Address Patrick's comments

core/src/main/scala/org/apache/spark/deploy/history/HistoryPage.scala

@@ -25,7 +25,7 @@ import org.apache.spark.ui.{WebUIPage, UIUtils}
 
 private[spark] class IndexPage(parent: HistoryServer) extends WebUIPage("") {
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val appRows = parent.appIdToInfo.values.toSeq.sortBy { app => -app.lastUpdated }
     val appTable = UIUtils.listingTable(appHeader, appRow, appRows)
     val content =

core/src/main/scala/org/apache/spark/deploy/history/HistoryServer.scala

@@ -131,7 +131,7 @@ class HistoryServer(
         // Remove any applications that should no longer be retained
         appIdToInfo.foreach { case (appId, info) =>
           if (!retainedAppIds.contains(appId)) {
-            detachUI(info.ui)
+            detachSparkUI(info.ui)
             appIdToInfo.remove(appId)
           }
         }
@@ -173,7 +173,7 @@ class HistoryServer(
     // Do not call ui.bind() to avoid creating a new server for each application
     replayBus.replay()
     if (appListener.applicationStarted) {
-      attachUI(ui)
+      attachSparkUI(ui)
       val appName = appListener.appName
       val sparkUser = appListener.sparkUser
       val startTime = appListener.startTime
@@ -193,13 +193,13 @@ class HistoryServer(
   }
 
   /** Attach a reconstructed UI to this server. Only valid after bind(). */
-  private def attachUI(ui: SparkUI) {
+  private def attachSparkUI(ui: SparkUI) {
     assert(serverInfo.isDefined, "HistoryServer must be bound before attaching SparkUIs")
     ui.getHandlers.foreach(attachHandler)
   }
 
   /** Detach a reconstructed UI from this server. Only valid after bind(). */
-  private def detachUI(ui: SparkUI) {
+  private def detachSparkUI(ui: SparkUI) {
     assert(serverInfo.isDefined, "HistoryServer must be bound before detaching SparkUIs")
     ui.getHandlers.foreach(detachHandler)
   }

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -625,7 +625,7 @@ private[spark] class Master(
       if (completedApps.size >= RETAINED_APPLICATIONS) {
         val toRemove = math.max(RETAINED_APPLICATIONS / 10, 1)
         completedApps.take(toRemove).foreach( a => {
-          appIdToUI.remove(a.id).foreach { ui => webUi.detachUI(ui) }
+          appIdToUI.remove(a.id).foreach { ui => webUi.detachSparkUI(ui) }
           applicationMetricsSystem.removeSource(a.appSource)
         })
         completedApps.trimStart(toRemove)
@@ -672,7 +672,7 @@ private[spark] class Master(
         replayBus.replay()
         app.desc.appUiUrl = ui.basePath
         appIdToUI(app.id) = ui
-        webUi.attachUI(ui)
+        webUi.attachSparkUI(ui)
         return true
       } catch {
         case t: Throwable =>

core/src/main/scala/org/apache/spark/deploy/master/ui/ApplicationPage.scala

@@ -31,8 +31,7 @@ import org.apache.spark.deploy.master.ExecutorInfo
 import org.apache.spark.ui.{WebUIPage, UIUtils}
 import org.apache.spark.util.Utils
 
-private[spark] class ApplicationPage(parent: MasterWebUI)
-  extends WebUIPage("app", includeJson = true) {
+private[spark] class ApplicationPage(parent: MasterWebUI) extends WebUIPage("app") {
 
   private val master = parent.masterActorRef
   private val timeout = parent.timeout
@@ -49,7 +48,7 @@ private[spark] class ApplicationPage(parent: MasterWebUI)
   }
 
   /** Executor details for a particular application */
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val appId = request.getParameter("appId")
     val stateFuture = (master ? RequestMasterState)(timeout).mapTo[MasterStateResponse]
     val state = Await.result(stateFuture, timeout)

core/src/main/scala/org/apache/spark/deploy/master/ui/MasterPage.scala

@@ -31,7 +31,7 @@ import org.apache.spark.deploy.master.{ApplicationInfo, DriverInfo, WorkerInfo}
 import org.apache.spark.ui.{WebUIPage, UIUtils}
 import org.apache.spark.util.Utils
 
-private[spark] class IndexPage(parent: MasterWebUI) extends WebUIPage("", includeJson = true) {
+private[spark] class IndexPage(parent: MasterWebUI) extends WebUIPage("") {
   private val master = parent.masterActorRef
   private val timeout = parent.timeout
 
@@ -42,7 +42,7 @@ private[spark] class IndexPage(parent: MasterWebUI) extends WebUIPage("", includ
   }
 
