Add comment for AccessChannel class

client/src/main/java/org/apache/rocketmq/client/AccessChannel.java

@@ -15,7 +15,19 @@
  * limitations under the License.
  */
 package org.apache.rocketmq.client;
+
+/**
+ * Used for set access channel, if need migrate the rocketmq service to cloud, it is We recommend set the value with
+ * "CLOUD". otherwise set with "LOCAL", especially used the message trace feature.
+ */
 public enum AccessChannel {
-    local,
-    cloud,
+    /**
+     * Means connect to private IDC cluster.
+     */
+    LOCAL,
+
+    /**
+     * Means connect to Cloud service.
+     */
+    CLOUD,
 }

client/src/main/java/org/apache/rocketmq/client/ClientConfig.java

@@ -37,7 +37,7 @@ public class ClientConfig {
     private String instanceName = System.getProperty("rocketmq.client.name", "DEFAULT");
     private int clientCallbackExecutorThreads = Runtime.getRuntime().availableProcessors();
     protected String namespace;
-    protected AccessChannel accessChannel = AccessChannel.local;
+    protected AccessChannel accessChannel = AccessChannel.LOCAL;
 
     /**
      * Pulling topic information interval from the named server

client/src/main/java/org/apache/rocketmq/client/trace/AsyncTraceDispatcher.java

@@ -72,7 +72,7 @@ public class AsyncTraceDispatcher implements TraceDispatcher {
     private String dispatcherId = UUID.randomUUID().toString();
     private String traceTopicName;
     private AtomicBoolean isStarted = new AtomicBoolean(false);
-    private AccessChannel accessChannel = AccessChannel.local;
+    private AccessChannel accessChannel = AccessChannel.LOCAL;
 
     public AsyncTraceDispatcher(String traceTopicName, RPCHook rpcHook) {
         // queueSize is greater than or equal to the n power of 2 of value
@@ -341,7 +341,7 @@ public class AsyncTraceDispatcher implements TraceDispatcher {
          */
         private void sendTraceDataByMQ(Set<String> keySet, final String data, String dataTopic, String regionId) {
             String traceTopic = traceTopicName;
-            if (AccessChannel.cloud == accessChannel){
+            if (AccessChannel.CLOUD == accessChannel) {
                 traceTopic = TraceConstants.TRACE_TOPIC_PREFIX + regionId;
             }
             final Message message = new Message(traceTopic, data.getBytes());