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Programming WebLogic RMI over IIOP

# Overview of RMI over IIOP

The following sections provide a high-level view of RMI over IIOP:

- What Are RMI and RMI over IIOP?
- Overview of WebLogic RMI-IIOP
- Protocol Compatibility

# What Are RMI and RMI over IIOP?

To understand RMI-IIOP, you should first have a working knowledge of RMI. Remote Method Invocation (RMI) is the standard for distributed object computing in Java. RMI enables an application to obtain a reference to an object that exists elsewhere in the network, and then invoke methods on that object as though it existed locally in the client's virtual machine. RMI specifies how distributed Java applications should operate over multiple Java virtual machines. RMI is written in Java and is designed exclusively for Java programs.

RMI over IIOP extends RMI to work across the IIOP protocol. This has two benefits that you can leverage. In a Java to Java paradigm this allows you to program against the standardized Internet Interop-Orb-Protocol (IIOP). If you are not working in a Java-only environment, it allows your Java programs to interact with Common Object Request Broker Architecture (CORBA) clients and execute CORBA objects.CORBA clients can be written in a variety of languages (including C++) and use the Interface-Definition-Language (IDL) to interact with a remote object.

# Overview of WebLogic RMI-IIOP

RMI over IIOP is based on the RMI programming model and, to a lesser extent, the Java Naming and Directory Interface (JNDI). For detailed information on WebLogic RMI and JNDI, refer to Using WebLogic RMI and Programming with WebLogic JNDI. Both technologies are crucial to RMI-IIOP and it is highly recommended that you become familiar with their general concepts before starting to build an RMI-IIOP application.

The WebLogic Server 8.1 implementation of RMI-IIOP allows you to:

- Connect Java RMI clients to WebLogic Server using the standardized IIOP protocol
- Connect CORBA/IDL clients, including those written in C++, to WebLogic Server
- Interoperate between WebLogic Server and Tuxedo clients
- Connect a variety of clients to EJBs hosted on WebLogic Server

This document describes how to create applications for various clients types that use RMI and RMI-IIOP. How you develop your RMI-IIOP applications depends on what services and clients you are trying to integrate.

Figure 1-1 shows RMI Object Relationships for objects that use IIOP.

Figure 1-1 RMI Object Relationships

## Support for RMI-IIOP with RMI (Java) Clients

You can use RMI-IIOP with Java/RMI clients, taking advantage of the standard IIOP protocol. WebLogic Server 8.1 provides multiple options for using RMI-IIOP in a Java-to-Java environment, including the new J2EE Application Client (thin client), which is based on the new small footprint client jar. To use the new thin client, you need to have the `wlclient.jar` (located in WL_HOME`/server/lib`) on the client side's CLASSPATH. For more information on RMI-IIOP client options, see Overview of RMI-IIOP Programming Models.

## Support for RMI-IIOP with Tuxedo Client

WebLogic Server 8.1 contains an implementation of the WebLogic Tuxedo Connector, an underlying technology that enables you to interoperate with Tuxedo servers. Using WebLogic Tuxedo Connector, you can leverage Tuxedo as an ORB, or integrate legacy Tuxedo systems with applications you have developed on WebLogic Server. For more information, see the WebLogic Tuxedo Connector Guide.

## Support for RMI-IIOP with CORBA/IDL Clients

The developer community requires the ability to access J2EE services from CORBA/IDL clients. However, Java and CORBA are based on very different object models. Because of this, sharing data between objects created in the two programming paradigms was, until recently, limited to Remote and CORBA primitive data types. Neither CORBA structures nor Java objects could be readily passed between disparate objects. To address this limitation, the Object Management Group (OMG) created the Objects-by-Value specification . This specification defines the enabling technology for exporting the Java object model into the CORBA/IDL programming model--allowing for the interchange of complex data types between the two models. WebLogic Server can support Objects-by-Value with any CORBA ORB that correctly implements the specification.

# Protocol Compatibility

Interoperability between WebLogic Server 8.1 and WebLogic Server 6.x and 7.0 is supported in the following scenarios:

- Server-to-Server Interoperability
- Client-to-Server Interoperability

## Server-to-Server Interoperability

The following table identifies supported options for achieving interoperability between two WebLogic Server instances.

