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ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

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ColdFusion: Article

ColdFusion MX and .NET 101

COM Interop to a .NET assembly can be successfully implemented with CFMX

Some of you may be thinking, ColdFusion (CF) and .NET? Why do it? We hear you. It is understandable that CF, running on top of J2EE, adds a layer of complexity when integrating with interfaces written with Microsoft-centric technologies. The mission of this article is to decipher the complexities and shed some light on how CF can be coupled with .NET solutions to allow for interoperability throughout your IT universe.

.NET is breaking in big in the IT arena and many organizations are adopting it as a standard for developing the business modules associated with their applications. A benefit that .NET brings with it is a true object-oriented methodology to developing software. I liken the C# language as the fraternal twin to Java; though with these benefits, it also brings an increased level of complexity for doing routine tasks that ColdFusion programmers have grown to take for granted.

You can't knock Joe programmer for wanting to learn a new technology. This outlook is preached continually from both Macromedia and Microsoft. With constant new releases and their advantages, the standouts must increase their understanding in all facets of the industry to stay a millimeter ahead of the curve. "What's that you say?" "You're not certified in CFMX...?" "Wait, what?" "You're not working on your MCAD/MCSD?" "Well, what are you waiting for?" Enough with our attempts at lighting a fire under you to expand your horizons, you're reading this article and we commend you for it.

With the J2EE release of ColdFusion MX (CFMX) and the new version 6.1, code-named "Red Sky," Macromedia has continued to support COM (Component Object Model)-based solutions via a COM bridge. CFMX uses a Java-to-COM wrapper that was developed by Intrinsyc. The package is known as J-Integra and details on this component can be found at http://ja.net.intrinsyc.com/. Their product info area has some excellent examples on how to implement J-Integra with various combinations of Java/COM components. J-Integra is instantiated through the cfobject tag or with cfscript utilizing the function CreateObject.

In our example in Figure 1, the cfobject tag was used. Notice the class that is called and the name we assign to the object. Once the object is successfully created, the CreateBarCodeImage method is accessed and the appropriate required parameters are passed to the component. The resulting page output is seen in Figure 2. The application structure is dumped, displaying the contents of the applicationname key and bcg (barcodgen) key. Notice how the object information and available related methods are displayed. CreateBarCodeImage is the method used to generate the barcode image seen in the output.

The ColdFusion code used for the example is an enhanced methodology for instantiating a COM component with ColdFusion. This enhanced methodology outlined in the following Macromedia TechNote, www.macromedia.com/support/coldfusion/ts/documents/tn18210.htm, allows the initial creation of the object to be stored in memory via application or session variables. This also enables the object to be shared across requests and easily accessed with a custom tag or cfmodule. This solution came about due to the observation that there was an increase in creation time in CFMX compared to CF 5. For the sake of argument, this technique is being demonstrated only to provide information in case you come across this issue. No performance issues were witnessed with the .NET/COM component utilized in this article.

So you can create an instance of a COM object in CFMX; ColdFusion has always made this an easy task. This gets interesting when you look at how this is actually achieved. Let's peek under the hood, shall we? Figure 3 shows how CFMX and J-Integra hook into various automation components. There is a similar diagram at http://ja.net.intrinsyc.com/j-integra/info/.

Now for a little light on what might be happening behind the scenes when you call into a .NET object through COM. Just to get the high-level talk out of the way, all .NET languages are compiled into an intermediate language called Microsoft Intermediate Language, also known as MSIL. Like Java, MSIL runs in a virtual machine, called the Common Language Runtime (CLR).

For those who have not dealt with COM before, it provides a binary specification allowing interaction between languages. COM also provides facilities for dynamic discovery of interfaces that an object has exposed.

COM was designed to provide a standard means of marshalling between languages; both platforms must perform some degree of marshalling between types in the respective runtimes and the facilities for accessing them specified by COM. The CLR provides a transparent proxy allowing .NET assemblies to be called from COM clients, called the COM Callable Wrapper (CCW). It is through the CCW that ColdFusion is able to indirectly interface with a .NET assembly (see Figure 4).

For this example we have chosen to implement a very simple component in C#, which when given a series of parameters, will generate an image of a barcode for use within a Web page. The component happily creates images of barcodes on request; it is not the job of this component to manage the lifespan of the files it creates. That task is better left to the consuming application (CFMX).

There are only a few steps needed to have a .NET component ready to be consumed directly from CFMX. First, the code must be written. Second, the assembly must be signed with a strong name and compiled. We generate a strong name key and associate it with the assembly by using the command-line utility sn.exe. Third, as with any .NET component, in order to be visible to COM clients, the assembly must be registered as a COM component. In our example we use regasm.exe to fulfill this task. Finally, we add our assembly to the Global Assembly Cache (GAC) where it is cached and ready to be called by a COM client.

