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Intro to ColdFusion

 

CPCUG Monitor

Creating dynamic websites with ColdFusion

Part 6: Error handling

by Michael Smith

TeraTech http://www.teratech.com/

What is ColdFusion?

In this article we continue to look at what ColdFusion is and how you can use it for dynamic website creation. We cover error handling and dealing with 404 errors in ColdFusion. Error handling is important to both make your site more professional and for security reasons.

 

In case you missed previous articles that introduced ColdFusion, let me explain what it is. ColdFusion is a programming language based on standard HTML (Hyper Text Markup Language) that is used to write dynamic webpages. It lets you create pages on the fly that differ depending on user input, database lookups, time of day or what ever other criteria you dream up! ColdFusion pages consist of standard HTML tags such as <FONT SIZE="+2"> together with CFML (ColdFusion Markup Language) tags such as <CFSEARCH>, <CFIF> and <CFLOOP>. ColdFusion was introduced by Allaire in 1996 and is currently on version 4.

 

 

Error handling

Cfcatch/cftry

CFERROR Error  page with js

Administrator settings

Email

Log file

Hacker notes

Tree in the forrest

Syntax checker,

Application.cfm and onpageend.cfm?

 

Cferror

Error.Diagnostics

 

Detailed error diagnostics from ColdFusion Server.

Error.MailTo

 

Email address of administrator who should be notified (corresponds to the value set in the MAILTO attribute of CFERROR).

Error.DateTime

 

Date and time when the error occurred.

Error.Browser

 

Browser that was running when the error occurred.

Error.RemoteAddress

 

IP address of the remote client.

Error.HTTPReferer

 

Page from which the client accessed the link to the page where the error occurred.

Error.Template

 

Page being executed when the error occurred.

Error.QueryString

 

URL query string of the client's request.

 

 

Structured Exception Handling

The ColdFusion Server offers a means for developers to catch and process exceptions in ColdFusion application pages, through the CFTRY, CFCATCH, and CFTHROW tags.

Contents

·         Overview of Exception Handling in ColdFusion

·         Exception-Handling Strategies

·         Exception Handling Example

·         Exception Information in CFCATCH

Overview of Exception Handling in ColdFusion

Used with one or more CFCATCH tags, the CFTRY tag allows developers to catch and process exceptions in ColdFusion pages. Exceptions include any event that disrupts the normal flow of instructions in a ColdFusion page, such as failed database operations, missing include files, or developer-specified events.

You use the following syntax for CFTRY/CFCATCH blocks:

<CFTRY>

... Add code here ...

 

    <CFCATCH TYPE="exception type">

    ... Add exception processing code here ...

    </CFCATCH>

 

    ... Additional CFCATCH blocks go here ...

</CFTRY>

In order for ColdFusion to handle an exception, it must appear within a CFTRY block. You might enclose an entire application page in a CFTRY block, using a CFCATCH block around a potential error.

To catch errors in a single problematic SQL statement, for example, you might narrow the focus by using a CFTRY block with a CFCATCH TYPE="Database" tag, outputting the CFCATCH.State information as well.

See the CFML Language Reference for information on the CFTRY, CFCATCH, and CFTHROW tags.

Types of recoverable exceptions supported

The ColdFusion Server supports several types of recoverable exceptions. Use the TYPE attribute in the CFCATCH tag to determine which type of exception to catch.

Application-defined exception events

ColdFusion applications can raise exceptions using the CFTHROW tag, with an optional diagnostic message. CFTHROW raises an exception that can be caught by a CFCATCH TYPE="Application" tag, or a CFCATCH TYPE="Any" tag. This exception can also be caught by a CFCATCH block that has no TYPE attribute.

Database failures

Use the CFCATCH tag with TYPE="Database" or CFCATCH TYPE="Any" to catch failed database operations, such as failed SQL statements, ODBC problems, and so on.

Template errors

Use the CFCATCH tag with TYPE="Template" or TYPE="Any" to catch general application page errors.

Missing included file errors

Use the CFCATCH tag with TYPE="MissingInclude" or TYPE="Any" to catch errors for missing included files.

Object exceptions

Use the CFCATCH TYPE="Object" tag to catch exceptions in ColdFusion code that works with objects.

Security exceptions

Use the CFCATCH TYPE="Security" tag to raise catchable exceptions in ColdFusion code that works with security.

Expression exceptions

Use the CFCATCH TYPE="Expression" tag to catch exceptions when an expression fails evaluation.

Locking exceptions

Use the CFCATCH tag with TYPE="Lock" to catch failed locking operations, such as when a CFLOCK critical section times out or fails at runtime.

