
   12	import android.os.AsyncTask;
   13	import android.util.Log;
   14	
   15	public class OnePingTask extends AsyncTask {
   16	    @Override
   17	    protected Void doInBackground(Object... params) {
   18	        MainActivity parent = (MainActivity) params[0];
   19	        String host = (String) params[1];
   20	        int port = (Integer) params[2];
   21	        try {
   22	            parent.print("Connecting to " + host + "...");
   23	            Socket socket = new Socket(host, port);
   24	            parent.print("Connected.");
   25	            BufferedReader from_server = new BufferedReader(new InputStreamReader(socket.getInputStream()));
   26	            PrintWriter to_server = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
   27	            // true: PrintWriter is line buffered
   28	            parent.print("Sending PING to server...");
   29	            to_server.println("PING");
   30	            Log.d("*** OnePinger", "Waiting for a line from the server...");
   31	            String line_from_server = from_server.readLine();
   32	            if (line_from_server == null) {
   33	                parent.print("Nothing to read from server.");
   34	            }
   35	            else {
   36	                parent.print("Got line from server: '" + line_from_server + "'");
   37	            }
   38	            to_server.close();
   39	            from_server.close();
   40	            socket.close();
   41	        } catch (UnknownHostException e) {
   42	            parent.warning("Unknown host: " + e.getMessage());
   43	        } catch (IOException e) {
   44	            parent.warning("I/O Exception: " + e.getMessage());
   45	        }
   46	        return null;
   47	    }
   48	} // OnePingTask

   35	    @Override
   36	    public void onClick(View view) {
   37	        Log.d("*** OnePinger", "Button clicked: view = " + view.toString() + "\n");
   38	        if (view == go_button) {
   39	            host = address_field.getText().toString();
   40	            OnePingTask t = new OnePingTask();
   41	            t.execute(this, host, PORT);
   42	        }
   43	    } // onClick

    1   package se.nekotronic.pinger;
    2   
    3   import se.nekotronic.pinger.R;
    4   import android.os.Bundle;
    5   import android.app.Activity;
    6   import android.text.format.Time;
    7   import android.util.Log;
    8   import android.view.View;
    9   import android.view.View.OnClickListener;
   10   import android.widget.Button;
   11   import android.widget.EditText;
   12   import android.widget.TextView;
   13   
   14   public class PingActivity extends Activity implements OnClickListener {
   15       private TextView output_area;
   16       private EditText address_field;
   17       private Button connect_button;
   18       private Button ping_button;
   19       private Button disconnect_button;
   20       private PingThread ping_thread = null;
   21       public static final String DEFAULT_HOST = "130.243.124.198";
   22       public String host;
   23       public static final int PORT = 2003;
   24   
   25       @Override
   26       public void onCreate(Bundle savedInstanceState) {
   27           super.onCreate(savedInstanceState);
   28           setContentView(R.layout.activity_ping);
   29           output_area = (TextView)findViewById(R.id.output_area);
   30           address_field = (EditText)findViewById(R.id.address_field);
   31           address_field.setText(DEFAULT_HOST);
   32           connect_button = (Button)findViewById(R.id.connect_button);
   33           connect_button.setOnClickListener(this);
   34           ping_button = (Button)findViewById(R.id.ping_button);
   35           ping_button.setOnClickListener(this);
   36           disconnect_button = (Button)findViewById(R.id.disconnect_button);
   37           disconnect_button.setOnClickListener(this);
   38   
   39           output_area.setText("");
   40           print("AndroidPinger: Appen startar.");
   41       }
   42       
   43       @Override
   44       protected void onPause() {
   45           super.onPause();
   46           if (ping_thread != null) {
   47               ping_thread.please_stop();
   48               ping_thread = null;
   49           }
   50       }
   51   
   52       @Override
   53       public void onClick(View view) {
   54           Log.d("*** ReadyPinger", "Button clicked: view = " + view.toString() + "\n");
   55           if (view == connect_button) {
   56               if (ping_thread != null) {
   57                   warning("Already connected.");
   58               }
   59               else {
   60                   host = address_field.getText().toString();
   61                   ping_thread = new PingThread(this, host, PORT);
   62                   ping_thread.start();
   63               }
   64           }
   65           else if (view == ping_button) {
   66                           if (ping_thread == null)
   67                   warning("Not connected.");
   68               else
   69                   ping_thread.send("PING");
   70           }
   71           else if (view == disconnect_button) {
   72               if (ping_thread == null)
   73                   warning("Not connected.");
   74               else
   75                   ping_thread.please_stop();
   76               ping_thread = null;
   77           }
   78       }
   79   
   80       public void done() {
   81           ping_thread = null;
   82       }
   83   
   84       public void print(String message) {
   85           Log.d("*** ReadyPinger", "message: " + message);
   86           Time now = new Time();
   87           now.setToNow();
   88           String timeString = now.format("%H:%M:%S");
   89           final String line = timeString + ": " + message + "\n";
   90           output_area.post(new Runnable() {
   91               @Override
   92               public void run() {
   93                   // output_area.setText(line + output_area.getText());
   94                   output_area.setText(output_area.getText() + line);
   95                   output_area.invalidate();
   96               }
   97           });
   98       } // print
   99   
  100       public void warning(String message) {
  101           print("Warning! " + message);
  102       }
  103   } // PingActivity

