ARROW-3923: Supporting a null Calendar in the config, and reverting t…

…he breaking change.

java/adapter/jdbc/src/main/java/org/apache/arrow/adapter/jdbc/JdbcToArrow.java

@@ -154,7 +154,7 @@ public static VectorSchemaRoot sqlToArrow(Connection connection, String query, J
  public static VectorSchemaRoot sqlToArrow(ResultSet resultSet) throws SQLException, IOException {
  Preconditions.checkNotNull(resultSet, "JDBC ResultSet object can not be null");
 
- return sqlToArrow(resultSet, (Calendar) null);
+ return sqlToArrow(resultSet, Calendar.getInstance(TimeZone.getTimeZone("UTC"), Locale.ROOT));
  }
 
  /**

java/adapter/jdbc/src/main/java/org/apache/arrow/adapter/jdbc/JdbcToArrowConfig.java

@@ -48,15 +48,15 @@ public final class JdbcToArrowConfig {
  */
  JdbcToArrowConfig(BaseAllocator allocator, Calendar calendar) {
  Preconditions.checkNotNull(allocator, "Memory allocator cannot be null");
- Preconditions.checkNotNull(calendar, "Calendar object can not be null");
 
  this.allocator = allocator;
  this.calendar = calendar;
  }
 
  /**
  * The calendar to use when defining Arrow Timestamp fields
- * and retrieving time-based fields from the database.
+ * and retrieving {@link Date}, {@link Time}, or {@link Timestamp}
+ * data types from the {@link ResultSet}, or <code>null</code> if not converting.
  * @return the calendar.
  */
  public Calendar getCalendar() {

java/adapter/jdbc/src/main/java/org/apache/arrow/adapter/jdbc/JdbcToArrowConfigBuilder.java

@@ -32,7 +32,7 @@ public class JdbcToArrowConfigBuilder {
 
  /**
  * Default constructor for the <code>JdbcToArrowConfigBuilder}</code>.
- * Use the setter methods for the allocator and calendar; both must be
+ * Use the setter methods for the allocator and calendar; the allocator must be
  * set. Otherwise, {@link #build()} will throw a {@link NullPointerException}.
  */
  public JdbcToArrowConfigBuilder() {
@@ -41,9 +41,9 @@ public JdbcToArrowConfigBuilder() {
  }
 
  /**
- * Constructor for the <code>JdbcToArrowConfigBuilder</code>. Both the
- * allocator and calendar are required. A {@link NullPointerException}
- * will be thrown if one of the arguments is <code>null</code>.
+ * Constructor for the <code>JdbcToArrowConfigBuilder</code>. The
+ * allocator is required, and a {@link NullPointerException}
+ * will be thrown if it is <code>null</code>.
  * <p>
  * The allocator is used to construct Arrow vectors from the JDBC ResultSet.
  * The calendar is used to determine the time zone of {@link java.sql.Timestamp}
@@ -59,7 +59,6 @@ public JdbcToArrowConfigBuilder(BaseAllocator allocator, Calendar calendar) {
  this();
 
  Preconditions.checkNotNull(allocator, "Memory allocator cannot be null");
- Preconditions.checkNotNull(calendar, "Calendar object can not be null");
 
  this.allocator = allocator;
  this.calendar = calendar;
@@ -82,10 +81,8 @@ public JdbcToArrowConfigBuilder setAllocator(BaseAllocator allocator) {
  * Arrow schema, and reading time-based fields from the JDBC <code>ResultSet</code>.
  *
  * @param calendar the calendar to set.
- * @exception NullPointerExeption if <code>calendar</code> is <code>null</code>.
  */
  public JdbcToArrowConfigBuilder setCalendar(Calendar calendar) {
- Preconditions.checkNotNull(calendar, "Calendar object can not be null");
  this.calendar = calendar;
  return this;
  }

java/adapter/jdbc/src/test/java/org/apache/arrow/adapter/jdbc/JdbcToArrowConfigTest.java

@@ -42,14 +42,16 @@ public void testBuilderNullArguments() {
  new JdbcToArrowConfigBuilder(null, null);
  }
 
- @Test(expected = NullPointerException.class)
  public void testConfigNullCalendar() {
- new JdbcToArrowConfig(allocator, null);
+ JdbcToArrowConfig config = new JdbcToArrowConfig(allocator, null);
+ assertNull(config.getCalendar());
  }
 
- @Test(expected = NullPointerException.class)
+ @Test
  public void testBuilderNullCalendar() {
- new JdbcToArrowConfigBuilder(allocator, null);
+ JdbcToArrowConfigBuilder builder = new JdbcToArrowConfigBuilder(allocator, null);
+ JdbcToArrowConfig config = builder.build();
+ assertNull(config.getCalendar());
  }
 
  @Test(expected = NullPointerException.class)
@@ -68,10 +70,11 @@ public void testSetNullAllocator() {
  builder.setAllocator(null);
  }
 
- @Test(expected = NullPointerException.class)
+ @Test
  public void testSetNullCalendar() {
  JdbcToArrowConfigBuilder builder = new JdbcToArrowConfigBuilder(allocator, calendar);
- builder.setCalendar(null);
+ JdbcToArrowConfig config = builder.setCalendar(null).build();
+ assertNull(config.getCalendar());
  }
 
  @Test