J2ME Networking

1
J2ME Networking
2
Introduction

• J2ME provides networking features to the mobile
  devices.
• It is possible to get up-to-the-minute stock
  quotes or updated currency exchange rates on a
  mobile phone.
• The javax.microedition.io classes and interfaces
  handle the networking capability of MIDP.
• The java.io package provides input/output (I/O)
  capability to MIDP.

3
J2ME Networking Categories

• J2ME networking has 3 categories
• Low-level IP networking
• HTTP networking
• Secure networking
• The most critical aspect of J2ME network
  connectivity is communication between a mobile
  device and Web server.

4
Low-level IP networking

• This category involves socket, datagram, serial
  port, and file I/O communication.
• Socket-based communication conforms to the
  connection-oriented TCP/IP protocol.
• Datagram-based communication conforms to the
  connectionless UDP/IP protocol.
• e.g. URI for a datagram connection for sending to
  a server on a certain port
• datagram//123.456.789.121234
• Low-level IP networking can also handle file I/O
  and can allow a MIDlet to use a local serial port.

5
HTTP networking

• The communication between a mobile device and a
  Web server is based on HTTP (Hypertext Transfer
  Protocol).
• HTTP is a connection-oriented request-response
  protocol.

6
Secure networking

• Secure Networking in J2ME involves additional
  interfaces available for secure communication
  with Web-based network services.
• Secure interfaces are provided by HTTPS and
  SSL/TLS protocol access over the IP network.

7
The Connection Framework

• J2ME networking was designed to address the
  diverse needs of a wide range of mobile devices.
• At the same time, the networking system must be
  device specific.
• To meet these challenges, it introduces the
  concept of a generic connection framework.
• Generic connection framework is to define the
  general aspects of the networking and file I/O in
  the form of Java interfaces for a broad range of
  handheld devices
• Leave the actual implementations of these
  interfaces to individual device manufacturers.

8
The Connection Framework
9
URL Handling in J2ME

• URL handling in J2ME involves opening a
  connection to the Web server from the mobile
  device and handling data I/O between the two.
• The process happens in the following stages
• Setup
• Connected
• Closed
• J2ME defines the javax.microedition.io.Connector
  class to create all the connection objects.
• In URL handling, Connector.open() is used to open
  a URL it returns an HttpConnection object.

10
URL Handling in J2ME

• The string parameter to the Connector.open()
  method is a valid URL.
• The URL string varies depending on the
  communication protocol, as Examples 1 through 5
  below demonstrate.
• Example 1. Invoking HTTP-based
  communicationConnection conn Connector.open("h
  ttp//www.yahoo.com") Example 2. Invoking
  stream-based socket communicationConnection conn
  Connector.open("socket//localhost9000")

11
URL Handling in J2ME

• Example 3. Invoking datagram-based socket
  communicationConnection conn
  Connector.open("datagram//9000") Example
  4. Invoking serial port communicationConnection
  conn Connector.open("comm0baudrate9000")
  Example 5. Invoking file I/O communicationConne
  ction conn Connector.open("file//myfile.dat")
  

12
URL Handling in J2ME

• The Connector.open() method also accepts the
  access mode (values READ, WRITE, and READ_WRITE),
  and a flag to indicate that the caller wants a
  timeout notification.
• static Connection open(String name, int mode)
  
• static Connection open(String name, int mode,
  boolean timeouts)
• The method openInputStream() of Connector opens
  an input stream of bytes (java.io.InputStream).

13
URL Handling in J2ME

• Similarly, a java.io.OutputStream representing an
  output stream of bytes.
• The counterparts of InputStream and OutputStream
  are java.io.DataInputStream and
  java.io.DataOutputStream, respectively.
• A DataInputStream/DataOutputStream lets an
  application read/write primitive Java data types.

14
Example - Fetch a Page

• Use a HttpConnection to fetch a web page and
  display the content using a TextBox.

Source of ict web page http//www.vtc.edu.hk/ive/
ty/ict/
15
Example - Fetch a Page

• import java.io.
• import javax.microedition.io.
• import javax.microedition.lcdui.
• import javax.microedition.midlet.
• public class NetworkFetchAPage extends MIDlet
• private Display display
• String url "http//www.vtc.edu.hk/ive/ty/ict
  /"
• public NetworkFetchAPage()
• display Display.getDisplay(this)
• public void startApp()
• HttpConnection c null
• InputStream s null
• StringBuffer b new StringBuffer()
• TextBox t null

16
Example - Fetch a Page

• try
• c (HttpConnection)
  Connector.open(url)
• s c.openInputStream()
• int ch
• while((ch s.read()) ! -1)
• b.append((char) ch)
• System.out.println(b.toString())
• t new TextBox("ICT",
• b.toString(), 1024, 0)
• catch (IOException e)
• System.out.println("IOException "
  e)
• e.printStackTrace()

17
Example - Fetch a Page

• try
• if(s ! null)
• s.close()
• if(c ! null)
• c.close()
• catch (IOException e)
• System.out.println("IOException "
  e)
• e.printStackTrace()
• // display the contents of the file in a
  text box.
• display.setCurrent(t)
• public void pauseApp()
• public void destroyApp(boolean unconditional)
  

18
Passing Parameters to Server

• Typically, an HTTP request to a server is
  accompanied by information needed by the server
  to process the request.

