Transcript Programming Mobile and Wireless Devices using J2ME

Programming Mobile
and Wireless Devices
using J2ME
Ola Bø
Molde University College INF 245 Fall 2007
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Motivation
added nov 2005
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Content
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Overview over the J2ME-plattform
Close up of technologies for Mobile and
Wireless applications
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CLDC Connected Limited Device Configuration
MIDP Mobile Information Device Profile
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J2ME in the Java landscape
Set top boxes
Smartphones
(Source
Sun
Microsyste
ms Inc.)
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Problem and solution
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The problem is device heterogeneity
 Memory, Screen, Filesystem, Available storage for libraries,
Camera, GPS, ... differs widely
 That means the Java Platform can not be the same on all
devices
Solution:
 Different configurations and profiles in different devices
 Extensions called JSRs
Nightmare
 Programming an application aimed at a wide selection of
heterogeneous devices is arduous even with J2ME.
 Making the same application ”native” is probably far worse.
 Even if a device has a certain functionality (GPS, Camera, MP3
player...), the functionality can only be controlled from a J2ME
program through a working JSR library in device firmware.
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No library – no control
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add
material from mikkonen
J2ME Configurations
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A configuration sets a standard for the
available Java technology on a class of
devices
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CLDC Connected Limited Device Configuration
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Limited devices (160-512k RAM total for Java)
Mobile phones and PDA’s
CDC Connected Device Configuration
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Set top boxes
High end wireless devices
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material from mikkonen
J2ME Profiles
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MIDP Mobile Information Device Profile
Foundation Profile (non gui networked device)
Personal basis, Personal and RMI Profiles
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JCP Java Community process
JSR Java Specification Requests
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JCP organises further
standardisation of Java
When new requirements
emerges a new JSR is
created
Requirement work is driven
by people from various
industrial companies
JSR makes the extension of
Java flexible
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Implementation of new
JSRs in mobile devices
gives steadily increased
in the potential
functionality of Java
devices
The specifications are
available at jcp.org
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Four Generations Nokia
2002
2003
2004
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2005
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Top end devices
2007
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Sony Ericsson P1
Nokia E90 Communicator
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J2ME for mobile and wireless
devices
Special libraries for mobile and
wireless devices: GUI, storage
A subset of the Java libraries
adapted to a lowest common
denominator for mobile devices
The virtual machine –
corresponding to JVM in
standard Java
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What does CLDC contain
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Core java language and library
Libraries for i/o and communication
Security
Internationalization
The content is partly inherited from J2SE
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java.lang.*, java.util.*, java.io.*
and partly new
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java.microedition.*
And what does CLDC not contain:
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UI, application life cycle, Persistence, and special
interfaces for the device.
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CLDC is limited
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That means some Java language features
are missing
CLDC 1.0
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No Floating point
No Finalization, No Thread Groups, No JNI
Limited Error Handling
CLDC 1.1
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Floating point INCLUDED
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CLDC based classes need
special handlig
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Preverification and
Package steps are
mandatory for classes
to be run over CLDC.
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Supports faster start
up of CLDC based
apps.
Preverification and
packaging may be
done using
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Myapp.jar
Packaging
Command line tools
KToolbar in the WTK
An IDE
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CLDC System Properties
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Can ask for property to ascertain what profile we
have on the device
Can adapt the application to the capabilities of the
CLDC and MIDP present in the device
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java.lang.System.getProperty("microedition.profiles"), will
return "MIDP-1.0" if this is the profile implemented in the
phone.
Other possible properties are for example:
 microedition.platform
 microedition.encoding
 microedition.configuration
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MIDP 1.0
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MIDP 1.0 covers:
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Application Life Cycle
Toolkit for user interface – display and input
Device independent persistent data storage
GCF based networking using HTTP 1.1
New standard MIDP 2.0 released nov. 2002
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There will still be an installed base of MIDP 1.0
devices for some time.
New possibilities in MIDP 2.0 may be enticing
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MIDP applications AKA midlets
JAR
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A MIDP application is called a MIDlet
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Must extend the MIDlet class
A midlet suite is a bundle of midlets.
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File
can access same persistent data
Packaging
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Midlet suites are packaged in JAR files
 The preverified class files in the suite
 Resource files (for example icons,
sounds)
 A manifest with application properties
Each JAR file corresponds to a JAD file
describing its contents for deployment
(name, description, version etc.)
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Provisioning
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Provisioning is getting the application into the
device. Several scenarios for download:
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"Over The Air (OTA) " using HTTP over wireless
protocols
By device synchronization software from a
desktop computer using serial, usb, IR or
bluetooth
Not standardized in MIDP 1.0,
OTA provisioning standardized in MIDP 2.0
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Midlet Application Skeleton
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All MIDlets have this
common skeleton
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Constructor called once
startApp() called at start or
after pause
pauseApp() called at
pause – timer events may
be received
destroyApp() called when
application is terminated
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Application LifeCycle
Initialised and ready to
run
Paused
PauseApp StartApp
DestroyApp
Active
Resources acquired,
application running
DestroyApp
Destroyed
All resources released,
All threads stopped
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Application LifeCycle methods
(source javadoc for class javax.microedition.MIDlet, consult documentation for details)
Called by device
Called by midlet
startApp()*
resumeRequest()
Tells MIDlet it has entered the
active state and can start working
Tells device midlet want to
continue
pauseApp()*
notifyPaused()
Tells MIDlet it has been paused
Tells device midlet wants to pause
destroyApp(boolean)*
notifyDestroyed()
Tells MIDlet to release resources
and stop threads
Tells device midlet wants to be
destroyed. All resources and
threads should already have been
released
* abstract methods, to be implemented by programmer when subclassing
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MIDlet.
