JAX-RS Services Description

CXF JAX-RS supports (Web Application Description Language|http://www.w3.org/Submission/wadl] (WADL).
Users can use WADL documents to generate the initial code and have WADL auto-generated on demand.

WADL overview

WADL is a resource-centric description language which has been designed to facilitate the modeling, description and testing of
RESTful Web applications. Please check the official page for more information, this section provides a brief overview of main WADL constructs.

Basic example

A top level WADL document element is called "application". Usually it may contain a "grammars" section and "resources" element with one or more top-level "resource" elements, with each one representing a specific root resource, for example:

This document describes an application that has "http://localhost:8080/" base URI. It can handle GET requests such as
"http://localhost:8080/bookstore/1", "http://localhost:8080/bookstore/123", etc. Additionally it can handle similar GET requests at
"http://localhost:8080/books/bookstore/1", "http://localhost:8080/books/bookstore/123", etc, note an extra "books" path segment.

"application/xml" media type is supported and response representation elements link to "{http://superbooks}thebook" element declared in a schema inlined in the grammars section.

Note that "resources" element has two child "resource" elements, one with "/bookstore/{id}" path, another one with "/books" path.

These 2 resources can be represented as JAX-RS root resources. For example, these resources can be mapped to concrete Java classes such as BookStoreRootResource with @Path("/bookstore/{id}") and BooksResource with @Path("/books"). BookStoreRootResource root resource will have a single @GET resource method with no @Path, presumably returning Book (JAXB) bean. The second BooksResource root resource will have a single subresource locator with @Path("/bookstore/{id}") which will return a subresource with a single @GET resource method.

This is just one possible interpretation of how the above WADL description can be mapped to JAX-RS resources and methods.

Also note that the resource with the "/books" path has another child resource with the "/bookstore/{id}" path, but it could've had a "/books/bookstore/{id}" path instead and no child resource.

WADL with references

Basic WADL example in the previous section shows a "grammars" section with the inlined schema, as well as a "resource" description with the "/bookstore/{id}" path listed twice, as an immediate child of the "resources" and as a child of the "resource" element with the "/books" path.

Note that inlined schemas can be included instead by referencing external schemas. Likewise, most of WADL element declarations such as "resource", "method", "representation", etc can be shared by using the same document or external references. Here is how the basic example can be simplified with the help of references:

Note that a book.xsd schema resource located in the 'schemas' path relative to the location of this WADL document is referenced using wadl:include element. Abstract resource type "bookResource" is declared as an immediate child of wadl:application and is linked to concrete resource elements using a "#bookResource" reference.

Sharing declarations between multiple WADLs

WADL references allow for having WADL documents with abstract declarations only and concrete WADLs referencing them, thus making it possible to reuse resource declarations in different web application descriptions.

For example, the following baseApplication.wadl documents describes an abstract "bookResource" resource:

and this WADL document links to the abstract resource by using an external WADL reference with a "baseResource" fragment.

New: Starting from CXF 2.5.0 and 2.4.4 all WADL elements may link to top-level local declarations, see this example.

WADL-first Development

CXF 2.4.1 introduces a wadl2java code generator and cxf-wadl2java-plugin Maven plugin which can be used to generate server and client JAX-RS code and speed up the transition between modeling and implementation stages.

Note If you are looking for a wadl2java code generator from a Java.net project started by Marc Hadley then please follow this link.

Code generator expects WADL resource and method elements to have "id" attributes set which can provide hints on how to name generated classes and methods. For example:

Note that resource id is "org.apache.cxf.jaxrs.systest.BookStore". Alternatively, expanded QName can be used as "id":
"{http://systest.jaxrs.cxf.apache.org}BookStore".

Simple WADL documents containing a single resource only do not have to have "id" attributes set. In such cases a wadltojava "resource" and "-p" options can be used to specify a full root resource class name corresponding to a single WADL resource element, and if neither of these options is set then this single WADL resource will get an "application.Resource" root resource class generated.

Note that the code generation from the WADL documents containing multiple root resources with no "id" attributes is supported starting from CXF 2.5.0.

If WADL "method" element has no "id" attribute set then a combination of the element's "name" attribute and the current path will be used to name generated class methods, example: "getbookid", where the method name is "GET", and the path is "/book/{id}".

