JDJ 10-1.indd - sys-con.com's archive of magazines - SYS-CON Media

FeatureJAVA TECHNOLOGYToys or tools?FORTHEWIRELESS INDUSTRYby David Parsons, Ilan Kirsh,and Mark CranshawDavid Parsons is asenior lecturer ininformation systems atMassey University, Auckland,and a knowledge engineerfor Software EducationAssociates, Wellington.Until last year he wasthe director of emergingtechnologies at Valtech,London, and prior tothat, principal technologistat BEA Systems.d.p.parsons@massey.ac.nzThe Java Technology for the Wireless Industry specification(JTWI) encompasses a standard set of J2MEAPIs for mobile device development that is beingwidely adopted by mobile telephone service providers,making it an important platform for Java developers.Its core component, the Mobile Information DeviceProfile (MIDP), provides a number of specialized librariesfor multimedia and games development; however,its underlying subset of general purpose Java classes isstrictly limited. In addition, support for persistence viathe Record Management System is relatively poor. Thisraises an important question: Is JTWI a realistic applicationdevelopment tool or is it only good for games andother software trivia?In this article, we try to answer this question by exploringthe viability of MIDP as a tool for nontrivial applicationdevelopment. An enterprise application that includesmobile components might reasonably expect to devolvesome of its business processes and data management tomobile devices. Our chosen example, which considers bothof these aspects, is a proposed implementation of the JavaData Objects (JDO) specification. This includes a number ofinteresting features that highlight the constraints of workingwith J2ME APIs for limited devices. We describe the issuesaround the development of such an implementation andthe limitations that MIDP imposes, suggest some usefulworkarounds and architectural options, and finally drawsome conclusions about the usefulness of JTWI as a set ofAPIs for serious application development.IntroductionHandheld computers, such as the Pocket PC and the Palm,can support reasonably complete Java Application ProgrammingInterface (API) sets that can be used to develop seriousenterprise applications. However, smaller devices, such asmobile telephones, only support Java APIs that have beensignificantly reduced to work within the confines of limitedhardware. There is no support for the types of persistencemechanisms that we have come to expect on larger Java platforms.The question we address in this article is whether themobile telephone is a viable platform yet for serious businessor scientific applications that need to store and process datalocally and that expect the services of a reasonably rich set ofJava APIs.To date, we have seen considerable development inareas such as mobile games development, but more seriousbusiness and scientific applications will need to be developedif JTWI is to be a useful component of enterprisesoftware systems. Since such systems are likely to requireconsiderable support for persistence, we focus on the JDOspecification and examine some potential issues that arisewhen attempting to implement this specification usingMIDP. We extrapolate from this analysis to assess the generalusefulness of MIDP as a general purpose applicationprogramming platform. We also look at how MIDP devicesfit into larger distributed architectures that can mitigatethe limitations of mobile telephones as Java applicationplatforms.The Java 2 Micro Edition (J2ME)To cater to a wide range of small devices and applicationrequirements, the J2ME architecture (see Figure 1) providesmultiple configuration and profile layers that overlaythe specialized Java Virtual Machine (JVM) and operatingsystem. Configurations define the minimum set of availableJVM features and class libraries for a specific categoryof device and are hardware focused; profiles define the setof APIs available for a particular market category of devicesand are software focused.J2ME configurations specify the minimum requirementsfor memory, Java language features, JVM support, andruntime libraries. There are two standard J2ME configurations:the Connected Device Configuration (CDC) and theConnected Limited Device Configuration (CLDC). For thesmallest portable devices, such as mobile telephones, thestandard configuration is the CLDC. This configurationrequires a very small virtual machine, such as Sun’s KVM(Kilobyte Virtual Machine) or CLDC HotSpot Implementation,with footprints of only about 50–80K. These virtualmachines don’t have to comply with the full JVM specification,nor do they have to support the complete Java languagespecification. API support is limited to a selectionof classes from a few packages from the Java 2 StandardEdition (J2SE), plus the Generic Connection Framework(GCF), comprising a hierarchy of connection interfaces(and the Connector factory class) that are intended toprovide a generic way of expressing operations on connectionsregardless of the actual protocol.30 January 2005www.SYS-CON.com/JDJ