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

4.5 Mobile Gateways

In the previous sections, we discussed service and application bundles in clientside OSGi containers. Besides clientside containers, another major application area of the OSGi framework is to deploy and execute services on mobile gateway devices that do not have UI front ends. Small, pervasive devices delegate computationally expensive tasks to the more powerful gateway. In the gateway configuration, the OSGi powered hub provides services to a variety of devices:

The Jini service (service.jini) allows us to incorporate an OSGi-based gateway into a Jini network. For example, the gateway can drive a Jini printer over the local WiFi network to print out a pizza order receipt.

The UPnP service (service.upnp) allows an OSGi-based gateway to interact with UPnP network devices.

The HTTP service (service.http) we discussed earlier is available to any HTTP-compatible devices. For example, MIDP-based or browser-based devices on the local WiFi network can order pizza through the OSGi HTTP service on the gateway device.

The OSGi container also provides a generic device access service (service.device) that allows developers to plug in device drivers for arbitrary devices and network protocols.

The architecture is illustrated in Figure 4.8. But still, why do we need to run gateways in OSGi containers? Wouldn't a full-blown J2EE portal server be a much more powerful option? There are two important reasons.

Since OSGi containers run on J2ME, we can place the OSGi-based gateway in the same mobile network as the pervasive devices it serves. For example, in an in-hand network, the PDA can be the gateway; in an in-home network, the TV-set top box is the gateway; in an incar network, the entertainment console could be the gateway. Since the local wireless network is much faster, cheaper, and easier to maintain compared with national cellular networks, the local gateways are crucial to enable high-availability mobile applications.

The OSGi specification supports dynamic service provisioning and deployment through bundles. This is a very important feature when you have thousands of mobile gateways around in your company.