MACROMEDIA COLDFUSION 4.5-CFML LANGUAGE Bedienungsanleitung PDF herunterladen (Seite 38)

38 CHAPTER 30 Extending ColdFusion with CFX

Generating Debug Output

If your CFX tag encounters any problems during its execution, or if you need help ﬁguring out why

your tag isn’t doing what you expect it to, you can have your tag include debug messages in the call-

ing template. Debug messages can include whatever text you want; usually you use them to display

some kind of diagnostic information that indicates whether the tag was able to connect to some kind

of data source, was denied access to some kind of ﬁle, or encountered some other type of unexpected

condition.

In the

<CFX_ComputeStandardDeviation> example, the tag is expecting to ﬁnd only numbers in the

query column passed to the tag. It knows to skip over null values, and generally does so silently. But

since it’s avoiding a potential problem, you might want to be able to see which values are being

skipped over. The code in Listing 30.6 uses the following lines to output debug messages:

if ( pRequest->Debug() ) {

char buffer[50];

sprintf(buffer, “Skipping row %i because value is empty/NULL.”, Row);

pRequest->WriteDebug(buffer);

}

The pRequest->Debug() method always returns FALSE unless the tag is being called in debug mode,

so these lines are usually skipped and thus add almost no overhead to normal tag execution. To call

a CFX tag in debug mode, add a

debug ﬂag (attribute) to the CFX tag when you use it, like so:

<CFX_ComputeStandardDeviation query=”GetMerch”

column=”MerchPrice”

variable=”MerchStdDev”

debug>

Whenever a tag is called with the debug ﬂag, the pRequest->Debug() method (or the request.debug()

method if you’re using Java) always returns TRUE, and the WriteDebug() method includes the speci-

ﬁed text along with the tag name when the page is visited with a browser (Figure 30.11). You can

use this simple but effective debugging facility whenever you want to include special messages for

developers but not for the rest of the world.

NOTE

debug behaves like a flag rather than a Boolean (Yes or No) attribute, so the only thing that matters is whether it is present. The

value after the

= sign is ignored, so debug=”Yes” and debug=”No” both result in debug messages being shown. You must

remove the

debug flag altogether to stop the messages.

NOTE

The debug functionality is unfortunately not integrated with the Debugging Settings page of the ColdFusion Administrator, so the

settings on that page have no bearing on whether debug messages from CFX tags are shown. In particular, debug messages from

CFX tags are not restricted by the Debugging IP Addresses list in the Administrator.

NOTE

The CFX API for Java also includes an additional set of classes for debugging Java CFX tags. You can use the classes to test

CFX tags without actually supplying them with runtime attributes in ColdFusion pages. If you find this idea interesting, consult the

“ColdFusion Java CFX Reference” section of the CFML Reference that ships with ColdFusion.

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