docs: add comments to class GrpcMessagingApplication

proxy/src/main/java/org/apache/rocketmq/proxy/grpc/v2/GrpcMessagingApplication.java

@@ -71,6 +71,15 @@
 import org.apache.rocketmq.proxy.grpc.v2.common.ResponseWriter;
 import org.apache.rocketmq.proxy.processor.MessagingProcessor;
 
+/**
+ * RocketMQ gRPC protocol implementation
+ *
+ * <ul>
+ *   <li>implements gRPC protocol</li>
+ *   <li>execute request in independent thread pool</li>
+ *   <li>execute pipeline, ...</li>
+ * </ul>
+ */
 public class GrpcMessagingApplication extends MessagingServiceGrpc.MessagingServiceImplBase implements StartAndShutdown {
     private final static Logger log = LoggerFactory.getLogger(LoggerName.PROXY_LOGGER_NAME);
 
@@ -167,6 +176,16 @@ protected Status convertExceptionToStatus(Throwable t) {
         return ResponseBuilder.getInstance().buildStatus(t);
     }
 
+    /**
+     * submit grpc task to related thread pool.
+     *
+     * @param executor thread pool
+     * @param context context
+     * @param request grpc request
+     * @param runnable process task
+     * @param responseObserver grpc response observer
+     * @param statusResponseCreator error response creator
+     */
     protected <V, T> void addExecutor(ExecutorService executor, ProxyContext context, V request, Runnable runnable,
         StreamObserver<T> responseObserver, Function<Status, T> statusResponseCreator) {
         if (request instanceof GeneratedMessageV3) {
@@ -200,6 +219,12 @@ protected void validateContext(ProxyContext context) {
         }
     }
 
+    /**
+     * route query api, producer/consumer will call this api while starting.
+     *
+     * @param request request
+     * @param responseObserver gRPC response observer
+     */
     @Override
     public void queryRoute(QueryRouteRequest request, StreamObserver<QueryRouteResponse> responseObserver) {
         Function<Status, QueryRouteResponse> statusResponseCreator = status -> QueryRouteResponse.newBuilder().setStatus(status).build();
@@ -217,6 +242,12 @@ public void queryRoute(QueryRouteRequest request, StreamObserver<QueryRouteRespo
         }
     }
 
+    /**
+     * heartbeat api, register producer/consumer
+     *
+     * @param request request
+     * @param responseObserver responseObserver
+     */
     @Override
     public void heartbeat(HeartbeatRequest request, StreamObserver<HeartbeatResponse> responseObserver) {
         Function<Status, HeartbeatResponse> statusResponseCreator = status -> HeartbeatResponse.newBuilder().setStatus(status).build();
@@ -251,6 +282,12 @@ public void sendMessage(SendMessageRequest request, StreamObserver<SendMessageRe
         }
     }
 
+    /**
+     * assignment query api, consumer will call this api while starting.
+     *
+     * @param request request
+     * @param responseObserver gRPC response observer
+     */
     @Override
     public void queryAssignment(QueryAssignmentRequest request,
         StreamObserver<QueryAssignmentResponse> responseObserver) {
@@ -399,6 +436,15 @@ public void recallMessage(RecallMessageRequest request, StreamObserver<RecallMes
         }
     }
 
+    /**
+     * telemetry API
+     *
+     * <ul>
+     *   <li>register producer/consumer</li>
+     *   <li>process trace</li>
+     *   <li>verify message result</li>
+     * </ul>
+     */
     @Override
     public StreamObserver<TelemetryCommand> telemetry(StreamObserver<TelemetryCommand> responseObserver) {
         Function<Status, TelemetryCommand> statusResponseCreator = status -> TelemetryCommand.newBuilder().setStatus(status).build();