Pattern: Wire Tap
How do you inspect messages that travel on a point-to-point channel?
It can be very useful to see which messages traverse a channel. For example, for simple debugging purposes or to store messages in a Message Store.
You can't just add another listener to the Point-to-Point Channel because it would consume
messages off the channel.
You could also consider changing the channel to a Publish-Subscribe Channel. This would allow
additional listeners to inspect messages without disturbing the flow of messages. However, a
Publish-Subscribe Channel change the semantics of the channel. For example, multiple Competing
Consumers may be consuming messages off the channel, relying on the fact that only one
consumer can receive a specific message.
Insert a simple Recipient List into the channel that publishes each incoming message to the main channel and a secondary channel.
The Wire Tap is a fixed Recipient List with two output channels. It consumes messages off the
input channel and publishes the unmodified message to both output channels. To insert the Wire
Tap into a channel, you need to create an additional channel and change the destination receiver
to consume of the second channel. Because the analysis logic is located inside a second
component, we can insert a generic Wire Tap into any channel without any danger of modifying
the primary channel behavior. This improves reuse and reduces the risk of instrumenting an
existing solution.
No comments:
Post a Comment