Developing ColdFusion MX Applications with CFML
Handling Errors

Specifying custom error messages with cferror

Custom error pages let you control the error information that users see. You can specify custom error pages for different types of errors and handle different types of errors in different ways. For example, you can create specific pages to handle errors that could be recoverable, such as request time-outs. You can also make your error messages consistent with the look and feel of your application.

You can specify the following types of custom error message pages:

Type	Description
Validation	Handles server-side form field data validation errors. The validation error page cannot include CFML tags, but it can display error page variables. You can use this attribute only on the Application.cfm page. It has no effect when used on any other page. Therefore, you can specify only one validation error page per application, and that page applies to all server-side validation errors.
Exception	Handles specific exception errors. You can specify individual error pages for different types of exceptions.
Request	Handles any exception that is not otherwise-handled. The request error page runs after the CFML language processor finishes. As a result, the request error page cannot include CFML tags, but can display error page variables. A request error page is useful as a backup if errors occur in other error handlers.

Specifying a custom error page

You specify the custom error pages with the cferror tag. For Validation errors, the tag must be on the Application.cfm page. For Exception and Request errors, you can set the custom error pages on each application page. However, because custom error pages generally apply to an entire application, it is more efficient to put these cferror tags in the Application.cfm file also. For more information on using the Application.cfm page, see Chapter 13, "Designing and Optimizing a ColdFusion Application".

The cferror tag has the attributes listed in the following table:

Attribute	Description
Type	The type of error that will cause ColdFusion to display this page: Exception, Request, or Validation.
Exception	Use only for the Exception type. The specific exception or exception category that will cause the page to be displayed. This attribute can specify any of the types described in "About ColdFusion exceptions".
Template	The ColdFusion page to display.
MailTo	(Optional) An e-mail address. The cferror tag sets the error page error.mailTo variable to this value. The error page can use the error.mailTo value in a message that tells the user to send an error notification. ColdFusion does not send any message itself.

The following cferror tag specifies a custom error page for exceptions that occur in locking code and informs the error page of the of an e-mail address it can use to send a notification each time this type of error occurs:

<cferror type = "exception" 
exception = "lock" 
template = "../common/lockexcept.cfm"
mailto = "serverr@mycompany.com">

For detailed information on the cferror tag, see CFML Reference.

Creating an error application page

The following table lists the rules and considerations that apply to error application pages:

Type	Considerations
Validation	Cannot use CFML tags. Can use HTML tags. Can use the Error.InvalidFields, Error. validationHeader, and Error.validationFooter variables by enclosing them with pound sings (#). Cannot use any other CFML variables.
Request	Cannot use CFML tags. Can use HTML tags. Can use nine CFML error variables, such as Error.Diagnostics, by enclosing them with pound sings. Cannot use other CFML variables.
Exception	Can use full CFML syntax, including tags, functions, and variables. Can use nine standard CFML Error variables and cfcatch variables. Use either Error or cferror as the prefix for both types of variables. Can use other application-defined CFML variables. To display any CFML variable, use the cfoutput tag.

The following table describes the variables available on error pages:

Error page type	Error variable	Description
Validation	error.invalidFields	Unordered list of validation errors that occurred. This includes any text that you specify in the value attribute or a hidden tag used to validate form input.
	error.validationHeader	Text for the header of the default validation message.
	error.validationFooter	Text for the footer of the default validation message.
Exception and Request	error.browser	Browser that was running when the error occurred.
	error.dateTime	Date and time when the error occurred.
	error.diagnostics	Detailed error diagnostics.
	error.generatedContent	Any content that ColdFusion generated in response to the request prior to the error.
	error.HTTPReferer	Page containing the HTML link to the page on which the error occurred. This value is an empty string if the user specified the page directly in the browser.
	error.mailTo	E-mail address of the administrator who should be notified. This value is set in the mailTo attribute of the cferror tag.
	error.queryString	URL query string of the client's request, if any.
	error.remoteAddress	IP address of the remote client.
	error.template	Page being executed when the error occurred.
Exception only	error.messge	Error message associated with the exception.
	error.rootCause	Java servelet exception reported by the JVM as the cause of the "root cause" of the exception. This variable is a Java object.
	error.tagContext	Array of structures structure containing information for each tag in the tag stack The tag stack consists of each tag that is currently open. For more information, see "Exception information in cfcatch blocks"
	error.type	Exception type. For more information, see "About ColdFusion exceptions".

Exception error pages can also use all of the exception variables listed in the section "Exception information in cfcatch blocks". To use these variables, replace the cfcatch prefix with cferror or error. For example, to use the exception message in an error page, refer to it as error.message.

In general, production Exception and Request pages should not display detailed error information, such as that supplied by the error.diagnostics variable. Typically, Exception pages e-mail detailed error information to an administrative address or log the information using the cflog tag instead of displaying it to the user. For more information on using the cflog tag, see "Logging errors with the cflog tag".

Example of a request error page

The following example shows a custom error page for a request error:

<html>

<head>
<title>Products - Error</title>
</head>
<body>

<h2>Sorry</h2>

<p>An error occurred when you requested this page.</p>
<p>Please send e-mail with the following information to #error.mailTo# to report
this error.</p>

<table border=1>
<tr><td><b>Error Information</b> <br>
  Date and time: #error.DateTime# <br>
  Page: #error.template# <br>
  Remote Address: #error.remoteAddress# <br>
  HTTP Referer: #error.HTTPReferer#<br>
</td></tr></table>

<p>We apologize for the inconvenience and will work to correct the problem.</p>
</body>
</html>

Example of a validation error page

The following example shows a simple custom error page for a validation error:

<html>

<head>
<title>Products - Error</title>
</head>
<body>

<h2>Data Entry Error</h2>

<p>You failed to correctly complete all the fields
in the form. The following problems occurred:</p>

#error.invalidFields#

</body>
</html>

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