Simplified code

Author: sarutak

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

@@ -26,7 +26,7 @@ import org.apache.spark.ui.{WebUIPage, UIUtils}
 private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
 
   private val pageSize = 20
-  private val maxNumIndices = 2
+  private val plusOrMinus = 2
 
   def render(request: HttpServletRequest): Seq[Node] = {
     val requestedPage = Option(request.getParameter("page")).getOrElse("1").toInt
@@ -40,6 +40,9 @@ private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
     val last = Math.min(actualFirst + pageSize, allApps.size) - 1
     val pageCount = allApps.size / pageSize + (if (allApps.size % pageSize > 0) 1 else 0)
 
+    val secondPageFromLeft = 2
+    val secondPageFromRight = pageCount - 1
+
     val appTable = UIUtils.listingTable(appHeader, appRow, apps)
     val providerConfig = parent.getProviderConfig()
     val content =
@@ -49,10 +52,40 @@ private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
             {providerConfig.map { case (k, v) => <li><strong>{k}:</strong> {v}</li> }}
           </ul>
           {
+            // This displays the indices of pages that are within
+            // `plusOrMinus` pages of the current page.
+            // Regardless of where the current page is,
+            // this also links to the first and last page.
+            // If the current page +/- `plusOrMinux` is greater than the 2nd page
+            // from the first page or littler than the 2nd page from the last page,
+            // `...` will be displayed.
             if (allApps.size > 0) {
+              val leftSideIndices =
+                rangeIndices(actualPage - plusOrMinus until actualPage, 1 < _)
+              val rightSideIndices =
+                rangeIndices(actualPage + 1 to actualPage + plusOrMinus, _ < pageCount)
+
               <h4>
                 Showing {actualFirst + 1}-{last + 1} of {allApps.size}
-                  {pageIndices(pageCount, actualPage)}
+                  <span style="float: right">
+                    {
+                      if (actualPage > 1) {
+                        <a href={"/?page=" + (actualPage - 1)}>&lt; </a>
+                        <a href={"/?page=1"}>1</a>
+                      }
+                    }
+                    {if (actualPage - plusOrMinus > secondPageFromLeft) " ... "}
+                    {leftSideIndices}
+                    {actualPage}
+                    {rightSideIndices}
+                    {if (actualPage + plusOrMinus < secondPageFromRight) " ... "}
+                    {
+                      if (actualPage < pageCount) {
+                        <a href={"/?page=" + pageCount}>{pageCount}</a>
+                        <a href={"/?page=" + (actualPage + 1)}> &gt;</a>
+                      }
+                    }
+                  </span>
               </h4> ++
               appTable
             } else {
@@ -79,36 +112,8 @@ private[spark] class HistoryPage(parent: HistoryServer) extends WebUIPage("") {
     "Spark User",
     "Last Updated")
 
-  private def pageIndices(pageCount: Int, actualPage: Int): Seq[Node] = {
-
-    def rangeIndices(range: Seq[Int], condition: Int => Boolean): Seq[Node] = {
-      range.filter(condition).map(nextPage => <a href={"/?page=" + nextPage}> {nextPage} </a>)
-    }
-
-    val littlerSideIndices =
-      rangeIndices(actualPage - maxNumIndices until actualPage, 1 < _)
-    val greaterSideIndices =
-      rangeIndices(actualPage + 1 to actualPage + maxNumIndices, _ < pageCount)
-
-    <span style="float: right">
-      {
-        if (actualPage > 1) {
-          <a href={"/?page=" + (actualPage - 1)}>&lt; </a>
-          <a href={"/?page=1"}>1</a>
-        }
-      }
-      {if (actualPage - maxNumIndices > 2) " ... "}
-      {littlerSideIndices}
-      {actualPage}
-      {greaterSideIndices}
-      {if (actualPage + maxNumIndices < pageCount - 1) " ... "}
-      {
-        if (actualPage < pageCount) {
-          <a href={"/?page=" + pageCount}>{pageCount}</a>
-          <a href={"/?page=" + (actualPage + 1)}> &gt;</a>
-        }
-      }
-    </span>
+  private def rangeIndices(range: Seq[Int], condition: Int => Boolean): Seq[Node] = {
+    range.filter(condition).map(nextPage => <a href={"/?page=" + nextPage}> {nextPage} </a>)
   }
 
   private def appRow(info: ApplicationHistoryInfo): Seq[Node] = {