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DirectoryWatcher Event Gateway: Ditching the Scheduler

A textbook case for using the gateway

I remember sitting at a ColdFusion conferences (probably CFUN) back when CFMX 7 was still in its pre-beta stage and watching as Ben Forta revealed some of the new features. There was a mixed reaction when he talked about event gateways.

While the idea of having messaging built into ColdFusion seemed appealing to most of the audience, the idea of watching a directory for its content to change wasn't as convincing. As I looked around at people's faces, I saw a mixture of excitement, inspiration, and blank stares.

I would guess the blank stares belonged to those for whom directories are relatively static things. Files on the server only change at the behest of a developer, so what's the big deal about having the server watch to see when they change? Let's face it: directory listings are pretty boring on first consideration.

I, on the other hand, couldn't wait to get my hands on CFMX 7 in production, because the DirectoryWatcher event gateway promised to solve a problem that had become all too familiar at that point in my career. I'll bet it's a situation that you may have run into yourself at some point, though I'm sure the implementation details will be a bit different in your environment.

The project we were working on at that time involved interfaces with two other systems. For the first system, we had a very smooth interface that employed a Data Migration Zone (DMZ) database to allow our Oracle database to exchange data with the other system's Oracle database without either of us needing authorization to the other system. It all ran beautifully and automatically.

The second system, though, was a bit less elegant. Our interface on that end was done through the exchange of XML datasets between the other system (Microsoft SQL Server) and ours (Oracle). While the XML part of the equation was quite nice, the channel that had been chosen for transfers was FTP. So the other system was allowed to upload files to our server using an FTP script. To import the XML data from an uploaded file into our system we ran a CFML template that would read any files in the directory, parse the XML, insert the data into our system, and move the file to a permanent directory on the server. This template was scheduled to run once every 15 minutes, using the CF Scheduler. Figure 1 shows how the process worked.

Whenever the customer system needed to send us data, it would generate an XML dataset, save it according to an agreed-on naming convention, and send it to our server via FTP. Once the dataset was on our server, the scheduled job would detect the new file the next time the scheduled job ran, and handle it accordingly.

Now, considering possible alternatives (like e-mail or even snail mail), our scheduled template solution wasn't bad at all. It worked. However, the schedule meant that inbound data might sit in a queue of sorts (the FTP directory) for up to 15 minutes, waiting on the scheduled template to run. That's why I was immediately interested in the DirectoryWatcher event gateway. I wanted a way to get rid of the time lag between when we got a dataset and when it got processed into the database.

In fact this situation turned out to be a textbook case for using the gateway. We already had the process in place and tested; the only thing we had to do was set up the gateway to kick off the process instead of having it wait for the next scheduled time. All we had to do was set up the gateway and write a configuration file for it, and a CFC to handle the events.

Setting up the DirectoryWatcher is an exercise in simplicity. In the ColdFusion Administrator, select Gateway Instances under the Event Gateways menu item on the left, and fill out the form for the new gateway instance. An example is shown in Figure 1.

The Gateway ID is an arbitrary string. I used "ftpSentry" since I wanted this instance to watch over my FTP directory. The Gateway Type is, of course, DirectoryWatcher. CFC Path and Configuration File are full paths to the gateway's handler CFC and configuration file, respectively. In the example, I used DirectoryWatcher.cfc and DirectoryWatcher.conf, respectively.

After clicking OK, the new instance shows up in the list of Configured ColdFusion Event Gateway Instances, as shown in Figure 2 (the new instance is highlighted there). Note that it's not yet running - we'll take care of that after we write the handler CFC and configuration file. Also, I named the configuration file with a .conf extension - a bit of Linux influence sneaking in there - where the examples use .cfg. ColdFusion doesn't care what extension we use.

The configuration file for a DirectoryWatcher gateway is very simple - just name=value pairs, each on its own line. At a minimum, it contains the directory we want to watch in the form directory=c:/ftpInbox. The other values are optional and we didn't need any of them for this example, but I'll mention them briefly for reference purposes.

The recurse option allows the gateway to watch all sub-directories of the specified directory. Its default value is no. If it's set to yes, all sub-directories of the specified directory will be watched.

The interval option specifies how long to wait between checks of the directory. Its default is 60000 (60 seconds). The extensions option specifies which filename extensions to watch. Its default is * for all extensions. If we want to watch more than one extension, the value should be a comma-delimited list. So if we wanted to watch for XML and CSV files, we would need extensions=xml,csv.

The xFunction options specify which function in the gateway's CFC will be called in response to an action in the directory. They are changeFunction, addFunction, and deleteFunction and their default values are onChange, onAdd, and onDelete, respectively.

For simplicity's sake, we used all the defaults, so our configuration file only has one line: directory=c:/ftpInbox. The only thing left to do now is set up the handler CFC for the gateway. Since we already had the code in place to handle our import tasks, the CFC really only needed one function - onAdd - to call that code. But I liked the idea of monitoring the FTP directory for all file activities and keeping a log, so I started with the sample CFC from the DirectoryWatcher example that comes with CFMX and added a bit of code to the onAdd function to suit our needs. The code is in Listing 1.

Each event triggers its corresponding function, and each function writes a line to the ftpSentry log. In addition, the onAdd event uses <cfmodule> to call the desired template, and writes an error message to the log if any errors are thrown. Some example entries from the log are shown in Listing 2. You can see how the file ASDO200607112876.xml was added to the directory then deleted a minute later. This is due to the automated process reading the file, adding its data to the database then moving the file to an archive directory. (see Figure 3)

So using the DirectoryWatcher event gateway improved our customer response time by reducing the scheduled wait from a 15-minute maximum to one-minute maximum. The other benefit is that our handler code doesn't fire unless a change is made to the directory. Under the scheduler scenario, our process read the directory every 15 minutes and ran some logic to determine if there were new files present. If there were, it would call the template to read and insert the data and move the file to the archive directory. The new approach with the event gateway is much simpler in terms of the code we had to write and more efficient in processing terms.

Of course, this is just one application of the DirectoryWatcher event gateway. You can use instances of it in your own system to trigger all manner of processes based on the activity on your server. For example, you could monitor a directory for file-size limits, and remove any new files after the directory reaches the limit. Or maybe you want to remove older files first, providing space for new files. Really the sky's the limit in terms of file manipulation. The DirectoryWatcher just gives you a window into your filesystem so you can automate these tasks.

More Stories By Jeff Peters

Jeff Peters works for Open Source Data Integration Software company XAware.

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