DATACMNS-1551 - SortHandlerMethodArgumentResolver now drops dot-only property segments.

If plain dots were submitted as elements in a Sort expression to be parsed by SortHandlerMethodArgumentResolver, those dots would be considered a property of the sort expression, which is of course wrong. We now drop property candidates solely consisting of dots and whitespace.

src/main/java/org/springframework/data/web/SortHandlerMethodArgumentResolver.java

@@ -16,6 +16,7 @@
 package org.springframework.data.web;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
@@ -221,7 +222,9 @@ public class SortHandlerMethodArgumentResolver implements SortArgumentResolver {
 				continue;
 			}
 
-			String[] elements = part.split(delimiter);
+			String[] elements = Arrays.stream(part.split(delimiter)) //
+					.filter(SortHandlerMethodArgumentResolver::notOnlyDots) //
+					.toArray(String[]::new);
 
 			Optional<Direction> direction = elements.length == 0 ? Optional.empty()
 					: Direction.fromOptionalString(elements[elements.length - 1]);
@@ -236,6 +239,16 @@ public class SortHandlerMethodArgumentResolver implements SortArgumentResolver {
 		return allOrders.isEmpty() ? Sort.unsorted() : Sort.by(allOrders);
 	}
 
+	/**
+	 * Returns whether the given source {@link String} consists of dots only.
+	 *
+	 * @param source must not be {@literal null}.
+	 * @return
+	 */
+	private static boolean notOnlyDots(String source) {
+		return StringUtils.hasText(source.replace(".", ""));
+	}
+
 	private static Optional<Order> toOrder(String property, Optional<Direction> direction) {
 
 		if (!StringUtils.hasText(property)) {

src/test/java/org/springframework/data/web/SortHandlerMethodArgumentResolverUnitTests.java

@@ -18,6 +18,8 @@ package org.springframework.data.web;
 import static org.assertj.core.api.Assertions.*;
 import static org.springframework.data.domain.Sort.Direction.*;
 
+import java.util.stream.Stream;
+
 import javax.servlet.http.HttpServletRequest;
 
 import org.junit.BeforeClass;
@@ -182,6 +184,20 @@ public class SortHandlerMethodArgumentResolverUnitTests extends SortDefaultUnitT
 		assertThat(resolveSort(request, getParameterOfMethod("containeredDefault"))).isEqualTo(Sort.by("foo", "bar"));
 	}
 
+	@Test // DATACMNS-1551
+	public void resolvesDotOnlyInputToDefault() {
+
+		Stream.of(".", ".,ASC").forEach(it -> {
+
+			MockHttpServletRequest request = new MockHttpServletRequest();
+			request.addParameter("sort", it);
+
+			assertThatCode(() -> {
+				assertThat(resolveSort(request, PARAMETER)).isEqualTo(Sort.unsorted());
+			}).doesNotThrowAnyException();
+		});
+	}
+
 	private static Sort resolveSort(HttpServletRequest request, MethodParameter parameter) throws Exception {
 
 		SortHandlerMethodArgumentResolver resolver = new SortHandlerMethodArgumentResolver();