1. Department of Computer Science & Engineering
Developing MIDlets
Dr. Miguel A. Labrador
Department of Computer Science & Engineering

2. Outline MIDlet life cycle Hello World example
User interface classes and APIs
Lists, text boxes, forms, alerts
Media API
Record Management Systems
Security

3. MIDlets
Java program compiled using the APIs included in the CLDC and MIDP specifications
After compilation, several steps need to be done before using the MIDlet in a real device
Debugged in emulators
Passed through the offline preverifier
Packaged
Creates the Java Archive file (JAR) and Java Application Descriptor (JAD) file
JAR file contains the manifest file
Automatically generated by the jar tool
Information about the MIDlet, such as name, vendor, version and configuration and profile utilized
JAD file contains additional information, such as URL and size
Very useful for the mobile decide to decide whether to download the MIDlet or not

4. Manifest and JAD Examples
Manifest File Example
JAD File Example
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.7.0
Created-By: 1.6.0_03-b05 (Sun Microsystems Inc.)
MIDlet-2: CalculatorWebService, , edu.cse.usf.book.ws.CalculatorWebService
MIDlet-1: TCPTest, , edu.cse.usf.book.TCPTest
MIDlet-Vendor: Vendor
MIDlet-Name: TCPTest
MIDlet-Version: 1.0
MicroEdition-Configuration: CLDC-1.0
MicroEdition-Profile: MIDP-2.0
MIDlet-1: TCPTest, , edu.cse.usf.book.TCPTest
MIDlet-2: CalculatorWebService, , edu.cse.usf.book.ws.CalculatorWebService
MIDlet-Jar-Size: 12747
MIDlet-Jar-URL: TCPTest.jar
MIDlet-Name: TCPTest
MIDlet-Vendor: Vendor
MIDlet-Version: 1.0
MicroEdition-Configuration: CLDC-1.0
MicroEdition-Profile: MIDP-2.0

5. New Application Instance
MIDlets
All MIDlets have the same life cycle
Paused
Active
Destroyed
destroyApp()
pauseApp()
startApp()
New Application Instance
End

6. A Hello World MIDlet Example
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class HelloWorld extends MIDlet implements CommandListener{
private Command exitCommand;
private TextBox tbox;
// MIDlet constructor
public HelloWorld() {
// Create "Exit" Command
exitCommand = new Command("Exit", Command.Exit, 1);
// Create TextBox to display the output
tbox = new TextBox ("Hello World MIDlet", "Hello, World!", 15, 0);
// Include the Exit Command in the interface and set its Listener
tbox.addCommand(exitCommand);
tbox.setCommandListener(this);
// Set the TextBox as the current screen
Display.getDisplay(this).setCurrent(tbox); }

7. A Hello World MIDlet Example
// The system calls this function to start the MIDlet
protected void startApp() {}
// The application is switched to the paused state
protected void pauseApp() {}
// The application is destroyed
protected void destroyApp() {boolean force}
// MIDlet destroys itself if user gives the Exit Command
public void commandAction (Command c, Displayable d) {
if (c==exitCommand) {
destroyApp(false);
notifyDestroyed{}; }

8. Hello World MIDlet

9. The User Interface Hierarchy of Classes
The package javax.microedition.lcdui contains most of the classes and methods needed to design GUIs
Display
Displayable
Command
Canvas
Screen
List
StringItem
TextBox
Alert
Form
Item
CustomItem
Spacer
ChoiceGroup
TextField
ImageItem
DateField
Gauge
0 ... n

10. The User Interface API Hierarchy of classes Display class at the top
Manages the display and input devices of the system
Contains methods to retrieve the properties of the device and to request the display of object
Only one instance of Display per MIDlet
Reference of that instance can be obtained by getDisplay() method
Displayable object contains the UI objects that are shown in the display
setCurrent() and getCurrent() utilized to set and retrieve the current Displayable
The application changes the current Displayable based on user action
Displayable object may have listener and command objects associated
User uses these objects to interact with the UI
When the user selects a command, the application is automatically notified
The application may react changing the Displayable by another one

11. The User Interface API
Commands provide users with a way to navigate through the Displayables of an application
If a Displayable has no command associated with it, the user has no way to change the current Displayable
All commands have a string label, priority, and command type
Commands are added or removed using the addCommand() and removeCommand() methods
Six command types:
BACK, OK, CANCEL, HELP, EXIT, STOP
Following example shows the implementation of three commands, two generic commands, save and delete, and one specific command, the exit command

