Content Enricher

Camel supports the Content Enricher from the EIP patterns using a Message Translator, an arbitrary Processor in the routing logic or using the enrich DSL element to enrich the message.

Content enrichment using a Message Translator or a Processor

Using the Fluent Builders

You can use Templating to consume a message from one destination, transform it with something like Velocity or XQuery and then send it on to another destination. For example using InOnly (one way messaging)

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm").
  to("activemq:Another.Queue");

If you want to use InOut (request-reply) semantics to process requests on the My.Queue queue on ActiveMQ with a template generated response, then sending responses back to the JMSReplyTo Destination you could use this:

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm");

Here is a simple example using the DSL directly to transform the message body

from("direct:start").setBody(body().append(" World!")).to("mock:result");

In this example we add our own Processor using explicit Java code

from("direct:start").process(new Processor() {
    public void process(Exchange exchange) {
        Message in = exchange.getIn();
        in.setBody(in.getBody(String.class) + " World!");
    }
}).to("mock:result");

Finally we can use Bean Integration to use any Java method on any bean to act as the transformer

from("activemq:My.Queue").
  beanRef("myBeanName", "myMethodName").
  to("activemq:Another.Queue");

For further examples of this pattern in use you could look at one of the JUnit tests

Using Spring XML

<route>
  <from uri="activemq:Input"/>
  <bean ref="myBeanName" method="doTransform"/>
  <to uri="activemq:Output"/>
</route>

Content enrichment using the enrich DSL element

Camel comes with two flavors of content enricher in the DSL

  • enrich
  • pollEnrich

enrich is using a Producer to obtain the additional data. It is usually used for Request Reply messaging, for instance to invoke an external web service.
pollEnrich on the other hand is using a Polling Consumer to obtain the additional data. It is usually used for Event Message messaging, for instance to read a file or download a FTP file.

Enrich Options

Name Default Value Description
uri   The endpoint uri for the external service to enrich from. You must use either uri or ref.
ref   Refers to the endpoint for the external service to enrich from. You must use either uri or ref.
strategyRef   Refers to an AggregationStrategy to be used to merge the reply from the external service, into a single outgoing message. By default Camel will use the reply from the external service as outgoing message.

Using the Fluent Builders

AggregationStrategy aggregationStrategy = ...

from("direct:start")
.enrich("direct:resource", aggregationStrategy)
.to("direct:result");

from("direct:resource")
...

The content enricher (enrich) retrieves additional data from a resource endpoint in order to enrich an incoming message (contained in the original exchange). An aggregation strategy is used to combine the original exchange and the resource exchange. The first parameter of the AggregationStrategy.aggregate(Exchange, Exchange) method corresponds to the the original exchange, the second parameter the resource exchange. The results from the resource endpoint are stored in the resource exchange's out-message. Here's an example template for implementing an aggregation strategy:

public class ExampleAggregationStrategy implements AggregationStrategy {

    public Exchange aggregate(Exchange original, Exchange resource) {
        Object originalBody = original.getIn().getBody();
        Object resourceResponse = resource.getOut().getBody();
        Object mergeResult = ... // combine original body and resource response
        if (original.getPattern().isOutCapable()) {
            original.getOut().setBody(mergeResult);
        } else {
            original.getIn().setBody(mergeResult);
        }
        return original;
    }
    
}

Using this template the original exchange can be of any pattern. The resource exchange created by the enricher is always an in-out exchange.

Using Spring XML

The same example in the Spring DSL

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <enrich uri="direct:resource" strategyRef="aggregationStrategy"/>
    <to uri="direct:result"/>
  </route>
  <route>
    <from uri="direct:resource"/>
    ...
  </route>
</camelContext>

<bean id="aggregationStrategy" class="..." />

Aggregation strategy is optional

The aggregation strategy is optional. If you do not provide it Camel will by default just use the body obtained from the resource.

from("direct:start")
  .enrich("direct:resource")
  .to("direct:result");

In the route above the message sent to the direct:result endpoint will contain the output from the direct:resource as we do not use any custom aggregation.

And for Spring DSL just omit the strategyRef attribute:

  <route>
    <from uri="direct:start"/>
    <enrich uri="direct:resource"/>
    <to uri="direct:result"/>
  </route>

Content enrichment using pollEnrich

The pollEnrich works just as the enrich however as it uses a Polling Consumer we have 3 methods when polling

  • receive
  • receiveNoWait
  • receive(timeout)

PollEnrich Options

Name Default Value Description
uri   The endpoint uri for the external service to enrich from. You must use either uri or ref.
ref   Refers to the endpoint for the external service to enrich from. You must use either uri or ref.
strategyRef   Refers to an AggregationStrategy to be used to merge the reply from the external service, into a single outgoing message. By default Camel will use the reply from the external service as outgoing message.
timeout 0 Timeout in millis when polling from the external service. See below for important details about the timeout.

By default Camel will use the receiveNoWait.
If there is no data then the newExchange in the aggregation strategy is null.

You can pass in a timeout value that determines which method to use

  • if timeout is -1 or other negative number then receive is selected
  • if timeout is 0 then receiveNoWait is selected
  • otherwise receive(timeout) is selected

The timeout values is in millis.

Data from current Exchange not used
pollEnrich does not access any data from the current Exchange which means when polling it cannot use any of the existing headers you may have set on the Exchange. For example you cannot set a filename in the Exchange.FILE_NAME header and use pollEnrich to consume only that file. For that you must set the filename in the endpoint URI.

Example

In this example we enrich the message by loading the content from the file named inbox/data.txt.

from("direct:start")
  .pollEnrich("file:inbox?fileName=data.txt")
  .to("direct:result");

And in XML DSL you do:

  <route>
    <from uri="direct:start"/>
    <pollEnrich uri="file:inbox?fileName=data.txt"/>
    <to uri="direct:result"/>
  </route>

If there is no file then the message is empty. We can use a timeout to either wait (potentially forever) until a file exists, or use a timeout to wait a certain period.

For example to wait up to 5 seconds you can do:

  <route>
    <from uri="direct:start"/>
    <pollEnrich uri="file:inbox?fileName=data.txt" timeout="5000"/>
    <to uri="direct:result"/>
  </route>

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

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