#126, #123 - Added support for HAL curies.

Introduced CurieProvider interface as well as a DefaultCurieProvider that can be registered as Spring Bean to enable Links being rendered in a curie namespace and an additional curie link exposing the metadata of how to lookup the rel definition.

Deprecated Jackson 1 integration. Added helper class to find out whether a relation type is defined by the IANA.

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

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2013 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.hateoas;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+
+/**
+ * Static class to find out whether a relation type is defined by the IANA.
+ * 
+ * @see http://www.iana.org/assignments/link-relations/link-relations.xhtml
+ * @author Oliver Gierke
+ */
+public class IanaRels {
+
+	private static final Collection<String> RELS;
+
+	static {
+
+		Collection<String> rels = new HashSet<String>();
+
+		rels.addAll(Arrays.asList("about", "alternate", "appendix", "archives", "author", "bookmark", "canonical",
+				"chapter", "collection", "contents", "copyright", "create-form", "current", "describedby", "describes",
+				"disclosure", "duplicate", "edit", "edit-form", "edit-media", "enclosure", "first", "glossary", "help",
+				"hosts", "hub", "icon", "index", "item", "last", "latest-version", "license", "lrdd", "memento", "monitor",
+				"monitor-group", "next", "next-archive", "nofollow", "noreferrer", "original", "payment",
+				"predecessor-version", "prefetch", "prev", "preview", "previous", "prev-archive", "privacy-policy", "profile",
+				"related", "replies", "search", "section", "self", "service", "start", "stylesheet", "subsection",
+				"successor-version", "tag", "terms-of-service", "timegate", "timemap", "type", "up", "version-history", "via",
+				"working-copy", "working-copy-of"));
+
+		RELS = Collections.unmodifiableCollection(rels);
+	}
+
+	/**
+	 * Returns whether the given relation type is defined by the IANA.
+	 * 
+	 * @param rel the relation type to check
+	 * @return
+	 */
+	public static boolean isIanaRel(String rel) {
+		return rel == null ? false : RELS.contains(rel);
+	}
+}

src/main/java/org/springframework/hateoas/config/HypermediaSupportBeanDefinitionRegistrar.java

@@ -23,6 +23,7 @@ import java.util.Map;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.BeanPostProcessor;
@@ -42,6 +43,7 @@ import org.springframework.hateoas.core.DefaultLinkDiscoverer;
 import org.springframework.hateoas.core.DefaultRelProvider;
 import org.springframework.hateoas.core.DelegatingRelProvider;
 import org.springframework.hateoas.core.EvoInflectorRelProvider;
+import org.springframework.hateoas.hal.CurieProvider;
 import org.springframework.hateoas.hal.HalLinkDiscoverer;
 import org.springframework.hateoas.hal.Jackson1HalModule;
 import org.springframework.hateoas.hal.Jackson2HalModule;
@@ -63,6 +65,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
  * 
  * @author Oliver Gierke
  */
+@SuppressWarnings("deprecation")
 class HypermediaSupportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
 
 	private static final String LINK_DISCOVERER_BEAN_NAME = "_linkDiscoverer";
@@ -172,7 +175,8 @@ class HypermediaSupportBeanDefinitionRegistrar implements ImportBeanDefinitionRe
 
 		private BeanFactory factory;
 
-		/* (non-Javadoc)
+		/* 
+		 * (non-Javadoc)
 		 * @see org.springframework.beans.factory.BeanFactoryAware#setBeanFactory(org.springframework.beans.factory.BeanFactory)
 		 */
 		@Override
@@ -226,7 +230,16 @@ class HypermediaSupportBeanDefinitionRegistrar implements ImportBeanDefinitionRe
 
 			ObjectMapper mapper = (ObjectMapper) objectMapper;
 			mapper.registerModule(new Jackson2HalModule());
-			mapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(provider));
+			mapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(provider, getCurieProvider()));
+		}
+
+		private CurieProvider getCurieProvider() {
+
+			try {
+				return factory.getBean(CurieProvider.class);
+			} catch (NoSuchBeanDefinitionException e) {
+				return null;
+			}
 		}
 	}
 
