Welcome!

Weblogic Authors: Yeshim Deniz, Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

EJB, CORBA, and COM

EJB, CORBA, and COM

In EJB/CORBA integration, complexity can range from simple to complex and depends in part on the direction of the communication. From EJB to CORBA, communication is relatively simple because the EJB bean invokes CORBA as it does any external resource. CORBA-to-EJB communication, however, depends on the application server's support of RMI-IIOP. If the application server doesn't support RMI-IIOP, then it's best to create a wrapper or adapter class that redirects or delegates the function calls from the client via a CORBA servant, which then calls the EJB.

Part 1: EJB/CORBA Integration
Communicating from EJB to CORBA is the simplest case. The EJB will require an ORB and some means of looking up the remote CORBA object, the servant, in a directory service that could be CosNaming or JNDI over CosNaming. Note: It isn't necessary to use CORBA 2.3, which is required by RMI-IIOP (see below). Like any external resource, such as a socket or file descriptor, any ORB can be initialized and used by the EJB.

ORB initialization should be performed once using the singleton design pattern that can act as a factory for looking up remote CORBA servants. A suitable design to ensure this scenario requires the use of a stateless session bean, which is never passivated. Entity or stateful session beans may be passivated and reactivated and would require the disposal and cleanup of the ORB, which has a high performance cost as well.

Using the stateless session bean fits the EJB model best, and the ORB can be a static data member in the bean or in the above mentioned singleton support class to help ensure one instance. A deployment descriptor can also be set, for example, in WebLogic, which allows the container to create only one stateless session bean.

Currently, there's no standard mapping between EJB and CORBA for passing user identity and transaction propagation. So, if transaction and security services are required in your implementation, then the EJB bean wrapping this CORBA call should invoke the appropriate CORBA services in the desired way. In other words there's no automatic solution, and transaction and security will need to be customized for your situation.

In Listing 1 (see www.JavaDevelopers Journal.com for listings) the Call CorbaBean is a stateless session bean implementation that makes a call to an object R which initializes the ORB (if it's not initialized) and calls the CORBA servant. The idl is also shown; the servant CORBA implementation isn't included but follows standard CORBA. More important, the R class shows the encapsulation of the CORBA processes in a singleton and as a cascade pattern to ensure single initialization and a simple interface - actually too simple, as an actual implementation would more likely provide factories for different types of objects as required by the application. A client would look up the home interface, CallCorba, and create a CallCorba bean to call the remote function "call."

CORBA to EJB
Ideally, communication from EJB to CORBA should be over RMI-IIOP. However, RMI-IIOP requires a CORBA 2.3 ORB and an EJB container that supports RMI-IIOP. Because the EJB 1.1 specification only recommends RMI-IIOP but doesn't require it, many of the application servers currently available are in compliance with the EJB1.1 specification and don't fully support RMI-IIOP. In EJB 2.0, released in July 2000, RMI-IIOP is required, and interoperability will eventually be available in all the major container vendors.

Nevertheless, it's still possible to use RMI-IIOP in some application servers, although it's likely to range in complexity from easy to perhaps impossible. For example, Inprise's Application Server product allows easy interoperability with CORBA because it's built on RMI-IIOP as would be expected, as Inprise has integrated it with their Visigenic product. On the other hand, other application servers may not provide RMI-IIOP easily for EJBs and will require creating CORBA idl stubs for all the EJB objects, then successfully compiling the resulting idl with an idl compiler. Sometimes the resulting idl must be tweaked or modified. To create RMI-IIOP between a CORBA client and EJB, follow these steps:

  1. Use rmic, which comes with RMI-IIOP, to create idl files from your EJB Home interface.
  2. Use a CORBA 2.3-compliant idl compiler to generate your stubs.
  3. Create your EJB CORBA client.
As in any new standard, interoperability between vendors is particularly difficult.

Even if the above steps can be accomplished with your application server, there's no standard for passing user identity and the transaction propagation over RMI-IIOP to the client. EJB transaction and security services aren't accessible over RMI-IIOP; consequently, these services will lack any current RMI-IIOP solution.

So although RMI-IIOP is the preferred solution for interoperability between EJBs and CORBA and will certainly be the better solution in the future, it may be required to communicate without RMI-IIOP. One flexible solution is to provide a CORBA wrapper servant that directs CORBA calls to the EJB object. Because this solution can easily be replaced with RMI-IIOP in the future, it will provide a design that evolves.

