fix to jdbc read to handle null values in array data type column

Author: sureshthalamati

external/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/PostgresIntegrationSuite.scala

@@ -51,12 +51,16 @@ class PostgresIntegrationSuite extends DockerJDBCIntegrationSuite {
       + "B'1000100101', E'\\\\xDEADBEEF', true, '172.16.0.42', '192.168.0.0/16', "
       + """'{1, 2}', '{"a", null, "b"}', '{0.11, 0.22}', '{0.11, 0.22}', 'd1', 1.01, 1)"""
     ).executeUpdate()
+    conn.prepareStatement("INSERT INTO bar VALUES (null, null, null, null, null, "
+      + "null, null, null, null, null, "
+      + "null, null, null, null, null, null, null)"
+    ).executeUpdate()
   }
 
   test("Type mapping for various types") {
     val df = sqlContext.read.jdbc(jdbcUrl, "bar", new Properties)
-    val rows = df.collect()
-    assert(rows.length == 1)
+    val rows = df.collect().sortBy(_.toString())
+    assert(rows.length == 2)
     val types = rows(0).toSeq.map(x => x.getClass)
     assert(types.length == 17)
     assert(classOf[String].isAssignableFrom(types(0)))
@@ -96,6 +100,9 @@ class PostgresIntegrationSuite extends DockerJDBCIntegrationSuite {
     assert(rows(0).getString(14) == "d1")
     assert(rows(0).getFloat(15) == 1.01f)
     assert(rows(0).getShort(16) == 1)
+
+    // Test reading null values.
+    assert(0.until(16).forall(rows(1).isNullAt(_)))
   }
 
   test("Basic write test") {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala

@@ -465,9 +465,9 @@ object JdbcUtils extends Logging {
       }
 
       (rs: ResultSet, row: InternalRow, pos: Int) =>
-        val array = nullSafeConvert[Object](
-          rs.getArray(pos + 1).getArray,
-          array => new GenericArrayData(elementConversion.apply(array)))
+        val array = nullSafeConvert[java.sql.Array](
+          rs.getArray(pos + 1),
+          array => new GenericArrayData(elementConversion.apply(array.getArray)))
         row.update(pos, array)
 
     case _ => throw new IllegalArgumentException(s"Unsupported type ${dt.simpleString}")