OBø
MIDP 1.0 High Level User
Interface
Windowing not appropriate on limited devices
Interface using whole Screens – four kinds
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1.
2.
3.
4.
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Alert - message
TextBox – Editable or non-editable textbox
Form
List
Screens have a title
Commands can be added to screens
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How commands appear is device dependent
(Soft key, Menu item, ... )
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Commands must be handled by class implementing the
CommandListener Interface
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(for further details see javax microedition.lcdui.Command)
Show a screen by using display.setCurrent(myForm)
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TextBox, a high level screen
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Used to show or edit a text on the whole screen
Input constraints specifies content type and other
aspects of the TextBox
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ANY
•PASSWORD
•UNEDITABLE (MIDP 2.0)
EMAILADDR
•SENSITIVE (MIDP 2.0)
NUMERIC
•NON_PREDICTIVE(MIDP 2.0)
PHONENUMBER
•INITIAL_CAPS_WORD(MIDP 2.0)
•INITIAL_CAPS_SENTENCE(MIDP 2.0)
URL
DECIMAL
How are these input constraints related to the limited input
capabilities of mobile devices and to the T9 algorithm?
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Texbox Code
Title
Command
Initial text
Constraint
Maximum
text length
Soft Key
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MIDP UI – Alert a high level
screen
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Used to show a message
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A timeout can be set
An image can be added
A gauge can be added showing progress (MIDP
2.0)
Is displayed by a special version of
display.setCurrent(Alert,Screen)
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The second parameter is what to display when alert
screen gone. (display.getCurrent can be used here)
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Alert and CommandListener
Code
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List
Uses the whole screen for a list
Three use scenarios depending on
Choice.type
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1.
2.
3.
IMPLICIT selecting invokes command
EXCLUSIVE selecting one deselects previous
MULTIPLE selecting more than one possible
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Code for Implicit List
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Code for Multiple List
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Code for implicit list
String[] elements = { ... }; //Menu items as List elements
List menuList = new List("Menu", List.IMPLICIT, elements, null);
Command selectCommand = new Command("Open", Command.ITEM, 1);
menuList.setSelectCommand(selectCommand);
menuList.setCommandListener(...);
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Form
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A form displays a number of Items
Items can be:
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Commands can be connected to Items
Layout is specified both in form and in items
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Texfield for flexible text entry
StringItem for text display
ImageItem for image display
DateField for date display and entry
Choicegroup selectable list of text and/or images
Gauge a bargraph display of a numeric quantity
CustomItem an item you can develop
Spacer, a layout assistance item
Layout directives are hints only.
If form too high for display, it will scroll
What Items where used on the form shown?
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ImageItem, StringItem
two
Textfields
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High Level Interface – an Overview
Same Form, different devices,
different results
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Form Code
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High level UI – Form
an overview
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Guidelines for UI Design
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HCI on mobile and wireless devices a challenge!
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Use simple forms with few Items
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Small screen means small changes not easy to spot
Use uniform appearance for easy learning
Always provide commands like OK, BACK and EXIT on screen
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Remember: Small screen size, mobile context of use
Can you avoid scrolling?
Minimize input, use RMS to store user settings
Use static form content
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Why?
use uniform command configuration on all forms to ease
learning and use
Use soft keys rather than on-screen keys
Use Threads and Gauges to avoid UI-blocking during network IO
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improves user experience
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Top 10 Usability Guidelines
for Enterprise Applications
(Nokia 2004) http://www.forum.nokia.com/main/0,,23_56,00.html#tips
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Provide a clear navigation model
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Use familiar language
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Short network coverage problems should not stop or cause loss of users' work
Connection status should be displayed clearly.
Synchronization should be automatic but under user control.
Provide useful feedback
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Terminology familiar to target users should be used instead of technical terminology.
Terminology should be consistent with the Series 60 UI style.
Target users’ native language should be used.
Hide the complexity of connectivity
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Core features of the application should be available from the main view.
Navigation model should be focused on the main tasks.
Advanced functionality should be hidden from novice users.
Let the user know if an action was succesful or not.
If processing takes more than 0.5 seconds, indicate that something is happening.
Be consistent with controls
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Minimize errors and the need for learning by using softkeys as in the Series 60 UI style
Build shortcuts for advanced users, use shortcuts similar to other applications.
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More guidelines
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Provide a simple Options menu
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Use tabs wisely
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Instead of text entry, prefer alternative forms of information entry, such as selecting
from a list or capturing images.
Offer reasonable default values.
Information presentation
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The most essential functionality should be provided in the first tab. Underlying tabs can
be used to hide advanced functionality.
