#199 - Refactorings in HalEmbeddedBuilder.

We now provide a dedicated EmbeddedWrappers API that HalEmbeddedBuilder uses to transparently handle the collection enforcement etc. It also allow manually hand in EmbeddedWrapper instances to enforce a certain behavior independent of the global settings in HalEmbeddedBuilder.

Simplified HalResourcesSerializer in Jackson2Hal module as we now don't have to deploy custom serializers for the embedded elements anymore.

Supersedes some of the API introduced for #195.

src/main/java/org/springframework/hateoas/hal/HalEmbeddedBuilder.java

@@ -16,17 +16,18 @@
 package org.springframework.hateoas.hal;
 
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import org.springframework.aop.support.AopUtils;
-import org.springframework.hateoas.RelAware;
 import org.springframework.hateoas.RelProvider;
 import org.springframework.hateoas.Resource;
-import org.springframework.hateoas.core.ObjectUtils;
+import org.springframework.hateoas.core.EmbeddedWrapper;
+import org.springframework.hateoas.core.EmbeddedWrappers;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 
 /**
  * Builder class that allows collecting objects under the relation types defined for the objects but moving from the
@@ -39,11 +40,9 @@ class HalEmbeddedBuilder {
 
 	private static final String DEFAULT_REL = "content";
 
-	private final Map<String, List<Object>> embeddeds = new HashMap<String, List<Object>>();
+	private final Map<String, Object> embeddeds = new HashMap<String, Object>();
 	private final RelProvider provider;
-	private final boolean preferCollectionRels;
-
-	private boolean relAwareFound;
+	private final EmbeddedWrappers wrappers;
 
 	/**
 	 * Creates a new {@link HalEmbeddedBuilder} using the given {@link RelProvider} and prefer collection rels flag.
@@ -56,76 +55,76 @@ class HalEmbeddedBuilder {
 		Assert.notNull(provider, "Relprovider must not be null!");
 
 		this.provider = provider;
-		this.preferCollectionRels = preferCollectionRels;
+		this.wrappers = new EmbeddedWrappers(preferCollectionRels);
 	}
 
 	/**
 	 * Adds the given value to the embeddeds. Will skip doing so if the value is {@literal null} or the content of a
 	 * {@link Resource} is {@literal null}.
 	 * 
-	 * @param value
+	 * @param value can be {@literal null}.
 	 */
-	public void add(Object value) {
+	public void add(Object source) {
 
-		if (ObjectUtils.getResourceType(value) == null) {
+		EmbeddedWrapper wrapper = wrappers.wrap(source);
+
+		if (wrapper == null) {
 			return;
 		}
 
-		String rel = getDefaultedRelFor(value, true);
+		String collectionRel = getDefaultedRelFor(wrapper, true);
+		String collectionOrItemRel = collectionRel;
 
-		if (!embeddeds.containsKey(rel)) {
-			rel = getDefaultedRelFor(value, preferCollectionRels);
+		if (!embeddeds.containsKey(collectionRel)) {
+			collectionOrItemRel = getDefaultedRelFor(wrapper, wrapper.isCollectionValue());
 		}
 
-		List<Object> currentValue = embeddeds.get(rel);
+		Object currentValue = embeddeds.get(collectionOrItemRel);
+		Object value = wrapper.getValue();
 
-		if (currentValue == null) {
-			ArrayList<Object> arrayList = new ArrayList<Object>();
-			arrayList.add(value);
-			embeddeds.put(rel, arrayList);
-		} else if (currentValue.size() == 1) {
-			currentValue.add(value);
-			embeddeds.remove(rel);
-			embeddeds.put(getDefaultedRelFor(value, true), currentValue);
-		} else {
-			currentValue.add(value);
+		if (currentValue == null && !wrapper.isCollectionValue()) {
+			embeddeds.put(collectionOrItemRel, value);
+			return;
 		}
+
+		List<Object> list = new ArrayList<Object>();
+		list.addAll(asCollection(currentValue));
+		list.addAll(asCollection(wrapper.getValue()));
+
+		embeddeds.remove(collectionOrItemRel);
+		embeddeds.put(collectionRel, list);
 	}
 
-	private String getDefaultedRelFor(Object value, boolean forCollection) {
+	@SuppressWarnings("unchecked")
+	private Collection<Object> asCollection(Object source) {
+		return source instanceof Collection ? (Collection<Object>) source : source == null ? Collections.emptySet()
+				: Collections.singleton(source);
+	}
 
-		Object unwrapped = ObjectUtils.getResourceType(value);
+	private String getDefaultedRelFor(EmbeddedWrapper wrapper, boolean forCollection) {
 
-		if (value instanceof RelAware) {
-			this.relAwareFound = true;
-			return ((RelAware) value).getRel();
+		String valueRel = wrapper.getRel();
+
+		if (StringUtils.hasText(valueRel)) {
+			return valueRel;
 		}
 
 		if (provider == null) {
 			return DEFAULT_REL;
 		}
 
-		Class<?> type = AopUtils.getTargetClass(unwrapped);
+		Class<?> type = wrapper.getRelTargetType();
 
 		String rel = forCollection ? provider.getCollectionResourceRelFor(type) : provider.getItemResourceRelFor(type);
 		return rel == null ? DEFAULT_REL : rel;
 	}
 
-	/**
-	 * Returns whether the builder only created collection rels.
-	 * 
-	 * @return
-	 */
-	public boolean hasOnlyCollections() {
-		return preferCollectionRels && !relAwareFound;
-	}
-
 	/**
 	 * Returns the added objects keyed up by their relation types.
 	 * 
 	 * @return
 	 */
-	public Map<String, List<Object>> asMap() {
+	public Map<String, Object> asMap() {
 		return Collections.unmodifiableMap(embeddeds);
 	}
 }

src/main/java/org/springframework/hateoas/hal/Jackson2HalModule.java

@@ -269,18 +269,7 @@ public class Jackson2HalModule extends SimpleModule {
 				builder.add(resource);
 			}
 
-			TypeFactory typeFactory = provider.getConfig().getTypeFactory();
-			JavaType keyType = typeFactory.uncheckedSimpleType(String.class);
-			JavaType valueType = typeFactory.constructCollectionType(ArrayList.class, Resource.class);
-			JavaType mapType = typeFactory.constructMapType(HashMap.class, keyType, valueType);
-
-			JsonSerializer<Object> valueSerializer = builder.hasOnlyCollections() ? provider.findValueSerializer(valueType,
-					property) : new OptionalListJackson2Serializer(property);
-
-			MapSerializer serializer = MapSerializer.construct(new String[] {}, mapType, true, null,
-					provider.findKeySerializer(keyType, null), valueSerializer, null);
-
-			serializer.serialize(builder.asMap(), jgen, provider);
+			provider.findValueSerializer(Map.class, property).serialize(builder.asMap(), jgen, provider);
 		}
 
 		@Override