[CONF] Apache Camel: Intercept (page edited)

confluence Sat, 02 May 2009 00:59:31 -0700

Page Edited : CAMEL : Intercept

Intercept has been edited by Claus Ibsen (May 02, 2009).

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Content:

Intercept

The intercept feature in Camel supports intercepting Exchanges while they are on route.

Camel supports three kinds of interceptors:

intercept that intercepts each and every processing step while routing an Exchange in the route.
interceptFrom that intercepts incoming Exchange in the route.
interceptSendToEndpoint new in Camel 2.0 that intercepts when an Exchange is about to be sent to the given Endpoint.

TODO: Is being reworked in Camel 2.0
These interceptors supports the following features:

Predicate using when to only trigger the interceptor in certain conditions
proceed when used with interceptFrom to continue routing from the point of interception when the interceptor is finished. proceed is default and can be omitted.
stop when used with interceptFrom will stops routing the Exchange completely. Camel will by default not stop.
skip when used with interceptSendToEndpoint will skip sending the Exchange to the original intended endpoint. Camel will by default not skip.

Intercept

Intercept is like a regular interceptor that is applied each each processing step the Exchange undergo while its being routed. You can think of it as a AOP before that is applied at each DSL keyword you have defined in your route.

The classic Hello World example would be:

intercept().to("log:hello");


from("jms:queue:order").to("bean:validateOrder").to("bean:processOrder");

What happens is that the Exchange is intercepted before each processing step, that means that it will be intercepted before

.to("bean:validateOrder")
.to("bean:processOrder")
So in this sample we intercept the Exchange twice.

TODO: Add support for when predicate
TODO: Add support for stop predicate (proceed is default)

Using from Spring DSL

The same hello world sample in Spring DSL would be:

<camelContext ...>
    <intercept>
        <to uri="log:hello"/>
    </intercept>

    <route>
        <from uri="jms:queue:order"/>
        <to uri="bean:validateOrder"/>
        <to uri="bean:handleOrder"/>
    </route>
</camelContext>

InterceptFrom

InterceptFrom is for intercepting any incoming Exchange, in any route (it intercepts all the from DSLs). This allows you to do some custom behavior for received Exchanges. You can provide a specific uri for a given Endpoint then it only applies for that particular route.

So lets start with the logging example. We want to log all the incoming requests so we use interceptFrom to route to the Log component. As proceed is default then the Exchange will continue its route, and thus it will continue to mock:first.

// intercept all incomming routes and log it
interceptFrom().to("log:received");

// and here we have a couple of routes
from("direct:start").to("mock:first").to("seda:bar");

from("seda:bar").to("mock:result");

You can also attach a Predicate to only trigger if certain conditions is meet. For instance in the route below we intercept when a test message is send to us, so we can do some custom processing before we continue routing:

interceptFrom()
    .when(header("usertype").isEqualTo("test"))
    .process(new MyTestServiceProcessor())
    .to("mock:intercepted");

// and here is our route
from("direct:start").to("seda:bar").to("mock:result");

And if we want to filter out certain messages we can use the stop() to instruct Camel to stop continue routing the Exchange:

interceptFrom()
    .when(header("usertype").isEqualTo("test"))
    // here we use stop() to tell Camel to NOT continue routing the message.
    // this let us act as a filter, to drop certain messages.
    .stop();

// and here is our route
from("direct:start").to("seda:bar").to("mock:result");

And if want to only apply a specific endpoint, as the seda:bar endpoint in the sample below, we can do it like this:

// only trigger when incoming from seda:bar endpoint
interceptFrom("seda:bar").to("mock:bar");

// and here we have a couple of routes
from("direct:start").to("mock:first").to("seda:bar");

from("seda:bar").to("mock:result");

from("seda:foo").to("mock:result");

Using from Spring DSL

Intercept is of course also available using Spring DSL as shown in the sample below:

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
    <!-- intercept incoming messages and route them to the mock:middle1 endpoint
         before we proceed and continue routing from the point of interceptions, that
         is mock:end will be the next target -->
    <interceptFrom>
        <to uri="mock:middle1"/>
    </interceptFrom>

    <!-- here we have a very simple route -->
    <route>
        <from uri="direct:start"/>
        <to uri="mock:end"/>
    </route>
</camelContext>

InterceptSendToEndpoint

Available as of Camel 2.0

Intercept send to endpoint is triggered when an Exchange is being sent to the intercepted endpoint. This allows you to route the Exchange to a Detour or do some custom processing before the Exchange is sent to the original intended destination. You can also skip sending to the intended destination. By default Camel will send to the original intended destination after the intercepted route completes. And as the regular intercept you can also define an when Predicate so we only intercept if the Predicate evaluates to true. This allows you do do a bit of filtering, to only intercept when certain criteria is meet.

