add support for reading from multiple kafka topics

ingestion/src/main/java/feast/ingestion/transform/FeatureRowKafkaIO.java

@@ -1,3 +1,20 @@
+/*
+ * Copyright 2018 The Feast Authors
+ *
+ * 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
+ *
+ *     https://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 feast.ingestion.transform;
 
 import com.google.common.base.Preconditions;
@@ -15,12 +32,22 @@
 import org.apache.beam.sdk.values.PCollection;
 import org.apache.beam.sdk.values.PInput;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
 import static com.google.common.base.Preconditions.checkArgument;
 
 public class FeatureRowKafkaIO {
 
     static final String KAFKA_TYPE = "kafka";
 
+
+    /**
+     * Transform for reading {@link feast.types.FeatureRowProto.FeatureRow FeatureRow}
+     * proto messages from kafka one or more kafka topics.
+     *
+     */
     public static Read read(ImportSpec importSpec) {
         return new Read(importSpec);
     }
@@ -43,14 +70,16 @@ public PCollection<FeatureRow> expand(PInput input) {
             Preconditions.checkArgument(
                     !Strings.isNullOrEmpty(bootstrapServer), "kafka bootstrap server must be set");
 
-            String topic = importSpec.getOptionsMap().get("topic");
+            String topics = importSpec.getOptionsMap().get("topics");
 
             Preconditions.checkArgument(
-                    !Strings.isNullOrEmpty(topic), "kafka topic must be set");
+                    !Strings.isNullOrEmpty(topics), "kafka topic(s) must be set");
+
+            List<String> topicsList = new ArrayList<>(Arrays.asList(topics.split(",")));
 
             KafkaIO.Read<FeatureRowKey, FeatureRow> kafkaIOReader = KafkaIO.<FeatureRowKey, FeatureRow>read()
                     .withBootstrapServers(bootstrapServer)
-                    .withTopic(topic)
+                    .withTopics(topicsList)
                     .withKeyDeserializer(FeatureRowKeyDeserializer.class)
                                     .withValueDeserializer(FeatureRowDeserializer.class);