First, check your CORBA and EJB products. If they easily support RMI-IIOP interoperability, then use that approach. If not, the example code demonstrates a wrapper that delegates CORBA calls to EJB.

In Listing 2, the call.idl is the idl for the call to the EJB. The EJBWrapper wraps the EJB and allows the CORBA client, WrapperClient, to access the EJB though the EJBWrapper. The EJBWrapper follows the standard adapter or wrapper pattern and simply delegates the calls from the client to the EJB. Note that we're actually using the same session stateless bean used in the previous example for simplicity, although one would never make a call from CORBA through EJB to CORBA; the example is heuristic.

Design Issues
The design issues regarding communication from CORBA to EJB concern the usage of RMI-IIOP where possible, and where not possible the usage of the adapter design pattern, which ensures that the external resource, the ORB, is carefully handled. The stateless session bean offers the best EJB for EJB-to-CORBA communication because it allows easy management of the ORB. In addition, because the future J2EE software will evolve to support CORBA-EJB interoperability more fully, any effective design must be able to easily absorb future changes.

Part II: COM/EJB Integration
Before looking at COM-EJB communication, it's worth pointing out that SOAP is a strategic direction Microsoft is taking for interoperability. Consequently, SOAP should be considered for communication between EJB and COM. However, it would be a custom solution without the support of current application servers or J2EE technology. In addition, SOAP is relatively new, and not many stable implementations exist.

For some packages using SOAP see www.alphaworks.ibm.com/tech/soap4j or http://msdn.microsoft.com/xml/default.asp. For a stable production solution, COM/EJB bridges provide the best synchronous solution and are described below, leaving SOAP for a future investigation.

Bridges

COM to EJB
Many COM-to-Java bridges exist. Sun has an early access Client Access Services (CAS) COM Bridge available at http://developer.java.sun.com/developer/earlyAccess/j2eecas/, that will allow any COM-enabled client to access any EJB object. In addition, bridges such as J-Integra (see www.linar.com/) and WebLogic provide bidirectional communication. Below we look at WebLogic's COM bridge; it's a popular application server that simplifies the aspect of bridging between COM and EJB.

Communicating from COM to EJB usually means that Visual Basic clients are accessing EJBs. WebLogic, for example, supports the ability of Visual Basic clients or other Microsoft services to access EJBs. Because bridges support this communication rather well, it won't be addressed in any more detail, and the remaining discussion will be on communicating from EJB to COM, which is more difficult.

EJB to COM
Communication from EJB to COM is necessary if services in Microsoft are required by EJBs. WebLogic's COM solution hosts the COM object as an RMI object. As a representative example, we'll address this bridge in detail.

WebLogic Wraps COM
Note that the WebLogic Server wraps the COM object, Test.dll, and provides an RMI interface any Java client on NT can access. WebLogic provides a "com compiler," which takes a dll file and produces the Java classes, including the interface used by RMI clients. No programming is required, as the code is automatically generated. The command is

jview weblogic.comc -nothreads -register
c:\weblogic\examples\com\testser\TestServer.dll

Unfortunately, because the standard (Sun) Java Virtual Machine differs from the Microsoft Java Virtual Machine in serialization across RMI, any network connection between the two JVMs is incompatible. Sun Microsystems is suing Microsoft over this and other differences. Consequently, WebLogic certifies that COM will work only if the WebLogic server is run on the Microsoft VM, and only Java clients running under the Microsoft VM will be able to connect to the WebLogic server, so the COM bridge will work only on NT and using only the Microsoft VM. Note: Even if the Sun and Microsoft JVMs were interoperable, C++ clients still couldn't connect to WebLogic's RMI. Therefore, the second CORBA wrapper is needed to provide true interoperability (see COM/CORBA/ EJB Integration below).

Tests Performed
Three tests of increasing complexity were performed using the above bridge. The first was a simple function that returned void. The second returned a String. The third test returned various Microsoft COM objects that dealt with the data access (DAO) directly. Both the void and String functions worked successfully, but the more complex test hung after processing one database record and suggests not making Microsoft's Data Access Layer remote. In addition, even if making these COM objects worked easily in Java, the training issue for a Java developer to learn the COM API for data access is knowledge unlikely to be found in one person. Consequently, the best design approach is to return Strings or perhaps XML, simple objects where possible, or domain business objects that encapsulate and hide Microsoft's data access classes. Other bridges may suggest other approaches.

