What is the use of cftry / cfcatch? And How useful is it?

Without looking into what cftry actually does, the first thought that popped into my head was probably good for preventing errors. But error handling is sometimes time consuming and you need to know exactly what error could happen. This type of thought is why I overlooked the great tags of cftry and cfcatch. It is extremely easy to use and only makes your code more bullet proof.

The logic behind cftry / cfcatch is simple:
<cftry>
Run some code
<cfcatch type=”any”>

What to do if the code generated an error
</cfcatch>
</cftry>

This concept seems simple, but the beauty of it is that if the code generates an error, the page will continue to load as if nothing is wrong. The user sees no blue error screen of death. Furthermore, if you catch the error you can run some other code that gives different output.

If you look at the cftry / cfcatch tags in terms of an IF clause, the code becomes very easy to use and understand.

<cfif> this code works
then use it.
<cfelse> that code didn’t work
then use this code.
</cfif>

Now let’s see some example code:
<cfif ISDEFINED(FORM.btnSubmit)>
                <cfquery name=”getUserName” datasource=”DSNdatasource”>
                                SELECT UserName
                                FROM tlbCustomer
                                WHERE UserID = 1;
                </cfquery>
</cfif>
<cfoutput> #getUserName.UserName# </cfoutput>

In this code, if the query fails, the user will get a database query error (i.e.) Blue Error Screen.

Now let’s see what a cftry / cfcatch can do for us:


<cfif ISDEFINED(FORM.btnSubmit)>
                <cftry>
                                <cfquery name=”getUserName” datasource=”DSNdatasource”>
                                                SELECT UserName
                                                FROM tlbCustomer
                                                WHERE UserID = 1;
                                </cfquery>
                                <cfset name=”myuser” value=”getUserName.UserName”>
                <cfcatch type=”database”>
                                
                                <cfset name=”myuser” value=”UNKNOWN”>
                </cfcatch>
                </cftry>
</cfif>
<cfoutput> #myuser# </cfoutput>

If the query fails and generates an error, you will not see the ColdFusion Error page, but you will see the output of “UNKNOWN”.