[[wireTap-eip]]
== Wire Tap EIP

http://www.enterpriseintegrationpatterns.com/WireTap.html[Wire Tap]
(from the link:enterprise-integration-patterns.html[EIP patterns])
allows you to route messages to a separate location while they are being
forwarded to the ultimate destination.

image:http://www.enterpriseintegrationpatterns.com/img/WireTap.gif[image]

=== Streams

If you link:wire-tap.html[Wire Tap] a stream message body then you
should consider enabling link:stream-caching.html[Stream caching] to
ensure the message body can be read at each endpoint. See more details
at link:stream-caching.html[Stream caching].

=== Options

// eip options: START
The Wire Tap EIP supports 11 options which are listed below:

[width="100%",cols="2,5,^1,2",options="header"]
|===
| Name | Description | Default | Type
| *processorRef* | Reference to a Processor to use for creating a new body as the message to use for wire tapping |  | String
| *body* | Uses the expression for creating a new body as the message to use for wire tapping |  | NamespaceAware Expression
| *executorServiceRef* | Uses a custom thread pool |  | String
| *copy* | Uses a copy of the original exchange | true | Boolean
| *dynamicUri* | Whether the uri is dynamic or static. If the uri is dynamic then the simple language is used to evaluate a dynamic uri to use as the wire-tap destination, for each incoming message. This works similar to how the toD EIP pattern works. If static then the uri is used as-is as the wire-tap destination. | true | Boolean
| *onPrepareRef* | Uses the Processor when preparing the org.apache.camel.Exchange to be send. This can be used to deep-clone messages that should be send, or any custom logic needed before the exchange is send. |  | String
| *uri* | *Required* The uri of the endpoint to send to. The uri can be dynamic computed using the org.apache.camel.language.simple.SimpleLanguage expression. |  | String
| *pattern* | Sets the optional ExchangePattern used to invoke this endpoint |  | ExchangePattern
| *cacheSize* | Sets the maximum size used by the org.apache.camel.impl.ConsumerCache which is used to cache and reuse producers. |  | Integer
| *ignoreInvalidEndpoint* | Ignore the invalidate endpoint exception when try to create a producer with that endpoint | false | Boolean
| *allowOptimisedComponents* | Whether to allow components to optimise toD if they are org.apache.camel.spi.SendDynamicAware. | true | Boolean
|===
// eip options: END

=== WireTap Thread pool

The WireTap uses a thread pool to process the
tapped messages. This thread pool will by default use the settings
detailed at link:threading-model.html[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 link:wire-tap.html[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
link:exchange.html[Exchange]:

- With the traditional Wire Tap, Camel will copy the original
link:exchange.html[Exchange] and set its
link:exchange-pattern.html[Exchange Pattern] to *`InOnly`*, as we want
the tapped link:exchange.html[Exchange] to be sent in a fire and forget
style. The tapped link:exchange.html[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
link:exchange.html[Exchange] allowing you to populate it with new
values.

=== Sending a Copy (traditional wiretap)

* Using the link:fluent-builders.html[Fluent
Builders]

[source,java]
----
    protected RouteBuilder createRouteBuilder() {
        return new RouteBuilder() {
            public void configure() {
                // START SNIPPET: e1
                from("direct:start")
                    .to("log:foo")
                    .wireTap("direct:tap")
                    .to("mock:result");
                // END SNIPPET: e1

                from("direct:tap")
                    .delay(1000).setBody().constant("Tapped")
                    .to("mock:result", "mock:tap");
                
                from("direct:test").wireTap("direct:a").id("wiretap_1").to("mock:a");
                from("direct:a").to("mock:b");
            }
        };
    }
----

=== Sending a New link:exchange.html[Exchange]

*Using the link:fluent-builders.html[Fluent Builders]* 
 Camel supports either a processor or an
link:expression.html[Expression] to populate the new
link:exchange.html[Exchange]. Using a processor gives you full power
over how the link:exchange.html[Exchange] is populated as you can set
properties, headers, etc. An link:expression.html[Expression] can only
be used to set the *`IN`* body.

From *Camel 2.3*: the link:expression.html[Expression] or
link:processor.html[Processor] is pre-populated with a copy of the
original link:exchange.html[Exchange], which allows you to access the
original message when you prepare a new link:exchange.html[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 link:exchange.html[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
link:exchange.html[Exchange]

[source,java]
----
    public void testFireAndForgetUsingProcessor() throws Exception {
        context.addRoutes(new RouteBuilder() {
            @SuppressWarnings("deprecation")
            @Override
            public void configure() throws Exception {
                // START SNIPPET: e1
                from("direct:start")
                    .wireTap("direct:foo", false, new Processor() {
                        public void process(Exchange exchange) throws Exception {
                            exchange.getIn().setBody("Bye World");
                            exchange.getIn().setHeader("foo", "bar");
                        }
                    }).to("mock:result");


                from("direct:foo").to("mock:foo");
                // END SNIPPET: e1
            }
        });
    }
----


=== 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 link:message-endpoint.html[Message
Endpoint]. For example to wire tap to a JMS queue where the header ID is
part of the queue name:

[source,java]
----
    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 link:wire-tap.html[Wire Tap], then you
could only set the message body using an
link:expression.html[Expression] from the DSL. If you also need to set
headers, you would have to use a link:processor.html[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

[source,java]
----
    @Override
    protected RouteBuilder createRouteBuilder() throws Exception {
        return new RouteBuilder() {
            @Override
            public void configure() throws Exception {
                // START SNIPPET: e1
                from("direct:start")
                    // tap a new message and send it to direct:tap
                    // the new message should be Bye World with 2 headers
                    .wireTap("direct:tap")
                        // create the new tap message body and headers
                        .newExchangeBody(constant("Bye World"))
                        .newExchangeHeader("id", constant(123))
                        .newExchangeHeader("date", simple("${date:now:yyyyMMdd}"))
                    .end()
                    // here we continue routing the original messages
                    .to("mock:result");

                // this is the tapped route
                from("direct:tap")
                    .to("mock:tap");
                // END SNIPPET: e1
            }
        };
    }

----

=== Using `onPrepare` to Execute Custom Logic when Preparing Messages

*Available as of Camel 2.8*

See details at link:multicast.html[Multicast]

link:using-this-pattern.html[Using This Pattern]
