SPARK-2869 - Fix tiny bug in JdbcRdd for closing jdbc connection

I inquired on  dev mailing list about the motivation for checking the jdbc statement instead of the connection in the close() logic of JdbcRDD. Ted Yu believes there essentially is none-  it is a simple cut and paste issue. So here is the tiny fix to patch it.

Author: Stephen Boesch <javadba>
Author: Stephen Boesch <[email protected]>

Closes #1792 from javadba/closejdbc and squashes the following commits:

363be4f [Stephen Boesch] SPARK-2869 - Fix tiny bug in JdbcRdd for closing jdbc connection (reformat with braces)
6518d36 [Stephen Boesch] SPARK-2689 Fix tiny bug in JdbcRdd for closing jdbc connection
3fb23ed [Stephen Boesch] SPARK-2689 Fix potential leak of connection/PreparedStatement in case of error in JdbcRDD
095b2c9 [Stephen Boesch] Fix tiny bug (likely copy and paste error) in closing jdbc connection

(cherry picked from commit 2643e66)
Signed-off-by: Reynold Xin <[email protected]>

core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala

@@ -96,17 +96,23 @@ class JdbcRDD[T: ClassTag](
 
     override def close() {
       try {
-        if (null != rs && ! rs.isClosed()) rs.close()
+        if (null != rs && ! rs.isClosed()) {
+          rs.close()
+        }
       } catch {
         case e: Exception => logWarning("Exception closing resultset", e)
       }
       try {
-        if (null != stmt && ! stmt.isClosed()) stmt.close()
+        if (null != stmt && ! stmt.isClosed()) {
+          stmt.close()
+        }
       } catch {
         case e: Exception => logWarning("Exception closing statement", e)
       }
       try {
-        if (null != conn && ! stmt.isClosed()) conn.close()
+        if (null != conn && ! conn.isClosed()) {
+          conn.close()
+        }
         logInfo("closed connection")
       } catch {
         case e: Exception => logWarning("Exception closing connection", e)
@@ -120,3 +126,4 @@ object JdbcRDD {
     Array.tabulate[Object](rs.getMetaData.getColumnCount)(i => rs.getObject(i + 1))
   }
 }
+