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cosc 4730. Brief return Sockets And HttpClient (and with AsyncTask ) DownloadManager. Android. Networking is based on standard Java SE methods And get the BufferedReader / PrintWriter Most Java SE network code works with almost no modifications. . typical Android network code.

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cosc 4730

cosc 4730

Brief return Sockets

And HttpClient (and with AsyncTask)


  • Networking is based on standard Java SE methods
    • And get the BufferedReader/PrintWriter
    • Most Java SE network code works with almost no modifications.
typical android network code
typical Android network code.

try {

InetAddressserverAddr = InetAddress.getByName(host);

//make the connection

Socket socket = new Socket(serverAddr, port);

String message = "Hello from Client android emulator";

try {

//receive a message

PrintWriterout = new PrintWriter( new BufferedWriter( new OutputStreamWriter(socket.getOutputStream())), true);


//send a message now

BufferedReaderin = new BufferedReader(new InputStreamReader(socket.getInputStream()));

String str = in.readLine();

} catch(Exception e) {


} finally {

socket.close(); in.close(); out.close();


} catch (Exception e) { //unable to connect }

android client code
Android Client Code
  • Making a connection, the code is pretty straight forward

String hostname = “localhost”; // remote machine

Int port = 3012; //remote port number

//make the connection

InetAddressserverAddr = InetAddress.getByName(hostname);

Socket socket = new Socket(serverAddr, port);

//now we have a connection to the server

android server code
Android Server Code
  • Again pretty straight forward

Int port = 3012; //this is the local port number

//create the server socket

ServerSocketserverSocket = new ServerSocket(port);

//wait for a client to connect

Socket socket= serverSocket.accept();

//now we have a connection to the client.

reading and writing
Reading and writing.
  • This works for both client and server.
  • Once we have the socket connection, we need to get the read and write part of the socket.

//Write side

PrintWriterout = new PrintWriter( new BufferedWriter( new OutputStreamWriter( socket.getOutputStream())),true);

        • Note the true, turns on autoflush.

//Read side.

BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

  • Networking is normally a text based protocol.
    • So while there are many function to send int, long, etc. I’m ignoring them.
    • out.print(String) and out.println(String)
      • They both do the same thing, send a line of text. printlnwill add an end of line marker.
      • This is important for the read side.
  • The read method reads a single character and returns it as a int.
    • Second version uses a length and char[].
  • readLine() returns line of text as a string. It stops at the end of line marker.
    • Back to the print and println methods for the writer.
  • There is a ready() methods that return true or false. True if there is a data to be read, false other. Using the read() and ready() allows to prevent blocking reads.
    • Example: if ( { read() } else { do something else}
  • Don’t forget to close everything when you are done with the network.

in.close(); out.close();


android example code
Android example code
  • There is a TCPclient and TCPServ examples for the android
    • For the sever code you will need to tell the emulator to accept the port number
    • In android-sdk-windows\tools directory, run the following dos command
      • adb forward tcp:3012 tcp:3012
        • assuming you are using port 3012
android notes
Android notes
  • You will need to put
    • <uses-permission android:name= "android.permission.INTERNET" />
    • In the AndroidManifest.xml file
  • At this point you should be able to use it in both the simulator and on the phone.
last note
Last Note.
  • You must connect your phone to UW’s UWyo wireless network to talk to a local cosc machine.
    • See for help.
androidmanifest xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android=""




<application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".TCPclient"



<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />




<uses-sdkandroid:minSdkVersion="5" />

<uses-permission android:name="android.permission.INTERNET" />


  • Android networking is built on standard Java SE
    • So use the same network code you learned earlier.
    • See the source code example, Android TCPclient and TCPserv for examples that run on the Android platform.
  • For server code, you need to tell the simulator to accept the port number
  • In android-sdk-windows\tools directory, run the following dos command
    • adb forward tcp:3012 tcp:3012
      • assuming you are using port 3012
  • Android dev site of course
  • Socket programming tutorial.
main thread and network
Main thread and network.
  • Networking can take some time and should not be done on the main thread
    • Ie it can lock up the drawing.
  • As of v11 (honeycomb)
    • It will force close if you attempt networking on the main thread.
      • It must be done in a thread
        • Or a AsyncTask
  • This is a modified version of Apache’s HttpClient
    • Used a lot with the J2EE space
  • Create an HttpClient
  • Instantiate a new HTTP method
    • PostMethod or GetMethod
  • Set HTTP parameter names/values
  • Execute the HTTP call using the HttpClient
  • Process the HTTP response.
example get
Example get

HttpClientclient = new DefaultHttpClient();

HttpGetrequest = new HttpGet();

request.setURI(new URI(""));

HttpResponseresponse = client.execute(request);

