Github user tweise commented on a diff in the pull request:
https://github.com/apache/incubator-apex-malhar/pull/134#discussion_r48452268
--- Diff:
kafka/src/main/java/org/apache/apex/malhar/kafka/KafkaConsumerWrapper.java ---
@@ -0,0 +1,408 @@
+/**
+ * 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.apex.malhar.kafka;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import javax.validation.constraints.Pattern;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.commons.io.IOUtils;
+import org.apache.commons.lang3.tuple.Pair;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.clients.consumer.ConsumerRecord;
+import org.apache.kafka.clients.consumer.ConsumerRecords;
+import org.apache.kafka.clients.consumer.KafkaConsumer;
+import org.apache.kafka.clients.consumer.NoOffsetForPartitionException;
+import org.apache.kafka.clients.consumer.OffsetAndMetadata;
+import org.apache.kafka.clients.consumer.OffsetCommitCallback;
+import org.apache.kafka.common.Metric;
+import org.apache.kafka.common.MetricName;
+import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.errors.WakeupException;
+
+import com.google.common.base.Joiner;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+
+/**
+ * This is the wrapper class for new Kafka consumer API
+ *
+ * It starts number of consumers(one for each cluster) in same number of
threads.
+ * Maintains the consumer offsets
+ *
+ * It also use the consumers to commit the application processed offsets
along with the application name
+ *
+ * @param <K> The key object, needs to be used with
http://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/ConsumerConfig.html#KEY_DESERIALIZER_CLASS_CONFIG
+ * @param <V> The value object, needs to be used with
http://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/ConsumerConfig.html#VALUE_DESERIALIZER_CLASS_CONFIG
+ */
+public class KafkaConsumerWrapper<K, V> implements Closeable
+{
+
+ private static final Logger logger =
LoggerFactory.getLogger(KafkaConsumerWrapper.class);
+
+ /**
+ * number of messages in buffer
+ */
+ private int cacheSize = 1024;
+
+ /**
+ * consumer timeout
+ */
+ private long timeout = 5000;
+
+ private boolean isAlive = false;
+
+ private transient Map<String, KafkaConsumer<K, V>> consumers = new
HashMap<>();
+
+ // The in memory buffer hold consumed messages
+ private transient ArrayBlockingQueue<Pair<String, ConsumerRecord<K, V>>>
holdingBuffer;
+
+
+ /**
+ * refer to AbstractKafkaInputOperator.initialOffset
+ */
+ @Pattern(flags = {Pattern.Flag.CASE_INSENSITIVE},
+ regexp =
"earliest|latest|application_or_earliest|application_or_latest")
+ private String initialOffset = "latest";
+
+ private transient AbstractKafkaInputOperator<K, V> ownerOperator = null;
+
+ private transient ExecutorService kafkaConsumerExecutor;
+
+ private transient Map<String, Map<TopicPartition, OffsetAndMetadata>>
offsetsToCommit = new HashMap<>();
+
+ /**
+ * You can customize the offsetCommit
+ */
+ private transient OffsetCommitCallback offsetCommitCallback = new
OffsetCommitCallback()
+ {
+ @Override
+ public void onComplete(Map<TopicPartition, OffsetAndMetadata> map,
Exception e)
+ {
+ if (logger.isDebugEnabled()) {
--- End diff --
What's the purpose of this implementation?
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