Java Reference
In-Depth Information
■
Note
A parallel implementation of Java RMI provides RMI over Internet Inter-Orb Protocol (RMI-IIOP).
Now part of Java SE and in the
javax.rmi
hierarchy, it has no corresponding support in Java ME.
To implement the server side of a distributed system, some additional code is
necessary. The
java.rmi.server
hierarchy provides this code, including the
java.rmi.
server.UnicastRemoteObject
and
java.rmi.activation.Activatable
classes. The differ-
ence between the two classes is that remote objects extending
UnicastRemoteObject
require a server to run for the lifetime of the object, while an object extending
Activatable
runs in the context of Java's RMI daemon
rmid
.
Understanding the Java RMI Optional Package
The Java RMI OP, formalized in JSR 66, came about fairly early in the history of mobile
Java. Approved in 2000, it arose from efforts by Motorola, Siemens, Sun, and others to
bring RMI to mobile platforms running J2ME, the predecessor to Java ME. These partners
developed RMI OP to meet the needs of highly connected, distributed applications that
leverage Java standards for information passing. Today, Sun provides a reference imple-
mentation of Java RMI OP implemented entirely in Java to licensees that can be
integrated directly onto hardware that meets the minimum requirements. RMI OP is
interoperable with the Java SE RMI implementation, making it ideal for integrating
embedded devices with existing RMI-based solutions.
Looking at the Requirements for the Java RMI Optional Package
Although carefully streamlined to meet the needs of embedded devices, RMI OP still has
some sizable requirements, including the following:
• 2.5MB of available ROM over the existing requirements for Java ME and other
platform concerns
• 1MB or more of available RAM over the existing requirements for Java ME and
other platform concerns
• TCP/IP connectivity to the network
• Support for the Java ME Foundation Profile running atop the Java ME Connected
Device Configuration
