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XML in the J2METM
September 29, 2002
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Acknowledgements
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JavaTM Technology and XML Programming for
Wireless Devices - A Primer, TS-1137, JavaOne 2002
Srikanth Raju
Raghavan "Rags" Srinivas
Technology Evangelists
Sun Microsystems, Inc.
Parsing XML in the JavaTM 2 Platform, Micro Edition
(J2METM) - XML in a MIDP Environment, Session
2716, JavaOne 2002
Jonathan Knudsen
Technical Writer
Sun Microsystems, Inc.
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JavaTM Technology and XML
Programming for Wireless Devices – A
Primer
TS-1137, JavaOne 2002
Srikanth Raju
Raghavan “Rags” Srinivas
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The J2ME Platform, CLDC and MIDP
Overview
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Java 2 Platform
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J2ME Configuration
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A configuration for the J2ME platform ("J2ME
configuration") defines a minimum Java platform for:
Broad range of devices in different areas
Similar requirements of memory size and processing
capabilities
A configuration defines
Minimum Java technology libraries
Virtual machine capabilities
Platform Security Model
Defined through the Java Community ProcessSM (JCP)
program
Subject to compatibility tests
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CLDC (Connected, Limited Device
Configuration)
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Targeted at devices with
160KB to 512KB total memory available for Java
technology
Limited power (often battery)
Limited, perhaps intermittent connectivity to a
network (often wireless)
Extremely constrained UIs, small screens
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(MIDP) Mobile information Device Profile
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Targets mobile two-way devices implementing "J2ME
CLDC" (CLDC for the J2ME platform)
Profile addresses
Display toolkit, User input methods
Persistent data storage using simple record-oriented
database model
HTTP 1.1-based networking using CLDC Generic Connection
framework
MIDP 1.0.3 spec and implementation available for
download now
MIDP Next Generation in progress via the JCP
program
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Example: J2ME Platform-based Wireless
Device Stack
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CLDC Networking and I/O
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Standard networking for the J2SE platform, I/O, and
storage libraries:
Are too large for CLDC devices
Assume TCP/IP is available
CLDC specifies a Generic Connection framework,
which enables:
Consistent way of supporting various protocols
Improved portability of applications
Smaller footprint
Usage General form:
Connector.open("<protocol>://<address>:<parameters>");
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Scope of the MIDP Specification
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Application model (lifecycle, packaging)
javax.microedition.midlet.MIDlet
Persistent storage
javax.microedition.rms
Networking
Implements CLDC Generic Connections
javax.microedition.io
User interface support
javax.microedition.lcdui
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MIDP Networking
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MIDP devices must
implement client
portion of HTTP 1.1
protocol
May or may not use
IP-based transport
underneath
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MIDP UI Design Principles
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Must be usable in all devices
One handed, two handed, stylus operation
Small screens (tens of pixels by tens of pixels)
Not all devices have a pointing device
Must constantly think of end users
Mobile Information Devices are consumer products,
not desktop computers
MIDP applications should use simple traversing
and selection metaphors
MIDP applications and native apps should look and
behave consistently on any given device
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MIDP UI: A Tale of Two Layers
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Use the MIDP High-level UI APIs for portability
Apps run in all MIDP compliant devices
No direct access to native device features
High-level UI screens are based upon
javax.microedition.lcdui.Screen
Low-level APIs ("Game" APIs)
Provide access to native drawing primitives, device key
events, native input devices, etc.
Allow developers to choose to compromise portability for
user experience, if required
Handle low level events and drive graphics via
javax.microedition.lcdui.Canvas
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XML Overview
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Java 2 Platform and the Web Services
Model
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SAX: Simple API for XML
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DOM: Document Object Model
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XML Transformations
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XML separates content from presentation
Transformations can be used to convert from XML to
some other format including a new XML file
Transformations can be used to style XML documents
Example of XML transformation:
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XSLT Processor
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Using XML in Enterprise Applications for
the java platform (“Enterprise Java
Application”)
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Using Applets With XML
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Applets can provide client-side processing of
documents
Applets can use DOM to create XML documents and
send them to a server
All validation, parsing and transformation can be
handled by the client
Any XSL stylesheets or DTDs would also have to be
delivered along with classes
Use a jar file for packaging
Apache Xalan can be used from within an applet
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Using “Servlets” With XML
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Java Servlet API-based components
("Servlets")could provide server-side
processing of documents
A client could send data via a form that could
then be used to construct an XML document
Servlets eliminate the need for clients to be
XML-aware
Clients would just see transformed and styled
output (like HTML)
Apache Xalan can be used within a servlet
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Using JSP(JavaServer Pages) Technology
With XML
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The JSP specification-based page ("JSP page") can
handle the task of presentation (the view)
A JavaBeans specification-based component
("JavaBeans component") can be used from the JSP
page to handle client interaction (the controller)
Business methods of the component can manipulate
XML documents (the model)
By ensuring the use of JavaBeans components, a
cleaner separation of view from controller/model is
possible
Use the jsp:useBean tag or custom tags to
manipulate XML documents
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The JMS(Java Message Service) API and
XML
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The JMS API is a Java technology API to a
message service
The JMS API supports both publish/subscribe
and point-to-point
TransportMessage in the JMS API is designed
for XML
By utilizing XML, the data is as transparent as
the messaging system
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Using XML With Databases
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XML is a great fit for representing database content
Tables map directly to an XML element tree
Complex joins could be represented with element
nesting or attributes
The XML tree could be a logical representation of the
data
Each database query could be an XML document
Each database result could become an XML
document
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MIDlet Development Steps
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Here are the steps to follow to create and
execute your MIDlet
Write the "Java code" (Java programming
language-based code)
Compile it
Preverify the class
Create a Manifest file
Package it into a Jar file
Create the MIDlet Descriptor file
Run the MIDlet on the emulator
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Compiling the Source
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Preverifying the Class
