#1114 - Provide HalFormsConfiguration API to order fields.

Register various patterns of sorting based on types.

src/main/asciidoc/mediatypes.adoc

@@ -222,6 +222,8 @@ Spring HATEOAS allows to customize those by shaping the model type for the input
 
 For types that you cannot annotate manually, you can register a custom pattern via a `HalFormsConfiguration` bean present in the application context.
 
+.Registering regex patterns for types
+====
 [source, java]
 ----
 @Configuration
@@ -235,9 +237,35 @@ class CustomConfiguration {
   }
 }
 ----
+====
 
 This setup will cause the HAL-FORMS template properties for representation model properties of type `CreditCardNumber` to declare a `regex` field with value `[0-9]{16}`.
 
+[[mediatypes.hal-forms.property-order]]
+=== Ordering template properties
+
+By default, HAL-FORMS properties are gleaned from the related domain object using Spring Framework's `BeanUtils`. There is no defined ordering. If you wish to enforce a
+particular order on these properties, you can specify that through `HalFormsConfiguration`.
+
+.Registering order of template properties for types
+====
+[source,java]
+----
+@Configuration
+class CustomConfiguration {
+
+  @Bean
+  HalFormsConfiguration halFormsConfiguration() {
+
+    HalFormsConfiguration configuration = new HalFormsConfiguration();
+    configuration.withFieldOrderFor(Employee.class, "employeeId", "name", "role");
+  }
+}
+----
+====
+
+The listed properties will be rendered first, followed by any not cited.
+
 [[mediatypes.hal-forms.i18n]]
 === Internationalization of form attributes
 HAL-FORMS contains attributes that are intended for human interpretation, like a template's title or property prompts.

src/main/java/org/springframework/hateoas/AffordanceModel.java

@@ -161,6 +161,8 @@ static InputPayloadMetadata from(PayloadMetadata metadata) {
 		 * @return
 		 */
 		List<String> getI18nCodes();
+
+		Optional<ResolvableType> getType();
 	}
 
 	/**
@@ -210,7 +212,17 @@ public <T extends Named> T customize(T target, Function<PropertyMetadata, T> cus
 		public List<String> getI18nCodes() {
 			return Collections.emptyList();
 		}
-	}
+
+        @Override
+        public Optional<ResolvableType> getType() {
+
+            if (metadata instanceof InputPayloadMetadata) {
+                ((InputPayloadMetadata) metadata).getType();
+            }
+
+            return Optional.empty();
+        }
+    }
 
 	/**
 	 * Metadata about the property model of a representation.

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

@@ -308,17 +308,10 @@ private String getNameOrDefault() {
 
 			String name = method.toString().toLowerCase();
 
-			ResolvableType type = TypeBasedPayloadMetadata.class.isInstance(inputMetdata) //
-					? TypeBasedPayloadMetadata.class.cast(inputMetdata).getType() //
-					: null;
-
-			if (type == null) {
-				return name;
-			}
-
-			Class<?> resolvedType = type.resolve();
-
-			return resolvedType == null ? name : name.concat(resolvedType.getSimpleName());
+			return inputMetdata.getType() //
+					.map(ResolvableType::resolve) //
+					.map(resolvedType -> resolvedType == null ? name : name.concat(resolvedType.getSimpleName())) //
+					.orElse(name);
 		}
 	}
 }

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

@@ -20,6 +20,7 @@
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.Optional;
 import java.util.SortedMap;
 import java.util.TreeMap;
 import java.util.function.Function;
@@ -39,7 +40,7 @@
  */
 class TypeBasedPayloadMetadata implements InputPayloadMetadata {
 
-	private final @Getter(AccessLevel.PACKAGE) ResolvableType type;
+	private final ResolvableType type;
 	private final SortedMap<String, PropertyMetadata> properties;
 
 	TypeBasedPayloadMetadata(ResolvableType type, Stream<PropertyMetadata> properties) {
@@ -93,4 +94,9 @@ public List<String> getI18nCodes() {
 
 		return Arrays.asList(type.getName(), type.getSimpleName());
 	}
+
+    @Override
+    public Optional<ResolvableType> getType() {
+        return Optional.ofNullable(this.type);
+    }
 }

src/main/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsConfiguration.java

@@ -18,7 +18,9 @@
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
+import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
@@ -36,6 +38,7 @@ public class HalFormsConfiguration {
 
 	private final @Getter HalConfiguration halConfiguration;
 	private final Map<Class<?>, String> patterns = new HashMap<>();
+	private final Map<Class<?>, List<String>> fieldOrder = new HashMap<>();
 
 	/**
 	 * Creates a new {@link HalFormsConfiguration} backed by a default {@link HalConfiguration}.
@@ -60,4 +63,15 @@ public HalFormsConfiguration registerPattern(Class<?> type, String pattern) {
 	Optional<String> getTypePatternFor(ResolvableType type) {
 		return Optional.ofNullable(patterns.get(type.resolve(Object.class)));
 	}
+
+	public HalFormsConfiguration withFieldOrderFor(Class<?> type, String... fieldNames) {
+
+		this.fieldOrder.put(type, Arrays.asList(fieldNames));
+
+		return this;
+	}
+
+	Optional<List<String>> getFieldOrderFor(ResolvableType type) {
+		return Optional.ofNullable(fieldOrder.get(type.resolve(Object.class)));
+	}
 }

src/main/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsTemplateBuilder.java

