Github user hmcl commented on a diff in the pull request:
https://github.com/apache/storm/pull/2538#discussion_r165852989
--- Diff:
external/storm-kafka-client/src/main/java/org/apache/storm/kafka/spout/internal/CommitMetadataManager.java
---
@@ -0,0 +1,90 @@
+/*
+ * Copyright 2018 The Apache Software Foundation.
+ *
+ * Licensed 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.storm.kafka.spout.internal;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import java.io.IOException;
+import java.util.Map;
+import org.apache.kafka.clients.consumer.OffsetAndMetadata;
+import org.apache.kafka.common.TopicPartition;
+import org.apache.storm.kafka.spout.KafkaSpout;
+import org.apache.storm.kafka.spout.KafkaSpoutConfig.ProcessingGuarantee;
+import org.apache.storm.task.TopologyContext;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Generates and reads commit metadata.
+ */
+public class CommitMetadataManager {
+
+ private static final ObjectMapper JSON_MAPPER = new ObjectMapper();
+ private static final Logger LOG =
LoggerFactory.getLogger(CommitMetadata.class);
+ // Metadata information to commit to Kafka. It is unique per spout
instance.
+ private final String commitMetadata;
+ private final ProcessingGuarantee processingGuarantee;
+ private final TopologyContext context;
+
+ /**
+ * Create a manager with the given context.
+ */
+ public CommitMetadataManager(TopologyContext context,
ProcessingGuarantee processingGuarantee) {
+ this.context = context;
+ try {
+ commitMetadata = JSON_MAPPER.writeValueAsString(new
CommitMetadata(
--- End diff --
Ideally commitMetadata would be passed in the constructor to facilitate
unit testing. We could have a factory method in this class itself with this code
```java
public CommitMetadataManager(TopologyContext context, ProcessingGuarantee
processingGuarantee, String commitMetadata)
```
```java
public static CommitMetadataManager newInstance(TopologyContext context,
ProcessingGuarantee processingGuarantee) {
return new CommitMetadataManager(context, processingGuarantee,
JSON_MAPPER.writeValueAsString(new CommitMetadata(context.getStormId(),
context.getThisTaskId(), Thread.currentThread().getName())));
}
```
handling the JsonProcessingException in the factory method
---
