This is an introduction into distributed computing using Java Remote Method Invocation (RMI) technology. RMI allows java applications to communicate to server or distributed applications across the network seamlessly. RMI can leverage proprietary protocols or standard CORBA IIOP protocol to send/receive messages. The presentation covered the following topics. Presentation ------------ Session Outline: - Overview of RMI - Features of RMI - Layers in RMI - Creating an application - Conclusion Example code available at ChrisMatthews.us Author: Chris Matthews Copyright: eLink Business Innovations 2002

1. Introduction to Remote
Method Invocation (RMI)
Chris Matthews
eLink Business Innovations, Inc

2. Notices
• The following terms are copyrights or trademarks in US
and/or other countries.
- Java
- Sun Microsystems

3. Introduction to Java RMI
• What is Java RMI ?
• Features of Java RMI ?
• Who would use Java RMI ?
• How do I use Java RMI ?
• Additional Resources .
• Questions ?

4. What is Java RMI ?
• Java Remote Method Invocation (RMI) is a
distributive system programming interface
introduced in JDK 1.1

5. Features of Java RMI
• Object Parameter Passing via Serialization
• Built in Security Model
• Platform Independence (Write Once Run Anywhere 100%
Pure Java)
• Client/Server architecture
• Support included in JDK with no external dependencies
• Transport layer is TCP/IP based

6. Features of Java RMI (continued)
• Distributive Garbage Collector
• Legacy connection can be supported via Corba IIOP,
Java Native Interface (JNI), JDBC, J2EE Services like
(JNDI, JMS) or JDO.

7. Who Would Use Java RMI ?
• Anyone wanting to use the benefits of Java to do
distributive computing development on the network
– Developers wanting to externalize their local classes to
network computing environment
– Developers writing distributive computing applications
or parallel processing applications
– Server developers wanting better interactivity clients
and/or other servers, like EJBs.

8. How Do I Use Java RMI ?
• The Java RMI architecture
• Components of Java RMI
• Java Interfaces and how they relate to RMI
• RMI and Java Serialization
• Building an RMI Sample Client/Server Application
• Distributive garbage collection

9. Architecture Overview

10. RMI Layers
• Stubs/Skeleton Interface
• Remote Reference Layer (RRL)
• Java Remote Method Protocol (JRMP)
• Transport Layer (TCP/IP)

11. Java Interfaces
• Interfaces are native to the Java Language
• Interfaces allow externalization of methods without
exposing the code
• Java RMI utilizes interfaces for exposing distributed
methods to clients

12. Serialization of Objects
• Serialization is part of the Java Language
• RMI uses the power of serialization pass objects by value.
It “flattens” the object into a byte stream to transmit
between the client/server.
• Local objects passed as parameters or returned from
methods are done by copy and not by reference.

13. Serialization of Objects (continued)
• Remote objects are passed by reference and the remote
reference layer manages the liveliness of the objects

14. Create a RMI Application
• How do I build an application ?

15. Relationship of Layers

16. Interface Definitions
• Defining the remote interface
• Managing exceptions on the interface
• See LoanCalc.java for interface definitions.

17. Interface Implementation
• Adding the implementation code to support the remote
interface
• Extend the UnicastRemoteObject class
• Managing remote exceptions
• See LoanCalcImpl.java for interface implementation

18. Stubs & Skeleton Generation
• Use the rmic compiler to compile and generate the stubs &
skeletons form LoanCalcImpl.java
• See LoanCalcImpl_Stub.class and
LoanCalcImpl_Skel.class as generated files
• Use the –keepgenerated flag on the rmic compiler to
generate the .java files LoanCalcImpl_Stub.java and
LoanCalcImpl_Skel.java

19. Creating the Server
• Extending the RMI Interface
• Registering a security manager for the server
• Creating an instance of the RMI registry
• Binding a name to a remote object for registry lookup by
the client.
• See CalcServer.java for more details.

20. Creating The Client
• Registering a Security Manager
– Applications require registration of a security manager
– Applets have build in security registration via the
browser or applet viewer.
• Name lookup of remote object
• Execute routines on the remote server using defined
externalized interfaces
• See CalcClient.java for the client code

21. Building the RMI Sample
• Compile interface implementation class
– javac LoanCalcImpl.java
• Create stubs/skeletons using the implementation
class
– rmic LoanCalcImpl.java
• Compile client and server classes
– javac CalcClient.java
– javac CalcServer.java

22. Starting the RMI Sample
• Starting the registry
• Starting the server
• Starting the client

23. RMI Registry
• RMI Registry provides name lookup for clients to resolve
the server’s remote objects
• Two ways to start the RMI Registry
– Command Line
• rmiregistry (optional port:Default is 1099)
– Dynamically with static method
• LocateRegistry.createRegistry( port )

24. Starting the Server
• Starts the RMI Server
– java CalcServer

25. Starting the Client
• Start the client, passing it the URL name of the server
along with the remote object to reference
– java CalcClient //www.server.com/objectname

26. Distributive Garbage Collector
• RMI runtime garbage collector manages liveliness of the
remote object. When the object becomes “out of scope”
the server’s distributive garbage collector flags the object.

27. RMI Conclusion
• It is simple to develop distributive computing applications
• RMI is designed to be a natural interface for writing
distributive computing applications in Java using existing
features of the language
• It is a cross platform solution for distributive computing
development

28. Advanced Topics on RMI
• Externalization of Objects without a registry
• Closed vs. Open RMI systems
• Security in RMI
• Distributive Garbage Collector in Detail
• RMI Transaction Log
• IIOP instead of JRMP for RMI Protocol
• Persistent References
• Other RMI Enhancements

29. Additional References
• RMI – Javasoft
– http://www.javasoft.com
• Orielly - Java Network Programming,
– ISBN 1-56592-227-1
• RMI/IIOP JavaWorld
– http://www.javaworld.com
• IIOP – Object Management Group (OMG) CORBA
– http://www.omg.org

30. Questions ?