@@ -236,6 +249,7 @@ class HypermediaSupportBeanDefinitionRegistrar implements ImportBeanDefinitionRe
 	 * 
 	 * @author Oliver Gierke
 	 */
+	@Deprecated
 	private static class Jackson1ModuleRegisteringBeanPostProcessor implements BeanPostProcessor, BeanFactoryAware {
 
 		private BeanFactory beanFactory;

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

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2013 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.hateoas.hal;
+
+import org.springframework.hateoas.Link;
+
+/**
+ * API to provide HAL curie information for links.
+ * 
+ * @see http://tools.ietf.org/html/draft-kelly-json-hal#section-8.2
+ * @author Oliver Gierke
+ */
+public interface CurieProvider {
+
+	/**
+	 * Returns the rel to be rendered for the given {@link Link}. Will potentially prefix the rel but also might decide
+	 * not to, depending on the actual rel.
+	 * 
+	 * @param link
+	 * @return
+	 */
+	String getNamespacedRelFrom(Link link);
+
+	/**
+	 * Returns an object to render as the base curie information. Implementations have to make sure, the retunred
+	 * instances renders as defined in the spec.
+	 * 
+	 * @return must not be {@literal null}.
+	 */
+	Object getCurieInformation();
+}

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

@@ -0,0 +1,95 @@
+/*
+ * Copyright 2013 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.hateoas.hal;
+
+import org.springframework.hateoas.IanaRels;
+import org.springframework.hateoas.Link;
+import org.springframework.util.Assert;
+import org.springframework.web.util.UriTemplate;
+
+/**
+ * @author Oliver Gierke
+ */
+public class DefaultCurieProvider implements CurieProvider {
+
+	private final Curie curie;
+
+	/**
+	 * Creates a new {@link DefaultCurieProvider} for the given name and {@link UriTemplate}.
+	 * 
+	 * @param name must not be {@literal null} or empty.
+	 * @param uriTemplate must not be {@literal null} and contain exactly one template variable.
+	 */
+	public DefaultCurieProvider(String name, UriTemplate uriTemplate) {
+
+		Assert.hasText(name, "Name must not be null or empty!");
+		Assert.notNull(uriTemplate, "UriTemplate must not be null!");
+		Assert.isTrue(uriTemplate.getVariableNames().size() == 1,
+				String.format("Expected a single template variable in the UriTemplate %s!", uriTemplate.toString()));
+
+		this.curie = new Curie(name, uriTemplate.toString());
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.hateoas.hal.CurieProvider#getCurieInformation()
+	 */
+	@Override
+	public Curie getCurieInformation() {
+		return curie;
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.hateoas.hal.CurieProvider#getNamespacedRelFrom(org.springframework.hateoas.Link)
+	 */
+	@Override
+	public String getNamespacedRelFrom(Link link) {
+
+		String rel = link.getRel();
+
+		boolean prefixingNeeded = !IanaRels.isIanaRel(rel) && !rel.contains(":");
+		return prefixingNeeded ? String.format("%s:%s", curie.name, rel) : rel;
+	}
+
+	/**
+	 * Value object to get the curie {@link Link} rendered in JSON.
+	 * 
+	 * @author Oliver Gierke
+	 */
+	@SuppressWarnings("unused")
+	private static class Curie extends Link {
+
+		private static final long serialVersionUID = 1L;
+
+		private final String name;
+		private final boolean templated = true;
+
+		public Curie(String name, String href) {
+
+			super(href, "curies");
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public boolean isTemplated() {
+			return templated;
+		}
+	}
+}

src/main/java/org/springframework/hateoas/hal/Jackson1HalModule.java

@@ -66,9 +66,11 @@ import org.springframework.util.StringUtils;
 /**
  * Jackson 1 module implementation to render {@link Link} and {@link ResourceSupport} instances in HAL compatible JSON.
  * 
+ * @deprecated use Jackson 2 instead
  * @author Alexander Baetz
  * @author Oliver Gierke
  */
+@Deprecated
 public class Jackson1HalModule extends SimpleModule {
 
