#1382 - Add ability to customize the ObjectMapper for HAL and HAL-FORMS.

Use HalConfiguration to allow applying customizations to the ObjectMapper.

Original pull request: #1383.

src/main/java/org/springframework/hateoas/mediatype/hal/HalConfiguration.java

@@ -18,6 +18,7 @@ package org.springframework.hateoas.mediatype.hal;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.function.Consumer;
 
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.LinkRelation;
@@ -25,6 +26,8 @@ import org.springframework.util.AntPathMatcher;
 import org.springframework.util.Assert;
 import org.springframework.util.PathMatcher;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
+
 /**
  * HAL specific configuration.
  *
@@ -41,6 +44,7 @@ public class HalConfiguration {
 	 */
 	private final RenderSingleLinks renderSingleLinks;
 	private final Map<String, RenderSingleLinks> singleLinksPerPattern;
+	private final Consumer<ObjectMapper> objectMapperCustomizer;
 
 	/**
 	 * Configures whether the Jackson property naming strategy is applied to link relations and within {@code _embedded}
@@ -63,15 +67,18 @@ public class HalConfiguration {
 		this.singleLinksPerPattern = new LinkedHashMap<>();
 		this.applyPropertyNamingStrategy = true;
 		this.enforceEmbeddedCollections = true;
+		this.objectMapperCustomizer = objectMapper -> {}; // Default to no action.
 	}
 
 	private HalConfiguration(RenderSingleLinks renderSingleLinks, Map<String, RenderSingleLinks> singleLinksPerPattern,
-			boolean applyPropertyNamingStrategy, boolean enforceEmbeddedCollections) {
+			boolean applyPropertyNamingStrategy, boolean enforceEmbeddedCollections,
+			Consumer<ObjectMapper> objectMapperCustomizer) {
 
 		this.renderSingleLinks = renderSingleLinks;
 		this.singleLinksPerPattern = singleLinksPerPattern;
 		this.applyPropertyNamingStrategy = applyPropertyNamingStrategy;
 		this.enforceEmbeddedCollections = enforceEmbeddedCollections;
+		this.objectMapperCustomizer = objectMapperCustomizer;
 	}
 
 	/**
@@ -132,7 +139,7 @@ public class HalConfiguration {
 
 		return this.renderSingleLinks == renderSingleLinks ? this
 				: new HalConfiguration(renderSingleLinks, this.singleLinksPerPattern, this.applyPropertyNamingStrategy,
-						this.enforceEmbeddedCollections);
+						this.enforceEmbeddedCollections, this.objectMapperCustomizer);
 	}
 
 	/**
@@ -145,7 +152,7 @@ public class HalConfiguration {
 
 		return this.singleLinksPerPattern == singleLinksPerPattern ? this
 				: new HalConfiguration(this.renderSingleLinks, singleLinksPerPattern, this.applyPropertyNamingStrategy,
-						this.enforceEmbeddedCollections);
+						this.enforceEmbeddedCollections, this.objectMapperCustomizer);
 	}
 
 	/**
@@ -159,7 +166,7 @@ public class HalConfiguration {
 
 		return this.applyPropertyNamingStrategy == applyPropertyNamingStrategy ? this
 				: new HalConfiguration(this.renderSingleLinks, this.singleLinksPerPattern, applyPropertyNamingStrategy,
-						this.enforceEmbeddedCollections);
+						this.enforceEmbeddedCollections, this.objectMapperCustomizer);
 	}
 
 	/**
@@ -173,7 +180,14 @@ public class HalConfiguration {
 
 		return this.enforceEmbeddedCollections == enforceEmbeddedCollections ? this
 				: new HalConfiguration(this.renderSingleLinks, this.singleLinksPerPattern, this.applyPropertyNamingStrategy,
-						enforceEmbeddedCollections);
+						enforceEmbeddedCollections, this.objectMapperCustomizer);
+	}
+
+	public HalConfiguration withObjectMapperCustomizer(Consumer<ObjectMapper> objectMapperCustomizer) {
+
+		return this.objectMapperCustomizer == objectMapperCustomizer ? this
+				: new HalConfiguration(this.renderSingleLinks, this.singleLinksPerPattern, this.applyPropertyNamingStrategy,
+						this.enforceEmbeddedCollections, objectMapperCustomizer);
 	}
 
 	public RenderSingleLinks getRenderSingleLinks() {
@@ -188,6 +202,10 @@ public class HalConfiguration {
 		return this.enforceEmbeddedCollections;
 	}
 
+	public Consumer<ObjectMapper> getObjectMapperCustomizer() {
+		return this.objectMapperCustomizer;
+	}
+
 	/**
 	 * Configuration option how to render single links of a given {@link LinkRelation}.
 	 *

src/main/java/org/springframework/hateoas/mediatype/hal/HalMediaTypeConfiguration.java

@@ -79,11 +79,14 @@ public class HalMediaTypeConfiguration implements HypermediaMappingInformation {
 	@Override
 	public ObjectMapper configureObjectMapper(ObjectMapper mapper) {
 
+		HalConfiguration halConfiguration = this.halConfiguration.getIfAvailable(HalConfiguration::new);
+
 		mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
 		mapper.registerModule(new Jackson2HalModule());
 		mapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider,
-				curieProvider.getIfAvailable(() -> CurieProvider.NONE), resolver,
-				halConfiguration.getIfAvailable(HalConfiguration::new), beanFactory));
+				curieProvider.getIfAvailable(() -> CurieProvider.NONE), resolver, halConfiguration, beanFactory));
+
+		halConfiguration.getObjectMapperCustomizer().accept(mapper);
 
 		return mapper;
 	}

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

@@ -82,6 +82,8 @@ class HalFormsMediaTypeConfiguration implements HypermediaMappingInformation {
 		mapper.setHandlerInstantiator(new Jackson2HalFormsModule.HalFormsHandlerInstantiator(relProvider,
 				curieProvider.getIfAvailable(() -> CurieProvider.NONE), resolver, configuration, beanFactory));
 
+		configuration.getHalConfiguration().getObjectMapperCustomizer().accept(mapper);
+
 		return mapper;
 	}