[SPARK-29087][SS] Use DelegatingServletContextHandler to avoid CCE

Author: dongjoon-hyun

core/src/main/scala/org/apache/spark/ui/WebUI.scala

@@ -236,4 +236,8 @@ private[spark] class DelegatingServletContextHandler(handler: ServletContextHand
   def filterCount(): Int = {
     handler.getServletHandler.getFilters.length
   }
+
+  def getContextPath(): String = {
+    handler.getContextPath
+  }
 }

streaming/src/test/scala/org/apache/spark/streaming/UISeleniumSuite.scala

@@ -97,7 +97,7 @@ class UISeleniumSuite
 
       val sparkUI = ssc.sparkContext.ui.get
 
-      sparkUI.getHandlers.count(_.getContextPath.contains("/streaming")) should be (5)
+      sparkUI.getDelegatingHandlers.count(_.getContextPath.contains("/streaming")) should be (5)
 
       eventually(timeout(10.seconds), interval(50.milliseconds)) {
         go to (sparkUI.webUrl.stripSuffix("/"))
@@ -198,7 +198,7 @@ class UISeleniumSuite
 
       ssc.stop(false)
 
-      sparkUI.getHandlers.count(_.getContextPath.contains("/streaming")) should be (0)
+      sparkUI.getDelegatingHandlers.count(_.getContextPath.contains("/streaming")) should be (0)
 
       eventually(timeout(10.seconds), interval(50.milliseconds)) {
         go to (sparkUI.webUrl.stripSuffix("/"))