Error Handling in ColdFusion

By default, ColdFusion generates its own error messages when it encounters errors. In addition, it provides a variety of tools and techniques for you to customize error information and handle errors when they occur, including the following techniques:

You can specify custom pages for ColdFusion to display when a ColdFusion page is missing or if it encounters an exception error during the processing of a page (the Site-wide Error Handling page). You specify these pages on the ColdFusion Administrator Server Settings page.
You can use the cferror tag to specify ColdFusion pages to handle specific types of errors.
You can use the cftry, cfcatch, and cfthrow tags to catch and handle exception errors directly.

The remaining sections in this chapter provide the following information:

The basic building blocks for understating types of ColdFusion errors and how ColdFusion handles them
How to use the cferror tag to specify error-handling pages
Logging errors
How to handle ColdFusion exceptions

Understanding ColdFusion errors

Before you can effectively managee ColdFusion errors, you must understand the error types and how ColdFusion handles them.

ColdFusion error types

ColdFusion errors can help you to debug your application and provide feedback to users. There are several types of errors in ColdFusion:

Missing template These errors occur if ColdFusion Server gets a request for a page that it cannot find.
Validation These errors occur when a user violates the server-side form field validation rules in a form being submitted. You specify server-side form validation by using hidden form fields. Data validation errors should not be confused with code validation.
Exception Exceptions are events that disrupt an application's normal flow of instructions. There are three general types of exceptions:
- Error responses from external services, such as an ODBC driver or CORBA server
- CFML errors or the results of cfthrow or cfabort tags
- Internal errors in the ColdFusion Server

How ColdFusion handles errors

The following pseudo-code program illustrates how ColdFusion handles errors. The rest of this expands on this outline:

Case missing template error

  ColdFusion displays either a standard error page or an error page

  that you specify as the Missing Template Handler in the Administrator

  Server Settings Missing Template Handler field.

Case validation error

  If cferror in application.cfm specifies a validation error handler

    Use error page specified by cferror

  Else

    Use standard CFML validation error message format

  Endif

Case exception error

  If a cferror tag in aplication.cfm specifies a monitor error handler

      for the exception type

    Use the Monitor error page; when the page exits continue handling

    the error as follows

  Endif

  If code with error is inside a cftry tag and the exception type is

       specified in a cfcatch tag (see Note)

    Execute code in cfcatch tag

  Else If a cferror tag specifies an exception error handler for the

      exception type

    Use error page specified by cferror

  Else If Administrator Settings Site-wide Error Handler field

      specifies an error handler page

    Use custom error page

  Else If a cferror tag specifies an request error handler

    Use error page specified by cferror

  Else

      Use standard CFML error message

  Endif

Note

If the current tag is nested inside other tags, the CFML processor checks the entire stack of open tags until it finds a suitable cftry/cfcatch combination or reaches the end of the stack.

Developing ColdFusion Applications
Preventing and Handling Errors