#64 - Extended support for PagedResources.

Changed Relation type to identify previous links to standardized value of prev. Added integration tests for HAL rendering of PagedResources.

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

@@ -42,7 +42,7 @@ public class Link implements Serializable {
 
 	public static final String REL_SELF = "self";
 	public static final String REL_FIRST = "first";
-	public static final String REL_PREVIOUS = "previous";
+	public static final String REL_PREVIOUS = "prev";
 	public static final String REL_NEXT = "next";
 	public static final String REL_LAST = "last";
 
@@ -101,6 +101,25 @@ public class Link implements Serializable {
 		return rel;
 	}
 
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the given relation.
+	 * 
+	 * @param rel must not be {@literal null} or empty.
+	 * @return
+	 */
+	public Link withRel(String rel) {
+		return new Link(href, rel);
+	}
+
+	/**
+	 * Returns a {@link Link} pointing to the same URI but with the {@code self} relation.
+	 * 
+	 * @return
+	 */
+	public Link withSelfRel() {
+		return withRel(Link.REL_SELF);
+	}
+
 	/* 
 	 * (non-Javadoc)
 	 * @see java.lang.Object#equals(java.lang.Object)

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

@@ -87,6 +87,16 @@ public class Links implements Iterable<Link> {
 		return result;
 	}
 
+	/**
+	 * Returns whether the {@link Links} container contains a {@link Link} with the given rel.
+	 * 
+	 * @param rel
+	 * @return
+	 */
+	public boolean hasLink(String rel) {
+		return getLink(rel) != null;
+	}
+
 	/**
 	 * Creates a {@link Links} instance from the given RFC5988-compatible link format.
 	 * 
@@ -114,6 +124,15 @@ public class Links implements Iterable<Link> {
 		return new Links(links);
 	}
 
+	/**
+	 * Returns whether the {@link Links} containter is empty.
+	 * 
+	 * @return
+	 */
+	public boolean isEmpty() {
+		return links.isEmpty();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Object#toString()

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

@@ -34,6 +34,8 @@ import org.springframework.util.Assert;
 @com.fasterxml.jackson.annotation.JsonAutoDetect(fieldVisibility = com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.ANY)
 public class PagedResources<T> extends Resources<T> {
 
+	public static PagedResources<?> NO_PAGE = new PagedResources<Object>();
+
 	@org.codehaus.jackson.annotate.JsonProperty("page")
 	@com.fasterxml.jackson.annotation.JsonProperty("page")
 	private PageMetadata metadata;
@@ -97,13 +99,37 @@ public class PagedResources<T> extends Resources<T> {
 		return new PagedResources<T>(resources, metadata);
 	}
 
+	/**
+	 * Returns the Link pointing to the next page (if set).
+	 * 
+	 * @see #addPaginationLinks(Link)
+	 * @return
+	 */
+	@com.fasterxml.jackson.annotation.JsonIgnore
+	@org.codehaus.jackson.annotate.JsonIgnore
+	public Link getNextLink() {
+		return getLink(Link.REL_NEXT);
+	}
+
+	/**
+	 * Returns the Link pointing to the previous page (if set).
+	 * 
+	 * @see #addPaginationLinks(Link)
+	 * @return
+	 */
+	@com.fasterxml.jackson.annotation.JsonIgnore
+	@org.codehaus.jackson.annotate.JsonIgnore
+	public Link getPreviousLink() {
+		return getLink(Link.REL_PREVIOUS);
+	}
+
 	/* 
 	 * (non-Javadoc)
 	 * @see org.springframework.hateoas.ResourceSupport#toString()
 	 */
 	@Override
 	public String toString() {
-		return String.format("PagedResource { content: %s, metadata: %s }", getContent(), metadata);
+		return String.format("PagedResource { content: %s, metadata: %s, links: %s }", getContent(), metadata, getLinks());
 	}
 
 	/* 
@@ -173,19 +199,35 @@ public class PagedResources<T> extends Resources<T> {
 		}
 
 		/**
+		 * Creates a new {@link PageMetadata} from the given size, number, total elements and total pages.
+		 * 
 		 * @param size
-		 * @param number
+		 * @param number zero-indexed, must be less than totalPages
 		 * @param totalElements
 		 * @param totalPages
 		 */
 		public PageMetadata(long size, long number, long totalElements, long totalPages) {
 
+			Assert.isTrue(number < totalPages,
+					"The current page number cannot be greater or equal to the total number of pages!");
+
 			this.size = size;
 			this.number = number;
 			this.totalElements = totalElements;
 			this.totalPages = totalPages;
 		}
 
+		/**
+		 * Creates a new {@link PageMetadata} from the given size, numer and total elements.
+		 * 
+		 * @param size the size of the page
+		 * @param number the number of the page
+		 * @param totalElements the total number of elements available
+		 */
+		public PageMetadata(long size, long number, long totalElements) {
+			this(size, number, totalElements, totalElements / size);
+		}
+
 		/**
 		 * Returns the requested size of the page.
 		 *