cosc 4730

Brief return SocketsAnd HttpURLConnection (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.try {

InetAddress serverAddr = InetAddress.getByName(host);//make the connectionSocket socket = new Socket(serverAddr, port);String message = "Hello from Client android emulator";

try {//receive a messagePrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter(socket.getOutputStream())),

true);out.println(message);//send a message nowBufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

String str = in.readLine(); } catch(Exception e) {

//error! } finally { socket.close(); in.close(); out.close(); } } catch (Exception e) { //unable to connect }

Android Client Code

• Making a connection, the code is pretty straight forward

String hostname = “localhost”; // remote machineInt port = 3012; //remote port number

//make the connectionInetAddress serverAddr = InetAddress.getByName(hostname);Socket socket = new Socket(serverAddr, port);//now we have a connection to the server

Android Server Code

• Again pretty straight forwardInt port = 3012; //this is the local port number//create the server socketServerSocket serverSocket = new ServerSocket(port);//wait for a client to connectSocket socket = serverSocket.accept();//now we have a connection to the client.

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 sidePrintWriter out = 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()));

PrintWriter

• 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.

println will add an end of line marker.• This is important for the read side.

BufferedReader

• 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 (in.read()) { read() } else { do something else}

Lastly.

• Don’t forget to close everything when you are done with the network.

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

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

• 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.

• You must connect your phone to UW’s UWyo wireless network to talk to a local cosc machine.– See http://

www.uwyo.edu/askit/displaydoc.asp?askitdocid=1769&parentid=1 for help.

AndroidManifest.xml<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.cosc4730.TCPclient" android:versionCode="1" android:versionName="1.0"> <uses-permission android:name="android.permission.INTERNET" /> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".TCPclient" android:label="@string/app_name">

<intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity>

</application> <uses-sdk android:minSdkVersion="10" android:targetSdkVersion="20"/></manifest>

Networking

• 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.

simulator

• 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

References

• Android dev site of course – http://developer.android.com/intl/zh-CN/

reference/android/net/package-summary.html• Socket programming tutorial.

http://www.anddev.org/socket_programming-t325-s30.html

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

HTTPURLCONNECTION

HttpURLConnection

• An URLConnection for HTTP (RFC 2616) used to send and receive data over the web. – Data may be of any type and length. This class may

be used to send and receive streaming data whose length is not known in advance.

– Requests can be setup to include credentials, content types, and session cookies.

Use• Obtain a new HttpURLConnection by calling URL.openConnection() and casting

the result to HttpURLConnection.– Prepare the request. The primary property of a request is its URI. Request headers may

also include metadata such as credentials, preferred content types, and session cookies.– Optionally upload a request body. Instances must be configured with setDoOutput(true)

if they include a request body. Transmit data by writing to the stream returned by getOutputStream().

• Read the response. – Response headers typically include metadata such as the response body's content type

and length, modified dates and session cookies. • The response body may be read from the stream returned by getInputStream().

– If the response has no body, that method returns an empty stream.• disconnect().

– Disconnecting releases the resources held by a connection so they may be closed or reused.

Example get• HttpURLConnection con = (HttpURLConnection)

url.openConnection();• page = readStream(con.getInputStream());• con.disconnect();• Where readStream is method to read the InputStream. It may look

something like this:• StringBuilder sb = new StringBuilder("");• reader = new BufferedReader(new InputStreamReader(in));• while ((line = reader.readLine()) != null) {• sb.append(line + “\n”);• }• Return sb.tostring();

Authentication• If the website uses basic authentication (instead of

username/password login system of it’s own)• Setup the authenticator before the connection and you have

login for you.Authenticator.setDefault(new Authenticator() { protected PasswordAuthentication getPasswordAuthentication() { return new PasswordAuthentication(username, password.toCharArray()); });• Where both username and password are Strings.

Authentication login systems

• Where the website uses logins and cookies, setup the and use the cookie manager.– Normally use a login page, which will set a cookie

on the “browser”, in our case we use the CookieManager.

• CookieManager cookieManager = new CookieManager();

• CookieHandler.setDefault(cookieManager);

Post methods.• While get is easy, post methods are harder.conn = … url.openConnection();conn.setDoOutput(true); //there is outputcon.setChunkedStreamingMode(0); //write as we goOutputStream out = new BufferedOutputStream(urlConnection.getOutputStream());• Write out the parameters correctly for a post method.

– This is shown in the ReST API code.out.flush();//ensure all the data is written out.out.close();//close this side, we are done here.• Now read as before.

ASYNCTASKA second look.

AsyncTask

• 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 private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> { protected Long doInBackground(URL... urls) { int count = urls.length; long totalSize = 0; for (int i = 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

more examples

• See the GitHub page pages for the rest of the source code for the examples.

• Both examples do the same thing except– HttpURLConDemoThread uses threads– HttpURLConDemoAysnc uses AsyncTask

DOWNLOADMANGER (API 9+)

DownloadManager

• 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• Get the service via getSystemServiceDownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);• Make a request via the request methodsDownloadManager.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)

– VISIBILITY_HIDDEN, VISIBILITY_VISIBLE, VISIBILITY_VISIBLE_NOTIFY_COMPLETED.– 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)

• 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_DO

WNLOADS, "nasapic.jpg");• allowScanningByMediaScanner ()

– If setting above, add this so the media scanner is called as well.

Receiver• 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

IntentFilter intentFilter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);registerReceiver(downloadReceiver, intentFilter);

• Where downloadReceiver is our methodunregisterReceiver(downloadReceiver);

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)

DownloadManager.Query query = new DownloadManager.Query();query.setFilterById(intentdownloadId);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

• DownloadDemo– 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• http://

developer.android.com/reference/java/net/HttpURLConnection.html– And sub pages, click the links to find them.

• Download Manager– http://

developer.android.com/reference/android/app/DownloadManager.html

– http://stackoverflow.com/questions/7239996/android-downloadmanager-api-opening-file-after-download

– http://blog.vogella.com/2011/06/14/android-downloadmanager-example/

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