Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

9.1 TECHNOLOGIES UNDERPINNING J2EE

As Figure 9.1 reminds us, J2EE is a platform that divides the gamut of software needed to implement a scalable robust solution into two parts. The first is infrastructure services that are likely to be commonly required for all applications. We call this infrastructure ‘middleware’ and it provides a host of powerful functions like distributed processing, transaction management, security management, multithreading and so on.

The other half of our software is the custom application itself, which we implement in units called Enterprise Java Beans (known as EJBs) where we construct the value-added business services that make the overall application do something useful. With J2EE, we have an approach that enables us to focus on ‘our’ bit whilst the application server does the rest (middleware). When introducing J2EE, we also learnt how the J2EE platform comes with a wide range of powerful system interfaces, such as the capability to connect with industrial strength database servers or mail servers. There is no need for us to implement any of these services. We utilise these services in our application by accessing the platform services via Application Programming Interfaces, or APIs. These interfaces are common to all J2EE implementations. Similarly, the low-level interfaces to enable the infrastructure services to function on behalf of our application are also common to all J2EE applications. This commonality is thanks to the J2EE specification being ...