 	/**

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

@@ -17,6 +17,7 @@ package org.springframework.hateoas.hal;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -91,15 +92,17 @@ public class Jackson2HalModule extends SimpleModule {
 	public static class HalLinkListSerializer extends ContainerSerializer<List<Link>> implements ContextualSerializer {
 
 		private final BeanProperty property;
+		private final CurieProvider curieProvider;
 
-		public HalLinkListSerializer() {
-			this(null);
+		public HalLinkListSerializer(CurieProvider curieProvider) {
+			this(null, curieProvider);
 		}
 
-		public HalLinkListSerializer(BeanProperty property) {
+		public HalLinkListSerializer(BeanProperty property, CurieProvider curieProvider) {
 
 			super(List.class, false);
 			this.property = property;
+			this.curieProvider = curieProvider;
 		}
 
 		/*
@@ -113,17 +116,28 @@ public class Jackson2HalModule extends SimpleModule {
 				JsonGenerationException {
 
 			// sort links according to their relation
-			Map<String, List<Link>> sortedLinks = new LinkedHashMap<String, List<Link>>();
+			Map<String, List<Object>> sortedLinks = new LinkedHashMap<String, List<Object>>();
+			boolean prefixingRequired = curieProvider != null;
+
 			for (Link link : value) {
-				if (sortedLinks.get(link.getRel()) == null) {
-					sortedLinks.put(link.getRel(), new ArrayList<Link>());
+
+				String rel = prefixingRequired ? curieProvider.getNamespacedRelFrom(link) : link.getRel();
+
+				if (sortedLinks.get(rel) == null) {
+					sortedLinks.put(rel, new ArrayList<Object>());
 				}
-				sortedLinks.get(link.getRel()).add(link);
+
+				sortedLinks.get(rel).add(link);
+			}
+
+			if (prefixingRequired) {
+				Object curieInformation = curieProvider.getCurieInformation();
+				sortedLinks.put("curies", Arrays.asList(curieInformation));
 			}
 
 			TypeFactory typeFactory = provider.getConfig().getTypeFactory();
 			JavaType keyType = typeFactory.uncheckedSimpleType(String.class);
-			JavaType valueType = typeFactory.constructCollectionType(ArrayList.class, Link.class);
+			JavaType valueType = typeFactory.constructCollectionType(ArrayList.class, Object.class);
 			JavaType mapType = typeFactory.constructMapType(HashMap.class, keyType, valueType);
 
 			MapSerializer serializer = MapSerializer.construct(new String[] {}, mapType, true, null,
@@ -141,7 +155,7 @@ public class Jackson2HalModule extends SimpleModule {
 		@Override
 		public JsonSerializer<?> createContextual(SerializerProvider provider, BeanProperty property)
 				throws JsonMappingException {
-			return new HalLinkListSerializer(property);
+			return new HalLinkListSerializer(property, curieProvider);
 		}
 
 		/*
@@ -294,7 +308,7 @@ public class Jackson2HalModule extends SimpleModule {
 			ContextualSerializer {
 
 		private final BeanProperty property;
-		private JsonSerializer<Object> serializer;
+		private final Map<Class<?>, JsonSerializer<Object>> serializers;
 
 		public OptionalListJackson2Serializer() {
 			this(null);
@@ -309,13 +323,12 @@ public class Jackson2HalModule extends SimpleModule {
 
 			super(List.class, false);
 			this.property = property;
+			this.serializers = new HashMap<Class<?>, JsonSerializer<Object>>();
 		}
 
