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CFDJ: Article

Part 1: Gateways to Fun

Here We Are Again!

The new release of ColdFusion has some interesting new Java features that just beg for a return and so here we are again! As with the previous series, I'll take the time to cover the basics of these new features before I dig a bit deeper.

Event Gateways
Undoubtedly one of the coolest new Java features in ColdFusion MX 7 is event gateways - opening up a whole new set of possibilities that were, at best, difficult, and at worst, impossible, with previous versions of ColdFusion. Providing a ColdFusion-friendlier means for working with new network protocols to more mundane things like interacting with operating system services, gateways will allow you to expand your Web applications in directions that were previously inaccessible.

The product team did an amazing job of providing a number of samples that really demonstrate the capabilities of this new feature. Add to that the really excellent Macromedia Developer Center article, some exciting postings in various blogs and some advanced articles waiting in the wings for CFDJ - all in all, there's definitely more than a little material available.

So what's the goal with this series? To provide easy-to-consume walkthroughs and tutorials for doing simple things like working with the gateway pages in the ColdFusion Administrator; and to provide a solid ground about the nuts and bolts of writing gateways.

The Basics
An event gateway is just a Java class that acts like a service to extend the ColdFusion Server. It differs from things like CFX tags in that they are threaded and can provide asynchronous communication with a ColdFusion application.

A template can call a CFX tag but that template will hang around until it is done processing before continuing to the next tag in the template. The expectation is that the CFX will perform some immediate task and return. It's possible to write a multithreaded CFX tag but there is no framework for having those subordinate threads report back once the main body of the CFX has returned control to the calling template. Event gateways solve this problem.

Event Gateway Administrator Pages
More than merely allowing you to configure things, the ColdFusion Administrator's Event Gateway pages can tell you a great deal about this new facility. As I cover the configuration pages I will introduce you to bits of gateway jargon that will be useful later when we start building applications that use gateways (for a complete list of the jargon check the product documentation; Developing ColdFusion MX Applications, Using Event Gateways, Event gateway terms and concepts).

The Event Gateways Settings page (see Figure 1) offers up a few minor, but important options, though in the Developer Edition of the product most of these settings are locked. The first is a check box for enabling gateways, which is checked by default. The second and third settings, processing threads and the size of the event queue respectively, will allow you to fine-tune gateway performance. The Developer Edition has these locked at 10 threads and 25000 events, which is quite generous for basic development.

[Note: Also on this page is a button to start the built-in SMS test server. You can use this sample SMS gateway and client simulator to explore more. I'm not going to cover it in this article as it is already discussed in some detail in the product documentation.

Gateway Types
The Event Gateways Gateway Types page (see Figure 2) provides a way for you to identify gateway classes to the ColdFusion Server, thus creating a type. There are four editable fields and a check box on this page for creating a gateway type and a list of the presently configured gateway types.

The first field, Type Name, is the name you will give the type (this is the gateway type in the jargon). There are no specific requirements, such as matching the name of the Java class or such, only something that is unique and at best meaningful to the purpose of the gateway.

The Description field provides an opportunity to input some textual content for providing more explanatory information about a gateway. The field has a limitation of 550 characters - so try to keep it simple.

The Java Class field is where you enter the name of the gateway's Java class, complete with package. This field is not so frugal as the Type Name or the Description, though if you've a class name in excess of 550 characters you might consider some package reordering and less verbose naming standards. The Java class must indicate a class that is already present in the ColdFusion Server's classpath or else it will fail when you try to add the new gateway type. Since adding jars to the Server's classpath requires a restart you will want to verify this prior to adding new gateway types. New jars can be added in the ColdFusion Class Path field on the Java and JVM page in the Server Settings section of the Administrator.

The Startup Timeout field indicates the number of seconds that the Server will allow during the startup of an event gateway before it kills it; by default this is 30 seconds. This seems a bit excessive since most system operations occur in milliseconds - and even long operations in the thousands of milliseconds fall well below this threshold.

Out of the box the Developer Edition has seven gateway types configured (shown in Figure 2 above). These default gateways provide a number of very useful facilities that satisfy many of the both basic and things-in-vogue services.

Gateway Instances
The Event Gateways Gateway Instances page (see Figure 3) allows you to create instances of a specific gateway type (a gateway instance in the jargon). This page provides three edit fields and two dropdown lists for configuring an instance and a list of the configured gateway instances.

The Gateway ID field allows you to specify a label name for a particular instance. This is the name (or gateway ID in the jargon) that will be used to programmatically reference the event gateway for sending messages. It does not have any specific requirements, though it should be unique and meaningful. The form field displayed in the browser has a limit of 550 characters which ought to be plenty even for host providers that might like to prefix a specific gateway instance name with a domain name or a corporate server prefixing with a department name.

More Stories By Guy Rish

Guy Rish is a ColdFusion and .NET developer at Vente as well as President at Gestaltech. He is an active developer and writer for various languages and technologies, and has contributed work in books on ColdFusion MX, Flash MX, and Dreamweaver MX. He blogs at ccoj.coldfusionjournal.com.

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