1. Java 2 Micro Edition Mano Chen Senior Technical Consultant
Sun Microsystems

2. Computing Is Becoming Ubiquitous
Mainframe era
One computer, many users
PC era
One computer, one user
Consumer era
One user, many computers, and these computers are networked

3. A Game What am I? I have the following: CPU some memory screen
keyboard
networked
runs applications

4. Meet Your New Computers

5. Agenda
Overview of J2ME
Developing J2ME Application

6. Agenda
Overview of J2ME
Developing J2ME Application

7. Problems No software market !!! Everything is proprietary
Hardware, software and tools
Handsets are useless without a network
No compelling content

8. J2ME is the Solution Designed for small devices
Online and offline activities
Rich user and network interaction models
Fully programmable
Portable

9. Where Does J2ME Fit In?

10. J2ME Configurations and Profiles
Java HotSpot ™
Java Virtual Machine (JVM)
Card VM
Java Programming Language
Java 2
Enterprise
Edition
(J2EE)
Core APIs
Standard
(J2SE)
Java 2 Micro Edition Core APIs
Personal
Profile
RMI
Other
CDC
Profiles
...
Foundation
Mobile Information
Device Profile
Optional
Packages
Java™ 2 Platform, Micro Edition (J2ME™) encompasses VMs and core APIs specified via Configurations as well as vertical— or market-specific—APIs specified in Profiles
KVM
Java Card APIs

11. What Is a Configuration?
Defines the minimum capabilities and libraries for a JVM that will be available on all devices belonging to the same “horizontal” family of devices
Similar requirements in memory size and processing capabilities
Subject to compatibility test
Two configuration defined
Connected, Limited Device Configuration
Connected Device Configuration

12. Connected Limited Device Configuration
Targeted at devices with
160KB to 512KB total memory available for Java™ technology
Slow processor
Limited power (often battery)
Limited, perhaps intermittent connectivity to a network (often wireless)
Extremely constrained UIs, small screens
CLDC 1.0 specification available for free download now
Sun provides CLDC reference implementation built using the KVM

13. What Is a Profile?
A collection of Java technology-based APIs that supplement a Configuration to provide capabilities for a specific “vertical” market or device type
Adds features that are specific to a certain device category such as cell phones or PDAs
One profile defined
Mobile Information Device Profile

14. Mobile Information Device Profile
Targets mobile two-way communication devices implementing J2ME CLDC
Profile addresses
Display toolkit, User input methods
Persistent data storage using simple record-oriented database model
HTTP-based networking using CLDC Generic Connection framework
MIDP 1.0 spec and implementation available for download now

15. CLDC and MIDP Architecture
MIDP Profile
Applications
OEM
MID Profile
CLDC (KVM)
Operating System
APIs

16. MIDP Application Lifecycle
Pause
Active
Destroyed
startApp
destroyApp
pauseApp
MIDP applications are known as “MIDlets”
MIDlets move from state to state in the lifecycle, as indicated.
Start – acquire resources and start executing
Pause – release resources and become quiescent (wait)
Destroy – release all resources, destroy threads, and end all activity

17. Typical J2ME Technology Stack
Mobile Information Device Profile
KVM
CLDC = KVM + J2ME Core APIs in this example
DSP chip (e.g., ARM)
J2ME core APIs
Your
MIDlet
Yellow Pages, train schedules and ticketing, games…
UI, HTTP networking...
Threads, no Floats…
32-bit RISC, 256K ROM, 256K Flash, 64K RAM

18. MIDlet Suite MIDlets are package as a JAR
MIDlets that are in the same suite can access each others database
A descriptor file contains information pertaining to the suite
Vendor name, version, size
Name of each MIDlet
Icons

19. Application Loading Process
Web Page
JAM
Downloads
App
User
Selects
Advertise
App on
Network Transfer
Java Application
Manager
(Name,
Version,
Size, …)
Jar File
Descriptor
File

20. J2ME Application Screenshots

21. Agenda
Overview of J2ME
Developing J2ME Application

22. J2EE Architecture Client Tier Web Tier EIS Tier Integration Tier
Business Tier

23. Key J2EE Components Enterprise Java Bean Servlet Java Server Pages
Business logic packaging, distribution and access
Servlet
Java classes that extends the function of a web server
Java Server Pages
Templates used to generate content dynamically
J2EE Connectors
Generic access to back end EIS

