Developing MIDlets

1. Developing MIDlets Dr. Miguel A. Labrador Department of Computer Science & Engineering labrador@csee.usf.edu http://www.csee.usf.edu/~labrador

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 File Example Manifest and JAD Examples JAD File Example • 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 • 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

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

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 TextBoxtbox; // 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 • StringItem • List • ImageItem • The package javax.microedition.lcduicontains most of the classes and methods needed to design GUIs • Display • TextBox • TextField • Screen • Alert 0 ... 1 • DateField • Displayable • Form • Gauge • Canvas 0 ... n 0 ... n • ChoiceGroup • Command • Item • Spacer • CustomItem

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 • Displayableobject 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}; MIDletmidlet; public ExampleCommand (MIDletmymidlet) { 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, EMAILADDR • 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, intlistType, 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, ``labrador@cse.usf.edu, ajperez@cse.usf.edu, pedrow@cse.usf.edu'', 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.controlpackage 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(``http://hello.wav'');

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., InputStreamistream = 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.rmspackage • 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{ RecordStorers = 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 • UntrustedMIDlet 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