#1757 - Add support for javax.validation.constraints.NotBlank.

The presence of @NonBlank on a representation model's property now causes it to be considered required. It will also cause a default pattern exposed that allows clients to validate input values.

Fixes #1757.

src/main/java/org/springframework/hateoas/mediatype/PropertyUtils.java

@@ -31,6 +31,7 @@ import javax.validation.constraints.DecimalMin;
 import javax.validation.constraints.Email;
 import javax.validation.constraints.Max;
 import javax.validation.constraints.Min;
+import javax.validation.constraints.NotBlank;
 import javax.validation.constraints.NotNull;
 import javax.validation.constraints.Pattern;
 
@@ -68,6 +69,8 @@ import com.fasterxml.jackson.annotation.JsonUnwrapped;
  */
 public class PropertyUtils {
 
+	static final String NOT_BLANK_REGEX = "^\\s*(\\S+\\s*)+$";
+
 	private static final Map<ResolvableType, ResolvableType> DOMAIN_TYPE_CACHE = new ConcurrentReferenceHashMap<>();
 	private static final Map<ResolvableType, InputPayloadMetadata> METADATA_CACHE = new ConcurrentReferenceHashMap<>();
 	private static final Set<String> FIELDS_TO_IGNORE = new HashSet<>(Arrays.asList("class", "links"));
@@ -601,7 +604,10 @@ public class PropertyUtils {
 		 */
 		@Override
 		public boolean isRequired() {
-			return super.isRequired() || property.getAnnotation(NotNull.class).isPresent();
+
+			return super.isRequired() //
+					|| property.getAnnotation(NotNull.class).isPresent() //
+					|| property.getAnnotation(NotBlank.class).isPresent();
 		}
 
 		/*
@@ -610,7 +616,14 @@ public class PropertyUtils {
 		 */
 		@Override
 		public Optional<String> getPattern() {
-			return getAnnotationAttribute(Pattern.class, "regexp", String.class);
+
+			Optional<String> attribute = getAnnotationAttribute(Pattern.class, "regexp", String.class);
+
+			if (!attribute.isPresent() && property.getAnnotation(NotBlank.class).isPresent()) {
+				attribute = Optional.of(NOT_BLANK_REGEX);
+			}
+
+			return attribute;
 		}
 
 		/*

src/test/java/org/springframework/hateoas/mediatype/PropertyUtilsTest.java

@@ -31,6 +31,7 @@ import java.util.Optional;
 import java.util.stream.Stream;
 
 import javax.validation.constraints.Email;
+import javax.validation.constraints.NotBlank;
 import javax.validation.constraints.NotNull;
 import javax.validation.constraints.Pattern;
 
@@ -158,10 +159,20 @@ class PropertyUtilsTest {
 			assertThat(it.isRequired()).isTrue();
 		});
 
+        assertThat(getProperty(metadata, "nonBlank")).hasValueSatisfying(it -> {
+            assertThat(it.isRequired()).isTrue();
+            assertThat(it.getPattern()).hasValue(PropertyUtils.NOT_BLANK_REGEX);
+        });
+
 		assertThat(getProperty(metadata, "pattern")).hasValueSatisfying(it -> {
 			assertThat(it.getPattern()).hasValue("\\w");
 		});
 
+        assertThat(getProperty(metadata, "nonBlankPattern")).hasValueSatisfying(it -> {
+            assertThat(it.isRequired()).isTrue();
+            assertThat(it.getPattern()).hasValue("\\w");
+        });
+
 		assertThat(getProperty(metadata, "annotated")).hasValueSatisfying(it -> {
 			assertThat(it.getPattern()).hasValue("regex");
 		});
@@ -250,7 +261,9 @@ class PropertyUtilsTest {
 	static class Jsr303SamplePayload {
 
 		@NotNull String nonNull;
+		@NotBlank String nonBlank;
 		@Pattern(regexp = "\\w") String pattern;
+        @NotBlank @Pattern(regexp = "\\w") String nonBlankPattern;
 		TypeAnnotated annotated;
 	}