19
Passing Parameters to Server

• e.g. Login in case.
• A server must authenticate a client using the
  clients user ID and password.
• The client sends the user ID and password along
  with the HTTP request.
• Two techniques are used to send data to the
  server GET or POST request methods.
• The GET request method requires that data be
  concatenated to the URL of the server.
• The POST request method requires that each pair
  value be written to the output stream.

20
Passing Parameters to Server

• Data sent to a server must be in a pair value
  set
• field name
• the value associated with the field.
• The field name and value must be separated by an
  equal sign ().
• The pair value sets are separated from the URL by
  a question mark (?).
• Each pair value set is separated from other pair
  value sets by an ampersand ().
• The space character is converted to a plus ()
  sign.
• For example, the following request sends two
  parameters pOne"one bit" and pTwo"two"http//
  localhost/midp/simple?pOneonebitpTwotwo

21
Example Login - Get Method

• User enters a login id and a password
• The MIDlet sends the request to the web server
• The web server executes a simple php script and
  validates the user according to the following
  table
• Login ID Password
• andy cat
• paul panda
• jacky doctor
• peter a1 b

22
Example - Successful Login

• If password is correct, display the menu screen

23
Example - Login Fails

• If login fails, display an Alert screen to tell
  the user to try again.

• NoteThe network connection should be done in a
  separated thread other than the CommandAction
  thread.

24
Example - Login

• import java.io.
• import javax.microedition.io.
• import javax.microedition.lcdui.
• import javax.microedition.midlet.
• public class NetworkLoginDemo extends MIDlet
• implements CommandListener, Runnable
• private Display display
• private TextField userName
• private TextField password
• private Form form
• private Command cancel
• private Command login
• public NetworkLoginDemo()
• display Display.getDisplay(this)
• userName new TextField("LoginID", "",
  10, TextField.ANY)
• password new TextField("Password", "",
  10,
• TextField.PASSWORD)

25
Example - Login

• form new Form("Sign in")
• cancel new Command("Cancel", Command.CANCEL,
  2)
• login new Command("Login", Command.OK, 2)
• public void startApp()
• HttpConnection c null
• InputStream s null
• display Display.getDisplay(this)
• form.append(userName)
• form.append(password)
• form.addCommand(cancel)
• form.addCommand(login)
• form.setCommandListener(this)
• display.setCurrent(form)

26
Example - Login

• public void validateUser()
• // Do network loading in a separate
  thread.
• Thread t new Thread(this)
• t.start()
• public void run()
• String name userName.getString()
• String pwd password.getString()
• StringBuffer b new StringBuffer("")
• HttpConnection hc null
• InputStream in null
• String parameter
• String result
• String url
• "http//ictlab.tyict.vtc.edu.hk/nelsonc
  /mobile/login_demo.php?"

27
Example - Login

• parameter "name" name
• parameter "password" pwd.replace('
  ', '')
• System.out.println(urlparameter)
• try
• hc (HttpConnection)Connector.open(ur
  lparameter)
• in hc.openInputStream()
• int ch
• while((ch in.read()) ! -1)
• b.append((char) ch)
• catch (IOException e)
• e.printStackTrace()

Hint To debug your program, copy and paste the
link (e.g. http//ictlab.tyict.vtc.edu.hk/nelsonc
/mobile/login_demo.php?nameandypasswordcat) to
the browser and check the connection and result
returned.
28
Example - Login

• try
• if(in ! null)
• in.close()
• if(hc ! null)
• hc.close()
• catch (IOException e)
• e.printStackTrace()
• result b.toString().trim()
• if (result.equals("OK"))
• menu()
• else
• tryAgain()

The sever side php script lt?php name_GET'name
' pwd_GET'password' if (name"andy"
pwd"cat") echo "OK" else if (name"paul"
pwd"panda") echo "OK" else if
(name"jacky" pwd"doctor") echo
"OK" else if (name"peter" pwd"a1 b")
echo "OK" else echo "invalid" ?gt
29
Example - Login

• public void menu()
• List services new List("Choose one",
  Choice.EXCLUSIVE)
• services.append("Check Mail", null)
• services.append("Compose", null)
• services.append("Addresses", null)
• services.append("Options", null)
• services.append("Sign Out", null)
• display.setCurrent(services)
• public void tryAgain()
• Alert error new Alert("Login
  Incorrect", "Please try again",
• null,
  AlertType.ERROR)
• error.setTimeout(Alert.FOREVER)
• password.setString("")
• display.setCurrent(error, form)

