There is no configuration required to be able to inject Atom links in your resource representation, you just have to have this maven artifact in your path:

You need three things in order to tell RESTEasy to inject Atom links in your entities:

The following example illustrates how you would declare everything in order to get the Atom links injected in your book store:

@Path("/")

@Consumes({"application/xml", "application/json"})

@Produces({"application/xml", "application/json"})

public interface BookStore {


    @AddLinks

    @LinkResource(value = Book.class)

    @GET

    @Path("books")

    public Collection<Book> getBooks();


    @LinkResource

    @POST

    @Path("books")

    public void addBook(Book book);


    @AddLinks

    @LinkResource

    @GET

    @Path("book/{id}")

    public Book getBook(@PathParam("id") String id);


    @LinkResource

    @PUT

    @Path("book/{id}")

    public void updateBook(@PathParam("id") String id, Book book);


    @LinkResource(value = Book.class)

    @DELETE

    @Path("book/{id}")

    public void deleteBook(@PathParam("id") String id);

}

And this is the definition of the Book resource:

@Mapped(namespaceMap = @XmlNsMap(jsonName = "atom", namespace = "http://www.w3.org/2005/Atom"))

@XmlRootElement

@XmlAccessorType(XmlAccessType.NONE)

public class Book {

    @XmlAttribute

    private String author;


    @XmlID

    @XmlAttribute

    private String title;


    @XmlElementRef

    private RESTServiceDiscovery rest;

}

If you do a GET /order/foo you will then get this XML representation:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<book xmlns:atom="http://www.w3.org/2005/Atom" title="foo" author="bar">

 <atom:link href="http://localhost:8081/books" rel="list"/>

 <atom:link href="http://localhost:8081/books" rel="add"/>

 <atom:link href="http://localhost:8081/book/foo" rel="self"/>

 <atom:link href="http://localhost:8081/book/foo" rel="update"/>

 <atom:link href="http://localhost:8081/book/foo" rel="remove"/>

</book>

And in JSON format:

{
 "book":
 {
  "@title":"foo",
  "@author":"bar",
  "atom.link":
   [
    {"@href":"http://localhost:8081/books","@rel":"list"},
    {"@href":"http://localhost:8081/books","@rel":"add"},
    {"@href":"http://localhost:8081/book/foo","@rel":"self"},
    {"@href":"http://localhost:8081/book/foo","@rel":"update"},
    {"@href":"http://localhost:8081/book/foo","@rel":"remove"}
   ]
 }
}

Because the RESTServiceDiscovery is in fact a JAXB type which inherits from List you are free to annotate it as you want to customise the JAXB serialisation, or just rely on the default with @XmlElementRef.

This is all done by annotating the methods with the @LinkResource annotation. It supports the following optional parameters:

You can add several @LinkResource annotations on a single method by enclosing them in a @LinkResources annotation. This way you can add links to the same method on several resource types. For example the /order/foo/comments operation can belongs on the Order resource with the comments relation, and on the Comment resource with the list relation.

When RESTEasy adds links to your resources it needs to insert the right values in the URI template. This is done either automatically by guessing the list of values from the entity, or by specifying the values in the @LinkResource pathParameters parameter.

You can restrict which links are injected in the resource based on security restrictions for the client, so that if the current client doesn't have permission to delete a resource he will not be presented with the "delete" link relation.

Security restrictions can either be specified on the @LinkResource annotation, or using RESTEasy and EJB's security annotation @RolesAllowed on the JAX-RS method.

We've seen that both the URI template values and the security constraints of @LinkResource use UEL to evaluate expressions, and we provide a basic UEL context with access only to the entity we're injecting links in, and nothing more.

If you want to add more variables or functions in this context, you can by adding a @LinkELProvider annotation on the JAX-RS method, its class, or its package. This annotation's value should point to a class that implements the ELProvider interface, which wraps the default ELContext in order to add any missing functions.