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Jar Up the Preverified Class
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Create the MIDlet Descriptor File
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Running the MIDlet
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The J2ME Wireless Toolkit
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Provides two GUI-based development environments
with a choice of emulators
Ktoolbar
The Forte For Java IDE
URL
http://java.sun.com/products/j2mewtoolkit
kToolBar IDE in the J2ME Wireless Toolkit
Use kToolBar to compile, build, and execute a MIDlet with
the Emulator
Use your own editor
Simple to use
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kToolBar (in the J2ME Wireless Toolkit,
v.1.0.4)
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Parsing XML in the JavaTM 2 Platform,
Micro Edition (J2METM) - XML in a MIDP
Environment
Session 2716, JavaOne 2002
Jonathan Knudsen
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Multi-tier System Architecture
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3-tier System Architecture
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Everything Is Small in MIDP
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Network setup is slow
Data rates are slow
Processor is slow
Memory is scarce
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MIDP Clients Need Server Support
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No HTML browsers here
No complex protocols: no JNDI, no RMI
Server steps up to the plate
Mashes data into formats the client understands
Handles complex protocols for the client
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Three Tiers With MIDP
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Parser Roundup
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Don't Supersize Me
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Code size is constrained
JAR size maximum is about 50 kB (varies by
carrier, manufacturer)
Available memory is generally small
Open Source is attractive
Customizable in size and features
Fixable
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Parser Types
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Model
Creates an object representation of a document in
memory (e.g., DOM)
Push
Parses through an entire document, spitting out
events to registered listeners (e.g., SAX)
Pull
Parses a little at a time, returning a single element
or tag
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The Small Parser Lineup
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Links
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Near Misses
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NanoXML 2.2 Lite
6 kB
http://nanoxml.sourceforge.net/
XMLtp 1.7
25 kB
http://members.tripod.de/xmltp/
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Porting Techniques
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Remove features you don…t need
Supply missing classes
java.* naming is questionable
Dummy classes or real implementations
Rewrite unavailable functionality
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Performance Consideration
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Overview
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Not specific to XML applications
An XML parser may push you to the wall
Runtime performance
Connection setup: number of documents
Connection speed: document size
User perception
Deployment
Code size
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Document Design
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Connection setup time is long
Make each document count
Perhaps aggregate documents on the server
Connection speed is slow
Only send essential information
Make documents as short as possible
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Threading
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Network activity has to go in a separate
thread
Don't lock up the application's interface
Ideally, allow the user to do other work while
network activity occurs in the background
Parsing should likely occur in a separate
thread
Depends on your parser
Depends on your document
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Code Size
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Carriers or devices may impose restrictions on
code size
Nextel/Motorola: 50 kB (soft)
Devices don't have much storage space
Wireless bandwidth is small
Code size refers to the size of the MIDlet suite
JAR
.class files
Resource files (images, icons, others)
Use an obfuscator to reduce class file size
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What Does an Obfuscator Do?
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Depends on the product: read the
documentation
Original purpose was to render code
impervious to decompilation
Some possibilities:
Removes unused classes
Removes unused methods and variables
Renames classes, packages and variables
Adds illegal stuff that confuses decompilers
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Using an Obfuscator
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The obfuscator may not play nicely with your
development environment
Build without obfuscation:
Compile  Preverify  JAR
Build with obfuscation:
Compile  Obfuscate  Preverify  JAR
Another possibility:
Compile  Preverify  JAR4Obfuscate  Preverify
 JAR
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Some Free Stuff
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JAX
http://www.alphaworks.ibm.com/tech/JAX/
Removes unused classes and interfaces
Prunes unused methods and variables
Shortens internal method and field names
Retroguard
http://www.retrologic.com/retroguard-main.html
Renames class, method, and field names
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DEMO
An Example: Parsing RSS
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An example of the output from Meerkat
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RSSPaser.java and RSSListener.java
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RSSMIDlet.java
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DEMO
Sample XML Midlet: Interaction with
the Middle-tier
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MIDP and XML-Issues to Be Aware of
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MIDP networking allows access to data
formats such as XML, WML, etc.
XML Parsing == Heavy String Manipulation;
Adding XML parser adds to footprint;
MIDP_NG proposal calls for an XML parser
Of course, as always think about alternatives
Example
XML parsing on the Server instead of the MIDP Client
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ServletXML.java
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ServletXML.java
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ServletXML.java
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HelloMIDlet.java
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HelloMIDlet.java
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HelloMIDlet.java
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HelloMIDlet.java
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HelloMIDlet.java
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HelloMIDlet.java
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Summary
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MIDlet and XML
The J2ME platform, CLDC, and MIDP Technical Overview
XML Overview and XML in enterprise Java technology
Developing a MIDlet - Steps
MIDlet accessing XML data in enterprise Java technology
Three-tier application architecture
May include XML and transformations for different client
types
May make sense to send XML to a MIDP client
Various small parsers exist
Differentiated by execution model, license, size
Optimizations
Document size, network connections
Code size
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Resources
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Parsing XML in J2ME
http://wireless.java.sun.com/midp/articles/parsingxml/
Connected, Limited Device Configuration
http://java.sun.com/products/cldc
Mobile Information Device Profile
http://java.sun.com/products/midp
Download the Sun J2ME Wireless Toolkit:
http://java.sun.com/products/j2mewtoolkit
The J2ME Platform and Wireless Webcasts:
http://java.sun.com/jdc/onlineTraining/webcasts
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참고 서적
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Questions …
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[email protected]