#235: modified the Link class to support adding target attributes

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

@@ -16,17 +16,22 @@
 package org.springframework.hateoas;
 
 import java.io.Serializable;
+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 java.util.TreeMap;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlTransient;
 import javax.xml.bind.annotation.XmlType;
 
+import com.fasterxml.jackson.annotation.JsonAnyGetter;
+import com.fasterxml.jackson.annotation.JsonInclude;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
@@ -55,6 +60,7 @@ public class Link implements Serializable {
 	@XmlAttribute private String rel;
 	@XmlAttribute private String href;
 	@XmlTransient @JsonIgnore private UriTemplate template;
+	private Map<String,Object> attributes = new TreeMap<String, Object>();
 
 	/**
 	 * Creates a new link to the given URI with the self rel.
@@ -99,6 +105,17 @@ protected Link() {
 
 	}
 
+	/**
+	 * Copy constructor needed for the various with methods.
+	 */
+	private Link(Link linkToCopy) {
+
+		this.template = linkToCopy.template;
+		this.href = linkToCopy.href;
+		this.rel = linkToCopy.rel;
+		this.attributes = linkToCopy.attributes;
+	}
+
 	/**
 	 * Returns the actual URI the link is pointing to.
 	 * 
@@ -117,6 +134,18 @@ public String getRel() {
 		return rel;
 	}
 
+	/**
+	 * Returns the attributes of the link.
+	 * 
+	 * @return
+	 */
+	@JsonInclude(JsonInclude.Include.NON_EMPTY)
+	@JsonAnyGetter
+	public Map<String,Object> getAttributes() {
+
+		return Collections.unmodifiableMap(attributes);
+	}
+
 	/**
 	 * Returns a {@link Link} pointing to the same URI but with the given relation.
 	 * 
@@ -136,6 +165,83 @@ public Link withSelfRel() {
 		return withRel(Link.REL_SELF);
 	}
 
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified anchor value.
+	 * 
+	 * @param anchor
+	 * @return
+	 */
+	public Link withAnchor(String anchor) {
+
+		Link link = new Link(this);
+		link.setAttributeValue("anchor", anchor);
+		return link;
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified hreflang value.
+	 * 
+	 * @param hreflang
+	 * @return
+	 */
+	public Link withHreflang(String hreflang) {
+
+		return withAttribute("hreflang", hreflang);
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified media value.
+	 * 
+	 * @param media
+	 * @return
+	 */
+	public Link withMedia(String media) {
+
+		Link link = new Link(this);
+		link.setAttributeValue("media", media);
+		return link;
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified title value.
+	 * 
+	 * @param title
+	 * @return
+	 */
+	public Link withTitle(String title) {
+
+		Link link = new Link(this);
+		link.setAttributeValue("title", title);
+		return link;
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified type value.
+	 * 
+	 * @param type
+	 * @return
+	 */
+	public Link withType(String type) {
+
+		Link link = new Link(this);
+		link.setAttributeValue("type", type);
+		return link;
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the specified attribute
+	 * 
+	 * @param key
+	 * @param value
+	 * @return
+	 */
+	public Link withAttribute(String key, String value) {
+
+		Link link = new Link(this);
+		link.setAttributeValue(key, value);
+		return link;
+	}
+
 	/**
 	 * Returns the variable names contained in the template.
 	 * 
@@ -233,7 +339,59 @@ public int hashCode() {
 	 */
 	@Override
 	public String toString() {
-		return String.format("<%s>;rel=\"%s\"", href, rel);
+
+		StringBuilder str = new StringBuilder();
+
+		str.append("<");
+		str.append(href);
+		str.append(">");
+
+		if (rel != null) {
+			str.append(";rel=\"");
+			str.append(rel);
+			str.append("\"");
+		}
+
+		for (String key : attributes.keySet()) {
+			Object value = attributes.get(key);
+
+			if (value instanceof Collection) {
+				for (String item : (Collection<String>)value) {
+					str.append(";");
+					str.append(key);
+					str.append("=\"");
+					str.append(item);
+					str.append("\"");
+				}
+			}
+			else {
+				str.append(";");
+				str.append(key);
+				str.append("=\"");
+				str.append(value);
+				str.append("\"");
+			}
+		}
+
+		return str.toString();
+	}
+
+	private void setAttributeValue(String key, String value) {
+
+		Object currentValue = attributes.get(key);
+
+		if (currentValue instanceof Collection) {
+			((Collection<String>)currentValue).add(value);
+		}
+		else if (currentValue instanceof String) {
+			Collection<String> values = new ArrayList<String>();
+			attributes.put(key, values);
+			values.add(currentValue.toString());
+			values.add(value);
+		}
+		else {
+			attributes.put(key, value);
+		}
 	}
 
