MACROMEDIA ColdFusion MX, Develop Manual

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308 Chapter 14: Handling Errors
Catching and displaying thrown errors
The
cfcatch
tag catches a custom exception when you use any of the following values for the
cfcatch type
attribute:
•
The custom exception type specified in the
cfthrow
tag.
•
A custom exception type that hierarchically matches the initial portion of the type specified in
the
cfthrow
tag. For more information, see the next section, “Custom error type name
hierarchy” .
•
Application
, which matches an exception that is thrown with the
Application type
attribute or with no
type
attribute.
•
Any
, which matches any exception that is not caught by a more specific
cfcatch
tag.
Similarly, if you specify any of these types in a
cferror
tag, the specified error page will display
information about the thrown error.
Because the
cfthrow
tag generates an exception, a Request error handler or the Site-wide error
handler can also display these errors.
Custom error type name hierarchy
You can name custom exception types using a method that is similar to Java class naming
conventions: domain name in reverse order, followed by project identifiers, as in the following
example:
<cfthrow
type="com.myCompany.myApp.Invalid_field.codeValue"
errorcode="Dodge14B">
This fully qualified naming method is not required; you can use shorter naming rules, for
example, just myApp.Invalid_field.codeValue, or even codeValue.
This naming method is not just a convention, however; ColdFusion MX uses the naming
hierarchy to select from a possible hierarchy of error handlers. For example, assume you use the
following
cfthrow
statement:
<cfthrow type="MyApp.BusinessRuleException.InvalidAccount">
Any of the following
cfcatch
error handlers would handle this error:
<cfcatch type="MyApp.BusinessRuleException.InvalidAccount">
<cfcatch type="MyApp.BusinessRuleException">
<cfcatch type="MyApp">
The handler that most exactly matches handles the error. Therefore, in this case, the
MyApp.BusinessRuleException.InvalidAccount
handler gets invoked. However, if you used
the following
cfthrow
tag:
<cfthrow type="MyApp.BusinessRuleException.InvalidVendorCode
the
MyApp.BusinessRuleException
handler receives the error.
The type comparison is no case-sensitive.
When to use cfthrow
Use the
cfthrow
tag when your application can identify and handle application-specific errors.
One typical use for the
cfthrow
tag is in implementing custom data validation. The
cfthrow
tag
is also useful for throwing errors from a custom tag page to the calling page.