Java ME Networking

Bruce Scharlau, University of Aberdeen, 2010

Java ME Networking

Mobile Computing

Some slides from MobEduNet

This covers HTTP in detail, and mentions other means. Bluetooth will be covered later.


Getting the application onto the device with OTA

OTA is Over the Air provisioning and lets users acquire the jad/jar as required via their browser

http://developers.sun.com/mobility/midp/articles/ota/


OTA using Java


OTA can be done with Antenna• The following steps are necessary to run the OTA servlet: • Install a servlet-capable Web server• Add a new Web application under "<tomcat>/webapps". • Copy the "web.xml" file from the "etc" directory of the Antenna source

distribution to "WEB-INF" and adjust. Copy the "antenna-bin.jar" binary distribution file to "WEB-INF/lib".

• You should have a working configuration now. If the servlet URL is "http://localhost/antenna", the HTML and WML pages are available as "http://localhost/antenna/index.html" and "http://localhost/antenna/index.wml", respectively.

• Test deployment by running the "deploy" sample (modify "build.xml" first).

• To create your own layout for the pages, copy the two files from the "res" directory of the Antenna source distribution (or from CVS) to "WEB-INF" and modify them. There's documentation inside the "index.html" file that tells you how to do this.

http://antenna.sourceforge.net/index.php


Servlet templates are provided

OTAServer (servlet) available under C:\Java\antenna-src-1.2.0\src\de\pleumann\antenna\http

OTAServer (servlet) available under C:\Java\antenna-src-1.2.0\src\de\pleumann\antenna\http


Java uses Internet for direct connections

http://developers.sun.com/mobility/midp/articles/network/

Network operator


Java end to end is possible

From pdfs at:http://java.sun.com/blueprints/guidelines/designing_wireless_enterprise_applications/index.html


CLDC - GCF

• Connected Limited Device Configuration offers Generic Connection Framework– Takes in URI as String and returns a

connection object– All use pattern of:

<protocol>://<address>;<parameters>


MIDP 2.0 Additions moved beyond required HTTP

• Added other interfaces and classes– HTTPSConnection for secure http connections– PushListener for use with PushRegistry and listens for

inbound connections– SecureConnection to establish SSL or TLS connections– SecurityInfo interface provides methods to access

secure networks– ServerSocketConnection defines this type of connection– UDPDatagramConnection


‘extra’ APIs can enhance applications

Just remember that they are ‘optional’, so may not be available

http://java.sun.com/javame/overview/products.jsp


Network URIs

• http://java.sun.com for HttpConnection• socket://time-a.nist.gov:13 for StreamConnection• serversocket://:4444 for StreamConnectionNotifier• comm:0;baudrate=2400 for CommConnection• datagram://127.0.0.1 for DatagramConnection• file://address.dat for FileConnection• “bluetooth://psm=1001” for StreamConnection


Generic Connection Framework


Variety of Interfaces used for connections

• Connection (basic, generic connection)– close method– open method defined in Connector-class

• InputConnection (capabilities needed in input stream connection)– openDataInputStream, openInputStream

• OutputConnection (capabilities needed in output stream connection)– openDataOutputStream, openOutputStream

• StreamConnection (combines input and output)– All methods inherited

• ContentConnection (defines streamconnection over which content is passed)– getEncoding, getType

• CommConnection (defines a logical serial port connection)

• SocketConnection (defines socekt stream connection)

Connection

InputConnection

OutputConnection

DatagramConnection

StreamConnectionNotifier

StreamConnection

ContentConnection

HttpConnection

HttpsConnection

CommConnection

SocketConnection

SecureConnection


Basic Architecture is simple

Internet MIDPDevice

Web Server

User requests information from an Application (e.g. MyServlet)

Web server passes output from MyServlet back to the MIDlet

Web Server launches MyServlet program and sends it parameters the MIDlet requested

Web Server retrieves output fromthe MyServlet


What is needed ?

