Update javadoc for CommandCenterProvider

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/CommandCenterProvider.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 1999-2019 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.command;
 
 import com.alibaba.csp.sentinel.log.RecordLog;
@@ -8,7 +23,7 @@ import com.alibaba.csp.sentinel.util.SpiLoader;
  * Provider for a universal {@link CommandCenter} instance.
  *
  * @author cdfive
- * @date 2019-01-11
+ * @since 1.5.0
  */
 public class CommandCenterProvider {
 
@@ -25,10 +40,16 @@ public class CommandCenterProvider {
             RecordLog.warn("[CommandCenterProvider] No existing CommandCenter, resolve failed");
         } else {
             commandCenter = resolveCommandCenter;
-            RecordLog.info("[CommandCenterProvider] CommandCenter resolved: " + resolveCommandCenter.getClass().getCanonicalName());
+            RecordLog.info("[CommandCenterProvider] CommandCenter resolved: " + resolveCommandCenter.getClass()
+                .getCanonicalName());
         }
     }
 
+    /**
+     * Get resolved {@link CommandCenter} instance.
+     *
+     * @return resolved {@code CommandCenter} instance
+     */
     public static CommandCenter getCommandCenter() {
         return commandCenter;
     }