Enterprise J2ME Developing Mobile Java Applications [Electronic resources] نسخه متنی

10.1 Mobile Enterprise Messaging

In Chapters 3 and 5, we explored ways to integrate smart clients with backend servers using RPC. More examples on the RPC scheme can be found in Chapters 16 and 17. Although RPC style integration is simple and does not require any middleware, it is sometimes not optimal in the occasionally connected, unreliable, and heterogeneous mobile environments. Error handling and quality-of-service (QoS)-level guarantees are difficult to implement in RPC environments. The messaging scheme, however, offers great advantages in some key enterprise areas. The benefits of enterprise messaging are as follows.

Universal integration: In the messaging scheme, the message sender and receiver are completely decoupled. They interact only with standard interfaces defined by the messaging protocol and do not need to know the status or availability of the other party. This allows automatic and seamless integration between enterprise components. For mobile applications that run on many different devices and use different network transport protocols, messaging-based integration is crucial.

Reliability: Due to the intermittent nature of wireless networks, communication reliability is a big concern for mission-critical mobile applications. In a messaging application, we can guarantee message delivery or at least notify the sender when the delivery is failed or not completed after a certain amount of time.

Scalability: In an asynchronous messaging solution, the server resource is not tied up by idle connections. Therefore, more concurrent users can be supported. Compared with the one-user-one-PC scenario in the wired world, each mobile worker might have several pervasive devices. Asynchronous messaging solutions allow us to build an infrastructure that accommodates those extra connection points.

Quality-of-service: Another advantage of asynchronous messaging is that it provides ways to differentiate service levels. During network "rush hours," the messaging system can prioritize messages and deliver the urgent and important ones first. For mobile applications, it is a smart use of precious bandwidth.

In real-world enterprise applications, we probably need a hybrid of RPC and messaging schemes.

10.1.1 Mobile MOM

The key infrastructure component in any messaging solution is messaging middleware servers. The middleware servers route, filter, hold, and deliver the messages when the client becomes available. Examples of such servers include email servers (e.g., SMTP, POP3 and IMAP), SMS Service Centers, and instant messaging servers (e.g., Jabber, AIM, MSN and Yahoo!). Those servers are available as part of the worldwide data communication infrastructure.

However, for enterprise applications, companies want to have fine control over their own messaging servers. The key technology behind enterprise solutions is MOM products. Mobile MOM solutions should support the following features.

Handle multiple client protocols.

Manage one-to-one or publish-subscribe message queues.

Store and forward messages.

Confirm message delivery.

Provide interfaces for popular backend messaging systems.

Provide interfaces for J2ME, native or even thin client devices.

The JMS specification defines MOM servers with the above features. In the next several sections, we discuss the JMS and then go through two mobile MOM products.