AVRO-4229 - Update StatsServer resource handler (#3648)

* AVRO-4229 - Update StatsServer resource handler

* Fix review comments

- moved ASFv2 to the top
- static content only served when it is available

Author: terjekid

lang/java/ipc-jetty/src/main/java/org/apache/avro/ipc/jetty/StaticServlet.java

@@ -1,7 +1,3 @@
-package org.apache.avro.ipc.jetty;
-
-import org.apache.avro.ipc.stats.StatsPlugin;
-import org.apache.avro.ipc.stats.StatsServlet;
 /*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
@@ -19,9 +15,19 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+package org.apache.avro.ipc.jetty;
+
+import org.apache.avro.ipc.stats.StatsPlugin;
+import org.apache.avro.ipc.stats.StatsServlet;
+
 import org.eclipse.jetty.server.Server;
-import org.eclipse.jetty.servlet.ServletHandler;
+import org.eclipse.jetty.server.handler.ContextHandler;
+import org.eclipse.jetty.server.handler.HandlerList;
+import org.eclipse.jetty.server.handler.ResourceHandler;
+import org.eclipse.jetty.servlet.ServletContextHandler;
 import org.eclipse.jetty.servlet.ServletHolder;
+import org.eclipse.jetty.util.resource.Resource;
 
 /* This is a server that displays live information from a StatsPlugin.
  *
@@ -42,11 +48,28 @@ public StatsServer(StatsPlugin plugin, int port) throws Exception {
     this.httpServer = new Server(port);
     this.plugin = plugin;
 
-    ServletHandler handler = new ServletHandler();
-    httpServer.setHandler(handler);
-    handler.addServletWithMapping(new ServletHolder(new StaticServlet()), "/");
+    ServletContextHandler servletContext = new ServletContextHandler(ServletContextHandler.SESSIONS);
+    servletContext.setContextPath("/");
+
+    ServletHolder servletHolder = new ServletHolder(new StatsServlet(plugin));
+    servletContext.addServlet(servletHolder, "/");
+
+    HandlerList handlers = new HandlerList(servletContext);
+
+    Resource classPathResource = Resource.newClassPathResource("/org/apache/avro/ipc/stats/static");
+    if (classPathResource.exists() && classPathResource.isDirectory()) {
+      ResourceHandler resourceHandler = new ResourceHandler();
+      resourceHandler.setBaseResource(classPathResource);
+      resourceHandler.setDirectoriesListed(false); // Optional: prevent directory listing
+
+      ContextHandler staticContext = new ContextHandler();
+      staticContext.setContextPath("/static");
+      staticContext.setHandler(resourceHandler);
+
+      handlers.prependHandler(staticContext);
+    }
 
-    handler.addServletWithMapping(new ServletHolder(new StatsServlet(plugin)), "/");
+    httpServer.setHandler(handlers);
 
     httpServer.start();
   }