    1   package se.nekotronic.pinger;
    2   
    3   import java.io.BufferedReader;
    4   import java.io.BufferedWriter;
    5   import java.io.IOException;
    6   import java.io.InputStreamReader;
    7   import java.io.OutputStreamWriter;
    8   import java.io.PrintWriter;
    9   import java.net.Socket;
   10   import java.net.UnknownHostException;
   11   
   12   import android.util.Log;
   13   
   14   public class PingThread extends Thread {
   15       private PingActivity parent;
   16       private boolean quit = false;
   17       private String host;
   18       private int port;
   19       Socket socket;
   20       BufferedReader from_server;
   21       PrintWriter to_server;
   22       
   23       public PingThread(PingActivity parent, String host, int port) {
   24           this.parent = parent;
   25           this.host = host;
   26           this.port = port;
   27       }
   28   
   29       public void please_stop() {
   30           quit = true;
   31           try {
   32               to_server.flush();
   33               socket.shutdownInput();
   34           } catch (IOException e) {
   35               // Couldn't close. Not much we can do.
   36               parent.print("Problem closing connection");
   37           }
   38       }
   39   
   40       public void run() {
   41           try {
   42               parent.print("Connecting to " + host + "...");
   43               socket = new Socket(host, port);
   44               parent.print("Connected.");
   45               if (quit)
   46                   return;
   47               from_server = new BufferedReader(new InputStreamReader(socket.getInputStream()));
   48               to_server = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
   49               // true: PrintWriter is line buffered
   50   
   51               while (!quit) {
   52                   Log.d("*** ReadyPinger", "Waiting for a line from the server...");
   53                   String line_from_server = from_server.readLine();
   54                   if (line_from_server == null) {
   55                       parent.print("Nothing more to read from server.");
   56                       quit = true;
   57                   }
   58                   else {
   59                       parent.print("Got line from server: '" + line_from_server + "'");
   60                   }
   61               }
   62               
   63               to_server.close();
   64               from_server.close();
   65               socket.close();
   66               // parent.done();
   67           }
   68           catch (UnknownHostException e) {
   69               parent.warning("Unknown host: " + e.getMessage());
   70           } catch (IOException e) {
   71               parent.warning("I/O Exception: " + e.getMessage());
   72           }
   73           parent.done();
   74       }
   75       
   76       void send(String line) {
   77           if (to_server == null) {
   78               parent.warning("Not connected yet.");
   79           }
   80           else {
   81               parent.print("Sending " + line);
   82               to_server.println(line);
   83           }
   84       }
   85   } // PingThread