Table 1-1 WebLogic Server-to-Server Interoperability

To Server From Server | WebLogic Server 6.0 | WebLogic Server 6.1 SP2 and any service pack higher than SP2 | WebLogic Server 7.0 | WebLogic Server 8.1
--- | --- | --- | --- | ---
WebLogic Server 6.0 | RMI/T3 HTTP | HTTP | HTTP Web Services1 | HTTP Web Services2
WebLogic Server 6.1 SP2 and any service pack higher than SP2 | HTTP | RMI/T3 RMI/IIOP3 HTTP Web Services | RMI/T3 RMI/IIOP4 HTTP Web Services | RMI/T35 RMI/IIOP6 HTTP Web Services7
WebLogic Server 7.0 | HTTP | RMI/T3 RMI/IIOP8 HTTP | RMI/T3 RMI/IIOP9 HTTP Web Services | RMI/T3 RMI/IIOP10 HTTP Web Services11
WebLogic Server 8.1 | HTTP | RMI/T3 RMI/IIOP12 HTTP | RMI/T3 RMI/IIOP13 HTTP Web Services14 | RMI/T3 RMI/IIOP HTTP Web Services
Sun JDK ORB client15 | RMI/IIOP16 | RMI/IIOP17 | RMI/IIOP18 | RMI/IIOP19

1. Must use portable client stubs generated from the "To Server" version
2. Must use portable client stubs generated from the "To Server" version
3. No support for clustered URLs and no transaction propagation
4. No support for clustered URLs and no transaction propagation
5. Known problems with exception marshalling with releases prior to 6.1 SP4
6. No support for clustered URLs and no transaction propagation. Known problems with exception marshalling.
7. Must use portable client stubs generated from the "To Server" version
8. No support for clustered URLs and no transaction propagation
9. No support for clustered URLs
10. No support for clustered URLs
11. Must use portable client stubs generated from the "To Server" version
12. No support for clustered URLs and no transaction propagation. Known problems with exception marshalling
13. No support for clustered URLs and no transaction propagation
14. Must use portable client stubs generated from the "To Server" version
15. This option involves calling directly into the JDK ORB from within application hosted on WebLogic Server.
16. JDK 1.3.x only. No clustering. No transaction propagation
17. JDK 1.3.x only. No clustering. No transaction propagation
18. JDK 1.3.x or 1.4.1. No clustering. No transaction propagation
19. JDK 1.3.x or 1.4.1. No clustering. No transaction propagation

## Client-to-Server Interoperability

The following table identifies supported options for achieving interoperability between a stand-alone Java client application and a WebLogic Server instance.

Table 1-2 Client-to-Server Interoperability

To Server From Client (stand-alone) | WebLogic Server 6.0 | WebLogic Server 6.1 | WebLogic Server 7.0 | WebLogic Server 8.1
--- | --- | --- | --- | ---
WebLogic Server 6.0 | RMI HTTP | HTTP | HTTP Web Services1 | HTTP Web Services2
WebLogic Server 6.1 | HTTP | RMI/T3 HTTP Web Services | RMI/T3 HTTP Web Services3 | RMI/T34 HTTP Web Services5
WebLogic Server 7.0 | HTTP | RMI/T3 RMI/IIOP6 HTTP | RMI/T3 RMI/IIOP7 HTTP Web Services | RMI/T3 RMI/IIOP8 HTTP Web Services9
WebLogic Server 8.1 | HTTP | RMI/T3 RMI/IIOP10 HTTP | RMI/T3 RMI/IIOP11 HTTP Web Services12 | RMI/T3 RMI/IIOP HTTP Web Services
Sun JDK ORB client13 | RMI/IIOP14 | RMI/IIOP15 | RMI/IIOP16 | RMI/IIOP17

1. Must use portable client stubs generated from the "To Server" version
2. Must use portable client stubs generated from the "To Server" version
3. Must use portable client stubs generated from the "To Server" version
4. Known problems with exception marshalling with releases prior to 6.1 SP4
5. Must use portable client stubs generated from the "To Server" version
6. No Cluster or Failover support. No transaction propagation
7. No Cluster or Failover support
8. No Cluster or Failover support
9. Must use portable client stubs generated from the "To Server" version
10. No Cluster or Failover support and no transaction propogation. Known problems with exception marshalling
11. No Cluster or Failover support and no transaction propogation. Known problems with exception marshalling
12. Must use portable client stubs generated from the "To Server" version
13. This option involved calling directly into the JDK ORB from within a client application.
14. JDK 1.3.x only. No clustering. No transaction propagation
15. JDK 1.3.x only. No clustering. No transaction propagation
16. JDK 1.3.x or 1.4.1. No clustering. No transaction propagation
17. JDK 1.3.x or 1.4.1. No clustering. No transaction propagation