[GitHub] [pulsar] jiazhai commented on a change in pull request #4911: expose getLastMessageId method in ConsumerImpl

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jiazhai commented on a change in pull request #4911: expose getLastMessageId method in ConsumerImpl
URL: https://github.com/apache/pulsar/pull/4911#discussion_r313306254
 
 

 ##########
 File path: pulsar-client/src/main/java/org/apache/pulsar/client/impl/MultiMessageIdImpl.java
 ##########
 @@ -0,0 +1,111 @@
+/**
+ * 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.pulsar.client.impl;
+
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+import lombok.Getter;
+import org.apache.pulsar.client.api.MessageId;
+import sun.reflect.generics.reflectiveObjects.NotImplementedException;
+
+/**
+ * A MessageId implementation that contains a map of <partitionName, MessageId>.
+ * This is useful when MessageId is need for partition/multi-topics/pattern consumer.
+ * e.g. seek(), ackCumulative(), getLastMessageId().
+ */
+public class MultiMessageIdImpl implements MessageId {
+    @Getter
+    private Map<String, MessageId> map;
+
+    MultiMessageIdImpl(Map<String, MessageId> map) {
+        this.map = map;
+    }
+
+    // TODO: Add support for Serialization and Deserialization
+    //  https://github.com/apache/pulsar/issues/4940
+    @Override
+    public byte[] toByteArray() {
+        throw new NotImplementedException();
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(map);
+    }
+
+    // If all messageId in map are same size, and all bigger/smaller than the other, return valid value.
+    @Override
+    public int compareTo(MessageId o) {
+        if (!(o instanceof MultiMessageIdImpl)) {
+            throw new IllegalArgumentException(
+                "expected MultiMessageIdImpl object. Got instance of " + o.getClass().getName());
+        }
+
+        MultiMessageIdImpl other = (MultiMessageIdImpl) o;
+        Map<String, MessageId> otherMap = other.getMap();
+
+        if ((map == null || map.isEmpty()) && (otherMap == null || otherMap.isEmpty())) {
+            return 0;
+        }
+
+        if (otherMap == null || map == null || otherMap.size() != map.size()) {
+            throw new IllegalArgumentException("Current size and other size not equals");
+        }
+
+        int result = 0;
+        for (Entry<String, MessageId> entry : map.entrySet()) {
+            MessageId otherMessage = otherMap.get(entry.getKey());
+            if (otherMessage == null) {
+                throw new IllegalArgumentException(
+                    "Other MessageId not have topic " + entry.getKey());
+            }
+
+            int currentResult = entry.getValue().compareTo(otherMessage);
+            if (result == 0) {
+                result = currentResult;
 
 Review comment:
   1. result == 0 && currentResult ==0, then this reset has no effect.
   2. result ==0 && currentResult !=0, then we keep the non-zero result, this is the result that may be finally returned. 
   

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