[SPARK-24529][Build][test-maven] Add spotbugs into maven build process

core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala

@@ -369,7 +369,7 @@ private[spark] class ExternalSorter[K, V, C](
     type Iter = BufferedIterator[Product2[K, C]]
     val heap = new mutable.PriorityQueue[Iter]()(new Ordering[Iter] {
       // Use the reverse of comparator.compare because PriorityQueue dequeues the max
-      override def compare(x: Iter, y: Iter): Int = -comparator.compare(x.head._1, y.head._1)
+      override def compare(x: Iter, y: Iter): Int = comparator.compare(y.head._1, x.head._1)
     })
     heap.enqueue(bufferedIters: _*)  // Will contain only the iterators with hasNext = true
     new Iterator[Product2[K, C]] {

mllib/src/main/scala/org/apache/spark/ml/image/HadoopUtils.scala

@@ -42,9 +42,11 @@ private object RecursiveFlag {
     val old = Option(hadoopConf.get(flagName))
     hadoopConf.set(flagName, value.toString)
     try f finally {
-      old match {
-        case Some(v) => hadoopConf.set(flagName, v)
-        case None => hadoopConf.unset(flagName)
+      // avoid false positive of DLS_DEAD_LOCAL_STORE_IN_RETURN by SpotBugs
+      if (old.isDefined) {
+        hadoopConf.set(flagName, old.get)
+      } else {
+        hadoopConf.unset(flagName)
       }
     }
   }

pom.xml

@@ -2606,6 +2606,35 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>com.github.spotbugs</groupId>
+        <artifactId>spotbugs-maven-plugin</artifactId>
+        <version>3.1.3</version>
+        <configuration>
+          <classFilesDirectory>${basedir}/target/scala-2.11/classes</classFilesDirectory>
+          <testClassFilesDirectory>${basedir}/target/scala-2.11/test-classes</testClassFilesDirectory>
+          <effort>Max</effort>
+          <threshold>Low</threshold>
+          <xmlOutput>true</xmlOutput>
+          <visitors>FindPuzzlers</visitors>
+          <fork>false</fork>
+        </configuration>
+        <dependencies>
+          <dependency>
+            <groupId>com.github.spotbugs</groupId>
+            <artifactId>spotbugs</artifactId>
+            <version>3.1.3</version>
+          </dependency>
+        </dependencies>
+        <executions>
+          <execution>
+            <goals>
+              <goal>check</goal>
+            </goals>
+            <phase>compile</phase>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala

@@ -523,7 +523,7 @@ trait ArraySortLike extends ExpectsInputTypes {
         } else if (o2 == null) {
           nullOrder
         } else {
-          -ordering.compare(o1, o2)
+          ordering.compare(o2, o1)
         }
       }
     }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala

@@ -294,7 +294,8 @@ object CaseWhen {
       case cond :: value :: Nil => Some((cond, value))
       case value :: Nil => None
     }.toArray.toSeq  // force materialization to make the seq serializable
-    val elseValue = if (branches.size % 2 == 1) Some(branches.last) else None
+    // avoid false positive of IM_BAD_CHECK_FOR_ODD by SpotBugs
+    val elseValue = if (branches.size % 2 != 0) Some(branches.last) else None
     CaseWhen(cases, elseValue)
   }
 }
@@ -309,7 +310,8 @@ object CaseKeyWhen {
       case Seq(cond, value) => Some((EqualTo(key, cond), value))
       case Seq(value) => None
     }.toArray.toSeq  // force materialization to make the seq serializable
-    val elseValue = if (branches.size % 2 == 1) Some(branches.last) else None
+    // avoid false positive of IM_BAD_CHECK_FOR_ODD by SpotBugs
+    val elseValue = if (branches.size % 2 != 0) Some(branches.last) else None
     CaseWhen(cases, elseValue)
   }
 }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -1507,7 +1507,8 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
         case "TIMESTAMP" =>
           Literal(Timestamp.valueOf(value))
         case "X" =>
-          val padding = if (value.length % 2 == 1) "0" else ""
+          // avoid false positive of IM_BAD_CHECK_FOR_ODD by SpotBugs
+          val padding = if (value.length % 2 != 0) "0" else ""
           Literal(DatatypeConverter.parseHexBinary(padding + value))
         case other =>
           throw new ParseException(s"Literals of type '$other' are currently not supported.", ctx)