svn merge -c 1483974 FIXES: MAPREDUCE-4927. Historyserver 500 error due to NPE when accessing specific counters page for failed job. Contributed by Ashwin Shankar

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1483978 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -34,6 +34,9 @@ Release 0.23.8 - UNRELEASED
     MAPREDUCE-5168. Reducer can OOM during shuffle because on-disk output
     stream not released (jlowe)
 
+    MAPREDUCE-4927. Historyserver 500 error due to NPE when accessing specific
+    counters page for failed job. (Ashwin Shankar via jlowe)
+
 Release 0.23.7 - 2013-04-18
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/webapp/SingleCounterBlock.java

@@ -143,8 +143,9 @@ public class SingleCounterBlock extends HtmlBlock {
     Map<TaskId, Task> tasks = job.getTasks();
     for(Map.Entry<TaskId, Task> entry : tasks.entrySet()) {
       long value = 0;
-      CounterGroup group = entry.getValue().getCounters()
-        .getGroup($(COUNTER_GROUP));
+      Counters counters = entry.getValue().getCounters();
+      CounterGroup group = (counters != null) ? counters
+        .getGroup($(COUNTER_GROUP)) : null;
       if(group != null)  {
         Counter c = group.findCounter($(COUNTER_NAME));
         if(c != null) {

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/webapp/TestAMWebApp.java

@@ -182,6 +182,11 @@ public class TestAMWebApp {
   
   @Test public void testSingleCounterView() {
     AppContext appContext = new TestAppContext();
+    Job job = appContext.getAllJobs().values().iterator().next();
+    // add a failed task to the job without any counters
+    Task failedTask = MockJobs.newTask(job.getID(), 2, 1, true);
+    Map<TaskId,Task> tasks = job.getTasks();
+    tasks.put(failedTask.getID(), failedTask);
     Map<String, String> params = getJobParams(appContext);
     params.put(AMParams.COUNTER_GROUP, 
         "org.apache.hadoop.mapreduce.FileSystemCounter");