Exception events are generated by FM-Classic whenever an unusual
event occurs when a template is processed. For instance, if a
TemplateModelException
is thrown by a TemplateModel
,
an exception event will be propagated up to the current
TemplateEventAdapter
.
FM-Classic exception events are encapsulated in the
TemplateExceptionEvent
class. Objects of this class provide
information about the exception that occurred, whereabouts in the code the
exception occurred, and the severity of the exception. For convenience,
TemplateExceptionEvent
s also contain the current
Writer
, so that exception messages can be sent directly
to the template output stream.
TemplateExceptionListener
s are notified of
TemplateExceptionEvent
s whenever they are generated by FM-Classic
at processing time. TemplateExceptionListener
s are registered
with a TemplateEventAdapter
to indicate that they should receive
these notifications.
FM-Classic comes with two implementations of
TemplateExceptionListener
: HtmlExceptionListener
,
which performs the standard output of FM-Classic exceptions into the template
output stream, in the form of an HTML comment, and
Log4jExceptionListener
, which adapts FM-Classic exception events
into Log4j
logging messages. See the JavaDoc
for more details of these implementations.
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