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

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chenzlalvin commented on a change in pull request #4019:
URL: https://github.com/apache/rocketmq/pull/4019#discussion_r840151907



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File path: apis/src/main/java/org/apache/rocketmq/apis/consumer/SimpleConsumer.java
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@@ -0,0 +1,154 @@
+/*
+ * 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.List;
+import java.util.concurrent.CompletableFuture;
+
+import org.apache.rocketmq.apis.exception.*;
+import org.apache.rocketmq.apis.message.MessageView;
+
+/**
+ * SimpleConsumer is a thread-safe rocketmq client which is used to consume message by group.
+ *
+ * <p>Simple consumer is lightweight consumer , if you want fully control the message consumption operation by yourself,
+ * simple consumer should be your first consideration.
+ *
+ * <p>Consumers belong to the same consumer group share messages from server,
+ * so consumer in the same group must have the same {@link SubscriptionExpression}s, otherwise the behavior is
+ * undefined. If a new consumer group's consumer is started first time, it consumes from the latest position. Once
+ * consumer is started, server records its consumption progress and derives it in subsequent startup.
+ *
+ * <p>You may intend to maintain different consumption progress for different consumer, different consumer group
+ * should be set in this case.
+ *
+ * <p> Simple consumer divide message consumption to 3 parts.
+ * Firstly, call receive api get messages from server; Then process message by yourself; At last, your must call Ack api to commit this message.
+ * If there is error when process message ,your can reconsume the message later which control by the invisibleDuration parameter.
+ * Also, you can change the invisibleDuration by call changeInvisibleDuration api.
+ */
+public interface SimpleConsumer extends Closeable {
+    /**
+     * Get the load balancing group for simple consumer.
+     *
+     * @return consumer load balancing group.
+     */
+    String getConsumerGroup();
+
+    /**
+     * Add subscription expression dynamically.
+     *
+     * <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 simple consumer instance.
+     */
+    SimpleConsumer subscribe(SubscriptionExpression subscriptionExpression) throws ClientException;

Review comment:
       Abstracting subscription behavior alone is not of great value and is easy to complicate the class interface.




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