  • To add parameters to a get

HttpGet method = new HttpGet( "");

HttpResponse response = client.execute(method);

example post
Example Post
  • HttpClient client = new DefaultHttpClient();
  • HttpPost request = new HttpPost("http://somewebsite/do.php");
  • List<NameValuePair> postParameters = new ArrayList<NameValuePair>();
  • postParameters.add(new BasicNameValuePair("one", "valueGoesHere"));
  • UrlEncodedFormEntityformEntity = new UrlEncodedFormEntity(postParameters);
  • request.setEntity(formEntity);
  • HttpResponse response = client.execute(request);
  • Networking can’t be used on the main thread, so an AsyncTask can be ideal for short networking tasks, say file downloads or other things.
    • otherwise you should use threads and handlers.
asynctask download example
AsyncTask download Example

 private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {     protected Long doInBackground(URL... urls) {int count = urls.length;         long totalSize = 0;         for (inti = 0; i < count; i++) {totalSize += Downloader.downloadFile(urls[i]);publishProgress((int) ((i / (float) count) * 100));             // Escape early if cancel() is called             if (isCancelled()) break;         }return totalSize;} //background thread     protected void onProgressUpdate(Integer... progress) {setProgressPercent(progress[0]);} //UI thread     protected void onPostExecute(Long result) {showDialog("Downloaded " + result + " bytes");} //UI thread}

  • Once created, a task is executed very simply:

new DownloadFilesTask().execute(url1, url2, url3);

URL is pamaters to doInBackground

Integer is the value for publishProgress and onProgressUpdate

And Long is the return value and parameter to onPostExecute

The call, uses URL to create the “list” used in doInBackground

rest of the examples
Rest of the examples
  • See the hand page pages for the rest of the source code for the examples.
  • uses threads
  • uses AsyncTask
  • The download manager is a system service that handles long-running HTTP downloads.
    • Clients may request that a URI be downloaded to a particular destination file.
  • The download manager will conduct the download in the background, taking care of HTTP interactions and retrying downloads after failures or across connectivity changes and system reboots.
  • Note that the application must have the INTERNET permission to use this class.
how it works
How it works
  • Get the service via getSystemService

DownloadManagerdownloadManager= (DownloadManager) getSystemService(DOWNLOAD_SERVICE);

  • Make a request via the request methods

DownloadManager.Request request = new DownloadManager.Request(URI)

long download_id = downloadManager.enqueue(request);

  • Setup a broadcastReciever to receive an broadcast when it’s done.
    • The downloadmanager uses the download_id number, so you need to store it for use in the receiver.
      • The intent will contain the id number for the file downloaded, so you know which one (when downloading more then one at a time.)
downloadmanager request uri
  • Request has a lot of parameters you can set
    • .setAllowedNetworkTypes( DownloadManager.Request.NETWORK_WIFI| DownloadManager.Request.NETWORK_MOBILE)
      • All networks by default
    • setDescription( String)
    • setTitle (CharSequence title)
      • Sets the title and description for the notification line if enabled
    • setShowRunningNotification (boolean)
      • Show notification, true. Deprecated for api 11+
      • setNotificationVisibility (int visibility)
        • If hidden, this requires the permission android.permission.DOWNLOAD_WITHOUT_NOTIFICATION.

A note, setShowRunningNotification(false) didn’t work on 4.1.x

downloadmanager request uri 2
DownloadManager.Request(URI) (2)
  • setDestinationInExternalFilesDir(String dirType, String subPath)
    • dirType is the directory type to pass to getExternalStoragePublicDirectory(String)
    • subPath is the path within the external directory, including the destination filename
    • Example:
    • .setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "nasapic.jpg");
  • allowScanningByMediaScanner()
    • If setting above, add this so the media scanner is called as well.
  • Set to receive DownloadManager.ACTION_DOWNLOAD_COMPLETE
  • Since we don’t allows want to get download notifications, we set this on up dyanamically in onResume/OnPause

IntentFilterintentFilter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);

registerReceiver(downloadReceiver, intentFilter);

  • Where downloadReceiver is our method


downloadermanager query
  • In the receiver, we deal with the query methods to find out the status of the download
    • Successful or failure
    • Based on the download_id (which we can get from the intent or keep from the enqueue method)
    • We filter and get a Cursor with the information
downloadermanager query 2
DownloaderManager.Query (2)

DownloadManager.Queryquery = new DownloadManager.Query();


Cursor cursor = downloadManager.query(query);

  • The example code shows you how to get the columns and information out of the cursor, including a file, so you can read the downloaded file.
example code
Example code
    • MainActivity has two buttons. One downloads and shows the notification, the second doesn’t
    • MainActivityORG stores the download_id in preferences, instead of a variable.
references downloadmanager
References (downloadManager)