Let's start by taking a look at the C# source file. We will break down each section with a brief explanation and detail any portions of the code that have particular significance to COM interop.

In the code block shown in Figure 5, we are specifying the namespaces that we will be utilizing, such as System.Drawing. We then specify that our class will be placed in the "BarCodeInterop" namespace. The namespace we use has significance in determining the common name we will use to refer to the component. In keeping with the binary interface concepts of COM, it is required that we define a public interface for the method that we will be implementing for our functionality.

COM components implement the IDispatch interface. The IDispatch interface exposes the contents of an object to all programs that support Microsoft Automation. The COM callable wrapper that is responsible for implementing IDispatch for our component will use the interface we have specified to return a COM signature for our method "CreateBarCodeImage". When we use OLEView to inspect the interface our COM object exposes, we get the method signature detailed in Figure 6.

In Figure 7 the first notable item is an "attribute" that provides direction to the compiler for the type of COM interface we want to implement. Using a class interface type of none, our class can provide access only through a late bound interface exposed by IDispatch. Note that our class implements the interface "IBarCodeGenerator" that we defined earlier.

Figure 8 contains the implementation of the required interface method "CreateBarCodeImage". The method creates an image file through the file path specified, with a width, height, and font size specified.

The steps that follow the writing of our code include signing the assembly, adding the assembly to the global assembly cache, and registering the assembly for COM interop. In order to sign our assembly we must first generate a strong name key. We use Microsoft's sn.exe to generate the key (see Figure 9).

Once we have a strong name key, we place the file in the root of our project and associate it with the assembly by editing the "AssemblyInfo.cs" source file. AssemblyInfo.cs contains attributes that allow you to specify component information such as company, version, etc. There are also three attributes that are involved in signing an assembly. We specify our strong name key file by editing the AssemblyKeyFile attribute as:

[assembly: AssemblyKeyFile("..\\..\\BarCodeInterop.snk")]

After signing the assembly and compiling it, the assembly is ready to be added to the global assembly cache. The .NET framework installs the .NET Configuration wizard located under Control Panel -> Administrative Tools, which allows the addition and configuration of assemblies to the global assembly cache, among other things (see Figure 10).

Simply click "Add an Assembly to the Assembly Cache" task link to browse to the assembly location and complete the step of adding the assembly to the global assembly cache.

The final step needed to expose our component to COM is registering the component as a COM component in the system registry. This task is accomplished using the command line utility regasm.exe (see Figure 11).

A typical registration would look like this: "regasm C:\BarCodeInterop.dll".

With the .NET component wrapped and registered, CFMX is able to see the objects' methods and their input parameters.

There you have it! An example that proves COM interop to a .NET assembly can be successfully implemented with CFMX. Why do it? This question has been answered.... It works, and it works well. Organizational leadership must assess costs respective to redesign with the ever-tightening budgets associated with IT. An environment that has been structured around COM and ColdFusion can now easily be converted to .NET and ColdFusion.

With all that goes into the base concepts of integrating CFMX and .NET solutions, we look forward to the next article on the subject of using a native .NET interface for CFMX known as Black Knight. We will also be discussing Web services solutions and their performance parameters. Until then...

More Stories By Jeffrey Bouley

Jeffrey Bouley is the founder of Strikefish, Inc., in Orlando, Florida. He is a certified ColdFusion developer and a former Macromedia Consultant. He currently provides software architecture and development solutions for ColdFusion, Java, .NET, XML, SQL Server, and Oracle Integration (www.strikefish.com).

More Stories By John Parrish

John Parrish has spent his career developing component-oriented systems for the Web. He also serves as director for Jikapa Interactive Inc, an interactive solutions firm providing software and corporate design solutions (www.jikapa.com).

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Most Recent Comments
Shane Sauer 07/12/05 01:25:13 PM EDT

Intrinsyc Software has just released a new J-Integra product for J2EE/.NET interop... J-Integra Espresso! J-Integra Espresso is a true CORBA solution for the Microsoft .NET framework. This Object Request Broker (ORB) has been written in C# and connects Java and CORBA with the .NET world. J-Integra Espresso has been developed entirely as managed code and can therefore be accessed by all .NET languages (C#, ASP.NET, etc...).

J-Integra Espresso features:
* Pure .NET implementation, 100% managed code
* Bi-directional: .NET to Java/CORBA and Java/CORBA to .NET
* Enables interoperability with any J2EE or CORBA infrastructure that is IIOP-compliant such as VisiBroker, Orbix, JacORB, JBoss, WebLogic, and WebSphere
* Support for IIOP transport protocols including SSL and TLS over IIOP (SSLIOP)
* Marshalling objects by reference or by value
* One-sided deployment (no touch on J2EE AppServer)

A free evaluation version can be downloaded at http://j-integra.intrinsyc.com/


Shane Sauer
Intrinsyc Software International, Inc.
J-Integra Interoperability Solutions
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