RabbitMQ拉模式批量消费消息

标签：rop   default   from   ini   icp   container   bit   推荐   log   

/**
 * Retrieve a message from a queue using {@link com.rabbitmq.client.AMQP.Basic.Get}
 * @see com.rabbitmq.client.AMQP.Basic.Get
 * @see com.rabbitmq.client.AMQP.Basic.GetOk
 * @see com.rabbitmq.client.AMQP.Basic.GetEmpty
 * @param queue the name of the queue
 * @param autoAck true if the server should consider messages
 * acknowledged once delivered; false if the server should expect
 * explicit acknowledgements
 * @return a {@link GetResponse} containing the retrieved message data
 * @throws java.io.IOException if an error is encountered
 */
GetResponse basicGet(String queue, boolean autoAck) throws IOException;

basicGet 返回 GetResponse 类。

public class GetResponse {
    private final Envelope envelope;
    private final BasicProperties props;
    private final byte[] body;
    private final int messageCount;

    // ...

rabbitmq-client版本4.0.3
使用 basicGet 拉取消息需要注意：

basicGet
DefaultConsumer

示例代码：

private void consume(Channel channel) throws IOException, InterruptedException {
    while (true) {
        if (!isConditionSatisfied()) {
            TimeUnit.MILLISECONDS.sleep(1);
            continue;
        }
        GetResponse response = channel.basicGet(CAOSH_TEST_QUEUE, false);
        if (response == null) {
            TimeUnit.MILLISECONDS.sleep(1);
            continue;
        }
        String data = new String(response.getBody());
        logger.info("Get message <= {}", data);
        channel.basicAck(response.getEnvelope().getDeliveryTag(), false);
    }
}

批量拉取消息
RabbitMQ支持客户端批量拉取消息，客户端可以连续调用 basicGet 方法拉取多条消息，处理完成之后一次性ACK。需要注意：

basicGet
basicAck

示例代码：

String bridgeQueueName = extractorProperties.getBridgeQueueName();
int batchSize = extractorProperties.getBatchSize();
List<GetResponse> responseList = Lists.newArrayListWithCapacity(batchSize);
long tag = 0;
while (responseList.size() < batchSize) {
    GetResponse getResponse = channel.basicGet(bridgeQueueName, false);
    if (getResponse == null) {
        break;
    }
    responseList.add(getResponse);
    tag = getResponse.getEnvelope().getDeliveryTag();
}
if (responseList.isEmpty()) {
    TimeUnit.MILLISECONDS.sleep(1);
} else {
    logger.info("Get <{}> responses this batch", responseList.size());
    // handle messages
    channel.basicAck(tag, true);
}

关于QueueingConsumer
QueueingConsumer 在客户端本地使用 BlockingQueue 缓冲消息，其nextDelivery方法也可以用于实现拉模式（其本质上是 BlockingQueue.take ），但是 QueueingConsumer 现在已经标记为Deprecated。

RabbitMQ拉模式批量消费消息

标签：rop   default   from   ini   icp   container   bit   推荐   log   

原文地址：http://blog.51cto.com/14028890/2326588