   /** Index view listing applications and executors */
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val stateFuture = (master ? RequestMasterState)(timeout).mapTo[MasterStateResponse]
     val state = Await.result(stateFuture, timeout)
 

core/src/main/scala/org/apache/spark/deploy/master/ui/MasterWebUI.scala

@@ -45,13 +45,13 @@ class MasterWebUI(val master: Master, requestedPort: Int)
   }
 
   /** Attach a reconstructed UI to this Master UI. Only valid after bind(). */
-  def attachUI(ui: SparkUI) {
+  def attachSparkUI(ui: SparkUI) {
     assert(serverInfo.isDefined, "Master UI must be bound to a server before attaching SparkUIs")
     ui.getHandlers.foreach(attachHandler)
   }
 
   /** Detach a reconstructed UI from this Master UI. Only valid after bind(). */
-  def detachUI(ui: SparkUI) {
+  def detachSparkUI(ui: SparkUI) {
     assert(serverInfo.isDefined, "Master UI must be bound to a server before detaching SparkUIs")
     ui.getHandlers.foreach(detachHandler)
   }

core/src/main/scala/org/apache/spark/deploy/worker/ui/LogPage.scala

@@ -56,7 +56,7 @@ private[spark] class LogPage(parent: WorkerWebUI) extends WebUIPage("logPage") {
     pre + Utils.offsetBytes(path, startByte, endByte)
   }
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val defaultBytes = 100 * 1024
     val appId = Option(request.getParameter("appId"))
     val executorId = Option(request.getParameter("executorId"))

core/src/main/scala/org/apache/spark/deploy/worker/ui/WorkerPage.scala

@@ -31,7 +31,7 @@ import org.apache.spark.deploy.worker.{DriverRunner, ExecutorRunner}
 import org.apache.spark.ui.{WebUIPage, UIUtils}
 import org.apache.spark.util.Utils
 
-private[spark] class IndexPage(parent: WorkerWebUI) extends WebUIPage("", includeJson = true) {
+private[spark] class IndexPage(parent: WorkerWebUI) extends WebUIPage("") {
   val workerActor = parent.worker.self
   val worker = parent.worker
   val timeout = parent.timeout
@@ -42,7 +42,7 @@ private[spark] class IndexPage(parent: WorkerWebUI) extends WebUIPage("", includ
     JsonProtocol.writeWorkerState(workerState)
   }
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val stateFuture = (workerActor ? RequestWorkerState)(timeout).mapTo[WorkerStateResponse]
     val workerState = Await.result(stateFuture, timeout)
 

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

@@ -27,7 +27,7 @@ import org.apache.spark.ui.jobs.JobProgressTab
 import org.apache.spark.ui.storage.StorageTab
 
 /**
- * Top level user interface for Spark.
+ * Top level user interface for a Spark application.
  */
 private[spark] class SparkUI(
     val sc: SparkContext,

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

@@ -229,7 +229,7 @@ private[spark] object UIUtils extends Logging {
       tableClass += " table-fixed"
     }
     val colWidth = 100.toDouble / headers.size
-    val colWidthAttr =if (fixedWidth) colWidth + "%" else ""
+    val colWidthAttr = if (fixedWidth) colWidth + "%" else ""
     val headerRow: Seq[Node] = {
       // if none of the headers have "\n" in them
       if (headers.forall(!_.contains("\n"))) {

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

@@ -63,10 +63,8 @@ private[spark] abstract class WebUI(
     val pagePath = "/" + page.prefix
     attachHandler(createServletHandler(pagePath,
       (request: HttpServletRequest) => page.render(request), securityManager, basePath))
-    if (page.includeJson) {
-      attachHandler(createServletHandler(pagePath.stripSuffix("/") + "/json",
-        (request: HttpServletRequest) => page.renderJson(request), securityManager, basePath))
-    }
+    attachHandler(createServletHandler(pagePath.stripSuffix("/") + "/json",
+      (request: HttpServletRequest) => page.renderJson(request), securityManager, basePath))
   }
 
   /** Attach a handler to this UI. */
@@ -121,6 +119,7 @@ private[spark] abstract class WebUI(
 
