[SPARK-24490][WEBUI] Use WebUI.addStaticHandler in web UIs

`WebUI` defines `addStaticHandler` that web UIs don't use (and simply introduce duplication). Let's clean them up and remove duplications.

Local build and waiting for Jenkins

Author: Jacek Laskowski <jacek@japila.pl>

Closes #21510 from jaceklaskowski/SPARK-24490-Use-WebUI.addStaticHandler.

Author: jaceklaskowski

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

@@ -124,7 +124,7 @@ class HistoryServer(
 
     attachHandler(ApiRootResource.getServletHandler(this))
 
-    attachHandler(createStaticHandler(SparkUI.STATIC_RESOURCE_DIR, "/static"))
+    addStaticHandler(SparkUI.STATIC_RESOURCE_DIR)
 
     val contextHandler = new ServletContextHandler
     contextHandler.setContextPath(HistoryServer.UI_PATH_PREFIX)

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

@@ -43,7 +43,7 @@ class MasterWebUI(
     val masterPage = new MasterPage(this)
     attachPage(new ApplicationPage(this))
     attachPage(masterPage)
-    attachHandler(createStaticHandler(MasterWebUI.STATIC_RESOURCE_DIR, "/static"))
+    addStaticHandler(MasterWebUI.STATIC_RESOURCE_DIR)
     attachHandler(createRedirectHandler(
       "/app/kill", "/", masterPage.handleAppKillRequest, httpMethods = Set("POST")))
     attachHandler(createRedirectHandler(

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

@@ -47,7 +47,7 @@ class WorkerWebUI(
     val logPage = new LogPage(this)
     attachPage(logPage)
     attachPage(new WorkerPage(this))
-    attachHandler(createStaticHandler(WorkerWebUI.STATIC_RESOURCE_BASE, "/static"))
+    addStaticHandler(WorkerWebUI.STATIC_RESOURCE_BASE)
     attachHandler(createServletHandler("/log",
       (request: HttpServletRequest) => logPage.renderLog(request),
       worker.securityMgr,

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

@@ -65,7 +65,7 @@ private[spark] class SparkUI private (
     attachTab(new StorageTab(this, store))
     attachTab(new EnvironmentTab(this, store))
     attachTab(new ExecutorsTab(this))
-    attachHandler(createStaticHandler(SparkUI.STATIC_RESOURCE_DIR, "/static"))
+    addStaticHandler(SparkUI.STATIC_RESOURCE_DIR)
     attachHandler(createRedirectHandler("/", "/jobs/", basePath = basePath))
     attachHandler(ApiRootResource.getServletHandler(this))
 

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

@@ -60,23 +60,25 @@ private[spark] abstract class WebUI(
   def getHandlers: Seq[ServletContextHandler] = handlers
   def getSecurityManager: SecurityManager = securityManager
 
-  /** Attach a tab to this UI, along with all of its attached pages. */
-  def attachTab(tab: WebUITab) {
+  /** Attaches a tab to this UI, along with all of its attached pages. */
+  def attachTab(tab: WebUITab): Unit = {
     tab.pages.foreach(attachPage)
     tabs += tab
   }
 
-  def detachTab(tab: WebUITab) {
+  /** Detaches a tab from this UI, along with all of its attached pages. */
+  def detachTab(tab: WebUITab): Unit = {
     tab.pages.foreach(detachPage)
     tabs -= tab
   }
 
-  def detachPage(page: WebUIPage) {
+  /** Detaches a page from this UI, along with all of its attached handlers. */
+  def detachPage(page: WebUIPage): Unit = {
     pageToHandlers.remove(page).foreach(_.foreach(detachHandler))
   }
 
-  /** Attach a page to this UI. */
-  def attachPage(page: WebUIPage) {
+  /** Attaches a page to this UI. */
+  def attachPage(page: WebUIPage): Unit = {
     val pagePath = "/" + page.prefix
     val renderHandler = createServletHandler(pagePath,
       (request: HttpServletRequest) => page.render(request), securityManager, conf, basePath)
@@ -88,41 +90,41 @@ private[spark] abstract class WebUI(
     handlers += renderHandler
   }
 