12. Commands Example
class ExampleCommand extends Screen implements CommandListener {
Command save = new Command ("Save", Command.SCREEN, 2};
Command delete = new Command ("Delete", Command.SCREEN, 3};
Command exit = new Command ("Exit", Command.EXIT, 4};
MIDlet midlet;
public ExampleCommand (MIDlet mymidlet) {
midlet = mymidlet;
setCommandListener(this);
addCommand(save);
addCommand(delete);
addCommand(exit); }
public void commandAction (Command c, Displayable d) {
if (c == save) {
\\ Save data
else if (c == delete) {
\\ Delete data
else if (c == exit) {
\\ Exit the application
midlet.notifyDestroyed();

13. Lists, Text Boxes, Forms, and Alerts
Displayable class has two subclasses: Canvas and Screen
Canvas contains objects that allow the developer to have precise control of what is drawn on the display
Screen contains high-level objects that implement complete user interface components such as lists, text boxes, and forms
List class is a Screen that displays a list of choice elements
Each element includes a string and may have an icon
Lists can be implicit, exclusive, and multiple choice
Append, delete, insert, set, getString, and getImage methods
The type of list is selected using the interface class Choice
TextBox class is a Screen that allows the user to input and edit text
Application can set input constraints
ANY, NUMERIC, DECIMAL, PHONENUMBER, URL, ADDR
A text box must have commands

14. Lists, Text Boxes, Forms, and Alerts
Form is a Screen that may contain StringItems, ImageItems, DateFields, TextFields, Gauges, and ChoiceGroups
Any of the subclasses of class Item
Form can be manipulated using the insert, append, delete, set, get, size, and deteleAll methods
Alerts are Screens that can inform the user about errors and other exceptions, or as short informational notes and reminders
Alerts are displayed for certain amount of time using the setTimeout method, or modal, which requires the user input to close it
ALARM, CONFIRMATION, ERROR, INFO, and WARNING types

15. List Example
List list = new List (String title, int listType, String[ ] stringElements, Image[ ] imageElements);
where listType can be IMPLICIT, EXCLUSIVE, or MULTIPLE; stringElements (imageElements) is the initial array of elements(images)
e.g., List list = new List (`` list'', Choice.IMPLICIT, null);

16. Alert Example
Alert alert = new Alert (String title, String alertText, Image alertImage, AlertType.XXX);
where XXX can be any of the alertType
e.g., Alert alert = new Alert (``Warning'', ``Delete all?'', null, AlertType.WARNING);

17. The Media API
Designed to support sound in resource-constrained devices
Subset of the Mobile Media API, an optional package meant for Java ME devices with advanced sound and multimedia capabilities
Supports tone generation and media flow control (audio playback)
Implemented in two packages
The javax.microedition.media package, which is a fully compatible subset of classes included in the Mobile Media API
The javax.microedition.media.control package that defines specific control types that can be used with a Player
Three main components
Manager: used by the application to request Players
Player: plays the media
Wav, MP3, MIDI files and tone sequences
Controls: implement the controls of the Player
Start, stop, close

18. Creating a Player
The createPlayer method of the Manager class can create a player in two different ways
Player Manager.createPlayer (String url)
where url specifies the protocol and content of the data as follows:
<protocol>:<content location>
e.g., Player p = Manager.createPlayer(``

19. Creating a Player
A player can also be created to playback media from an inputStream
Start(), stop(), close() methods
Player Manager.createPlayer (InputStream stream, String type);
e.g., InputStream istream = getClass().getResourceAsStream(``hello.wav'');
Player p = Manager.createPlayer(istream, ``audio/X-wav'');
p.start();
Where type can be: Wave audio files (audio/x-wav), AU audio files (audio/basic), MP3 audio files(audio/mpeg), MIDI files (audio/midi), Tone sequences (audio/x-tone-seq)

20. Generating Tones The Manager class can also be used to generate tones
Volume is a value from 0 to 100
Duration is the duration of the tone in milliseconds
Note defines the tone of the note
Number from 0 to 127
note = (12 x log2 (f/440)) + 69
Frequency 440 Hz corresponds to note 69, which is MIDI note A
Manager.playTone (int note, int duration, int volume)

