1. And HttpURLConnection (and with AsyncTask)
cosc 4730
Brief return Sockets
And HttpURLConnection (and with AsyncTask)
DownloadManager

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

3. typical Android network code.
try {
InetAddress serverAddr = InetAddress.getByName(host);
//make the connection
Socket socket = new Socket(serverAddr, port);
String message = "Hello from Client android emulator";
//receive a message
PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter(socket.getOutputStream())), true);
out.println(message);
//send a message now
BufferedReader 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 }

4. 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
InetAddress serverAddr = InetAddress.getByName(hostname);
Socket socket = new Socket(serverAddr, port);
//now we have a connection to the server

5. Android Server Code Again pretty straight forward
Int port = 3012; //this is the local port number
//create the server socket
ServerSocket serverSocket = new ServerSocket(port);
//wait for a client to connect
Socket socket = serverSocket.accept();
//now we have a connection to the client.

6. 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
PrintWriter 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()));

7. 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.

8. 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}

9. Lastly.
Don’t forget to close everything when you are done with the network.
in.close(); out.close();
socket.close();

10. 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

11. 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.

12. Last Note.
You must connect your phone to UW’s UWyo wireless network to talk to a local cosc machine.
See for help.

13. AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android=" package="com.cosc4730.TCPclient" android:versionCode="1" android:versionName="1.0"> <uses-permission android:name="android.permission.INTERNET" /> <application <activity android:name=".TCPclient" <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>

14. 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.

15. 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

16. References Android dev site of course
Socket programming tutorial.

17. 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, service, etc. It just can't be on the main UI thread.

18. HttpURLConnection

19. 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.

20. HttpURLConnection
by default httpURL will fail if it is not a https connection.
Also DownloadManager, ftpURLConnection, OkHttpURLStreamHandler, and Apache's HTTPclient(deprecated in 23 and removed in 28)
starting in marshmallow (API 23).
add to the androidmanifest.xml file in the application section
android:usesCleartextTraffic=["true" | "false"]
True to allow clear text traffic (ie http, instead https).
your app can check programmatically
NetworkSecurityPolicy.getInstance().isCleartextTrafficPermitted()

21. 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.

22. 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();

23. 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.

24. 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);

25. Post methods. While get is easy, post methods are harder.
conn = … url.openConnection();
conn.setDoOutput(true); //there is output
con.setChunkedStreamingMode(0); //write as we go
OutputStream 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.

26. A second look.
Asynctask

27. 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.

28. 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

29. 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

30. Downloadmanger (API 9+)

31. 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.

32. How it works Get the service via getSystemService
DownloadManager downloadManager = (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.)

33. 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+
A note, setShowRunningNotification(false) does not work on 4.1+
setNotificationVisibility (int visibility)
VISIBILITY_HIDDEN, VISIBILITY_VISIBLE, VISIBILITY_VISIBLE_NOTIFY_COMPLETED, VISIBILITY_VISIBLE_NOTIFY_ONLY_COMPLETION
If hidden, this requires the permission android.permission.DOWNLOAD_WITHOUT_NOTIFICATION.

34. 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.

35. 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 method
unregisterReceiver(downloadReceiver);

36. 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

37. 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.

38. 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.

39. References
And sub pages, click the links to find them.
Download Manager

40. Q A
&