24. Example of A J2EE Application
EJB is used to encapsulate business logic and apply them to EIS back office systems
Servlets are used to co-ordinate the interactions between users and EJBs
JSPs are used to present forms, information and results back to the user

25. J2ME To J2EE Communication
HTTP
HTML Servlet
J2ME Servlet
EJB
Container
Web
J2EE Application Server
forward
lookup
Book

26. Handling J2ME Client A request is made to the servlet
Process the request
Servlet determines if the type of client
Redirect to J2ME servlet for all J2ME client communications

27. Design Issues
Networking
Application messages
Working offline
Security

28. Networking J2ME side J2EE side
Use HTTP 1.1 – requirement for all MIDP devices
Use GET and POST communicating with web tier
Client is responsible for HTTP headers and data
J2EE side
Use servlet to handle client request

29. MIDP Networking – Request
01 String url = “ 02
03 HttpConnection con = (HttpConnection)Connection.open(url);
04 con.setRequestMethod(HttpConnection.POST); 05
06 con.setRequestProperty(“user-agent”, “CLDC-MIDP”);
07 con.setRequestProperty(“content-language”, “en”);
08 con.setRequestProperty(“content-type”
09 , “application/x-www-form-encoded”); 10
11 switch (con.getResponseCode( )) {
12 …

30. MIDP Networking – Response
01 InputStream is = con.openInputStream(); 02
03 if (is.getType( ) != “application/mybook-encoding”)
04 // Reject data stream 05
06 byte buffer = new byte[256];
07 int size;
08 while ((size = is.read(buffer)) != -1) {
09 // Do something with data 10
11 is.close( );
12 // Display the data

31. Servlet – Existing 01 public void doPost(HttpServletRequest req,
02 HttpServletResponse res) … { 03
04 // Looks up book
05 String isdn = req.getParameter(“isdn”); 06
07 if (req.getHeader(“user-agent”).equals(“CLDC-MIDP”) {
08 RequestDispatcher rd = req.getRequestDispatcher(
“MIDPcommunications”);
10 rd.forward(req, res);
11 return;
12 } 13
14 // Normal processing

32. Servlet – MIDP Servlet 01 public void doPost(HttpServletRequest req,
02 HttpServletResponse res) … { 03
04 res.setContentType(“application/mybook-encoding”); 05
06 ServletOutputStream os = res.getOutputStream( );
07 // Write data out 08
09 os.flush( );

33. Application Messages Since 3G is NOT with us yet… Conserve bandwidth
Send only the necessary data
Accommodate high latency
Send all required data in a single message
Use Gauge to provide progress indication
Message encodings
Use binary messages
Don’t use XML!!!

34. Working Offline MIDP supports record oriented database
Data can be stored locally on the CLDC device
Information stored in local databases can be manipulated
Need to implement data synchronization

35. Security – Authentication
Build HTTP basic authentication into MIDP application
Servlet Container
WWW-Authenticate: Basic realm=“fred”
Authorization: Basic QWxhZGpbjpvcG…
GET /get_list.html HTTP/1.1
01 if (con.getHeaderField(“www-authenticate”) != null) {
02 String authString = Base64.encode(login + “:” + password);
03 con.setRequestProperty(“authorization”, “basic “ + authString);
04 if (con.getResponseCode() != HttpConnection.HTTP_OK) {
05 // Do something …
06 else

36. Security – Authentication
Use JSP/Servlet form login
Use j_security_check method for authentication
Required parameters are j_username and j_password
01 String url = “
02 url += “?j_username=“ + username;
03 url += “&j_password=“ + password;
04 HttpConnection con = (HttpConnection)Connection.open(url); 05
06 con.setRequestMethod(HttpConnection.POST);

37. Security – Secure Transport
HTTPS is not a requirement for MIDP 1.0
However…
Vendors are implementing them
J2ME for Palm supports HTTPS
HTTPS support targeted for MIDP-NG

38. Summary Designed for small handheld devices Easy to program
Works with J2EE
It’s real and its available now!!!!

39. Getting Started on J2ME Java2 Standard Edition
Java2 Micro Edition Wireless Toolkit t/

40. Thank You