30
Example - Login

• public void commandAction(Command c,
  Displayable d)
• String label c.getLabel()
• if(label.equals("Cancel"))
• notifyDestroyed()
• else if(label.equals("Login"))
• validateUser()
• public void pauseApp()
• public void destroyApp(boolean unconditional)
  

31
Post Method

• Posting a form is a little more complicated on
  the MIDlet side.
• A few request headers need to be set in
  HttpConnection.
• You need to change the request method by calling
  setRequestMethod() and the header by calling
  setRequestProperty().
• Obtain the output stream for the HttpConnection
  by calling openOutputStream().
• Send the request parameters on the output stream
  returned from the HttpConnection.
• Parameters should be encoded as described earlier

32
Example Login - Post Method

• The only difference is in the run method. Other
  methods are the same as the previous example.
• public void run()
• String name userName.getString()
• String pwd password.getString()
• StringBuffer b new StringBuffer("")
• HttpConnection hc null
• InputStream in null
• OutputStream out null
• String parameter
• String result
• String url "http//ictlab.tyict.vtc.edu.
  hk/nelsonc/mobile/"
• 
  "login_post_demo.php?"
• parameter "name" name
• parameter "password" pwd.replace('
  ', '')

33
Example Login - Post Method

• try
• hc (HttpConnection)Connector.open(ur
  l)
• hc.setRequestMethod(HttpConnection.POS
  T)
• hc.setRequestProperty("CONTENT-TYPE",
• "application/x-www-fo
  rm-urlencoded")
• hc.setRequestProperty("User-Agent",
• "Profile/MIDP-2.0
  Configuration/CLDC-1.0")
• out hc.openOutputStream()
• byte postmsg parameter.getBytes(
  )
• for(int i0iltpostmsg.lengthi)
• out.write(postmsgi)
• out.flush()
• in hc.openInputStream()
• int ch
• // same as before ....

34
Read Binary Data From Network

• The data read from server is already in binary
  format.
• The following program (ImageLoader.java) reads an
  image file from a web server and display it as an
  ImageItem.

35
Example - ImageLoader

• import java.io.
• import javax.microedition.io.
• import javax.microedition.lcdui.
• import javax.microedition.midlet.
• public class ImageLoader extends MIDlet
• implements CommandListener, Runnable
• private Display mDisplay
• private Form mForm
• public ImageLoader()
• mForm new Form("Connecting...")
• mForm.addCommand(new Command("Exit",
  Command.EXIT, 0))
• mForm.setCommandListener(this)

36
Example - ImageLoader

• public void startApp()
• if (mDisplay null) mDisplay
  Display.getDisplay(this)
• mDisplay.setCurrent(mForm)
• // Do network loading in a separate
  thread.
• Thread t new Thread(this)
• t.start()
• public void pauseApp()
• public void destroyApp(boolean unconditional)
  
• public void commandAction(Command c,
  Displayable s)
• if (c.getCommandType() Command.EXIT)
• notifyDestroyed()

37
Example - ImageLoader

• public void run()
• HttpConnection hc null
• DataInputStream in null
• try
• String url
• "http//ictlab.tyict.vtc.edu.hk/
  nelsonc/mobile/ive_ty.png"
• hc (HttpConnection)
  Connector.open(url)
• int length (int)hc.getLength()
• byte data null
• if (length ! -1)
• data new bytelength
• in new DataInputStream(hc.openIn
  putStream())
• in.readFully(data)
• else
• throw new IOException("Unable to
  determine the length")

38
Example - ImageLoader

• Image image Image.createImage(data,
  0, length)
• ImageItem imageItem new
  ImageItem(null, image, 0, null)
• mForm.append(imageItem)
• mForm.setTitle("Done.")
• catch (IOException ioe)
• StringItem stringItem new
  StringItem(null, ioe.toString())
• mForm.append(stringItem)
• mForm.setTitle("Done.")
• finally
• try
• if (in ! null) in.close()
• if (hc ! null) hc.close()
• catch (IOException ioe)
• ioe.printStackTrace()

39
Using HTTPS

• HTTP is not a secure protocol.
• A more secure alternative, HTTPS, runs atop
  Transport Layer Security (TLS), Secure Sockets
  Layer (SSL), or a similar protocol.
• In typical TLS interactions, the server sends a
  certificate to the client to authenticate itself.
  
• The client must have Certificate Authority (CA)
  root certificates on hand to verify the server's
  certificate.
• If the client can verify the certificate, the
  client will then send a secret value to the
  server, encrypted with the server's public key.

40
Using HTTPS

• The server and the client both derive a session
  key from this secret value, which is used to
  encrypt all subsequent traffic sent between the
  client and server.
• The generic connection framework makes it very
  easy to obtain HTTPS connections.
• All you have to do is construct an HTTPS
  connection string. So instead of this
• HttpConnection hc (HttpConnection)
  Connector.open("http//www.cert.org/")
• You would do this
• HttpConnection hc (HttpConnection)
  Connector.open("https//www.cert.org/")
• It's really that simple.