The 21th century Repairman Agenda Introduction J2EE J2ME Demonstration.
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The 21th century Repairman Agenda Introduction J2EE J2ME Demonstration
Goal of the project The purpose of this project is: To get some experience with J2EE Investigate some of the possibilities with J2ME Build a semi-large distributed system
Pervasive Repairer We ended up with a system intended to support situated and distributed work of a repairer, who is working with large technological systems.
System overview Administrative clerk Company Server (J2EE) The repair company The situated repairer Customers place Subcontractor companies DB Http Vendor Subcontractor Manager XMLSOAPXML Interactive web services
Server side architecture J2MEWebSessionEntity Presentation Layer (Servlet/JSP) Business Layer (Session Beans) Model Layer (Entity Beans) J2ME FLAF / HTTP Web HTML / HTTP DB Container Managed Persistence Value Objects
Client(J2ME)-server interaction Client: a wireless, handheld device (cell phone, PDA): Limited resources (memory, CPU), limited connection bandwidth, reduced facilities for user interaction, etc. etc Challenges: –Minimize number of request-responses –Minimal amount of data sent per response –On the server side: minimize number of requests to session beans –Do as much data processing as possible server-side
Client-server interaction II A collection of Java Servlets translate value objects, supplied by session beans, to flat strings of data Data transmitted to J2ME client in HTTP headers – eases parsing on the client side This defines a protocol for sending data to J2ME client
Client-server interaction III Lists of objects (e.g. product types, orders) - the client requests a specific part of the list; detailed data only sent upon request Session tracking implemented (unable to use javax.servlet.http.HttpSession with J2ME client) Thread-safety
Deployment – what’s in it? IBM WebSphere, Device Developer –Create MIDlet suite –Install and run application: Run on handheld target device iPAQ –Install VM: copy files from workstation to iPAQ –Install Wireless communication card driver from workstation.
Evaluation: J2EE Advantages –A lot is granted: Transaction, Scalability Disadvantages –Hard to understand errors (combination of deployment description and Code) –Immature tools. Bugs, User Interfaces not always intuitive.