[SPARK-7378] [core] Handle deep links to unloaded apps.

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

@@ -82,31 +82,27 @@ class HistoryServer(
         return
       }
 
-      val appKey =
-        if (parts.length == 3) {
-          s"${parts(1)}/${parts(2)}"
-        } else {
-          parts(1)
+      val appId = parts(1)
+      val attemptId = if (parts.length >= 3) Some(parts(2)) else None
+
+      // Since we may have applications with multiple attempts mixed with applications with a
+      // single attempt, we need to try both. Try the single-attempt route first, and if an
+      // error is raised, then try the multiple attempt route.
+      if (!loadAppUi(appId, None) && (!attemptId.isDefined || !loadAppUi(appId, attemptId))) {
+        val msg = <div class="row-fluid">Application {appId} not found.</div>
+        res.setStatus(HttpServletResponse.SC_NOT_FOUND)
+        UIUtils.basicSparkPage(msg, "Not Found").foreach { n =>
+          res.getWriter().write(n.toString)
         }
+        return
+      }
 
       // Note we don't use the UI retrieved from the cache; the cache loader above will register
       // the app's UI, and all we need to do is redirect the user to the same URI that was
       // requested, and the proper data should be served at that point.
-      try {
-        appCache.get(appKey)
-        res.sendRedirect(res.encodeRedirectURL(req.getRequestURI()))
-      } catch {
-        case e: Exception => e.getCause() match {
-          case nsee: NoSuchElementException =>
-            val msg = <div class="row-fluid">Application {appKey} not found.</div>
-            res.setStatus(HttpServletResponse.SC_NOT_FOUND)
-            UIUtils.basicSparkPage(msg, "Not Found").foreach(
-              n => res.getWriter().write(n.toString))
-
-          case cause: Exception => throw cause
-        }
-      }
+      res.sendRedirect(res.encodeRedirectURL(req.getRequestURI()))
     }
+
     // SPARK-5983 ensure TRACE is not supported
     protected override def doTrace(req: HttpServletRequest, res: HttpServletResponse): Unit = {
       res.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED)
@@ -169,6 +165,20 @@ class HistoryServer(
    */
   def getProviderConfig(): Map[String, String] = provider.getConfig()
 
+  private def loadAppUi(appId: String, attemptId: Option[String]): Boolean = {
+    try {
+      appCache.get(appId + attemptId.map { id => s"/$id" }.getOrElse(""))
+      true
+    } catch {
+      case e: Exception => e.getCause() match {
+        case nsee: NoSuchElementException =>
+          false
+
+        case cause: Exception => throw cause
+      }
+    }
+  }
+
 }
 
 /**