Let start with a simple example, where we want to intercept when an Exchange is being sent to mock:foo:

// we intercept by endpoint, that means that whenever an exchange is about to be sent to
// this endpoint, its intercepted and routed with this detour route beforehand
// afterwards its send to the original intended destination. So this is kinda AOP before.
// That means mock:foo will receive the message (Bye World).
interceptSendToEndpoint("mock:foo").to("mock:detour").transform(constant("Bye World"));

from("direct:first")
    .to("mock:bar")
    .to("mock:foo")
    .to("mock:result");

And this time we add the Predicate so its only when the message body is Hello World we intercept.

// we can also attach a predicate to the endpoint interceptor. So in this example the exchange is
// only intercepted if the body is Hello World
interceptSendToEndpoint("mock:foo").when(body().isEqualTo("Hello World")).to("mock:detour").transform(constant("Bye World"));

from("direct:second")
    .to("mock:bar")
    .to("mock:foo")
    .to("mock:result");

And to skip sending to the mock:foo endpoint we use the *skip() DSL in the route at the end to instruct Camel to skip sending to the original intended endpoint.

// since we use the skip() at the end of the detour route we instruct Camel to skip
// sending the exchange to the original intended destination.
// That means that mock:foo will NOT receive the message, but the message
// is skipped and continued in the original route, so mock:result will receive
// the message.
interceptSendToEndpoint("mock:foo").transform(constant("Bye World")).to("mock:detour").skip();

from("direct:third")
    .to("mock:bar")
    .to("mock:foo")
    .to("mock:result");

Using from Spring DSL

Intercept endpoint is of course also available using Spring DSL.

We start with the first example from above in Spring DSL:

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">

    <!-- we intercept by endpoint, that means that whenever an exchange is about to be sent to
         this endpoint, its intercepted and routed with this detour route beforehand
         afterwards its send to the original intended destination. So this is kinda AOP before.
         That means mock:foo will receive the message (Bye World). -->
    <interceptSendToEndpoint uri="mock:foo">
        <to uri="mock:detour"/>
        <transform>
            <constant>Bye World</constant>
        </transform>
    </interceptSendToEndpoint>

    <route>
        <from uri="direct:first"/>
        <to uri="mock:bar"/>
        <to uri="mock:foo"/>
        <to uri="mock:result"/>
    </route>
</camelContext>

And the 2nd. Notice how we can leverage the Simple language for the Predicate:

An error occurred: http://svn.apache.org/repos/asf/camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/interceptSendToEndpointWhen.xml. The system administrator has been notified.

And the 3rd with the skip, notice skip is set with the skipSendToOriginalEndpoint attribute on the interceptSendToEndpoint tag:

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">

    <!-- since we set the skipSendToOriginalEndpoint attribute to true we instruct
         Camel to skip sending the exchange to the original intended destination.
         That means that mock:foo will NOT receive the message, but the message
         is skipped and continued in the original route, so mock:result will receive
         the message. -->
    <interceptSendToEndpoint uri="mock:foo" skipSendToOriginalEndpoint="true">
        <transform>
            <constant>Bye World</constant>
        </transform>
        <to uri="mock:detour"/>
    </interceptSendToEndpoint>

    <route>
        <from uri="direct:third"/>
        <to uri="mock:bar"/>
        <to uri="mock:foo"/>
        <to uri="mock:result"/>
    </route>
</camelContext>

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[CONF] Apache Camel: Intercept (page edited)

Intercept

Intercept

Using from Spring DSL

InterceptFrom

Using from Spring DSL

InterceptSendToEndpoint

Using from Spring DSL

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