• MIDlet & MIDP Device

• Servlet & Web Server

• Connection between MIDP Device & Web Server

• Common Protocol between MIDlet and Servlet


Opening a Connection is easyConnection throws IOException so can report errors back to

application

try {Connection connection = Connector.open(http://java.sun.com);} catch (IOException ioe) {//report error}

Connection also has close() method

MIDP 3 is MSA(Mobile Service Architecture)

• Aims to provide wider functionality for mobiles

• Should work with CDC and CLDC devices

• Should allow RFID and NFC object communication

• Should enable XML parsing



On Beyond Basics• web services via SOAP and REST

• RMI

• Location API

These require extra librariesThese require extra libraries

Need to check that they are present on deviceNeed to check that they are present on device


Use JSR 179 and JSR 280 to parse RESTful XML

http://developers.sun.com/mobility/midp/articles/parsingxml/

Parse the XML to object on handsetParse the XML to object on handset

Check links on course web siteCheck links on course web site


XML parsing requires several files

Go togetherGo together

Midlet plus parser handler class, and object class

Parsing errors not always obvious


midlet parsemidlet handlerorg.xml.sax.SAXParseException: - com.sun.ukit.xml.SAX$Parser.panic(), bci=6 - com.sun.ukit.xml.Parser.setinp(), bci=237 - com.sun.ukit.xml.SAX$Parser.parse(), bci=36 - com.sun.ukit.xml.SAX$ParserImp.parse(), bci=56 - com.auction.j2me.MyParsingMIDlet.loadXML(), bci=33 - com.auction.j2me.MyParsingMIDlet$1.run(), bci=11midlet alert

Need to catch errors, but sometimes only the emulator that causes problems


Need to use threads for multi-tasking in application

Start a connection in a new thread so the application doesn’t hang while waiting for a response


Wrap thread for connection in try/catch

public void commandAction(Command c, Displayable arg1) {if (c == mExitCommand) { notifyDestroyed();} else if (c == mLoginCommand) { login();} else if (c == mBackCommand) { mainMenu();} else if (c == mHelloCommand) {Thread thread = new Thread() {public void run() {try {invokeServlet();} catch (IOException e) { e.printStackTrace(); } } }; thread.start();} }


Duke’s Auction has two versions

AuctionServlet AuctionByteServlet

Use StringsUse Strings

Use bytes to determine optionsUse bytes to determine options


Bytes are easier to organise

Pass byte as option


Methods are similar

Get parameter (optional), create message, write reply


MIDlet works with bytes anyways

Same as hello() on next slideSame as hello() on next slide


Binary response to Midlet

Same as invokeServlet()Same as invokeServlet()


Round trip with octet-stream from client to servlet



Binary code makes it a pure Java solution

Tightly coupled to the service.Tightly coupled to the service.

Need to use web services to interoperate with other systems.

Need to use web services to interoperate with other systems.

A change in one will require change in otherA change in one will require change in other


There are trade-offs between binary and XML



Need to consider state in application

As with web apps, need to determine if, and how you will deal with state


Sessions can maintain state the same as in regular web applications

Use either cookies or, preferably, URL rewriting

However, network operators can mangle the headers though, so don’t rely upon them

However, network operators can mangle the headers though, so don’t rely upon them

Some operators use transcoding, which messes up your application See: http://wurfl.sourceforge.net/manifesto/index.htm for details


Object reuse and development

Same code in servlet and MIDletSame code in servlet and MIDlet

Repeated code in MIDletRepeated code in MIDlet

Need process such as Ant to cope with this, or use other solution

Need process such as Ant to cope with this, or use other solution


Use same OOD principles for MIDlets as for other code

Refactor out methods classesRefactor out methods classes

Apply design patterns as appropriate Apply design patterns as appropriate

Remember that it’s mobile, so constrain for reduced memory

Remember that it’s mobile, so constrain for reduced memory


Abstract out repeated code into methods

AuctionMIDlet repeats lots of code so that it’s clear what’s happening.

These could be removed to a method, or separate class – connection, try/catch, etc

There is also the issue of the shared code between the servlet and MIDlet


Extend Ant to cover building of web and midlet suite

Use Ant and Antenna to build whole application

Build MIDletBuild War

Deploy MIDlet Deploy War

Integrate and copy code as required


Summary

• Can use variety of means to connect Java ME devices to a network via GCF

• All MIDP 2.0 devices support at least HTTP – need to check for capabilities

• Sometimes need to share code across platforms (server and Java ME client) to ease programming

Java ME Networking

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