[GitHub] [rocketmq] zhouxinyu commented on a change in pull request #4019: [RIP-37] Add new APIs for consumer

[GitBox <gi...@apache.org>]

zhouxinyu commented on a change in pull request #4019:
URL: https://github.com/apache/rocketmq/pull/4019#discussion_r840995054



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File path: apis/src/main/java/org/apache/rocketmq/apis/consumer/PullConsumer.java
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@@ -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.




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