XML in the J2METM

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XML in the J2METM

• September 29, 2002
• from Yongwoos Park

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Acknowledgements

• 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

4
The J2ME Platform, CLDC and MIDP Overview
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Java 2 Platform
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J2ME Configuration

• 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)

• 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

• 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

• 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("//")

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Scope of the MIDP Specification

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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 jspuseBean tag or custom tags to
  manipulate XML documents

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The JMS(Java Message Service) API and XML

• 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

• 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

• 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

• 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

• Network setup is slow
• Data rates are slow
• Processor is slow
• Memory is scarce

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MIDP Clients Need Server Support

• 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

• 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

• 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

• 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

• Remove features you dont 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

• 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

• 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

• 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

• 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?

• 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

• 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

• 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

• 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

• 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

• Parsing XML in J2ME
• http//wireless.java.sun.com/midp/articles/parsing
  xml/
• 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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?? ??
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Questions
from Yongwoos Park ywoopark_at_penta.co.kr