21. The Record Management System (RMS)
Simple record-oriented database that allows MIDlets to persistently store data in the mobile device
Included in the javax.microedition.rms package
Uses the concept of record store, a collection of persistent records
Records are arrays of bytes of different lengths and types within a record store
Records are automatically identified by a recordID
Monotonically increasing-by-one mechanism with no wrap around
Adjacent records in a record store do not necessarily have subsequent record IDs
Record stores are uniquely named using the name of the MIDlet suite plus the name of the record store
MIDlet suites are identified using the attributes MIDlet-vendor and MIDlet-name of the application descriptor

22. The Record Management System (RMS)
The RMS API does not include locking mechanisms but ensures that record store operations are atomic, synchronous, and serialized
It is the programmer’s responsibility to coordinate access when multiple threads within the same MIDlet attempt to access the same record simultaneously
No corruption of data guarantee but the serialization mechanism might give MIDlets access to the record in an undesired sequence
Methods to manipulate record stores
listRecordStores, deleteRecordStore, openRecordStore, closeRecordStore, getNumRecords, getSize, getSizeAvailable, getNextRecordID, getVersion, getLastModified
Methods to manipulate records
addRecord, deleteRecord, getRecordSize, getRecord, setRecord

23. Opening a New Record Store
public void openRecStore(String recordStore_name) {
try{
RecordStore rs =
RecordStore.openRecordStore(recordStore_name,true); }
catch(Exception e)
System.err.println(e.toString());

24. Adding a New Record to a Record Store
public void writeRecord(String str) {
byte[] rec = str.getBytes();
try
rs.addRecord(rec, 0, rec.length); }
catch (Exception e)
System.err.println(e.toString());

25. Security Security is guided by the following goals Confidentiality
Disclosure of information only to authorized users or systems
Encryption is a common mechanism to provide confidentiality
Symmetric and Asymmetric encryption
Integrity
Data cannot be modified without proper authorization
Achieved by cryptographic methods plus additional information
Authenticity
Making sure the message is authentic; it comes from the real source
Digital signatures using asymmetric encryption
Availability
Making sure information is available when needed

26. MIDlet Security MIDP 1.0 specification used the sandbox model
Run in a controlled and separate environment and do not interfere with each other
MIDP 2.0 expands this model including the concepts of trusted MIDlet and protection domains
Untrusted MIDlet suite is one whose authenticity and integrity of JAR file cannot be trusted by the device
Executed in untrusted and restrictive domain
MIDP 2.0 includes the mechanisms to identify and trust a MIDlet suite and the concept of protection domain for trusted MIDlets
Protection domain is a set of permissions associated with a root certificate in the device
A specific domain can be defined in the device using the public key of the domain entity, e.g., a software development company
Then, a MIDlet signed by the company will be given access to all those resources included in the permissions of the domain

27. MIDlet Security
Digital signatures and authentication methods are utilized to decide whether to trust or not a MIDlet suite
Internet X.509 Public Key Infrastructure standard included in RFC 2459 and RFC 2437 “PKCS #1: RSA Cryptography Specifications, version 2.0”
First, the MIDlet is signed; then, at download time, it is authenticated
Entire process consists of the following steps
Sender creates a signing certificate sending its Distinguished Name and public key to a Certificate Authority (CA) to obtain a RSA X.509 certificate
Sender encodes and inserts certificate(s) in the JAD file
Sender signs the JAR file with its private key to provide MIDlet integrity; however, it does not include the JAD file
Receiver downloads the MIDlet, checks the JAD file and verifies signer certificates and JAR signature

28. MIDlet Security
Receiver verifies signer certificates by looking at the CA in the JAD file and the root certificate authorities stored in the device
If authentication fails, MIDlet is not installed
Receiver verifies JAR signature
Gets signer’s public key from the CA and uses this key, the signature included in the JAD file, and the digest included in the JAR file to verify it
Certificates are used in MIDP 2.0 security for authentication
Package javax.microedition.pki provides the Certificate interface
getIssuer(), getNotAfter(), getNotBefore(), getSerialNumber(), getSigAlgName(), getSubject(), getType(), and getVersion() methods
Networking security achieved by Secure Socket Layer (SSL) and the Transport Layer Security (TLS) protocols
HttpsConnection and SecureConnection interfaces
Method getSecurityInfo can be applied to an open connection to fill a SecurityInfo object
Obtain protocol name and version, cipher suite, certificate of the connection