AMQPConsumer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.nifi.amqp.processors;

import java.io.IOException;

import org.apache.nifi.processor.exception.ProcessException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.GetResponse;

/**
 * Generic consumer of messages from AMQP-based messaging system. It is based on
 * RabbitMQ client API (https://www.rabbitmq.com/api-guide.html)
 */
final class AMQPConsumer extends AMQPWorker {

    private final static Logger logger = LoggerFactory.getLogger(AMQPConsumer.class);

    private final String queueName;

    /**
     * Creates an instance of this consumer
     * @param connection instance of AMQP {@link Connection}
     * @param queueName name of the queue from which messages will be consumed.
     */
    AMQPConsumer(Connection connection, String queueName) {
        super(connection);
        this.validateStringProperty("queueName", queueName);
        this.queueName = queueName;
        logger.info("Successfully connected AMQPConsumer to " + connection.toString() + " and '" + queueName + "' queue");
    }

    /**
     * Consumes message from the queue identified by 'queueName' on each
     * invocation via {@link Channel#basicGet(String, boolean)} operation
     * returning instance of {@link GetResponse} In the event there are no
     * messages in the queue it will return null. In the event queue is not
     * defined in the system exception is raised by the target API. It will be
     * logged and propagated as {@link ProcessException}
     *
     * @return instance of {@link GetResponse}
     */
    public GetResponse consume() {
        try {
            return this.channel.basicGet(this.queueName, true);
        } catch (IOException e) {
            logger.error("Failed to receive message from AMQP; " + this + ". Possible reasons: Queue '" + this.queueName
                    + "' may not have been defined", e);
            throw new ProcessException(e);
        }
    }

    /**
     *
     */
    @Override
    public String toString() {
        return super.toString() + ", QUEUE:" + this.queueName;
    }
}