Jetty 9.4.x single context optimisation (#4909)

* Optimisation for single context

It is a frequent deployment mode to have only a single context.
In that case, the ContextHandlerCollection can bypass a bit of
looping/matching/selecting and just call the single context,
which it works out itself anyway if the request applies to it.

Signed-off-by: Greg Wilkins <gregw@webtide.com>

* Optimisation for single context

updates from review

Signed-off-by: Greg Wilkins <gregw@webtide.com>

jetty-server/src/main/java/org/eclipse/jetty/server/handler/ContextHandlerCollection.java

@@ -176,11 +176,23 @@ public class ContextHandlerCollection extends HandlerCollection
     @Override
     public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
     {
-        Handlers handlers = _handlers.get();
+        Mapping mapping = (Mapping)_handlers.get();
-        if (handlers == null)
+
+        // Handle no contexts
+        if (mapping == null)
+            return;
+        Handler[] handlers = mapping.getHandlers();
+        if (handlers == null || handlers.length == 0)
             return;
 
-        Mapping mapping = (Mapping)handlers;
+        // handle only a single context.
+        if (handlers.length == 1)
+        {
+            handlers[0].handle(target, baseRequest, request, response);
+            return;
+        }
+
+        // handle async dispatch to specific context
         HttpChannelState async = baseRequest.getHttpChannelState();
         if (async.isAsync())
         {
@@ -197,6 +209,7 @@ public class ContextHandlerCollection extends HandlerCollection
             }
         }
 
+        // handle many contexts
         if (target.startsWith("/"))
         {
             Trie<Map.Entry<String, Branch[]>> pathBranches = mapping._pathBranches;
@@ -229,11 +242,9 @@ public class ContextHandlerCollection extends HandlerCollection
         }
         else
         {
-            if (mapping.getHandlers() == null)
+            for (Handler handler : handlers)
-                return;
-            for (int i = 0; i < mapping.getHandlers().length; i++)
             {
-                mapping.getHandlers()[i].handle(target, baseRequest, request, response);
+                handler.handle(target, baseRequest, request, response);
                 if (baseRequest.isHandled())
                     return;
             }