HADOOP-17138. Fix spotbugs warnings surfaced after upgrade to 4.0.6.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java

@@ -3716,7 +3716,7 @@ void incrUserConnections(String user) {
         if (count == null) {
           count = 1;
         } else {
-          count++;
+          count = count + 1;
         }
         userToConnectionsMap.put(user, count);
       }
@@ -3728,7 +3728,7 @@ void decrUserConnections(String user) {
         if (count == null) {
           return;
         } else {
-          count--;
+          count = count - 1;
         }
         if (count == 0) {
           userToConnectionsMap.remove(user);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/DatasetVolumeChecker.java

@@ -352,23 +352,29 @@ private class ResultHandler
     }
 
     @Override
-    public void onSuccess(@Nonnull VolumeCheckResult result) {
-      switch(result) {
-      case HEALTHY:
-      case DEGRADED:
-        LOG.debug("Volume {} is {}.", reference.getVolume(), result);
-        markHealthy();
-        break;
-      case FAILED:
-        LOG.warn("Volume {} detected as being unhealthy",
+    public void onSuccess(VolumeCheckResult result) {
+      if (result == null) {
+        LOG.error("Unexpected health check result null for volume {}",
             reference.getVolume());
-        markFailed();
-        break;
-      default:
-        LOG.error("Unexpected health check result {} for volume {}",
-            result, reference.getVolume());
         markHealthy();
-        break;
+      } else {
+        switch(result) {
+        case HEALTHY:
+        case DEGRADED:
+          LOG.debug("Volume {} is {}.", reference.getVolume(), result);
+          markHealthy();
+          break;
+        case FAILED:
+          LOG.warn("Volume {} detected as being unhealthy",
+              reference.getVolume());
+          markFailed();
+          break;
+        default:
+          LOG.error("Unexpected health check result {} for volume {}",
+              result, reference.getVolume());
+          markHealthy();
+          break;
+        }
       }
       cleanup();
     }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/ThrottledAsyncChecker.java

@@ -166,7 +166,7 @@ private void addResultCachingCallback(
       Checkable<K, V> target, ListenableFuture<V> lf) {
     Futures.addCallback(lf, new FutureCallback<V>() {
       @Override
-      public void onSuccess(@Nullable V result) {
+      public void onSuccess(V result) {
         synchronized (ThrottledAsyncChecker.this) {
           checksInProgress.remove(target);
           completedChecks.put(target, new LastCheckResult<>(

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLogLoader.java

@@ -1237,7 +1237,7 @@ private void incrOpCount(FSEditLogOpCodes opCode,
       holder = new Holder<Integer>(1);
       opCounts.put(opCode, holder);
     } else {
-      holder.held++;
+      holder.held = holder.held + 1;
     }
     counter.increment();
   }

hadoop-mapreduce-project/dev-support/findbugs-exclude.xml

@@ -533,5 +533,17 @@
     <Class name="org.apache.hadoop.mapreduce.v2.hs.CachedHistoryStorage$1" />
     <Bug pattern="SE_BAD_FIELD_INNER_CLASS" />
   </Match>
-
+
+  <!--
+    HADOOP-17138: Suppress warnings about unchecked Nullable
+    since the methoad catches NullPointerException then registerError.
+  -->
+  <Match>
+    <Or>
+      <Class name="org.apache.hadoop.mapred.LocatedFileStatusFetcher$ProcessInputDirCallback" />
+      <Class name="org.apache.hadoop.mapred.LocatedFileStatusFetcher$ProcessInitialInputPathCallback" />
+    </Or>
+    <Method name="onSuccess" />
+    <Bug pattern="NP_PARAMETER_MUST_BE_NONNULL_BUT_MARKED_AS_NULLABLE" />
+  </Match>
  </FindBugsFilter>

hadoop-tools/hadoop-sls/src/main/java/org/apache/hadoop/yarn/sls/SLSRunner.java

@@ -764,7 +764,7 @@ private void increaseQueueAppNum(String queue) throws YarnException {
     if (appNum == null) {
       appNum = 1;
     } else {
-      appNum++;
+      appNum = appNum + 1;
     }
 
     queueAppNumMap.put(queueName, appNum);

hadoop-yarn-project/hadoop-yarn/dev-support/findbugs-exclude.xml

@@ -711,4 +711,9 @@
     <Bug pattern="NP_NONNULL_PARAM_VIOLATION"/>
   </Match>
 
+  <!-- Suppress warning about anonymous class for mocking. -->
+  <Match>
+    <Class name="~org\.apache\.hadoop\.yarn\.server\.timelineservice\.reader\.TestTimelineReaderWebServicesHBaseStorage.*" />
+    <Bug pattern="UMAC_UNCALLABLE_METHOD_OF_ANONYMOUS_CLASS" />
+  </Match>
 </FindBugsFilter>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-timelineservice-hbase-tests/src/test/java/org/apache/hadoop/yarn/server/timelineservice/storage/TestTimelineReaderHBaseDown.java

@@ -181,14 +181,13 @@ private static void waitForHBaseDown(HBaseTimelineReaderImpl htr) throws
     }
   }
 
-  private static void checkQuery(HBaseTimelineReaderImpl htr) throws
-      IOException {
+  private static Set<TimelineEntity> checkQuery(HBaseTimelineReaderImpl htr)
+      throws IOException {
     TimelineReaderContext context =
         new TimelineReaderContext(YarnConfiguration.DEFAULT_RM_CLUSTER_ID,
             null, null, null, null, TimelineEntityType
             .YARN_FLOW_ACTIVITY.toString(), null, null);
-    Set<TimelineEntity> entities = htr.getEntities(context, MONITOR_FILTERS,
-        DATA_TO_RETRIEVE);
+    return htr.getEntities(context, MONITOR_FILTERS, DATA_TO_RETRIEVE);
   }
 
   private static void configure(HBaseTestingUtility util) {