org.fcrepo.camel.processor.SparqlDeleteProcessor Maven / Gradle / Ivy

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Camel Component for interacting with a Fedora Repository
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/**
 * Copyright 2015 DuraSpace, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.fcrepo.camel.processor;

import static java.net.URLEncoder.encode;

import java.io.IOException;

import org.apache.camel.Exchange;
import org.apache.camel.Message;
import org.apache.camel.Processor;
import org.fcrepo.camel.FcrepoHeaders;

/**
 * Represends a message processor that deletes objects from an
 * external triplestore.
 *
 * @author Aaron Coburn
 * @since Nov 8, 2014
 */
public class SparqlDeleteProcessor implements Processor {
    /**
     * Define how the message should be processed.
     *
     * @param exchange the current camel message exchange
     */
    public void process(final Exchange exchange) throws IOException {

        final Message in = exchange.getIn();
        final String namedGraph = in.getHeader(FcrepoHeaders.FCREPO_NAMED_GRAPH, String.class);
        final String subject = ProcessorUtils.getSubjectUri(in);

        /*
         * N.B. The Sparql update command below deletes all triples with
         * the defined subject uri (coming from the FCREPO_IDENTIFIER
         * and FCREPO_BASE_URL headers). It also deletes triples that
         * have a subject corresponding to that Fcrepo URI plus the
         * "/fcr:export?format=jcr/xml" string appended to it. This
         * makes it possible to more completely remove any triples
         * for a given resource that were added earlier. If fcrepo
         * ever stops producing triples that are appended with
         * /fcr:export?format..., then that extra line can be removed.
         * It would also be possible to recursively delete triples
         * (by removing any triple whose subject is also an object of
         * the starting (or context) URI, but that approach tends to delete
         * too many triples from the triplestore. This command does
         * not remove blank nodes.
         */
        final StringBuilder query = new StringBuilder();

        query.append(ProcessorUtils.deleteWhere(subject, namedGraph));
        query.append(";\n");
        query.append(ProcessorUtils.deleteWhere(subject + "/fcr:export?format=jcr/xml", namedGraph));

        in.setBody("update=" + encode(query.toString(), "UTF-8"));
        in.setHeader(Exchange.HTTP_METHOD, "POST");
        in.setHeader(Exchange.CONTENT_TYPE, "application/x-www-form-urlencoded; charset=utf-8");
   }

}