ColdFusion CFCatch Tags Catch Exceptions Based On Type Hierarchy

Posted June 11, 2008 at 8:25 AM by Ben Nadel

Tags: ColdFusion

I learned an interesting fact from Brett last night at the New York ColdFusion User Group - ColdFusion's CFThrow / CFCatch combination works in a hierarchical fashion based on the dot-notation of the exception type being thrown. What this means is that as you add "dot-something" to an exception type, it becomes more specific. For example, my blog might throw a bunch of "kinky" exceptions:

Kinky

(This is all theoretical - my blog doesn't throw custom exceptions) However, if an error happens in the blog, it might throw a blog exception:

Kinky.BlogException

This is a really general to the blog section, but even in there, we can get more specific:

Kinky.BlogException.EntryNotFound

EntryNotFound is a type of BlogException which is a type of Kinky exception. That's what I mean when I say hierarchical.

Now, when it comes to catching errors that bubble up through the pipeline, most people just use a single CFCatch tag to catch all errors. You can, however, specify the type of error that gets caught by a specific CFCatch tag. This allows you have multitple CFCatch tags in a single CFTry / CFCatch statement, each of which is listening for a different type.

All that stuff, I already knew; what was new to me was that the CFCatch tag will catch errors based on the exception hierarchy. What I mean by this is that if you have a CFCatch tag that is listening for exceptions of type "Kinky", it will catch exceptions of type "Kinky" as well as type "Kinky.BlogException" because "Kinky.BlogException" is a sub-class (if you will) of the "Kinky" exception type.

Let's run a quick demo to see CFCatch in action:

  • <cftry>
  •  
  • <cfswitch expression="#RandRange( 1, 4 )#">
  • <cfcase value="1">
  •  
  • <!--- Throw exception. --->
  • <cfthrow type="Kinky" />
  •  
  • </cfcase>
  • <cfcase value="2">
  •  
  • <!--- Throw exception. --->
  • <cfthrow type="Kinky.BlogException" />
  •  
  • </cfcase>
  • <cfcase value="3">
  •  
  • <!--- Throw exception. --->
  • <cfthrow type="Kinky.BlogException.EntryNotFound" />
  •  
  • </cfcase>
  • <cfcase value="4">
  •  
  • <!--- Throw exception. --->
  • <cfthrow type="Kinky.InvalidUserAgent" />
  •  
  • </cfcase>
  • </cfswitch>
  •  
  •  
  • <!--- Catch all blog exceptions. --->
  • <cfcatch type="Kinky.BlogException">
  • <cfoutput>
  •  
  • <p>
  • #CFCATCH.Type#<br />
  • Kinky.BlogException
  • </p>
  •  
  • </cfoutput>
  • </cfcatch>
  •  
  • <!--- Catch all kinky unhandled kinky errors. --->
  • <cfcatch type="Kinky">
  • <cfoutput>
  •  
  • <p>
  • #CFCATCH.Type#<br />
  • Kinky
  • </p>
  •  
  • </cfoutput>
  • </cfcatch>
  •  
  • </cftry>

Notice that in this demo, we are throwing four possible exceptions, but only catching two types of exceptions. Running this code a few times, we get the following output:

Kinky.BlogException
Kinky.BlogException

Kinky.InvalidUserAgent
Kinky

Kinky
Kinky

Kinky.BlogException.EntryNotFound
Kinky.BlogException

Kinky.InvalidUserAgent
Kinky

Kinky.BlogException
Kinky.BlogException

Kinky.BlogException.EntryNotFound
Kinky.BlogException

Notice that the even though we had only two CFCatch tags, we were able to catch all four thrown exception types. This is because our CFCatch tags were catching general exception types which covered both the general and the more specific.

This seemed pretty cool to me. Overall, I have not really made much use of custom exceptions and exception handling, but the more I see it, the more it is something that I want to get into.



Reader Comments

Brett S
Jun 11, 2008 at 1:55 PM // reply »
16 Comments
11 Points

After all the tidbits I've learned from this blog over they years I'm glad I was able to give back. I've always enjoyed the way you get under the hood on your posts.

