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There are two mechanisms available in RESTEasy to link a resource to another, and to link resources to operations: the Link HTTP header, and Atom links inside the resource representations.
RESTEasy has both client and server side support for the Link header specification. See the javadocs for org.jboss.resteasy.spi.LinkHeader, org.jboss.resteasy.spi.Link, and org.jboss.resteasy.client.ClientResponse.
The main advantage of Link headers over Atom links in the resource is that those links are available without parsing the entity body.
RESTEasy allows you to inject Atom links directly inside the entity objects you are sending to the client, via auto-discovery.
This is only available when using the Jackson2 or JAXB providers (for JSON and XML).
The main advantage over Link headers is that you can have any number of Atom links directly over the concerned resources, for any number of resources in the response. For example, you can have Atom links for the root response entity, and also for each of its children entities.
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:
Group | Artifact | Version |
---|---|---|
org.jboss.resteasy | resteasy-links | 4.7.3.Final |
You need three things in order to tell RESTEasy to inject Atom links in your entities:
Annotate the JAX-RS method with @AddLinks
to indicate that you want
Atom links injected in your response entity.
Add RESTServiceDiscovery
fields to the resource classes where you
want Atom links injected.
Annotate the JAX-RS methods you want Atom links for with @LinkResource
,
so that RESTEasy knows which links to create for which resources.
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:
Parameter | Type | Function | Default |
---|---|---|---|
value | Class |
Declares an Atom link for the given type of resources. | Defaults to the entity body type (non-annotated parameter), or the method's return type.
This default does not work with Response or Collection
types, they need to be explicitly specified. |
rel | String |
The Atom link relation |
|
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.
URI template values are extracted from the entity from fields or Java Bean properties
annotated with @ResourceID
, JAXB's @XmlID
or
JPA's @Id
. If there are more than one URI template
value to find in a given entity, you can annotate your entity with @ResourceIDs
to list the names of fields or properties that make up this entity's Id. If there are other
URI template values required from a parent entity, we try to find that parent in a field or
Java Bean property
annotated with @ParentResource
. The list of URI template
values extracted up every @ParentResource
is then reversed and used
as the list of values for the URI template.
For example, let's consider the previous Book example, and a list of comments:
@XmlRootElement
@XmlAccessorType(XmlAccessType.NONE)
public class Comment {
@ParentResource
private Book book;
@XmlElement
private String author;
@XmlID
@XmlAttribute
private String id;
@XmlElementRef
private RESTServiceDiscovery rest;
}
Given the previous book store service augmented with comments:
@Path("/")
@Consumes({"application/xml", "application/json"})
@Produces({"application/xml", "application/json"})
public interface BookStore {
@AddLinks
@LinkResources({
@LinkResource(value = Book.class, rel = "comments"),
@LinkResource(value = Comment.class)
})
@GET
@Path("book/{id}/comments")
public Collection<Comment> getComments(@PathParam("id") String bookId);
@AddLinks
@LinkResource
@GET
@Path("book/{id}/comment/{cid}")
public Comment getComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);
@LinkResource
@POST
@Path("book/{id}/comments")
public void addComment(@PathParam("id") String bookId, Comment comment);
@LinkResource
@PUT
@Path("book/{id}/comment/{cid}")
public void updateComment(@PathParam("id") String bookId, @PathParam("cid") String commentId, Comment comment);
@LinkResource(Comment.class)
@DELETE
@Path("book/{id}/comment/{cid}")
public void deleteComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);
}
Whenever we need to make links for a Book
entity, we look up the ID
in the Book
's @XmlID
property. Whenever we make links
for Comment
entities, we have a list of values taken from the Comment
's
@XmlID
and its @ParentResource
: the Book
and
its @XmlID
.
For a Comment
with id
"1"
on a Book
with title
"foo"
we will therefore get a list of URI
template values of {"foo", "1"}
, to be replaced in the URI template, thus
obtaining either "/book/foo/comments"
or "/book/foo/comment/1"
.
If you do not want to annotate your entities with resource ID annotations (@ResourceID
,
@ResourceIDs
, @XmlID
or @Id
) and
@ParentResource
, you can also specify the URI template values inside the
@LinkResource
annotation, using Unified Expression Language expressions:
Parameter | Type | Function | Default |
---|---|---|---|
pathParameters | String[] |
Declares a list of UEL expressions to obtain the URI template values. | Defaults to using @ResourceID , @ResourceIDs ,
@XmlID or @Id and @ParentResource
annotations to extract the values from the model. |
The UEL expressions are evaluated in the context of the entity, which means that any unqualified
variable will be taken as a property for the entity itself, with the special variable
this
bound to the entity we're generating links for.
The previous example of Comment
service could be declared as such:
@Path("/")
@Consumes({"application/xml", "application/json"})
@Produces({"application/xml", "application/json"})
public interface BookStore {
@AddLinks
@LinkResources({
@LinkResource(value = Book.class, rel = "comments", pathParameters = "${title}"),
@LinkResource(value = Comment.class, pathParameters = {"${book.title}", "${id}"})
})
@GET
@Path("book/{id}/comments")
public Collection<Comment> getComments(@PathParam("id") String bookId);
@AddLinks
@LinkResource(pathParameters = {"${book.title}", "${id}"})
@GET
@Path("book/{id}/comment/{cid}")
public Comment getComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);
@LinkResource(pathParameters = {"${book.title}", "${id}"})
@POST
@Path("book/{id}/comments")
public void addComment(@PathParam("id") String bookId, Comment comment);
@LinkResource(pathParameters = {"${book.title}", "${id}"})
@PUT
@Path("book/{id}/comment/{cid}")
public void updateComment(@PathParam("id") String bookId, @PathParam("cid") String commentId, Comment comment);
@LinkResource(Comment.class, pathParameters = {"${book.title}", "${id}"})
@DELETE
@Path("book/{id}/comment/{cid}")
public void deleteComment(@PathParam("id") String bookId, @PathParam("cid") String commentId);
}
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.
Parameter | Type | Function | Default |
---|---|---|---|
constraint | String |
A UEL expression which must evaluate to true to inject this method's link in the response entity. | Defaults to using @RolesAllowed from 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 Comment
s:
@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>