    1	package se.nekotronic.udpsender;
    2	import java.io.IOException;
    3	import java.net.DatagramPacket;
    4	import java.net.DatagramSocket;
    5	import java.net.InetAddress;
    6	import java.net.SocketException;
    7	import java.net.UnknownHostException;
    8	
    9	public class UDPSendThread extends Thread {
   10	    private UDPSendActivity parent;
   11	    private String host;
   12	    private int port;
   13	    private String message;
   14	
   15	    public UDPSendThread(UDPSendActivity parent, String host, int port, String message) {
   16	        this.parent = parent;
   17	        this.host = host;
   18	        this.port = port;
   19	        this.message = message;
   20	    }
   21	    
   22	    public void run() {
   23	        try {
   24	            InetAddress receiver_address = InetAddress.getByName(host);
   25	            DatagramSocket socket = new DatagramSocket();
   26	            byte[] buffer = message.getBytes();
   27	            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, receiver_address, port);
   28	            parent.print("Sending '" + message + "'...");
   29	            socket.send(packet);
   30	            parent.print("Sent '" + message + "'");
   31	            socket.close();
   32	        } catch (UnknownHostException e) {
   33	            parent.warning("UnknownHostException e = " + e);
   34	        } catch (SocketException e) {
   35	            parent.warning("SocketException e = " + e);
   36	        } catch (IOException e) {
   37	            parent.warning("IOException e = " + e);
   38	        }
   39	    } // run
   40	} // UDPSendThread

    1	package se.nekotronic.udpreceiver;
    2	
    3	import java.io.IOException;
    4	import java.net.DatagramPacket;
    5	import java.net.DatagramSocket;
    6	import java.net.InetAddress;
    7	import java.net.NetworkInterface;
    8	import java.net.SocketException;
    9	import java.util.Enumeration;
   10	
   11	public class UDPServerThread extends Thread {
   12	    private UDPReceiveActivity parent;
   13	    private int port;
   14	    private boolean quit = false;
   15	    private DatagramSocket socket;
   16	
   17	    public UDPServerThread(UDPReceiveActivity parent, int port) {
   18	        this.parent = parent;
   19	        this.port = port;
   20	    }
   21	
   22	    public void run() {
   23	        try {
   24	            parent.print("Nätverksstatus...");
   25	            showNetworkStatus();
   26	
   27	            socket = new DatagramSocket(port);
   28	            byte[] buf = new byte[100];
   29	            while (!quit) {
   30	                DatagramPacket packet = new DatagramPacket(buf, buf.length);
   31	                parent.print("Waiting for packet...");
   32	                socket.receive(packet);
   33	                String message = new String(packet.getData());
   34	                parent.print("Received packet: '" + message + "'");
   35	            }
   36	        } catch (SocketException e) {
   37	            parent.print("SocketException: " + e);
   38	        } catch (IOException e) {
   39	            parent.print("IOExceptione: " + e);
   40	        }            
   41	    } // run
   42	
   43	    public void please_stop() {
   44	        quit = true;
   45	        socket.close();
   46	    }
   47	    
   48	    private void showNetworkStatus() {
   49	        try {
   50	                for (Enumeration is = NetworkInterface.getNetworkInterfaces(); is.hasMoreElements();) {
   51	                        NetworkInterface i = is.nextElement();
   52	                        // parent.print("Interface: " + i.getName() + ", " + (i.isUp() ? "up" : "down")); -- Requires API 9
   53	                        parent.print("Interface: " + i.getName());
   54	                        for (Enumeration ip = i.getInetAddresses(); ip.hasMoreElements();) {
   55	                                InetAddress a = ip.nextElement();
   56	                                parent.print("  Address: " + a.toString());
   57	                        }
   58	                }
   59	        }
   60	        catch (SocketException e) {
   61	                parent.print("Caught exception: " + e);
   62	        }
   63	    } // showNetworkStatus
   64	} // UDPServerThread