Welcome!

Java IoT Authors: Stackify Blog, Yeshim Deniz, Pat Romanski, Matt Lonstine, Glenda Sims

Related Topics: Java IoT, Open Source Cloud

Java IoT: Article

j-Interop: An Open Source Library for COM Interoperability Without JNI

A search for pure, non-native, bi-directional interoperability with COM servers

Phew! I have drawn a picture to explain this entire cycle, just follow the alphabet.

I hope I was able to provide a concise introduction to the discovery and activation cycle. Let's see how the "QueryInterface" works and how the API call "Add (...)" is handled.

12.  The remote connection has now been established and we have an interface pointer to the remote IUnknown (the "IRemUnknown"). A QueryInterface () call to obtain the "ITestCOMServer"" interface will result in the following activities taking place.
13.  When the client invokes the IUnknown::QueryInterface, the COM runtime invokes the IRemUnknown::RemQueryInterface method on the OXID object in the target object exporter. The OXID object then invokes the QueryInterface() method on (possibly multiple) interfaces in the exporter (remember, the exporter knows all the interfaces the COM server has exported out). Please note that the IRemUnknown::RemQueryInterface method differs from the IUnknown::QueryInterface method since it can request several interface pointers in one call. The standard IUnknown::QueryInterface method is actually used to carry out this request on the server side.
14.  If found, the requested interface from the COM server is then marshaled as a MIP and sent back to the callee. This MIP carries a new IPID symbolizing this interface. The OXID and OID remain the same.
15.  Now that we have the interface pointer let's call "Add" on it. Upon receiving the ptrTestServer->Add(1, 2, int *) call, the COM runtime marshals the parameters in the NDR format and channels the request to the target object exporter identified by the OXID-resolved RPC binding (we did that in steps 9 and 10).
16.  The COM runtime on the server side finds the target interface based on the IPID that's contained in the RPC header. This IPID is of the ITestCOMServer interface that was returned to the client during a previous QueryInterface call.
17.  With the help of the Object exporter, the COM runtime invokes the method Add(...) on the correct interface of the COM server object and marshals the return values in the NDR format. These values are sent back to the callee using RPC infrastructure.
18.  The same cycle follows during the Release() call, the COM runtime invokes the IRemUnknown::RemRe lease() method on the OXID object in the target object exporter. The OXID object then invokes the Release() method on (possibly multiple) interfaces in the exporter.

This completes the entire cycle of obtaining an interface, executing an API on it, and subsequently releasing it. There's an additional task that the COM runtime also does and that's keeping the COM Server objects alive during a session. This is done via a ping mechanism. Pinging is carried out on a per-object (per-OID), not a per-interface (per-IPID) basis. Architecturally, at its server machine, each exported object (each exported OID) has associated with it a "ping period" that must elapse without getting a ping on that OID before all the remote references to IPIDs associated with that OID can be considered to have expired. Once expiration has occurred, the interfaces behind the IPIDs might get reclaimed (exactly when is implementation-specific).

I've tried to keep the explanation of DCOM internals as simple as possible. There's much more that happens, but I'm running out of space and I think you're running out of patience, so let's get to j-Interop. (Figure 4)

j-Interop
Suffice it to say j-Interop implements almost the entire DCOM protocol with its own Oxid Resolver service, pinging mechanism, Object exporter, etc. These are required for handling event callbacks, proxying a Java server in place of a COM server (bi-directional access), and making sure that the COM server isn't garbage collected while a client is connected to it and vice versa.

The library comes with pre-implemented packages for automation. This includes support for IDispatch, ITypeInfo, and ITypeLib. For more flexibility, it provides an API set to invoke operations directly on a COM server without going through automation. Another important feature is to allow full access and manipulation of the Windows Registry in a platform-independent manner.

The implementation has been tested on all advanced Windows and Fedora platforms and displays upward compatibility from JRE 1.3.1. For more technical specifications please visit http://j-interop.sourceforge.net.

I'll show you an implementation using j-Interop to call the ITestCOMServer from Java is Listing 1.

As you can see it's pretty straightforward. The ITestCOMServer supports the IDispatch interface. I've shown both ways of accessing the COM server, i.e., via the dispatch interface as well as via a direct call. From my experience, I'd suggest using the IDispatch interface, whenever it's available. It's much easier to program that way.

Figure 5 is normally how a Windows COM client communicates with its COM server. j-Interop does this as well and so for the COM server it's like an ordinary COM client. Whether the Java application is on Windows or Unix, it doesn't matter.

More examples and documentation can be downloaded from the SourceForge site mentioned previously.

The advantages offered by using a non-native library like j-Interop include:

  • Clean integration of two of the leading technologies without writing any native code: j-Interop eliminates any need to write native (JNI) DLLs, cutting development time, and shortening the entire software lifecycle for the products (based on j-Interop). Such products are also saved from any kind of instable functions that result from poorly written native code (DLLs).
  • Accessing COM components from any type of Java client, including applets, EJBs, servlets, JSPs, and standalone applications: Since it's pure Java, j-Interop can be used within any J2EE server and on any platform (that supports Java).
  • Maximizing reuse of existing Java and COM components: All the plumbing on interoperating with COM servers is done by j-Interop, it makes reusing same components again, instead of porting back and forth between domains, a more lucrative and viable option.
  • There should no longer be a dependency on cross-platform resources thus minimizing cost and im-proving quality: The same resources for Java can be used without any additional training/competency building and the turnaround time can be brought down substantially. Not having to deal with native code also removes the complexity associated with maintaining the same. The code is now much cleaner and distinctly segregated between the two domains. Debugging the projects based on j-Interop is substantially easier than debugging JNI-based DLL projects.
  • Easier deployment since there's no custom code at the server: No special treatment has to be given to j-Interop clients, they just behave like standard DCOM clients. This is a big advantage in terms of administering the machines where the COM servers are deployed. The administrator doesn't have to care about security or the instability of native components bringing the server down (Denial of Service).
DCE/RPC
DCE/RPC stands for Distributed Computing Environment/Remote Procedure Calls. It originated from Network Computing System (NCS) RPC developed by Apollo (which later got acquired by HP).DCE/RPC specifies a complete set of APIs and Models to abstract the usual nuances of an RPC system like a named lookup, subsequent handshake\binding, passing of call data between two parties , handling communication errors, security etc.. It provides protocol support for both Connectionless and Connection Oriented communication and has a wide transport base, UDP, TCP/IP, SMB, HTTP to name a few. It also has a generic security model supporting several authentication mechanisms such as DCE, Kerberos and GSSAPI.

The full specification can be obtained from www.theopengroup.com.

More Stories By Vikram Roopchand

Vikram Roopchand is a Technical Architect working for Infosys Technologies Ltd. (www.infosys.com). He has about 8.5 years of experience and specializes in Cross Platform development across Content Management and Business Intelligence domains.

Comments (1) View Comments

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.


Most Recent Comments
Peter 01/11/07 07:17:29 PM EST

Fantastic article! I wish I had this library back in 99!

@ThingsExpo Stories
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Conference Guru has been named “Media Sponsor” of the 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to gre...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develop...
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...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Large industrial manufacturing organizations are adopting the agile principles of cloud software companies. The industrial manufacturing development process has not scaled over time. Now that design CAD teams are geographically distributed, centralizing their work is key. With large multi-gigabyte projects, outdated tools have stifled industrial team agility, time-to-market milestones, and impacted P&L stakeholders.
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
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 ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.