Risks and Disadvantages
One risk to the above approach is the dependence on the COM-Java bridge that's affected by the current lawsuit. Microsoft plans to not support Java in the future and will give Rational the development of the virtual machine (see "Microsoft, Rational strengthen ties on Java development front," www.zdnet.com/ eweek/stories/general/0,11011, 1015701,00.html). Nevertheless, WebLogic's support of the bridge provides insurance from a major vendor, and there are bridges not bound to the Microsoft VM (see www.linar.com/). Another disadvantage is that some of the features of the WebLogic Server can't be used. Because the Microsoft Java Virtual Machine must be used in order to use COM, clients can't be standard Java clients, which run on standard VMs, although wrapping the EJBs as CORBA objects would allow any client to access them (see COM/ CORBA/EJB Integration below). Note: JSP technology can't be used because it requires a standard usage of the classpath, that isn't available on the Microsoft Virtual Machine.

AdvantagesK
The WebLogic wrapper provides a simple way to bridge COM and Java with little or no programming. It provides a stable application server, which provides facilities for hosting distributed objects and easing distributed development.

Detailed Implementation Steps
To provide the above solution, WebLogic must run on the Microsoft Java Virtual Machine. In addition, the Microsoft SDK for Java ( http://www.microsoft.com/java/default.htm) must be installed on the machine. After installation, setting its classpath can be tricky, so it's worth noting that this is done in the registry (HKEY_LOCAL_MACHINE\ Software\Microsoft\JavaVM\Classpath). Some files can be automatically added to the classpath and break the WebLogic compiler. To correct the problem if it occurs, simply edit the registry to remove these files from the classpath.

Configure the WebLogic environment file, setEnv.cmd, to use the Microsoft compiler, then:

  1. Create a new directory and copy TestServer.dll into it (e.g., C:\weblogic\ examples\com\testser)
  2. Recompile com object

    jview weblogic.comc -nothreads -register
    c:\weblogic\examples\com\testser\TestServer.dll

  3. Copy the created directory weblogic to C:\weblogic\myserver\serverclasses
  4. Add the interface, ItestInterface, to jvc /d %CLIENT_CLASSES% ServerSideTestServer.java and write some code to use this interface
  5. Restart Web server after adding properties:

    weblogic.system.startupClass.testsertest=weblogic.com.remote.testserver.ITestInterfaceImpl
    weblogic.system.startupArgs.testsertest=TestServer

  6. Run the above ServerSideTestServer under the Microsoft Virtual Machine, jvc examples.com. ServerSideTestServer
Design Issues
The above can provide a simple way of integrating COM. Especially by using String-level interfaces, XML can be passed as a parameter thereby significantly reducing program effort and debugging. Restrictions exist because of the need to use the Microsoft Virtual Machine, making it more difficult to use the full feature set of J2EE. Also, the possibility that SOAP may become a better interface is worth noting. Nevertheless, the need for a production quality solution currently favors a bridge.

Part III: COM/EJB/CORBA Integration
In summary, these solutions can be used together to provide a complete COM-to-EJB-to-CORBA solution useful in those situations where these three object models need to be combined in one solution. Each model provides particular benefits and may be linked to certain legacy solutions in any given environment.

Certainly, COM allows easy integration with Microsoft, EJB provides ease of development and portability, and CORBA provides integration benefits. More importantly, in any environment there may be the presence of each model, and there may be a requirement to integrate them all. So, it's worthwhile creating a framework for integrating each model because some loss of performance will be outweighed by development and maintenance benefits.

Performance is a problem with integrating COM and CORBA through EJB. However, although two servers exist between the COM object (e.g., Test.dll) and the Client objects, both components are easily produced as described below. Certainly, this trade-off favors ease of development over performance. But this solution then provides a bridge between COM and any CORBA client that's highly flexible and can evolve with future changes. Only environments with all three of these technologies will benefit from this integration, but by placing EJB as the central standard, it simplifies the other two integrations. Furthermore, when RMI-IIOP becomes a standard, the server hosting the CORBA wrapper can be removed.

