[HOTFIX] History Server API docs error fix.

Minor error in the monitoring docs. Also made indentation changes in `ApiRootResource`

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #6628 from harishreedharan/eventlog-formatting and squashes the following commits:

a12553d [Hari Shreedharan] Javadoc updates.
ca399b6 [Hari Shreedharan] [HOTFIX] History Server API docs error fix.

core/src/main/scala/org/apache/spark/status/api/v1/ApiRootResource.scala

@@ -167,14 +167,14 @@ private[v1] class ApiRootResource extends UIRootFromServletContext {
 
   @Path("applications/{appId}/logs")
   def getEventLogs(
-    @PathParam("appId") appId: String): EventLogDownloadResource = {
+      @PathParam("appId") appId: String): EventLogDownloadResource = {
     new EventLogDownloadResource(uiRoot, appId, None)
   }
 
   @Path("applications/{appId}/{attemptId}/logs")
   def getEventLogs(
-    @PathParam("appId") appId: String,
-    @PathParam("attemptId") attemptId: String): EventLogDownloadResource = {
+      @PathParam("appId") appId: String,
+      @PathParam("attemptId") attemptId: String): EventLogDownloadResource = {
     new EventLogDownloadResource(uiRoot, appId, Some(attemptId))
   }
 }
@@ -206,6 +206,10 @@ private[spark] trait UIRoot {
   def getSparkUI(appKey: String): Option[SparkUI]
   def getApplicationInfoList: Iterator[ApplicationInfo]
 
+  /**
+   * Write the event logs for the given app to the [[ZipOutputStream]] instance. If attemptId is
+   * [[None]], event logs for all attempts of this application will be written out.
+   */
   def writeEventLogs(appId: String, attemptId: Option[String], zipStream: ZipOutputStream): Unit = {
     Response.serverError()
       .entity("Event logs are only available through the history server.")

core/src/main/scala/org/apache/spark/status/api/v1/EventLogDownloadResource.scala

@@ -44,7 +44,7 @@ private[v1] class EventLogDownloadResource(
       }
 
       val stream = new StreamingOutput {
-        override def write(output: OutputStream) = {
+        override def write(output: OutputStream): Unit = {
           val zipStream = new ZipOutputStream(output)
           try {
             uIRoot.writeEventLogs(appId, attemptId, zipStream)

docs/monitoring.md

@@ -233,7 +233,7 @@ for a running application, at `http://localhost:4040/api/v1`.
     <td>Download the event logs for all attempts of the given application as a zip file</td>
   </tr>
   <tr>
-    <td><code>/applications/[app-id]/[attempt-id/logs</code></td>
+    <td><code>/applications/[app-id]/[attempt-id]/logs</code></td>
     <td>Download the event logs for the specified attempt of the given application as a zip file</td>
   </tr>
 </table>