Github user srdo commented on a diff in the pull request:
https://github.com/apache/storm/pull/2538#discussion_r165854105
--- 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();
--- End diff --
Objectmappers are thread safe. I don't see anywhere in the documentation
that mentions whether there are internal locks being used in the ObjectMapper,
but this post suggests there aren't
https://stackoverflow.com/questions/18611565/how-do-i-correctly-reuse-jackson-objectmapper#comment27462917_18618918.
A quick google also suggests that it should be fine to use ObjectMapper as a
singleton.
---