CORBA to COM
To enable CORBA to COM, a CORBA client calls a wrapper or adapter to access an EJB, which then calls COM. Note that RMI-IIOP could be used between CORBA and EJBs, but a more versatile yet performative solution is to utilize the wrapper. The CORBA wrapper delegates any CORBA calls to the RMI interface hosted by WebLogic and provides a fully interoperable solution. The wrapper is essentially a client of WebLogic and looks up the RMI interface of the COM component and provides a remote interface to clients on UNIX or NT. The CORBA interface or idl can be developed manually by creating a matching CORBA interface or by using an automatic tool provided by Visigenic, which can take a Java interface and produce idl (i.e., java2idl). Once the idl is provided the delegation must be coded directly, although this programming is straightforward and could be generated automatically if such a generator were written. Note that by writing a simple code generator that automatically generates the CORBA wrapper, no code would need to be written for the bridge software, which would improve the speed of development and improve quality.

COM to CORBA
COM-to-CORBA communication can be achieved by using the soon-to-be-released CAS, COM to J2EE bridge being developed by Sun, and then having the EJBs call CORBA. Or WebLogic's bridge from COM to EJB can be used and have the EJBs call CORBA. COM to CORBA is in fact simpler than the opposite direction, as would be expected from details discussed above.

Design Issues
COM-to-CORBA communication is enabled by having the COM object presented as an RMI/EJB object by the WebLogic bridge, then a CORBA server is written that wraps the RMI object and provides a CORBA interface to any client. CORBA-to-COM communication is provided easily by having EJBs invoke CORBA directly and by having a bridge between EJB and COM.

The complexity of the interface can be a critical factor in the above approach because a complex interface requires larger amounts of code in the CORBA wrapper. One possibility is to pass XML back from the COM server through the CORBA wrapper, perhaps a hybrid SOAP solution. Automating the creation, the CORBA wrapper can speed development. A second solution is to build common domain business objects and pass them through to WebLogic and Java.

The selection of a particular bridge will be dependent on platforms and overall configuration. If WebLogic's bridge is used, then the Microsoft VM will be required, as it runs only on Windows NT. Other bridges will have different requirements. However, an EJB container does simplify many of the interoperability issues by providing one standard to map both CORBA and COM rather than mapping each standard to the other, which would create six mappings: CORBA to COM, CORBA to J2EE, and so on.

Conclusion
EJB, CORBA, and COM are different technologies and are likely to persist in production environments. Maintaining interoperability is essential for environments that have these technologies. A number of issues have been discussed that show many of the choices required for integrating these technologies. Various trade-offs and advantages exist for different approaches and tools, and any particular environment or configuration of software will favor a different combination of these solutions.

More Stories By Sirl Davis

Sirl Davis is an assistant director of IT at Dresdner Kleinwort Benson, London.
He has a bachelor's degree in electrical engineering/computer science and an MBA/finance with PhD-level work in information systems. His experience includes developing various
finance applications for trading risk, and data warehousing utilizing Java technology.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
DevOps at Cloud Expo – being held June 5-7, 2018, at the Javits Center in New York, NY – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Among the proven benefits,...
@DevOpsSummit at Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, is co-located with 22nd Cloud Expo | 1st DXWorld Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
SYS-CON Events announced today that T-Mobile exhibited at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on qua...
SYS-CON Events announced today that Cedexis will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cedexis is the leader in data-driven enterprise global traffic management. Whether optimizing traffic through datacenters, clouds, CDNs, or any combination, Cedexis solutions drive quality and cost-effectiveness. For more information, please visit https://www.cedexis.com.
SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.
SYS-CON Events announced today that Vivint to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. As a leading smart home technology provider, Vivint offers home security, energy management, home automation, local cloud storage, and high-speed Internet solutions to more than one million customers throughout the United States and Canada. The end result is a smart home solution that sav...
SYS-CON Events announced today that Opsani will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Opsani is the leading provider of deployment automation systems for running and scaling traditional enterprise applications on container infrastructure.
SYS-CON Events announced today that Nirmata will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nirmata provides a comprehensive platform, for deploying, operating, and optimizing containerized applications across clouds, powered by Kubernetes. Nirmata empowers enterprise DevOps teams by fully automating the complex operations and management of application containers and its underlying ...
SYS-CON Events announced today that Opsani to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. Opsani is creating the next generation of automated continuous deployment tools designed specifically for containers. How is continuous deployment different from continuous integration and continuous delivery? CI/CD tools provide build and test. Continuous Deployment is the means by which...