|By David Shadovitz||
|August 23, 2002 12:00 AM EDT||
As a member of Team Macromedia I respond to a lot of questions posted on the Macromedia Forums ( http://webforums.macromedia.com/coldfusion).
My responses often contain sample code, and I realized that many questions arose over and over again. So rather than repeatedly typing the same code snippets, I created a small Web site ( http://members.evolt.org/dshadovi) to hold them. Now I can simply point to the relevant page when I respond to a question.
Being a nosy guy, I wanted to know how the site was being used. Yes, there are tools that do a wonderful job of presenting this information, such as Analog and WebTrends. But they require access to the Web server logs, which I don't have. Anyway, I wanted to roll my own. That's the fun of CF!
My first cut at tracking traffic was to use session management and CFMAIL. I set up Application.cfm to send me a message whenever a new session was started. It worked, but sometimes the mail was overwhelming. The biggest problem with this technique, though, was that it made it hard to perform analysis. I couldn't easily determine which page was getting the most hits, or how many visitors use Netscape.
The right technique, and the one I'll describe in detail, is to record the site traffic in a database and use CF's graphing capabilities to display it.
Recording the Site Traffic
Using MySQL, I created a single table to record information on each hit. Listing 1 shows the structure of that table. As you can see, each record contains the page visited, the visitor's IP address and browser (the user agent), and the date and time of the visit.
A record is inserted into that database table each time the site is hit. Listing 2 shows the code to do this. This code belongs in Application.cfm.
Note that the INSERT statement doesn't include the time of the hit. When no value is specified for a field of type TIMESTAMP, which cannot be null, MySQL automatically inserts the current date and time. I could have passed the value #CreateODBC DateTime(Now())#, but it's more efficient to let the database take care of it.
You'll also see that I've massaged the name of the page a bit. For all of the pages on my site, CGI.SCRIPT_ NAME starts with "dshadovi/", so I strip this off. I also strip off the ".cfm" extension, since the name of the page, not the extension, is what's important for the graphical display of the traffic.
Don't chide me for not using CFQUERYPARAM. I do use it, but I omitted it here in the interest of readability.
Displaying the Site Traffic
Now that the pieces are in place to record the site traffic, we're ready to write the code to graphically display it. Listing 3 is a complete CFML template that does exactly that. Figure 1 is a screenshot of this template in action; you can also see it live at http://members.evolt.org/dshadovi/traffic.cfm.
An exception is an error that occurs at runtime. Most if not all programming languages offer a way to handle exceptions. The goal of this handling is to minimize the damage done by the exception. Sometimes it's possible to repair the problem or to work around it. If not, the application can at least provide a detailed error message.
ColdFusion provides CFTRY/CFCATCH, modeled on C's try/catch statements. Using this construct, the ColdFusion Server tries to execute a designated block of code, and if it catches any exceptions it executes another designated block of code.
I use CFTRY/CFCATCH in Listings 2 and 3. Let's take a closer look.
Listing 2 shows a snippet of code in Application.cfm, which inserts a record into the database. The record contains information about the current page visit. Now, the main goal of my Web site is to provide helpful code to other programmers. Tracking visits to the site is only a minor goal, mostly to satisfy my curiosity. I certainly wouldn't want problems with this minor goal to interfere with my major goal.
What kinds of problems might happen? Well, the database server could go down, or the database's transaction log may be full. Either of these would make it impossible to insert a record, but there's no reason why that should render my site unusable. So I put the CFQUERY tag in a CFTRY block. If there are any runtime errors, the CFCATCH code block is executed. The CFCATCH block here is empty because there's no remedial action to take. If a record can't be inserted, that's okay. Execution continues on with whatever code follows the entire CFTRY block.
In Listing 2 the protected code block, a CFQUERY tag, did under-the-covers work. Not so for Listing 3, in which the protected code block is a CFGRAPH tag. There is surely a user impact if the graph isn't displayed. So in this case the CFCATCH block isn't empty. Rather, it lets the user know there should have been a graph, and points to a possible cause of the problem. (Okay, I should also have code here to automatically e-mail the details of the problem to the server administrator, or to log the problem.)
I've shown here two uses of CFTRY/CFCATCH. Beyond this, CFTRY's TYPE attribute lets you take different actions based on the type of exception. The ColdFusion Server also provides CFCATCH variables that contain details of the exception. And CFTHROW gives you the power to declare that an exception has taken place.
Using CFTRY/CFCATCH to handle exceptions lets you compartmentalize your code, leading to more robust applications.
The code uses CFGRAPH, introduced in CF5. Those of you using earlier versions of CF are not out of luck, though. You laggards can use the old bar chart Java graphlet that used to come with CF. Do a Google search on "About ColdFusion Graphlets" for more information, or contact me. At the other end of the spectrum ColdFusion MX offers CFCHART in place of CFGRAPH, but that should be a straightforward change.
Each bar in the bar graph represents a page, and the bar's height indicates the number of hits on that page. CFGRAPH's URLColumn attribute provides a drill-down capability when using the Flash format. I've set it up so that clicking on a bar will lead you to that bar's page.
You may notice that although I record each visitor's IP address, I don't display it anywhere. That's because I record it for hacker control, not for a simple view of the site traffic.
A programmer's work is never done (especially when he's got a paying client), so here are some thoughts for future enhancements:
Let me close with thanks to evolt.org, a community for Web developers, for hosting my site.
|David Shadovitz 11/01/02 04:00:00 PM EST|
I've found a good use for my traffic information. One site which I track contains an important search feature. Now, on the page which displays the form for a search, I also display the user's last few searches. They are displayed as hyperlinks which the user can simply click on to re-do a search.
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