Unexpected internal exceptions

You can catch unexpected exceptions in the ColdFusion Server with the CFCATCH TYPE="Any" tag.

Note

Attempting to handle unexpected exceptions in CFML code can cause unpredictable results, and may seriously degrade or crash the ColdFusion Server.

Exception-Handling Strategies

Developers can use CFTRY with CFCATCH to handle exceptions based on their point of origin within an application page, or based on diagnostic information.

Handling exceptions based on point of origin

Use the CFTRY tag with one or more CFCATCH blocks to define a ColdFusion block for exception handling. When an application page raises an error condition, the ColdFusion server checks the stack of currently active blocks for a corresponding CFCATCH handler. At extremes, an exception-prone tag might be enclosed in a specialized combination of CFTRY and CFCATCH to immediately isolate the tag's exceptions, or to use CFTRY with CFCATCH TYPE="Any" at a main processing level to gracefully terminate a subsystem's processing in case of an unexpected error.

Handling exceptions based on diagnostic information

Use CFCATCH with the attribute TYPE="exception type" to catch specific types of exceptions. A CFCATCH handler can further analyze the exception's diagnostic information, and re-throw the exception if the exceptional condition requires further handling.

Exception Handling Example

The following example shows CFTRY and CFCATCH, using a sample data source called company and a sample included file, includeme.cfm.

If the data access driver raises an exception during the CFQUERY statement's execution, the application page flow continues to the CFCATCH TYPE="Database" exception handler. It then resumes with the next statement after the CFTRY block, once the CFCATCH TYPE="Database" handler completes.

Similarly, the CFCATCH TYPE="MissingInclude" block handles exceptions raised by the CFINCLUDE tag. Any unknown, but possibly recoverable, exceptions are handled by the CFCATCH TYPE="Any" block.

<!--- Wrap code you want to check in a CFTRY block --->

 

<CFTRY>

    <CFQUERY NAME="test" DATASOURCE="company">

        SELECT DepartmentID, FirstName, LastName

        FROM employees

        WHERE employeeID=#val(EmpID)#

    </CFQUERY>

 

    <HTML>

    <HEAD>

        <TITLE>Test CFTRY/CFCATCH</TITLE>

    </HEAD>

 

    <BODY>

    <HR>

    <CFINCLUDE TEMPLATE="includeme.cfm">

    <CFOUTPUT QUERY="test">

    <P>Department: #DepartmentID#

    <P>Last Name: #LastName#

    <P>First Name: #FirstName#

    </CFOUTPUT>

 

    <HR>

 

<!--- Use CFCATCH to test for missing included files.

        Print Message and Detail error messages. --->

 

    <CFCATCH TYPE="MissingInclude">

        <H1>Missing Include File</H1>

        <CFOUTPUT>

        <UL>

        <LI><b>Message:</b> #CFCATCH.Message#

        <LI><b>Detail:</b> #CFCATCH.Detail#

        <LI><b>File name:</b> #CFCATCH.MissingFilename#

        </UL>

        </CFOUTPUT>

    </CFCATCH>

 

<!--- Use CFCATCH to test for database errors.

        Print error messages. --->

 

    <CFCATCH TYPE="Database">

    <H1>Database Error</H1>

    <CFOUTPUT>

    <UL>

    <LI><b>Message:</b> #CFCATCH.Message#

    <LI><b>Native error code:</b> #CFCATCH.NativeErrorCode#

    <LI><b>SQLState:</b> #CFCATCH.SQLState#

    <LI><b>Detail:</b> #CFCATCH.Detail#

    </UL>

    </CFOUTPUT>

    </CFCATCH>

 

<!--- Use CFCATCH with TYPE="Any"

    to find unexpected exceptions. --->

 

    <CFCATCH TYPE="Any">

    <H1>Other Error: #CFCATCH.Type#</H1>

 

    <CFOUTPUT>

    <UL>

    <LI><b>Message:</b> #CFCATCH.message#

    <LI><b>Detail:</b> #CFCATCH.Detail#

    </UL>

    </CFOUTPUT>

    </CFCATCH>

</CFTRY>

    </BODY>

    </HTML>

CFTHROW syntax

Use CFTHROW within a CFTRY block to raise an error condition. The CFCATCH block can access this message through CFCATCH.message.

<CFTHROW MESSAGE="...diagnostic message...">

This form of the CFTHROW tag throws a new CFML-recoverable exception with the specified diagnostic message.

Using CFTHROW without the MESSAGE attribute throws a new CFML-recoverable exception with an empty diagnostic message.