For example, if you want to support the Seam annotation s:hasPermission(target, permission) in your security constraints, you can add a package-info.java file like this:

@LinkELProvider(SeamELProvider.class)

package org.jboss.resteasy.links.test;


import org.jboss.resteasy.links.*;

With the following provider implementation:

package org.jboss.resteasy.links.test;


import javax.el.ELContext;

import javax.el.ELResolver;

import javax.el.FunctionMapper;

import javax.el.VariableMapper;


import org.jboss.seam.el.SeamFunctionMapper;


import org.jboss.resteasy.links.ELProvider;


public class SeamELProvider implements ELProvider {


    public ELContext getContext(final ELContext ctx) {

        return new ELContext() {


            private SeamFunctionMapper functionMapper;


            @Override

            public ELResolver getELResolver() {

                return ctx.getELResolver();

            }


            @Override

            public FunctionMapper getFunctionMapper() {

                if (functionMapper == null)

                    functionMapper = new SeamFunctionMapper(ctx

                            .getFunctionMapper());

                return functionMapper;

            }


            @Override

            public VariableMapper getVariableMapper() {

                return ctx.getVariableMapper();

            }

        };

    }


}

And then use it as such:

@Path("/")

@Consumes({"application/xml", "application/json"})

@Produces({"application/xml", "application/json"})

public interface BookStore {


    @AddLinks

    @LinkResources({

        @LinkResource(value = Book.class, rel = "comments", constraint = "${s:hasPermission(this, 'add-comment')}"),

        @LinkResource(value = Comment.class, constraint = "${s:hasPermission(this, 'insert')}")

    })

    @GET

    @Path("book/{id}/comments")

    public Collection<Comment> getComments(@PathParam("id") String bookId);


    @AddLinks

    @LinkResource(constraint = "${s:hasPermission(this, 'read')}")

    @GET

    @Path("book/{id}/comment/{cid}")

    public Comment getComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);


    @LinkResource(constraint = "${s:hasPermission(this, 'insert')}")

    @POST

    @Path("book/{id}/comments")

    public void addComment(@PathParam("id") String bookId, Comment comment);


    @LinkResource(constraint = "${s:hasPermission(this, 'update')}")

    @PUT

    @Path("book/{id}/comment/{cid}")

    public void updateComment(@PathParam("id") String bookId, @PathParam("cid") String commentId, Comment comment);


    @LinkResource(Comment.class, constraint = "${s:hasPermission(this, 'delete')}")

    @DELETE

    @Path("book/{id}/comment/{cid}")

    public void deleteComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);


}

Sometimes it is useful to add resources which are just containers or layers on other resources. For example if you want to represent a collection of Comment with a start index and a certain number of entries, in order to implement paging. Such a collection is not really an entity in your model, but it should obtain the "add" and "list" link relations for the Comment entity.

This is possible using resource facades. A resource facade is a resource which implements the ResourceFacade<T> interface for the type T, and as such, should receive all links for that type.

Since in most cases the instance of the T type is not directly available in the resource facade, we need another way to extract its URI template values, and this is done by calling the resource facade's pathParameters() method to obtain a map of URI template values by name. This map will be used to fill in the URI template values for any link generated for T, if there are enough values in the map.

Here is an example of such a resource facade for a collection of Comments:

@XmlRootElement

@XmlAccessorType(XmlAccessType.NONE)

public class ScrollableCollection implements ResourceFacade<Comment> {


    private String bookId;

    @XmlAttribute

    private int start;

    @XmlAttribute

    private int totalRecords;

    @XmlElement

    private List<Comment> comments = new ArrayList<Comment>();

    @XmlElementRef

    private RESTServiceDiscovery rest;


    public Class<Comment> facadeFor() {

        return Comment.class;

    }


    public Map<String, ? extends Object> pathParameters() {

        HashMap<String, String> map = new HashMap<String, String>();

        map.put("id", bookId);

        return map;

    }

}

This will produce such an XML collection:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<collection xmlns:atom="http://www.w3.org/2005/Atom" totalRecords="2" start="0">

 <atom.link href="http://localhost:8081/book/foo/comments" rel="add"/>

 <atom.link href="http://localhost:8081/book/foo/comments" rel="list"/>

 <comment xmlid="0">

  <text>great book</text>

  <atom.link href="http://localhost:8081/book/foo/comment/0" rel="self"/>

  <atom.link href="http://localhost:8081/book/foo/comment/0" rel="update"/>

  <atom.link href="http://localhost:8081/book/foo/comment/0" rel="remove"/>

  <atom.link href="http://localhost:8081/book/foo/comments" rel="add"/>

  <atom.link href="http://localhost:8081/book/foo/comments" rel="list"/>

 </comment>

 <comment xmlid="1">

  <text>terrible book</text>

  <atom.link href="http://localhost:8081/book/foo/comment/1" rel="self"/>

  <atom.link href="http://localhost:8081/book/foo/comment/1" rel="update"/>

  <atom.link href="http://localhost:8081/book/foo/comment/1" rel="remove"/>

  <atom.link href="http://localhost:8081/book/foo/comments" rel="add"/>

  <atom.link href="http://localhost:8081/book/foo/comments" rel="list"/>

 </comment>

</collection>