MIDP Mobile Information Device Profile Johnny Yau CIS 642 Prof. Insup Lee

Introduction MIDP = Mobile Information Device Profile Spearheaded by Sun, Motorola, and Nokia Latest attempt by Sun to bring JAVA into embedded systems, specifically mobile phone

Motivation Behind MIDP Heterogeneous development platforms in mobile phone arena Short product life cycles MIDP attempts to solve that via offering a standard environment for application programmers

What is MIDP? Set of JAVA APIs Implements a MIDlet class Addresses issues such as user interface, persistent storage, networking, and application model Targeted towards mobile phones Basically JAVA for mobile phones

Implementation Stacked on top of Connected Limited Device Configuration (CLDC) and KVM

Implementation (cont) Operates over existing network protocols such as IrDA, Bluetooth, IEEE , and wireless networks Specifications are targeted towards mobile phones Other devices such as PDAs may find more use in a super set of the MIDP APIs

Service Model

Retrieval Medium Verification Figure out which communication device to use (e.g. Bluetooth or IEEE ) Negotiations

Server and mobile device exchange information about the MIDlet and mobile device, respectively Information such as device capabilities (e.g. processing power, volatile memory available), device size, MIDlet requirements may be exchanged

Negotiations (cont) Crux of the useful capabilities offered by MIDP Especially important when it comes to making things work over devices with different sized screens and different capabilities

Installation Download Security Verification Check that the MIDlet does not violate security issues Transformation Convert public representation to internal representation

Launch When selected by user application is moved into KVM and run

Upgrade & Removal Applications can be upgraded when new versions become available An application permanently stored locally on device can be removed from persistent storage when selected for removal by user

Provided by Mobile Device Classes and native code that implements CLDC JAVA Virtual Machine (KVM) Native code for the MIDP

Provided by JVM & CLDC Multi-threading Locking Synchronization Execution of byte code Method dispatching

MIDlet Class All MIDP applications MUST inherit from the MIDlet class Does not have a main() function Cannot call System.exit() It triggers a SecurityException to be thrown

JAVA Packages java.lang.* java.io.* java.util.* javax.microedition.io.* javax.microedition.ui.* javax.microedition.rms.* javax.microedition.midlet.*

javax.microedition.io StreamConnection To open a basic connection that reads/writes simple data. ContentConnection To open a connection that provides content length, type, and encoding information. This interface extends from the StreamConnection interface.

javax.microedition.io HttpConnection To open a connection that provides capabilities to interface through HTTP including getting/setting headers and HTTP-specific handling. This interface extends from the ContentConnection interface.

javax.microedition.ui Offers two major choices in interface design Canvas Used to construct a custom interface using the Graphics object Mainly used for multithreaded games or non-traditional interfaces

javax.microedition.ui Screen For the construction of form based user interfaces

javax.microedition.rms Contains the classes needed to implement a temporary storage database on the device Limited in capabilities because of the restrictions imposed by mobile phones

javax.microedition.midlet MIDlet Used to build MIDP applications

Hello World MIDlet import javax.microedition.midlet.*; import javax.microedition.lcdui.*; public class HelloMidlet extends MIDlet implements CommandListener { // Initialize the Midlet Display variable private Display midletDisplay; // Initialize a variable for the doneCommand private Command doneCommand; public HelloMidlet() { // Retrieve the display from the static display object midletDisplay = Display.getDisplay(this); // Initialize the doneCommand doneCommand = new Command("DONE", Command.SCREEN, 1); }

/** * Create the Hello Midlet World TextBox and associate * the exit command and listener. */ public void startApp() { // Create the TextBox containing the "Hello Midlet World!!" message TextBox textBox = new TextBox("Hello Midlet", "Hello Midlet World!!", 256, 0); // Add the done Command to the TextBox textBox.addCommand(doneCommand); // Set the command listener for the textbox to the current midlet textBox.setCommandListener( (CommandListener) this); // Set the current display of the midlet to the textBox screen midletDisplay.setCurrent(textBox); } /** * PauseApp is used to suspend background activities and release * resources on the device when the midlet is not active. */ public void pauseApp() { }

/** * DestroyApp is used to stop background activities and release * resources on the device when the midlet is at the end of its * life cycle. */ public void destroyApp(boolean unconditional) { } /* * The commandAction method is implemented by this midlet to * satisfy the CommandListener interface and handle the done action. */ public void commandAction(Command command, Displayable screen) { // If the command is the doneCommand if (command == doneCommand) { // Call the destroyApp method destroyApp(false); // Notify the midlet platform that the midlet has completed notifyDestroyed(); } } }

Screenshot

Development Cycle Write application using MIDP APIs Compile Pre-verify Pre-processes the class for use in KVM Test Package classes into a.jar file Test with Package

Hits Simpler development Runs on acceptably well on heterogeneous platforms

Misses Too bloated really for mobile phones Not powerful enough for devices like PDAs and Wireless Internet Appliances that have more resources available Though a superset of the APIs may work fine