...
| Code Block | ||
|---|---|---|
| ||
from("activemq:topic:fedora")
.to("fcrepo:localhost:8080/fedora/rest?accept=application/n-triples")
.process(new SparqlUpdateProcessor())
.setHeader(Exchange.CONTENT_TYPE).constant("application/sparql-update")
.to("http4:localhost:3030/fcrepo/update"); |
Event-based Routing
It is often helpful to route messages to different queues based on the eventType value. This example splits messages on eventType values and routes the messages to appropriate queues. Following this example, it would be prudent to aggregate the messages based on org.fcrepo.jms.identifier value after retrieving the messages from the downstream queues.
| Code Block | ||||||
|---|---|---|---|---|---|---|
| ||||||
<route id="fcrepo-event-splitter">
<description>
Retrieve messages from the fedora topic. Event types are comma-delimited, so split them into separate messages before routing them.
</description>
<from uri="activemq:topic:fedora"/>
<setBody>
<simple>${header.org.fcrepo.jms.eventType}</simple>
</setBody>
<split>
<tokenize token=","/>
<setHeader headerName="org.fcrepo.jms.eventType">
<simple>${body}</simple>
</setHeader>
<setBody>
<simple>null</simple>
</setBody>
<to uri="seda:fcrepo-event-router"/>
</split>
</route>
<route id="fcrepo-event-router">
<description>
Route messages based on the eventType.
</description>
<from uri="seda:fcrepo-event-router"/>
<choice>
<when>
<simple>${header.org.fcrepo.jms.eventType} == "http://fedora.info/definitions/v4/repository#NODE_REMOVED"</simple>
<to uri="activemq:queue:fcrepo.delete"/>
</when>
<when>
<simple>${header.org.fcrepo.jms.eventType} == "http://fedora.info/definitions/v4/repository#NODE_ADDED"</simple>
<to uri="activemq:queue:fcrepo.add"/>
</when>
<when>
<simple>${header.org.fcrepo.jms.eventType} == "http://fedora.info/definitions/v4/repository#PROPERTY_ADDED"</simple>
<to uri="activemq:queue:fcrepo.update"/>
</when>
<when>
<simple>${header.org.fcrepo.jms.eventType} == "http://fedora.info/definitions/v4/repository#PROPERTY_CHANGED"</simple>
<to uri="activemq:queue:fcrepo.update"/>
</when>
<when>
<simple>${header.org.fcrepo.jms.eventType} == "http://fedora.info/definitions/v4/repository#PROPERTY_REMOVED"</simple>
<to uri="activemq:queue:fcrepo.update"/>
</when>
<otherwise>
<log message="No router for ${header.org.fcrepo.jms.eventType}"/>
</otherwise>
</choice>
</route> |
Supporting Queues
The default configuration is fine for locally-deployed listeners, but it can be problematic in a distributed context. For instance, if the listener is restarted while a message is sent to the topic, that message may be missed. Furthermore, if there is a networking hiccup between fedora's local broker and the remote listener, that too can result in lost messages. Instead, in this case, a queue may be better suited.
...