MACROMEDIA COLDFUSION MX 61-DEVELOPING COLDFUSION MX, Руководство по разработке

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Understanding errors 287
Errors such as validation errors, for which the application cannot continue processing the request,
but can provide an error-specific response, can also be considered recoverable. For example, an
error that occurs when a user enters text where a number is required can be considered
recoverable, because the application can recognize the error and redisplay the data field with a
message providing information about the error’s cause and telling the user to reenter the data.
Some types of errors might be recoverable in some, but not all circumstances. For example, your
application can retry a request following a time-out error, but it must also be prepared for the case
where the request always times out.
Error causes fall in the broad categories listed in the following table:
Although these categories do not map completely to the way ColdFusion categorizes errors they
provide a useful way of thinking about errors and can help you in preventing and handling errors
in your code.
ColdFusion error types
Before you can effectively manage ColdFusion errors, you must understand how ColdFusion
classifies and handles them. ColdFusion categorizes errors as detailed in the following table:
Most ColdFusion errors are exceptions. The following sections describe them in detail.
Category Description
Program errors Can be in the code syntax or the program logic. The ColdFusion compiler
identifies and reports program syntax errors when it compiles CFML into Java
classes. Errors in your application logic are harder to locate. For information on
debugging tools and techniques, see
Chapter 18, “Debugging and
Troubleshooting Applications,” on page 389 .
Unlike ColdFusion syntax errors, SQL syntax errors are only caught at runtime.
Data errors Are typically user data input errors. You use validation techniques to identify
errors in user input data and enable the user to correct the errors.
System errors Can come from a variety of causes, including database system problems, time-
outs due to excessive demands on your server, out-of-memory errors in the
system, file errors, and disk errors.
Type Description
Exception An error that prevents normal processing from continuing. All ColdFusion
exceptions are, at their root, Java exceptions.
Missing template An HTTP request for a ColdFusion page that cannot be found. Generated if a
browser requests a ColdFusion page that does not exist.
Missing template errors are different from missing include exceptions, which
result from
cfinclude tags or custom tag calls that cannot find their targets.
Form field data
validation User data that does not meet the server-side form field validation rules in a
form being submitted. You specify server-side form validation by using hidden
HTML form fields. All other types of server-side validation, such as the
cfparam tag generate runtime exceptions. For more information on validating
form fields see “Validating form field data types” on page 579 .