GUI -- Further work on refactoring Topology View server side code.
- includes some cleanup of UiMessageHandler and subclasses thereof.

Change-Id: Ie48d830447a4abe1b3accda41a934530a4d55d0e
diff --git a/web/gui/src/main/java/org/onosproject/ui/impl/TopologyViewMessageHandler.java b/web/gui/src/main/java/org/onosproject/ui/impl/TopologyViewMessageHandler.java
index 232393c..478bfe7 100644
--- a/web/gui/src/main/java/org/onosproject/ui/impl/TopologyViewMessageHandler.java
+++ b/web/gui/src/main/java/org/onosproject/ui/impl/TopologyViewMessageHandler.java
@@ -167,7 +167,7 @@
     }
 
     @Override
-    protected Collection<RequestHandler> getHandlers() {
+    protected Collection<RequestHandler> createRequestHandlers() {
         return ImmutableSet.of(
                 new TopoStart(),
                 new TopoStop(),
@@ -254,8 +254,8 @@
 
         @Override
         public void process(long sid, ObjectNode payload) {
-            ObjectNode root = mapper.createObjectNode();
-            ArrayNode names = mapper.createArrayNode();
+            ObjectNode root = objectNode();
+            ArrayNode names = arrayNode();
             get(SpriteService.class).getNames().forEach(names::add);
             root.set("names", names);
             sendMessage("spriteListResponse", sid, root);
@@ -270,7 +270,7 @@
         @Override
         public void process(long sid, ObjectNode payload) {
             String name = string(payload, "name");
-            ObjectNode root = mapper.createObjectNode();
+            ObjectNode root = objectNode();
             root.set("data", get(SpriteService.class).get(name));
             sendMessage("spriteDataResponse", sid, root);
         }