 		/*
 		 * (non-Javadoc)
-		 * 
-		 * @see com.fasterxml.jackson.databind.ser.ContainerSerializer#_withValueTypeSerializer(com.fasterxml.jackson.databind.jsontype.
-		 * TypeSerializer)
+		 * @see com.fasterxml.jackson.databind.ser.ContainerSerializer#_withValueTypeSerializer(com.fasterxml.jackson.databind.jsontype.TypeSerializer)
 		 */
 		@Override
 		public ContainerSerializer<?> _withValueTypeSerializer(TypeSerializer vts) {
@@ -324,9 +337,7 @@ public class Jackson2HalModule extends SimpleModule {
 
 		/*
 		 * (non-Javadoc)
-		 * 
-		 * @see com.fasterxml.jackson.databind.ser.std.StdSerializer#serialize(java.lang.Object, com.fasterxml.jackson.core.JsonGenerator,
-		 * com.fasterxml.jackson.databind.SerializerProvider)
+		 * @see com.fasterxml.jackson.databind.ser.std.StdSerializer#serialize(java.lang.Object, com.fasterxml.jackson.core.JsonGenerator, com.fasterxml.jackson.databind.SerializerProvider)
 		 */
 		@Override
 		public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException,
@@ -334,6 +345,10 @@ public class Jackson2HalModule extends SimpleModule {
 
 			List<?> list = (List<?>) value;
 
+			if (list.isEmpty()) {
+				return;
+			}
+
 			if (list.size() == 1) {
 				serializeContents(list.iterator(), jgen, provider);
 				return;
@@ -352,27 +367,35 @@ public class Jackson2HalModule extends SimpleModule {
 				if (elem == null) {
 					provider.defaultSerializeNull(jgen);
 				} else {
-					if (serializer == null) {
-						serializer = provider.findValueSerializer(elem.getClass(), property);
-					}
-					serializer.serialize(elem, jgen, provider);
+					getOrLookupSerializerFor(elem.getClass(), provider).serialize(elem, jgen, provider);
 				}
 			}
 		}
 
-		/*
-		 * (non-Javadoc)
-		 * 
-		 * @see com.fasterxml.jackson.databind.ser.ContainerSerializer#getContentSerializer()
-		 */
-		@Override
-		public JsonSerializer<?> getContentSerializer() {
+		private JsonSerializer<Object> getOrLookupSerializerFor(Class<?> type, SerializerProvider provider)
+				throws JsonMappingException {
+
+			JsonSerializer<Object> serializer = serializers.get(type);
+
+			if (serializer == null) {
+				serializer = provider.findValueSerializer(type, property);
+				serializers.put(type, serializer);
+			}
+
 			return serializer;
 		}
 
 		/*
 		 * (non-Javadoc)
-		 * 
+		 * @see com.fasterxml.jackson.databind.ser.ContainerSerializer#getContentSerializer()
+		 */
+		@Override
+		public JsonSerializer<?> getContentSerializer() {
+			return null;
+		}
+
+		/*
+		 * (non-Javadoc)
 		 * @see com.fasterxml.jackson.databind.ser.ContainerSerializer#getContentType()
 		 */
 		@Override
@@ -561,10 +584,11 @@ public class Jackson2HalModule extends SimpleModule {
 
 		private final Map<Class<?>, Object> instanceMap = new HashMap<Class<?>, Object>();
 
-		public HalHandlerInstantiator(RelProvider resolver) {
+		public HalHandlerInstantiator(RelProvider resolver, CurieProvider curieProvider) {
 
 			Assert.notNull(resolver, "RelProvider must not be null!");
-			this.instanceMap.put(HalResourcesSerializer.class, new HalResourcesSerializer(null, resolver));
+			this.instanceMap.put(HalResourcesSerializer.class, new HalResourcesSerializer(resolver));
+			this.instanceMap.put(HalLinkListSerializer.class, new HalLinkListSerializer(curieProvider));
 		}
 
 		private Object findInstance(Class<?> type) {