Java Reference
In-Depth Information
Many device vendors have moved toward providing support for the CDC on mobile
and embedded devices, although few still provide the horsepower necessary to run RMI
OP. As the cost of memory and processors continues to fall and we see greater conver-
gence between personal computers and other consumer devices, it's likely that this will
change, and the RMI OP will move from being available only in specialized environments
to being more generally available.
Seeing What's Provided by the Java RMI Optional Package
How does RMI OP differ from RMI as provided by Java SE? It's first useful to determine
how RMI OP is the
same
as Java SE, because it's likely that you will design your solution
around Java SE RMI and use a Java SE- or Java EE-based server environment to support
your distributed application.
By definition, RMI OP must support the following features:
• Full support for the RMI call semantics, including support for the RMI wire
protocol
• Support for marshalling—that is, support for representing an object on a
remote host
• The ability to export remote objects from RMI OP-enabled devices through the
UnicastRemoteObject
class
• Distributed garbage collection and garbage collector interfaces across both client
and server
• Interfaces to support objects that don't persist between invocations and require a
full-time server to manage their activation
• Support for the registry interfaces and the ability for RMI OP-enabled devices to
export registry objects remotely
RMI OP is surprisingly comprehensive for a standard aimed at low-end devices. By
supporting
UnicastRemoteObject
, distributed garbage collection, and the ability to register
and export a remote object, RMI OP-enabled hardware can fully participate in distrib-
uted computation, acting as both clients and servers in the object-distribution process.
This symmetry is a key feature of RMI OP over the traditional web service model of com-
putation, both because it's required for full interoperability support with Java SE RMI and
because it lets embedded devices serve objects to remote servers. In fact, on devices pro-
viding RMI OP, RMI can be used for interapplication communication on the same device
or for truly distributed applications across the network.
