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LDPath Transformations

If an fcr:transform program has been installed as "mytransform", you can generate a JSON representation of an object and send it to a low-latency, highly available caching layerdocument store, such as Riak:

"activemq:topic:fedora" ==> {
    to("fcrepo:localhost:8080/fedora/rest")
    filter(xpathFilter) {
        to("fcrepo:localhost:8080/fedora/rest?accept=application/json&transform=mytransform")
		setHeader(Exchange.HTTP_METHOD, constant("PUT")
		process((exchange: Exchange) => {
			exchange.getIn.setHeader(
				Exchange.HTTP_PATH,
				"/buckets/fcrepo/keys/" + URLEncoder.encode(exchange.getIn.getHeader("org.fcrepo.jms.identifier", classOf[String]))
			)
		})
        to("http4:localhost:8098")
	}
}

External Triplestore

Some additional processing must be done to transform an application/n-triples response into a valid application/sparql-update payload before sending to Fuseki or Sesame. The fcrepo component contains some processors in org.fcrepo.camel.processor to handle this case.

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");

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.

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