add log and refine code style

helix-gateway/src/main/java/org/apache/helix/gateway/api/constant/GatewayServiceManagerConstant.java

@@ -0,0 +1,25 @@
+package org.apache.helix.gateway.api.constant;
+
+/*
+ * 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.
+ */
+
+public class GatewayServiceManagerConstant {
+  public static final String TARGET_STATE_ASSIGNMENT_KEY_NAME = "Assignment";
+  public static final String TIMESTAMP_KEY = "Timestamp";
+}

helix-gateway/src/main/java/org/apache/helix/gateway/participant/HelixGatewayParticipant.java

@@ -88,6 +88,7 @@ public void processStateTransitionMessage(Message message) throws Exception {
         throw new Exception("Failed to transition to state " + toState);
       }
     } finally {
+      logger.info("State transition finished for shard: {}{}", resourceId, shardId);
       _stateTransitionResultMap.remove(concatenatedShardName);
     }
   }
@@ -167,6 +168,7 @@ public void onDisconnected(HelixManager helixManager, Throwable error) throws Ex
   }
 
   public void disconnect() {
+    logger.info("Disconnecting from HelixManager {}", _helixManager.getInstanceName() );
     if (_helixManager.isConnected()) {
       _helixManager.disconnect();
     }

helix-gateway/src/main/java/org/apache/helix/gateway/service/GatewayServiceManager.java

@@ -19,7 +19,6 @@
  * under the License.
  */
 
-import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.google.common.collect.ImmutableSet;
@@ -37,11 +36,10 @@
 import org.apache.helix.gateway.participant.HelixGatewayParticipant;
 import org.apache.helix.gateway.util.GatewayCurrentStateCache;
 import org.apache.helix.gateway.util.PerKeyBlockingExecutor;
-import org.apache.helix.gateway.util.PollChannelUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import static org.apache.helix.gateway.api.constant.gatewayServiceManagerConstant.*;
+import static org.apache.helix.gateway.api.constant.GatewayServiceManagerConstant.*;
 
 
 /**
@@ -115,6 +113,7 @@ public void onGatewayServiceEvent(GatewayServiceEvent event) {
   }
 
   public void resetTargetStateCache(String clusterName, String instanceName) {
+    logger.info("Resetting target state cache for cluster: {}, instance: {}", clusterName, instanceName);
     getOrCreateCache(clusterName).resetTargetStateCache(instanceName);
   }
 
@@ -244,6 +243,7 @@ private void createHelixGatewayParticipant(String clusterName, String instanceNa
   }
 
   private void removeHelixGatewayParticipant(String clusterName, String instanceName) {
+    logger.info("Removing participant: {} from cluster: {}", instanceName, clusterName);
     // Disconnect and remove the participant from the participant map
     HelixGatewayParticipant participant = getHelixGatewayParticipant(clusterName, instanceName);
     if (participant != null) {