 	/**
@@ -262,7 +420,15 @@ public static Link valueOf(String element) {
 				throw new IllegalArgumentException("Link does not provide a rel attribute!");
 			}
 
-			return new Link(matcher.group(1), attributes.get("rel"));
+			Link link = new Link(matcher.group(1), attributes.get("rel"));
+
+			for (String key : attributes.keySet()) {
+				if (!key.equalsIgnoreCase("rel")) {
+					link = link.withAttribute(key, attributes.get(key));
+				}
+			}
+
+			return link;
 
 		} else {
 			throw new IllegalArgumentException(String.format("Given link header %s is not RFC5988 compliant!", element));
@@ -282,11 +448,19 @@ private static Map<String, String> getAttributeMap(String source) {
 		}
 
 		Map<String, String> attributes = new HashMap<String, String>();
-		Pattern keyAndValue = Pattern.compile("(\\w+)=\\\"(\\p{Alnum}*)\"");
-		Matcher matcher = keyAndValue.matcher(source);
 
-		while (matcher.find()) {
-			attributes.put(matcher.group(1), matcher.group(2));
+		Pattern attributesPattern = Pattern.compile("\\w+=\\\"[\\s\\p{Alnum}]*\"*");
+		Pattern keyAndValuePattern = Pattern.compile("(\\w+)=\\\"([\\s\\p{Alnum}]*)\"");
+
+		Matcher attributesMatcher = attributesPattern.matcher(source);
+
+		while (attributesMatcher.find()) {
+			String group = attributesMatcher.group();
+			Matcher keyValueMatcher = keyAndValuePattern.matcher(group);
+
+			if (keyValueMatcher.find()) {
+				attributes.put(keyValueMatcher.group(1), keyValueMatcher.group(2));
+			}
 		}
 
 		return attributes;

src/test/java/org/springframework/hateoas/LinkUnitTest.java

@@ -44,6 +44,26 @@ public void createsLinkFromRelAndHref() {
 		assertThat(link.getRel(), is(Link.REL_SELF));
 	}
 
+	@Test
+	public void createsLinkFromRelAndHrefWithParameters() {
+
+		Link link = new Link("foo", Link.REL_SELF)
+							.withAnchor("anchor")
+							.withHreflang("hreflang")
+							.withMedia("media")
+							.withTitle("title")
+							.withType("type")
+							.withAttribute("name", "name");
+		assertThat(link.getHref(), is("foo"));
+		assertThat(link.getRel(), is(Link.REL_SELF));
+		assertThat(link.getAttributes().get("anchor").toString(), is("anchor"));
+		assertThat(link.getAttributes().get("hreflang").toString(), is("hreflang"));
+		assertThat(link.getAttributes().get("media").toString(), is("media"));
+		assertThat(link.getAttributes().get("title").toString(), is("title"));
+		assertThat(link.getAttributes().get("type").toString(), is("type"));
+		assertThat(link.getAttributes().get("name").toString(), is("name"));
+	}
+
 	@Test(expected = IllegalArgumentException.class)
 	public void rejectsNullHref() {
 		new Link(null);
@@ -108,6 +128,32 @@ public void parsesRFC5988HeaderIntoLink() {
 