If more than five tabs are needed, use a list for accessing the tabs (see the Settings
application).
Text is preferable to icons in tab titles.
Make entering information easy
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Navigation key default action(s) should also be available in an Options menu.
Sort items in the Options menu according to Series 60 UI Style Guide.
Main actions should be available without scrolling.
Display the most relevant information first.
Essential information should not be displayed with icons only.
Use colors and symbols for highlighting and grouping items.
Provide Help
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Context-sensitive help should be provided in the application.
More detailed help should be provided on a Web site or in the user guide.
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Low Level UI – Canvas
Li and Knudsen Chapter 4
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Canvas is a displayable that is completely controlled
by program
An application can combine canvases and screens
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A list to choose racing track
A canvas to do the racing
Methods to handle game actions and pointer events
A Canvas must be subclassed!
paint method for painting must be implemented
The paint method provides a Graphics object having
methods for painting
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Canvas methods
Event delivery methods used to send events to application. Event delivery methods are called
serially
showNotify() // called before canvas becomes visible
hideNotify() // called after canvas has been hidden
keyPressed(), keyRepeated(), keyReleased()
pointerPressed(), pointerDragged(), pointerReleased()
(hasPointerEvents() checks if device supports a poiner)
paint() // tells app to paint screen again. (Not to be called by app)
sizeChanged()
Methods used by application to learn the meaning of the key pressed
getKeyCode() (returns KEY_NUM0..KEY_NUM9, KEY_STAR,...)
getGameAction() (returns UP, DOWN,.., FIRE, GAME_A, ..,GAME_D)
getKeyName() (returns a text describing the key)
Methods used by application
repaint() requests repaint of whole or partial screen
serviceRepaints() forces pending repaint requests
callSerially()
setFullScreenMode(boolean)
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Graphics Methods
DrawLine
DrawRect
DrawRoundRect
FillRect
drawString
drawArc
FillArc
drawChar
drawChars
drawImage
drawRegion
setFont
setColor
setStrokeStyle
setClip //sets region that will be changed by drawing
translate //sets origin for drawing
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Low Level UI, an overview
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MIDP 1.0 Communication
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Device must implement
a HTTP 1.1 client
interface
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Transport is not
necessarily over TCP/IP
Source: Bill Day J2ME
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Networking using GCF
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Need a more compact solution, than the standard
libraries
GCF: General Connection Framework is the answer
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In GCF all protocols can be specified using an URLapproach:
Connector.open("<protocol>://<address>:<parameters>")
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But no network protocol is mandatory in CLDC
What protocol can actually be used depend on the device
and the profile
Examples
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Connector.open("http://www.sis.pitt.edu/mwap/test.html")
Connector.open("file://pictures/picture12.jpg")
Connector.open("comm://9600:18N")
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SMS-messaging from Java ch11
WMA Wireless Messaging Api – JSR 120
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Supports
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sending ordinary SMS
App to App communication using SMS over a port
Simple API
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Connector
MessageConnection
Message
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BinaryMessage
TextMessage
MessageListener
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WMA-an overview
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Persistent storage
Li and Knudsen chapter 8
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Problem and solution
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Device storage mechanisms far from standardized
MIDP provides a standardized interface to device storage
called Record Management System – RMS
The Device platform – that is the MIDP implementation for
the device is responsible for best effort storing to what
media is available.
Atomic, synchronous, serialized record updates
guaranteed by implementation (no manual locking)
RMS store data as byte arrays in a named
RecordStore. Each byte array is accessible via an
integer record number. (A very crude solution indeed
– but standardized )
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Persistent storage methods
(Source Javadoc for class javax.microedition.rms – consult documetation for details)
static RecordStore openRecordStore(String recordStoreName,
boolean createIfNecessary)
Open (and possibly create) a record store associated with the given MIDlet
suite.
closeRecordStore()
This method is called when the MIDlet requests to have the record store
closed.
static void deleteRecordStore(String recordStoreName)
int addRecord(byte[] data, int offset, int numBytes)
void setRecord(int recordId, byte[] newData, int offset,
int numBytes)
byte[] getRecord(int recordId)
RecordEnumeration enumerateRecords(RecordFilter filter,
RecordComparator comparator, boolean keepUpdated)
Returns an enumeration for traversing a set of records in the record store in an
optionally specified order.
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Transfer from/to record store
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A record may be assembled with a DataOutputStream
ByteArrayOutputStream baos=new ByteArrayOutputStream(barr);
DataOutputStream dout=new DataOutputStream(baos);
dout.writeUTF(url);
dout.writeInt(qid);
dout.writeLong(timestamp);
dout.flush();
answerStore.addRecord(baos.toByteArray(),0,baos.size());
dout.close();
baos.close();
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A Record may be disassebled with a DataInputStream
RecordStore answerStore=RecordStore.openRecordStore(”answer”,true);
ByteArrayInputStream bais=new
ByteArrayInputStream(answerStore.getRecord(recordid)):
DataInputStream din=new DataInputStream(bais);
String url=din.readUTF();
int qid=din.readInt();
long timeStamp=din.readLong();
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