-  /** Attach a handler to this UI. */
-  def attachHandler(handler: ServletContextHandler) {
+  /** Attaches a handler to this UI. */
+  def attachHandler(handler: ServletContextHandler): Unit = {
     handlers += handler
     serverInfo.foreach(_.addHandler(handler))
   }
 
-  /** Detach a handler from this UI. */
-  def detachHandler(handler: ServletContextHandler) {
+  /** Detaches a handler from this UI. */
+  def detachHandler(handler: ServletContextHandler): Unit = {
     handlers -= handler
     serverInfo.foreach(_.removeHandler(handler))
   }
 
   /**
-   * Add a handler for static content.
+   * Detaches the content handler at `path` URI.
    *
-   * @param resourceBase Root of where to find resources to serve.
-   * @param path Path in UI where to mount the resources.
+   * @param path Path in UI to unmount.
    */
-  def addStaticHandler(resourceBase: String, path: String): Unit = {
-    attachHandler(JettyUtils.createStaticHandler(resourceBase, path))
+  def detachHandler(path: String): Unit = {
+    handlers.find(_.getContextPath() == path).foreach(detachHandler)
   }
 
   /**
-   * Remove a static content handler.
+   * Adds a handler for static content.
    *
-   * @param path Path in UI to unmount.
+   * @param resourceBase Root of where to find resources to serve.
+   * @param path Path in UI where to mount the resources.
    */
-  def removeStaticHandler(path: String): Unit = {
-    handlers.find(_.getContextPath() == path).foreach(detachHandler)
+  def addStaticHandler(resourceBase: String, path: String = "/static"): Unit = {
+    attachHandler(JettyUtils.createStaticHandler(resourceBase, path))
   }
 
-  /** Initialize all components of the server. */
+  /** A hook to initialize components of the UI */
   def initialize(): Unit
 
-  /** Bind to the HTTP server behind this web interface. */
+  /** Binds to the HTTP server behind this web interface. */
   def bind(): Unit = {
     assert(serverInfo.isEmpty, s"Attempted to bind $className more than once!")
     try {
@@ -136,17 +138,17 @@ private[spark] abstract class WebUI(
     }
   }
 
-  /** Return the url of web interface. Only valid after bind(). */
+  /** @return The url of web interface. Only valid after [[bind]]. */
   def webUrl: String = s"http://$publicHostName:$boundPort"
 
-  /** Return the actual port to which this server is bound. Only valid after bind(). */
+  /** @return The actual port to which this server is bound. Only valid after [[bind]]. */
   def boundPort: Int = serverInfo.map(_.boundPort).getOrElse(-1)
 
-  /** Stop the server behind this web interface. Only valid after bind(). */
+  /** Stops the server behind this web interface. Only valid after [[bind]]. */
   def stop(): Unit = {
     assert(serverInfo.isDefined,
       s"Attempted to stop $className before binding to a server!")
-    serverInfo.get.stop()
+    serverInfo.foreach(_.stop())
   }
 }
 

resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/ui/MesosClusterUI.scala

@@ -40,7 +40,7 @@ private[spark] class MesosClusterUI(
   override def initialize() {
     attachPage(new MesosClusterPage(this))
     attachPage(new DriverPage(this))
-    attachHandler(createStaticHandler(MesosClusterUI.STATIC_RESOURCE_DIR, "/static"))
+    addStaticHandler(MesosClusterUI.STATIC_RESOURCE_DIR)
   }
 }
 

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

@@ -49,7 +49,7 @@ private[spark] class StreamingTab(val ssc: StreamingContext)
 
   def detach() {
     getSparkUI(ssc).detachTab(this)
-    getSparkUI(ssc).removeStaticHandler("/static/streaming")
+    getSparkUI(ssc).detachHandler("/static/streaming")
   }
 }