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Listeners are the last step in logging. Listeners
receive formatted message, a
Date, and a
Severity from a
Logger, construct the final message, and persist that
message somewhere.
Listeners nominally follow the adapter
pattern, adapting some storage mechanism for holding log messages. The most common use of Listeners is
to wrap some other logging framework.
Listener implementations may use a MessageFormatter
to simplify creating the final message from a
Date,
Severity, and string message created by various
formatters.
Logahawk comes with a few Listener implementations in the
core package:
Below are implementations for well-know logging libraries. This code is not part of the core package
because they depend on external libraries. The code here is intended to be copied directly into your
code and customized to your needs. (This code is also part of the
sources package if you wish to download all of them at once.)
There are additional Listener implementations included in the
core package.
There are some simpler Listener implementations included with Logahawk. These can be used to help build
a custom Listener, or to write to some non-standard storage system.
One good scenario would be to use a StreamListener with a
CipherOutputStream
to handle writing a log that may contain confidential information.
Listeners can also be used for more than just writing directly to a storage system. For example, the
be used to control the flow of log messages. The
FailSafeListener is designed to handle
unreliable Listeners. The FailSafeListener takes two Listeners, a primary and a backup Listener. If
the primary Listener throws an exception, the log message is logged to the backup Listener.
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