Transcript Java Distributed Object Model

Java Distributed Object Model
A remote object is one whose methods can
be invoked from another JVM on a different
host.
It implements one or more remote interfaces
which are pure Java interfaces that declare
the methods of the remote object.
A method invocation on a remote object has
the same syntax as a method invocation on a
local object.
Java Distributed Object Model
A reference to a remote object can be passed as an
argument or returned as a result in any local or
remote method invocation (RMI)
Natural Java mechanisms can be used for typechecking and casting of remote objects
Clients of remote objects interact with remote
interfaces
If a remote object reference is passed, the receiver
will get a reference to the same remote object
The semantics of some of the methods defined by
class objects are specialized for remote objects
Remote Method Invocation (RMI) –
Three Layered Architecture
Stub/Skeleton – Client-side stubs (proxies) and
server-side skeletons
Remote Reference Layer - Reference/Invocation
behavior (e.g.. unicast, multicast)
Transport – Connection setup and management and
remote object tracking
RMI is a layer on top of the JVM which leverages the
Java system’s built-in garbage collection, security and
class-loading mechanisms
The application layer sits on top of RMI
Remote Method Invocation (RMI) –
Three Layered Architecture
The RMI Layers Abstract Invocation Calls,
hiding low-level Transport Mechanism
Remote Method Invocation (RMI)
RMI enables the programmer to create distributed Java-to-Java,
Java-to-C through JNI, applications, in which the methods of
remote Java objects can be invoked from other Java virtual
machines, possibly on different hosts.
A Java program can make a call on a remote object once it
obtains a reference to the remote object, either by looking up
the remote object in the bootstrap naming service provided by
RMI or by receiving the reference as an argument or a return
value.
A client can call a remote object in a server, and that server can
also be a client of other remote objects.
RMI uses Object Serialization to marshal and unmarshal
parameters and does not truncate types, supporting true objectoriented polymorphism.
Example of Distributed program
using Java RMI
The distributed example uses an applet to make a
remote method call to the server from which it was
downloaded to invoke the method. When the applet
runs, the return is invoked and displayed on the
client applet.
There are four source files for the remote server and
applet:
The Java remote interface
The Java remote object (server) which implements the
remote interface
The Java applet that remotely invokes the server’s method
The HTML code for the web page that references the applet
Remote Method Invocation (RMI)
Summary
With RMI, you can access the methods of remote
objects
On the server (JWS), you can run the RMI-Registry
program
A Java application that registers one or more objects with
the RMI Registry
On the client, you run a java application that accesses the
methods of the objects of the application running on the
server.
Run the RMI rmic command on the file and create the
client, client stub, server and server stub
Reference
Multi-Tier Architecture for TI with FaultTolerance and Automated Replication
Paul C. Barr
Technical Manager
Software Technology & Information Services
White paper on RMI
http://java.sun.com/marketing/collateral/javarmi.html