slides - Electrical and Information Technology

An Introduction to the Java ME Project

Jens A Andersson

Agenda  Java ME  MIDlets  NetBeans  Your task: The Application  Simple Session Protocol and SSPServer  SSP help classes  Why Threads

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Java ME 

Sun groupes its Java technologies into 3 editions: • • •



Java EE (Java Enterprise Edition) - servers Java SE (Java Standard Edition) – personal computers Java ME (Java Micro Edition) – mobile phones and PDAs

In this course we will use: •

MIDP (Mobile Information Device Profile) •

•

MIDP 1.0, 2.0, and 2.1 – backward compatible

CDLC (Connected Limited Device Configuration) •

CLDC 1.0 and 1.1 – backward compatible

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MIDlets  An application written for MIDP is called a MIDlet.  All MIDlets extend the MIDlet class: • public class MyMIDlet extends MIDlet { }

 The MIDlet class provides methods for starting, pausing,

and terminating the MIDlet application: • startApp() • pauseApp()

• destroyApp(boolean unconditional)

 The department has four Sony Ericsson K700 phones that

support MIDP 2.0. 4/12

A Complete MIDlet Example import javax.microedition.midlet.*; import javax.microedition.lcdui.*; public class HelloMIDlet extends MIDlet { public void startApp() { TextBox textBox = new TextBox(“My MIDlet", "Hello world :=)",15,0); Display.getDisplay(this).setCurrent(textBox); } public void pauseApp() { } public void destroyApp(boolean unconditional) { } } 5/12

NetBeans  NetBeans is a free and open-source IDE (Integrated

Development Environment) for developing Java applications.  NetBeans runs on Windows, Linux, Mac OS, etc.  It has support for CLDC 1.0/1.1 and MIDP 1.0/2.0/2.1.  With NetBeans you can write, emulate, and debug

applications for mobile phones. So they contain all you need to develop Java ME applications.

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Application (overview) Peer-to-peer application:  Of your choice

 Minimum: Simple chat application

Two mobile devices communicate and exchange messages Session server (hub/proxy) to find other party

Application (considerations) Hub to find other party NAT makes it impossible to communicate directly between mobile devices Proxy for two-way communication (tunnelling)

Application (figure) NAT!

Global addresses Private addresses Private addresses

NAT & PAT NAT = Network Address Translation PAT = Port and network Address Translation

zFigure 19.27

Translation

Alternative: Source address 200.24.5.8 goes here

Simple Session Protocol SSP UDP based Control messages Data/Tunnel messages

The SSPServer  SSP (Simple Session Protocol) is a simple protocol

developed for this course.  SSPServer is a Java SE application and allows mobile phones

to communicate to each other through a server.  Two ways of using the SSPServer: • Download and run it locally on any computer – connect your

application to port 3333 on localhost • No downloading needed - connect your mobile phone to port 3333 on sspserver.eit.lth.se (public address)

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SSPServer Users login/logout Holds a list of active users/opponents Controls state also on clients Reacts only on incoming packets  (no time outs)

Forwards application data to other party  TUNNEL

SSP packet format TYPE ID (1)

DATA (variable)

TYPE ID  CONTROL

0x01

• (The following data is control data)

 TUNNEL

0x02

• (The following data is application data)

Control Header Format TYPE ID (1)

CTRL TYPE ID (1)

USER ID (8)

PEER ID (8)

0x01

CTRL TYPE ID  LOGIN REQ

0x11

• (The user logs in with the specified user id)

 LOGIN ACC

0x12

• (The user login is accepted by the hub)

 LOGIN REJ

0x13

• (The user login is rejected by the hub)

 LOGIN ERR 0x1f • (Server in LOGIN state but receives ctrl packet for other state)

Control Header Format (cont)  TERMINATE REQ

0x21

• (The user/hub terminates and is logged out)

 SETUP LST REQ

0x04

• (The user requests a list over available opponents from the hub)

 SETUP LST RES

0x05

• (The hub sends a list with available opponents)

Control Header Format (cont)  SETUP REQ

0x01

• (The user requests the specified user as an opponent)

 SETUP ACC

0x02

• (The user accepts request from other user)

 SETUP REJ

0x03

• (The user rejects request from other user)

These ctrl packets are forwarded by the hub to the users.

Peer lists CONTROL HEADER (16)

NBR PEERS (1)

PEER1 (8)

SETUP LST RES  List of available opponents  From Hub to mobile device

PEER2 (8)

PEER3 (8) ...

Tunnel Header Format TYPE ID (1 )

RESERVED (1 )

USER ID (8)

PEER ID (8)

DATA (variable)

0x02

USERID = you; PEERID = opponent Your application protocol goes in the DATA field

Application Sequence Login to server If accepted  get user list  select peer  request session with peer

If accepted  Start ”application” and data transfer in tunnel

At end logout from server

SSP Java class Methods for datagram  Parse request  Build request  Validate request

See API on project web page for details  http://www.eit.lth.se/index.php?id=javame

ByteString Java Class Application data type = String DatagramConnection (sending/recieving UDP datagram) uses byte[ ] ByteString: ”interface” between String and byte[ ] See API on course home page for details

Application protocol Data transfer in UDP based tunnel  Best effort!

Application shall handle errors!  Time outs  Packet loss

 Packet out of sequence

How? You decide!  Select/Design error handling method

Tunnel Header Format TYPE ID (1 )

RESERVED (1 )

USER ID (8)

PEER ID (8)

DATA (variable)

0x02

Your application protocol goes in the DATA field

Applications protocol (cont.) Is control information needed? Keep track of messages/datagrams/packets? How is DATA field interpreted? …

This is your task for section 2

GUI GUI is handled by main thread

inhibited when waiting for response in your methods  Send REQ, Get response  Wait for move from opponent

GUI events must be handled!

An application “The Application” MyMIDlet startApp

commandAction

An application (cont.) “The Application” MyMIDlet startApp

GUI “stalled”

commandAction . . wait for response .

An application (cont..) “The Application” MyMIDlet startApp

GUI active

commandAction . . wait for response in thread .

Threads (cont.) Send REQ  application waiting for GPRS setup?  application waiting for free GPRS slots?  application sending datagram?

GUI blocked until Send REQ is completed

Threads (cont..) Get Response  application setup GPRS etc?  application waiting for incoming datagram?  application waiting for response from opponent?

GUI blocked until Get Response request is completed

Threads (cont…) Do in parallel thread  Send REQ  Get Response

In main thread  Wait for completion of parallel threads

 Handle GUI exceptions

Get Started! 1) Visit the home page of the project:

http://www.eit.lth.se/index.php?id=javame 2) Download the SSPServer and run it locally. 3) Download the skeleton code and run it. 4) Study and understand the structure of the skeleton

code.

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