 /**
  * A tab that represents a collection of pages.
+ * The prefix is appended to the parent address to form a full path, and must not contain slashes.
  */
 private[spark] abstract class WebUITab(parent: WebUI, val prefix: String) {
   val pages = ArrayBuffer[WebUIPage]()
@@ -141,10 +140,11 @@ private[spark] abstract class WebUITab(parent: WebUI, val prefix: String) {
  * A page that represents the leaf node in the UI hierarchy.
  *
  * The direct parent of a WebUIPage is not specified as it can be either a WebUI or a WebUITab.
- * If includeJson is true, the parent WebUI (direct or indirect) creates handlers for both the
- * HTML and the JSON content, rather than just the former.
+ * If the parent is a WebUI, the prefix is appended to the parent's address to form a full path.
+ * Else, if the parent is a WebUITab, the prefix is appended to the super prefix of the parent
+ * to form a relative path. The prefix must not contain slashes.
  */
-private[spark] abstract class WebUIPage(var prefix: String, val includeJson: Boolean = false) {
-  def render(request: HttpServletRequest): Seq[Node] = Seq[Node]()
+private[spark] abstract class WebUIPage(var prefix: String) {
+  def render(request: HttpServletRequest): Seq[Node]
   def renderJson(request: HttpServletRequest): JValue = JNothing
 }

core/src/main/scala/org/apache/spark/ui/env/EnvironmentPage.scala

@@ -28,7 +28,7 @@ private[ui] class IndexPage(parent: EnvironmentTab) extends WebUIPage("") {
   private val basePath = parent.basePath
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val runtimeInformationTable = UIUtils.listingTable(
       propertyHeader, jvmRow, listener.jvmInformation, fixedWidth = true)
     val sparkPropertiesTable = UIUtils.listingTable(

core/src/main/scala/org/apache/spark/ui/exec/ExecutorsPage.scala

@@ -29,7 +29,7 @@ private[ui] class IndexPage(parent: ExecutorsTab) extends WebUIPage("") {
   private val basePath = parent.basePath
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val storageStatusList = listener.storageStatusList
     val maxMem = storageStatusList.map(_.maxMem).fold(0L)(_ + _)
     val memUsed = storageStatusList.map(_.memUsed()).fold(0L)(_ + _)

core/src/main/scala/org/apache/spark/ui/jobs/JobProgressPage.scala

@@ -33,7 +33,7 @@ private[ui] class IndexPage(parent: JobProgressTab) extends WebUIPage("") {
   private val listener = parent.listener
   private lazy val isFairScheduler = parent.isFairScheduler
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     listener.synchronized {
       val activeStages = listener.activeStages.values.toSeq
       val completedStages = listener.completedStages.reverse.toSeq

core/src/main/scala/org/apache/spark/ui/jobs/PoolPage.scala

@@ -32,7 +32,7 @@ private[ui] class PoolPage(parent: JobProgressTab) extends WebUIPage("pool") {
   private val sc = parent.sc
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     listener.synchronized {
       val poolName = request.getParameter("poolname")
       val poolToActiveStages = listener.poolToActiveStages

core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala

@@ -31,7 +31,7 @@ private[ui] class StagePage(parent: JobProgressTab) extends WebUIPage("stage") {
   private val basePath = parent.basePath
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     listener.synchronized {
       val stageId = request.getParameter("id").toInt
 

core/src/main/scala/org/apache/spark/ui/storage/RDDPage.scala

@@ -31,7 +31,7 @@ private[ui] class RddPage(parent: StorageTab) extends WebUIPage("rdd") {
   private val basePath = parent.basePath
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val rddId = request.getParameter("id").toInt
     val storageStatusList = listener.storageStatusList
     val rddInfo = listener.rddInfoList.find(_.id == rddId).getOrElse {

core/src/main/scala/org/apache/spark/ui/storage/StoragePage.scala

@@ -31,7 +31,7 @@ private[ui] class IndexPage(parent: StorageTab) extends WebUIPage("") {
   private val basePath = parent.basePath
   private val listener = parent.listener
 
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val rdds = listener.rddInfoList
     val content = UIUtils.listingTable(rddHeader, rddRow, rdds)
     UIUtils.headerSparkPage(content, basePath, appName, "Storage ", parent.headerTabs, parent)

core/src/test/scala/org/apache/spark/ui/UISuite.scala

@@ -65,7 +65,7 @@ class UISuite extends FunSuite {
 
       val newTab = new WebUITab(sparkUI, "foo") {
         attachPage(new WebUIPage("") {
-          override def render(request: HttpServletRequest): Seq[Node] = {
+          def render(request: HttpServletRequest): Seq[Node] = {
             <b>"html magic"</b>
           }
         })

streaming/src/main/scala/org/apache/spark/streaming/ui/StreamingPage.scala

@@ -36,7 +36,7 @@ private[ui] class StreamingPage(parent: StreamingTab)
   private val emptyCellTest = "-"
 
   /** Render the page */
-  override def render(request: HttpServletRequest): Seq[Node] = {
+  def render(request: HttpServletRequest): Seq[Node] = {
     val content =
       generateBasicStats() ++
       <br></br><h4>Statistics over last {listener.completedBatches.size} processed batches</h4> ++