Developing MIDlets

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Developing MIDlets

Dr. Miguel A. LabradorDepartment of Computer Science & Engineering

[email protected]://www.csee.usf.edu/~labrador

2Copyright© Dr. Miguel A. Labrador


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Outline

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



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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



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Manifest and JAD Examples

Manifest File Example JAD File Example

Manifest-Version: 1.0Ant-Version: Apache Ant 1.7.0Created-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: VendorMIDlet-Name: TCPTestMIDlet-Version: 1.0MicroEdition-Configuration: CLDC-1.0MicroEdition-Profile: MIDP-2.0

MIDlet-1: TCPTest, , edu.cse.usf.book.TCPTest

MIDlet-2: CalculatorWebService, , edu.cse.usf.book.ws.CalculatorWebService

MIDlet-Jar-Size: 12747MIDlet-Jar-URL: TCPTest.jarMIDlet-Name: TCPTestMIDlet-Vendor: VendorMIDlet-Version: 1.0MicroEdition-Configuration: CLDC-1.0MicroEdition-Profile: MIDP-2.0



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MIDlets• All MIDlets have the same life cycle

Paused

Active

Destroyed

destroyApp()

destroyApp()

pauseApp()startApp()

New Application

Instance

End



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A Hello World MIDlet Exampleimport javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class HelloWorld extends MIDlet implements CommandListener{private Command exitCommand;private TextBox tbox;

// MIDlet constructorpublic HelloWorld() {

// Create "Exit" CommandexitCommand = new Command("Exit", Command.Exit, 1);

// Create TextBox to display the outputtbox = new TextBox ("Hello World MIDlet", "Hello, World!", 15, 0);

// Include the Exit Command in the interface and set its Listenertbox.addCommand(exitCommand);tbox.setCommandListener(this);

// Set the TextBox as the current screenDisplay.getDisplay(this).setCurrent(tbox);}



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A Hello World MIDlet Example

// The system calls this function to start the MIDletprotected void startApp() {}

// The application is switched to the paused stateprotected void pauseApp() {}

// The application is destroyedprotected void destroyApp() {boolean force}

// MIDlet destroys itself if user gives the Exit Commandpublic void commandAction (Command c, Displayable d) {

if (c==exitCommand) {destroyApp(false);notifyDestroyed{};}

}}



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Hello World MIDlet



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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 ... 1

0 ... n0 ... n



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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



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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



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Commands Exampleclass 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 applicationmidlet.notifyDestroyed();}

}}



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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, EMAILADDR• A text box must have commands



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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



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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 (``Email list'', Choice.IMPLICIT, ``[email protected], [email protected], [email protected]'', null);



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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);



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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



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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(``http://hello.wav'');



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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)



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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)



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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



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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



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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()); }}



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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()); }}



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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



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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



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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



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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

Documents

Developing MIDlets