 		assertThat(Link.valueOf("</something>;rel=\"foo\""), is(new Link("/something", "foo")));
 		assertThat(Link.valueOf("</something>;rel=\"foo\";title=\"Some title\""), is(new Link("/something", "foo")));
+		assertThat(Link.valueOf("</something>;title=\"Some title\";rel=\"foo\""), is(new Link("/something", "foo")));
+		assertThat(Link.valueOf("</something>;rel=\"foo\";title=\"Some title\"").getAttributes().get("title").toString(), is("Some title"));
+	}
+
+	@Test
+	public void testToStringWithNoAttributes() {
+
+		Link link = new Link("/foo", Link.REL_SELF);
+
+		assertThat(link.toString(), is("</foo>;rel=\"self\""));
+	}
+
+	@Test
+	public void testToStringWithAllAttributes() {
+
+		Link link = new Link("/foo", Link.REL_SELF)
+							.withAnchor("anchor")
+							.withHreflang("hreflang")
+							.withMedia("media")
+							.withTitle("title")
+							.withType("type")
+							.withAttribute("name", "name")
+							.withAttribute("custom", "custom1")
+							.withAttribute("custom", "custom2");
+
+		assertThat(link.toString(), is("</foo>;rel=\"self\";anchor=\"anchor\";custom=\"custom1\";custom=\"custom2\";hreflang=\"hreflang\";media=\"media\";name=\"name\";title=\"title\";type=\"type\""));
 	}
 
 	@Test(expected = IllegalArgumentException.class)

src/test/java/org/springframework/hateoas/hal/Jackson2HalIntegrationTest.java

@@ -51,6 +51,8 @@ public class Jackson2HalIntegrationTest extends AbstractJackson2MarshallingInteg
 	static final String SINGLE_LINK_REFERENCE = "{\"_links\":{\"self\":{\"href\":\"localhost\"}}}";
 	static final String LIST_LINK_REFERENCE = "{\"_links\":{\"self\":[{\"href\":\"localhost\"},{\"href\":\"localhost2\"}]}}";
 
+	static final String SINGLE_LINK_WITH_ATTRIBUTES_REFERENCE = "{\"_links\":{\"self\":{\"href\":\"localhost\",\"hreflang\":[\"lang1\",\"lang2\"],\"title\":\"The Title\"}}}";
+
 	static final String SIMPLE_EMBEDDED_RESOURCE_REFERENCE = "{\"_links\":{\"self\":{\"href\":\"localhost\"}},\"_embedded\":{\"content\":[\"first\",\"second\"]}}";
 	static final String SINGLE_EMBEDDED_RESOURCE_REFERENCE = "{\"_links\":{\"self\":{\"href\":\"localhost\"}},\"_embedded\":{\"content\":[{\"text\":\"test1\",\"number\":1,\"_links\":{\"self\":{\"href\":\"localhost\"}}}]}}";
 	static final String LIST_EMBEDDED_RESOURCE_REFERENCE = "{\"_links\":{\"self\":{\"href\":\"localhost\"}},\"_embedded\":{\"content\":[{\"text\":\"test1\",\"number\":1,\"_links\":{\"self\":{\"href\":\"localhost\"}}},{\"text\":\"test2\",\"number\":2,\"_links\":{\"self\":{\"href\":\"localhost\"}}}]}}";
@@ -95,6 +97,18 @@ public void deserializeSingleLink() throws Exception {
 		assertThat(read(SINGLE_LINK_REFERENCE, ResourceSupport.class), is(expected));
 	}
 
+	@Test
+	public void rendersSingleLinkWithAttributesAsObject() throws Exception {
+
+		ResourceSupport resourceSupport = new ResourceSupport();
+		resourceSupport.add(new Link("localhost")
+									  .withTitle("The Title")
+									  .withHreflang("lang1")
+									  .withHreflang("lang2"));
+
+		assertThat(write(resourceSupport), is(SINGLE_LINK_WITH_ATTRIBUTES_REFERENCE));
+	}
+
 	/**
 	 * @see #29
 	 */