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Wire Tap

Wire Tap (from the EIP patterns) allows you to route messages to a separate location while they are being forwarded to the ultimate destination.

Options

WireTap Threadpool

The Wire Tap uses a thread pool to process the tapped messages. This thread pool will by default use the settings detailed at Threading Model. In particular, when the pool is exhausted (with all threads utilized), further wiretaps will be executed synchronously by the calling thread. To remedy this, you can configure an explicit thread pool on the Wire Tap having either a different rejection policy, a larger worker queue, or more worker threads.

WireTap Node

Camel's Wire Tap node supports two flavors when tapping an Exchange:

• With the traditional Wire Tap, Camel will copy the original Exchange and set its Exchange Pattern to InOnly, as we want the tapped Exchange to be sent in a fire and forget style. The tapped Exchange is then sent in a separate thread so it can run in parallel with the original. Beware that only the Exchange is copied - Wire Tap won't do a deep clone (unless you specify a custom processor via onPrepareRef which does that). So all copies could share objects from the original Exchange.
• Camel also provides an option of sending a new Exchange allowing you to populate it with new values.

Sending a Copy (traditional wiretap)

Using the Fluent Builders

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/WireTapTest.java}

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringWireTapTest.xml}

Sending a New Exchange

Using the Fluent Builders
Camel supports either a processor or an Expression to populate the new Exchange. Using a processor gives you full power over how the Exchange is populated as you can set properties, headers, etc. An Expression can only be used to set the IN body.

From Camel 2.3: the Expression or Processor is pre-populated with a copy of the original Exchange, which allows you to access the original message when you prepare a new Exchange to be sent. You can use the copy option (enabled by default) to indicate whether you want this. If you set copy=false, then it works as in Camel 2.2 or older where the Exchange will be empty.

Below is the processor variation. This example is from Camel 2.3, where we disable copy by passing in false to create a new, empty Exchange.

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/WireTapUsingFireAndForgetTest.java}

{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/WireTapUsingFireAndForgetTest.java}

{snippet:id=e2|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringWireTapUsingFireAndForgetTest.xml}

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringWireTapUsingFireAndForgetTest.xml}

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringWireTapUsingFireAndForgetCopyTest.xml}

Further Example

For another example of this pattern, refer to the wire tap test case.

Using Dynamic URIs

Available as of Camel 2.16:

For example to wire tap to a dynamic URI, then it supports the same dynamic URIs as documented in Message Endpoint. For example to wire tap to a JMS queue where the header ID is part of the queue name:

from("direct:start")
   .wireTap("jms:queue:backup-${header.id}")
   .to("bean:doSomething");

Sending a New Exchange and Set Headers in DSL

Available as of Camel 2.8

If you send a new message using Wire Tap, then you could only set the message body using an Expression from the DSL. If you also need to set headers, you would have to use a Processor. From Camel 2.8: it's possible to set headers as well using the DSL.

The following example sends a new message which has

• Bye World as message body.
• A header with key id with the value 123.
• A header with key date which has current date as value.

Java DSL

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/WireTapNewExchangeTest.java}

XML DSL

The XML DSL is slightly different than Java DSL in how you configure the message body and headers using <body> and <setHeader>:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringWireTapNewExchangeTest.xml}

Using onPrepare to Execute Custom Logic when Preparing Messages

Available as of Camel 2.8

See details at Multicast