zhouxinyu commented on a change in pull request #4019: URL: https://github.com/apache/rocketmq/pull/4019#discussion_r840995054
########## File path: apis/src/main/java/org/apache/rocketmq/apis/consumer/PullConsumer.java ########## @@ -0,0 +1,186 @@ +/* + * 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.rocketmq.apis.consumer; + +import java.io.Closeable; +import java.time.Duration; +import java.util.Collection; +import java.util.Map; +import java.util.concurrent.CompletableFuture; + +import org.apache.rocketmq.apis.MessageQueue; +import org.apache.rocketmq.apis.exception.*; +import org.apache.rocketmq.apis.message.MessageView; + +/** + * <p>PullConsumer is a thread-safe rocketmq client which is used to consume message by queue. + * Unlike push consumer and simple consumer, pull consumer implement load balance based on queue granularity. + * + * <p>Pull consumer is lightweight consumer that better suited to streaming scenarios. + * If you want fully control the message consumption operation by yourself like scan by offset or reconsume repeatedly, + * pull consumer should be your first consideration. + * + * <p>Pull consumer support two load balance mode. First is subscription mode, which full manage the rebalance + * operation triggered when group membership or cluster and topic metadata change.Another mode is manual assignment mode,which manage the load balance by yourself. + * + * <p> Pull consumer divide message consumption to 3 parts. + * Firstly, determine whether to continue processing from the last consumption or reset the consumption starting point by call seek method; + * Then, pull message from servers. + * At last, pull consumer no need to commit message by offset meta. + * <p> If there is a consumption error, consumer just call seek api to reset the offset for reconsume message again. + */ +public interface PullConsumer extends Closeable { + /** + * Get metadata about the message queues for a given topic. This method will issue a remote call to the server if it + * does not already have any metadata about the given topic. + * + * @param topic message's topic + * @return message queues of topic. + */ + Collection<MessageQueue> topicMessageQueues(String topic) throws ClientException; + + /** + * Manually assign messageQueue collections to this consumer. + * <p> Pull consumer must enable manual assignment mode in {@link PullConsumerBuilder} first, then call assign api. + * <p> This interface does not allow for incremental assignment and will replace the previous assignment. + * If the given collection is empty, it's treated same as unsubscribe(). + * Manual assignment through this interface will disable the consumerGroup management functionality + * and there will be no rebalance operation triggered when group membership or cluster and topic metadata change. + * @param messageQueues are the collection for current consumer. + * @throws ClientException when assign + */ + void assign(Collection<MessageQueue> messageQueues) throws ClientException; + + /** + * Add subscription expression dynamically when use subscription mode. + * + * <p>If first {@link SubscriptionExpression} that contains topicA and tag1 is exists already in consumer, then + * second {@link SubscriptionExpression} which contains topicA and tag2, <strong>the result is that the second one + * replaces the first one instead of integrating them</strong>. + * + * @param subscriptionExpression new subscription expression to add. + * @return pull consumer instance. + */ + PullConsumer subscribe(SubscriptionExpression subscriptionExpression) throws ClientException; + + /** + * Remove subscription expression dynamically by topic. + * + * <p>Nothing occurs if the specified topic does not exist in subscription expressions of pull consumer. + * + * @param topic the topic to remove subscription. + * @return pull consumer instance. + */ + PullConsumer unsubscribe(String topic) throws ClientException; + + /** + * Get the collection of messageQueues currently assigned to current consumer. + * @return the collection of messageQueues currently assigned to current consumer + */ + Collection<MessageQueue> assignments(); + + /** + * Pull messages for the topics specified by subscribe or assign api synchronously. + * + * <p> This method returns immediately if there are messages available. + * Otherwise, it will await the passed timeout. If the timeout expires, an empty map will be returned. + * An error occurs if you do not subscribe or assign messageQueues before pulling for data. + * @param maxMessageNum max message num when server returns. + * @return map of messageQueue to messageViews. + */ + Map<MessageQueue, Collection<MessageView>> pull(int maxMessageNum) throws ClientException; + Review comment: But it's not convenient to catch the real exception(ClientException) when using pullAsync.get. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
