org.opencredo.couchdb.inbound.CouchDbChangesPollingMessageSource.java Source code

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Here is the source code for org.opencredo.couchdb.inbound.CouchDbChangesPollingMessageSource.java

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/*
 * Copyright 2011 the original author or authors
 *
 * 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.opencredo.couchdb.inbound;

import org.opencredo.couchdb.core.ChangedDocument;
import org.opencredo.couchdb.core.CouchDbChangesOperations;
import org.opencredo.couchdb.core.CouchDbChangesTemplate;
import org.springframework.messaging.Message;
import org.springframework.integration.context.IntegrationObjectSupport;
import org.springframework.integration.core.MessageSource;
import org.springframework.integration.support.MessageBuilder;

import java.net.URI;
import java.util.Collection;
import java.util.Comparator;
import java.util.Queue;
import java.util.concurrent.PriorityBlockingQueue;

/**
 * A MessageSource that receives messages by polling a CouchDB database. The polling is performed through
 * a CouchDbChangesOperations, typically using the changes API.
 * </p>
 * Each poll returns and stores internally the list of changed documents since the last poll, which means that instances
 * of this class are stateful.
 *
 * @author Tareq Abedrabbo
 * @author Tomas Lukosius
 * @since 24/01/2011
 */
public class CouchDbChangesPollingMessageSource extends IntegrationObjectSupport implements MessageSource<URI> {

    private static final int DEFAULT_INTERNAL_QUEUE_CAPACITY = 5;

    private final Queue<ChangedDocument> toBeReceived;

    private final CouchDbChangesOperations couchDbChangesOperations;

    /**
     * Creates an instance with a custom CouchDbChangesOperations.
     */
    public CouchDbChangesPollingMessageSource(CouchDbChangesOperations couchDbChangesOperations) {
        this.couchDbChangesOperations = couchDbChangesOperations;
        this.toBeReceived = new PriorityBlockingQueue<ChangedDocument>(DEFAULT_INTERNAL_QUEUE_CAPACITY,
                new Comparator<ChangedDocument>() {
                    public int compare(ChangedDocument doc1, ChangedDocument doc2) {
                        long diff = doc1.getSequence() - doc2.getSequence();
                        if (diff == 0) {
                            return 0;
                        } else {
                            return diff > 0 ? 1 : -1;
                        }
                    }
                });
    }

    /**
     * Creates an instance with a default database to connect to.
     */
    public CouchDbChangesPollingMessageSource(String databaseUrl) {
        this(new CouchDbChangesTemplate(databaseUrl));
    }

    public Message<URI> receive() {
        if (toBeReceived.isEmpty()) {
            Collection<ChangedDocument> changedDocuments = couchDbChangesOperations.pollForChanges();
            toBeReceived.addAll(changedDocuments);
        }

        ChangedDocument changedDocument = toBeReceived.poll();
        return prepareMessage(changedDocument);
    }

    private Message<URI> prepareMessage(ChangedDocument changedDocument) {
        Message<URI> message = null;
        if (changedDocument != null) {
            message = MessageBuilder.withPayload(changedDocument.getUri()).build();
        }
        return message;
    }
}