I use cfthrow *a_lot* and I've learned some other tricks and techniques that really come in handy. Perhaps I can follow on at another NYCFUG in the future.

cheers,

.brett


Ben Nadel
Jun 12, 2008 at 7:39 AM // reply »
10,640 Comments
69,065 Points

@Brett,

I am slowly getting more and more into exception usage. For the longest time, I had this weird feeling like I had to protect my users; I was always drying to recover from invalid data formats that would *only* occur if someone changed the HTML (ex. Altering a SELECT menu to return non-numeric values). For some reason, I felt the need to NOT give errors to people who were malicious.

But, that is changing. I no longer feel like I need to protect people from themselves. I am getting more comfortable with presenting error pages when people forcibly cause errors.

But, more than that, I am finding exceptions very useful for lots of other things. Right now, I am using them heavily within a web service API that I have for an AJAX application - the entire API is wrapped in CFTry / CFCatch and the different sub-parts can throw exceptions that the API will catch and return a more meaningful API response.

Anyway, cool stuff.


Don
May 14, 2009 at 1:03 PM // reply »
57 Comments
608 Points

I'm nibbling around the edges on this. It seems that exceptions could be a great tool, but I'm not quite seeing how I can integrate them. Do you have any other posts regarding their use? Especially custom exceptions.


Ben Nadel
May 19, 2009 at 9:42 AM // reply »
10,640 Comments
69,065 Points

@Don,

I have started to use exceptions more in validation; but, I am nowhere near having anything that I'm happy with. Still working on it.


Post A Comment

Comment Etiquette: Please do not post spam. Please keep the comments on-topic. Please do not post unrelated questions or large chunks of code. And, above all, please be nice to each other - we're trying to have a good conversation here.

Please review the following issues:

Author Name:
Author Email:
Author Website:
Comment:
Supported HTML tags for formatting: <strong>bold</strong>   <em>italic</em>   <code>code</code>







  • Help Wanted - Find Your Next ColdFusion Job
InVision App - Prototyping Made Beautiful With Prototyping Tools Ben Nadel's Company - Epicenter Consulting Recent Blog Comments
Misty
Feb 12, 2012 at 3:37 AM
Learning ColdFusion 8: CFImage Part III - Watermarks And Transparency
Hi Ben, Just to ask currently it is placed bottom right corner, if i need to replace the same rendered image on the bottom left side or in the bottom center, how that can be calculated. bottom ce ... read »
Raphael Mobis
Feb 11, 2012 at 9:29 PM
Use jQuery's SlideDown() With Fixed-Width Elements To Prevent Jumping
I can't say how glad I am that I found your post. Thank you very much. ... read »
Bartezz
Feb 10, 2012 at 7:21 PM
jQuery AJAX Strips Script Tags And Inserts Them After Parent-Most Elements
Update! Instead of $(eval(options.insertAfter)).after(data['insertData']); I now use: var ajaxNode = document.createElement('span'); var parent = $(eval(options.insertAfter))[0].parentNode; ... read »
Bartezz
Feb 10, 2012 at 6:18 PM
jQuery AJAX Strips Script Tags And Inserts Them After Parent-Most Elements
encountered this same, what I consider, jQuery bug last week. I'm building a site in which I load some content via AJAX. This content contains Linkedin share button placeholders which Linkedin API ne ... read »
Drew Wells
Feb 10, 2012 at 11:30 AM
Cross-Origin Resource Sharing (CORS) AJAX Requests Between jQuery And Node.js
After you understand the concepts here, this is an awesome cheatsheet for enabling CORS in just about anything http://enable-cors.org/ ... read »
JM
Feb 10, 2012 at 9:10 AM
My Safari Browser SQLite Database Hello World Example
@Amy, Here is a very good tutorial on how to use JOIN: http://www.sqltutorial.org/sqljoin-innerjoin.aspx ... read »
Stefan Richter
Feb 10, 2012 at 4:42 AM
Building A Twitter-Inspired RESTful API Architecture In ColdFusion
This is great, very useful Ben. I spotted a small typo in the api.cgm listing: <cfthrow type="Unauthroized" /> Cheers Stefan ... read »
Hugh
Feb 9, 2012 at 10:35 PM
CFDirectory Filtering Uses Pipe Character For Multiple Filters (Thanks Steve Withington)
I was wondering if there would be a filter you could apply so that you got everything but what you included in the filter. As in show me all docs that are not a .pdf. ... read »