CFTRY syntax

The CFTRY tag starts a ColdFusion exception-handling block. One or more CFCATCH tags must be included within a CFTRY block.

<CFTRY>

    ...Other CFML tags...

 

    <CFCATCH TYPE="Any">

</CFTRY>

Note

A CFCATCH block must be the last set of tags within a CFTRY block.

CFCATCH syntax

The CFCATCH tag catches exceptions of the type specified in the TYPE attribute, such as database, application, missing include, or application page.

<CFCATCH TYPE="exception type">

The following form of the CFCATCH tag catches all CFML-recoverable exceptions generated within the preceding CFTRY block, or within any of the CFTRY block's children.

<CFCATCH TYPE="Any">

A CFCATCH tag without a TYPE attribute is equivalent to CFCATCH TYPE="Any".

Order of evaluation

For a given CFTRY block, CFCATCH tags are tested in the order in which they appear in the application page.

Note

An exception raised within a CFCATCH block cannot be handled by the CFTRY block that immediately encloses the CFCATCH tag.

See the CFML Language Reference for information on the syntax of the exception handling tags, CFTRY, CFCATCH, and CFTHROW.

Exception Information in CFCATCH

Within a CFCATCH block, the active exception's properties can be accessed as variables:

CFCATCH.TYPE -- The exception's type, returned as a string:

·         Application

·         Database

·         Template

·         MissingInclude

·         Object

·         Security

·         Expression

·         Lock

·         Any

CFCATCH.MESSAGE -- The exception's diagnostic message, if one was provided. If no diagnostic message is available, this is an empty string.

CFCATCH.DETAIL -- A detailed message from the CFML interpreter. This message, which contains HTML formatting, can help to determine which tag threw the exception.

Database exceptions

For database exceptions, ColdFusion supplies some additional diagnostic information. The following variables are available whenever the exception type is database:

CFCATCH.NATIVEERRORCODE -- The native error code associated with this exception. Database drivers typically provide error codes to assist in the diagnosis of failing database operations. The values assumed by CFCATCH.NATIVEERRORCODE are driver-dependent. If no error code is provided, the value of NativeErrorCode is -1.

CFCATCH.SQLSTATE -- The SQLSTATE code associated with this exception. Database drivers typically provide error codes to assist in the diagnosis of failing database operations. The values assumed by CFCATCH.SQLSTATE are driver-dependent. If no SQLSTATE value was provided, the value of SQLSTATE is -1.

Locking exceptions

For exceptions related to CFLOCK sections, there is additional information available within the CFCATCH block:

CFCATCH.LOCKNAME -- The name of the affected lock. This is set to "anonymous" if the lock name is not known.

CFCATCH.LOCKOPERATION -- The operation that failed. This is set to "unknown" if the failed operation is unknown.

MissingInclude exceptions

For exceptions related to missing files, where the type of exception is MissingInclude, the following variable is available:

CFCATCH.MISSINGFILENAME -- The name of the file missing in an exception of type MissingInclude.

 

Summary

In this article we learned how to index both documents and large database queries for free text searches using Verity. We used the CFINDEX and CFSEARCH tags together with a CFOUTPUT to display results

To Learn More

You can download a free 30 day-evaluation version of ColdFusion from Allaire or request a free eval CD-ROM from

the Allaire website http://www.allaire.com/ 

 

Allaire Corporation

1 Alewife Center

Cambridge, MA 02140

 

Tel: 617.761.2000 voice

Fax: 617.761.2001 fax

Toll Free: 888.939.2545

Email: sales@allaire.com

Web: www.allaire.com

 

ColdFusion Resources

Allaire also maintains an extensive knowledge base and tech support forums on their website.

CPCUG and TeraTech ColdFusion Conference http://www.cfconf.org/

TeraTech maintains a ColdFusion code cuttings called ColdCuts at http://www.teratech.com/ColdCuts/. This page also has links to about a dozen ColdFusion white papers in the CF Info Center.

The Maryland ColdFusion User Group meets the second Tuesday of each month at Backstreets Cafe, 12352 Wilkins Avenue, Rockville. See http://www.cfug-md.org/ for details and directions.

The DC ColdFusion User Group meets the first Wednesday each month at Figleaf , 16th and P St NW, Washington DC. See the DCCFUG page on http://www.figleaf.com/ for details and directions.

Bio

Michael Smith is president of TeraTech, a ten year old Rockville Maryland based consulting company that specializes in ColdFusion, Database and Visual Basic development. You can reach Michael at michael@teratech.com or 301-424-3903.


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