DATACMNS-491 - Add support for configuring null handling hints in Sort.Order.

Null handling hints can now be configured on Order as being either NATIVE (we let the data store decide how to order nulls), NULLS_FIRST or NULLS_LAST.

This is the foundation for custom null-handling in other data store support modules like SD JPA and SD MongoDB.

Original pull request: #79.

src/main/java/org/springframework/data/domain/Sort.java

@@ -229,6 +229,30 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		}
 	}
 
+	/**
+	 * Enumeration for null handling hints that can be used in {@link Order} expressions.
+	 * 
+	 * @author Thomas Darimont
+	 * @since 1.7
+	 */
+	public static enum NullHandling {
+
+		/**
+		 * Lets the data store decide what to do with nulls.
+		 */
+		NATIVE, //
+
+		/**
+		 * A hint to the used data store to order entries with null values before non null entries.
+		 */
+		NULLS_FIRST, //
+
+		/**
+		 * A hint to the used data store to order entries with null values after non null entries.
+		 */
+		NULLS_LAST; //
+	}
+
 	/**
 	 * PropertyPath implements the pairing of an {@link Direction} and a property. It is used to provide input for
 	 * {@link Sort}
@@ -244,6 +268,7 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		private final Direction direction;
 		private final String property;
 		private final boolean ignoreCase;
+		private final NullHandling nullHandlingHint;
 
 		/**
 		 * Creates a new {@link Order} instance. if order is {@literal null} then order defaults to
@@ -254,7 +279,20 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		 */
 		public Order(Direction direction, String property) {
 
-			this(direction, property, DEFAULT_IGNORE_CASE);
+			this(direction, property, DEFAULT_IGNORE_CASE, null);
+		}
+
+		/**
+		 * Creates a new {@link Order} instance. if order is {@literal null} then order defaults to
+		 * {@link Sort#DEFAULT_DIRECTION}
+		 * 
+		 * @param direction can be {@literal null}, will default to {@link Sort#DEFAULT_DIRECTION}
+		 * @param property must not be {@literal null} or empty.
+		 * @param nullHandlingHint can be {@literal null}, will default to {@link NullHandling#NATIVE}.
+		 */
+		public Order(Direction direction, String property, NullHandling nullHandlingHint) {
+
+			this(direction, property, DEFAULT_IGNORE_CASE, nullHandlingHint);
 		}
 
 		/**
@@ -274,8 +312,10 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		 * @param direction can be {@literal null}, will default to {@link Sort#DEFAULT_DIRECTION}
 		 * @param property must not be {@literal null} or empty.
 		 * @param ignoreCase true if sorting should be case insensitive. false if sorting should be case sensitive.
+		 * @param nullHandlingHint can be {@literal null}, will default to {@link NullHandling#NATIVE}.
+		 * @since 1.7
 		 */
-		private Order(Direction direction, String property, boolean ignoreCase) {
+		private Order(Direction direction, String property, boolean ignoreCase, NullHandling nullHandlingHint) {
 
 			if (!StringUtils.hasText(property)) {
 				throw new IllegalArgumentException("Property must not null or empty!");
@@ -284,6 +324,7 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 			this.direction = direction == null ? DEFAULT_DIRECTION : direction;
 			this.property = property;
 			this.ignoreCase = ignoreCase;
+			this.nullHandlingHint = nullHandlingHint == null ? NullHandling.NATIVE : nullHandlingHint;
 		}
 
 		/**
@@ -342,7 +383,7 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		 * @return
 		 */
 		public Order with(Direction order) {
-			return new Order(order, this.property);
+			return new Order(order, this.property, nullHandlingHint);
 		}
 
 		/**
@@ -361,7 +402,58 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		 * @return
 		 */
 		public Order ignoreCase() {
-			return new Order(direction, property, true);
+			return new Order(direction, property, true, nullHandlingHint);
+		}
+
+		/**
+		 * Returns a {@link Order} with the given {@link NullHandling}.
+		 * 
+		 * @param nullHandling
+		 * @return
+		 * @since 1.7
+		 */
+		public Order withNullHandling(NullHandling nullHandling) {
+			return new Order(direction, this.property, ignoreCase, nullHandling);
+		}
+
+		/**
+		 * Returns a {@link Order} with {@link NullHandling#NULLS_FIRST} as null handling hint.
+		 * 
+		 * @return
+		 * @since 1.7
+		 */
+		public Order nullsFirst() {
+			return withNullHandling(NullHandling.NULLS_FIRST);
+		}
+
+		/**
+		 * Returns a {@link Order} with {@link NullHandling#NULLS_LAST} as null handling hint.
+		 * 
+		 * @return
+		 * @since 1.7
+		 */
+		public Order nullsLast() {
+			return withNullHandling(NullHandling.NULLS_LAST);
+		}
+
+		/**
+		 * Returns a {@link Order} with {@link NullHandling#NATIVE} as null handling hint.
+		 * 
+		 * @return
+		 * @since 1.7
+		 */
+		public Order nullsNative() {
+			return withNullHandling(NullHandling.NATIVE);
+		}
+
+		/**
+		 * Returns the used {@link NullHandling} hint, which can but may not be respected by the used datastore.
+		 * 
+		 * @return
+		 * @since 1.7
+		 */
+		public NullHandling getNullHandlingHint() {
+			return nullHandlingHint;
 		}
 
 		/*
@@ -376,6 +468,7 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 			result = 31 * result + direction.hashCode();
 			result = 31 * result + property.hashCode();
 			result = 31 * result + (ignoreCase ? 1 : 0);
+			result = 31 * result + (nullHandlingHint.hashCode());
 
 			return result;
 		}
@@ -398,7 +491,7 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 			Order that = (Order) obj;
 
 			return this.direction.equals(that.direction) && this.property.equals(that.property)
-					&& this.ignoreCase == that.ignoreCase;
+					&& this.ignoreCase == that.ignoreCase && this.nullHandlingHint.equals(that.nullHandlingHint);
 		}
 
 		/*
@@ -409,7 +502,16 @@ public class Sort implements Iterable<org.springframework.data.domain.Sort.Order
 		public String toString() {
 
 			String result = String.format("%s: %s", property, direction);
-			return ignoreCase ? result.concat(", ignoring case") : result;
+
+			if (!NullHandling.NATIVE.equals(nullHandlingHint)) {
+				result += ", " + nullHandlingHint;
+			}
+
+			if (ignoreCase) {
+				result += ", ignoring case";
+			}
+
+			return result;
 		}
 	}
 }