@@ -79,6 +79,8 @@ public Map<String, HalFormsTemplate> findTemplates(RepresentationModel<?> resour
 							.map(property -> it.hasHttpMethod(HttpMethod.PATCH) ? property.withRequired(false) : property)
 							.collect(Collectors.toList());
 
+					propertiesWithPrompt = sorted(propertiesWithPrompt, it.getInput());
+
 					HalFormsTemplate template = HalFormsTemplate.forMethod(it.getHttpMethod()) //
 							.withProperties(propertiesWithPrompt);
 
@@ -89,6 +91,33 @@ public Map<String, HalFormsTemplate> findTemplates(RepresentationModel<?> resour
 		return templates;
 	}
 
+	private List<HalFormsProperty> sorted(List<HalFormsProperty> properties, InputPayloadMetadata input) {
+
+		return input.getType() //
+				.flatMap(configuration::getFieldOrderFor) //
+				.map(fieldsToSortBy -> {
+
+					List<HalFormsProperty> propertiesToSort = new ArrayList<>(properties);
+					List<HalFormsProperty> sortedProperties = new ArrayList<>();
+
+					for (String propertyName : fieldsToSortBy) {
+						properties.stream() //
+								.filter(halFormsProperty -> halFormsProperty.getName().equals(propertyName)) //
+								.findFirst() //
+								.ifPresent(halFormsProperty -> {
+									sortedProperties.add(halFormsProperty);
+									propertiesToSort.remove(halFormsProperty);
+								});
+					}
+
+					// Whatever properties weren't listed, add them at the end.
+					sortedProperties.addAll(propertiesToSort);
+
+					return sortedProperties;
+				}) //
+				.orElse(properties);
+	}
+
 	public PropertyCustomizations forMetadata(InputPayloadMetadata metadata) {
 		return new PropertyCustomizations(metadata);
 	}

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

@@ -17,6 +17,7 @@
 
 import static org.assertj.core.api.Assertions.*;
 
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.stream.Stream;
 
@@ -113,8 +114,8 @@ public PayloadMetadataAssert(PayloadMetadata actual) {
 
 		public PayloadMetadataAssert isBackedBy(Class<?> type) {
 
-			Assertions.assertThat(actual).isInstanceOfSatisfying(TypeBasedPayloadMetadata.class, it -> {
-				Assertions.assertThat(it.getType()).isEqualTo(ResolvableType.forClass(type));
+			assertThat(actual).isInstanceOfSatisfying(TypeBasedPayloadMetadata.class, it -> {
+				assertThat(it.getType()).isEqualTo(Optional.of(ResolvableType.forClass(type)));
 			});
 
 			return this;

src/test/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsPropertyOrderingUnitTest.java

@@ -0,0 +1,80 @@
+package org.springframework.hateoas.mediatype.hal.forms;
+
+import lombok.Data;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.hateoas.Link;
+import org.springframework.hateoas.RepresentationModel;
+import org.springframework.hateoas.mediatype.Affordances;
+import org.springframework.hateoas.mediatype.MessageResolver;
+import org.springframework.http.HttpMethod;
+
+import static org.assertj.core.api.Assertions.*;
+
+public class HalFormsPropertyOrderingUnitTest {
+
+	private RepresentationModel<?> model;
+
+	@BeforeEach
+	void setUp() {
+
+		this.model = new RepresentationModel<>(Affordances.of(Link.of("/example")) //
+				.afford(HttpMethod.POST) //
+				.withInput(Thing.class) //
+				.toLink());
+	}
+
+	@Test
+	void noCustomOrdering() {
+
+		HalFormsConfiguration halFormsConfiguration = new HalFormsConfiguration();
+
+		assertThat(createTemplate(halFormsConfiguration).getProperties()).flatExtracting(HalFormsProperty::getName)
+				.containsExactly("a", "b", "z");
+
+	}
+
+	@Test
+	void specifyAllProperties() {
+
+		HalFormsConfiguration halFormsConfiguration = new HalFormsConfiguration() //
+				.withFieldOrderFor(Thing.class, "z", "b", "a");
+
+		assertThat(createTemplate(halFormsConfiguration).getProperties()).flatExtracting(HalFormsProperty::getName)
+				.containsExactly("z", "b", "a");
+	}
+
+	@Test
+	void specifySomeProperties() {
+
+		HalFormsConfiguration halFormsConfiguration = new HalFormsConfiguration() //
+				.withFieldOrderFor(Thing.class, "z");
+
+		assertThat(createTemplate(halFormsConfiguration).getProperties()).flatExtracting(HalFormsProperty::getName)
+				.containsExactly("z", "a", "b");
+	}
+
+	@Test
+	void nonExistentProperty() {
+
+		HalFormsConfiguration halFormsConfiguration = new HalFormsConfiguration() //
+				.withFieldOrderFor(Thing.class, "q", "b");
+
+		assertThat(createTemplate(halFormsConfiguration).getProperties()).flatExtracting(HalFormsProperty::getName)
+				.containsExactly("b", "a", "z");
+	}
+
+	private HalFormsTemplate createTemplate(HalFormsConfiguration halFormsConfiguration) {
+		return new HalFormsTemplateBuilder(halFormsConfiguration, MessageResolver.DEFAULTS_ONLY).findTemplates(this.model)
+				.get("default");
+	}
+
+	@Data
+	private static class Thing {
+
+		private String a;
+		private String b;
+		private String z;
+	}
+}