Classes generated from schemas will have a package name derived from a given schema target namespace by default. wadltojava tool lets customize it as well.

wadl2java command line tool

Running wadltojava from the command line will produce:

wadl2java -p <package-name> -sp <[schema-namespace =]package-name>* 
          -tMap <schema-type = java-type>* -repMap <media-type = java-type>*
          -resource <resource-name> -b <binding-file-name>* -catalog <catalog-file-name> 
          -d <output-directory> -compile -classdir <compile-classes-directory> -interface -impl 
          -noTypes -inheritResourceParams -generateEnums -supportMultipleXmlReps -async<methodNames>*
          -xjc<xjc-arguments>* 
          -h -v -verbose -quiet <wadl>

Note 'tMap', 'repMap', 'noTypes' and 'inheritResourceParams' options are supported starting from CXF 2.6.3, 'noVoidForEmptyResponses' - from 2.6.4, '-async' - from 2.7.1, '-xjc' - from 2.7.4

The options are reviewed in the following table.

Option

Interpretation

-?,-h,-help

Displays the online help for this utility and exits.

-p PackageName

Specifies the package name of root resource classes

-sp [ schema-namespace= ] PackageName

Specifies one or more package names corresponding to individual schema namespaces

-resource RootResourceName

Specifies a full name of root resource class if WADL contains a single resource

-interface

Default option unless -impl option is used - Java interfaces with JAX-RS annotations are generated

-impl

Generates starting implementation code. Can also be used with -interface option

-noTypes

Requests that no schema generation is needed. Can also be used with -tMap option

-tMap schema-type=java-type

Provides mapping between schema elements and java types

-repMap media-type=java-type

Provides mapping between media types and java types

-b binding-name

Specifies JAXB binding files. Use multiple -b flags to specify multiple entries.

-catalog catalog-file-name

Specifies catalog file to map referenced wadl/schemas

-d output-directory

Specifies the directory into which the generated code files are written.

-compile

Compiles generated Java files.

-classdir compile-class-dir

Specifies the directory into which the compiled class files are written.

-noVoidForEmptyResponses

Generate JAX-RS Response instead of 'void' for methods with no response representations.

-inheritResourceParams

Get current resource-level path or matrix parameters added to generated methods for all descendant resources.

-generateEnums

Generates Java enums for parameters with options.

-supportMultipleXmlReps

Generates separate method for every XML representation in a single WADL request element.

-async methodNames

Adds JAX-RS 2.0 AsyncResponse parameter to generated methods, methodNames is a comma-separated list of WADL method name or id attributes

-xjc<xjc args>

Specifies a comma separated list of arguments that are passed directly to the XJC processor, example -xjc-Xts.

wadlurl

The path and name of the WADL file to use in generating the code.

You must specify the absolute or relative path to the WADL document as the last argument.
OASIS catalog files can be used to help the tool resolve referenced WADL and schema documents.

Note 'tMap' option can be used to map between schema element references and java types and can be used to customize the default schema to Java type mapping. For example, in order to override a default parameter 'xs:date' to java.util.Date mapping one can do '-tMap {http://www.w3.org/2001/XMLSchema}date=javax.xml.datatype.XMLGregorianCalendar' - this can affect the "<wadl:param type='xs:date'>" declarations.
Alternatively, in combination with a '-noTypes' switch, this option can be used to request that a custom Java type reference should be generated. For example, if one prefers to use 'javax.xml.transform.Source' for handling a given XML payload, one can do
'-tMap {http://book}Book=javax.xml.transform.Source', this will affect "<wadl:representation element='ns:Book'>" declarations where 'ns' prefix is bound to the 'http://book' namespace. Similarly, a schema reference to Atom Feed element can be mapped to say Abdera Feed class.

The 'repMap' option is similar and provides a mapping between the representations of a given media type and Java type. For example, if one has to process different XML representations in one method, a mapping like '-repMap application/xml=javax.xml.transform.Source' will work, affecting declarations like "<wadl:representation mediaTpe='application/xml'". Similarly CXF org.apache.cxf.jaxrs.ext.multipart.MultipartBody class can be linked to 'multipart/form-data' representations, etc.

JAXB customizations

At the moment it is possible to apply external JAXB customizations to WADL grammars however it is not possible yet to restrict a given customization to a specific WADL document or explicitly inlined schema. Linking binding to external schemas works, for example, the following bindings file can be used:

wadl2java Maven plugin

If you need the code generated during Maven build then the following plugin can be used:

Add this plugin to the build section of your project's pom and specify a 'wadl2java' goal, for example:

Note that the minimum and maximum memory limits may need to be increased when using the plugin to process large WADL documents, for example, add "-Xms512M -Xmx1024M" to the list of Maven options.

CXF will generate artifacts in the <sourceRoot> directory. Configuration arguments which are included inside the <wadlOption> element are used to pass arguments to the tooling and correspond to the options outlined in the wadltojava section, they can be specified explicitly, as above, or using an "extraargs" wrapper, for example:

Integration

Two options are available to developers who wish to integrate CXF JAX-RS WADLToJava code generator.
First option is to pass the collected options directly to a wadltojava process.

Another approach is to use org.apache.cxf.tools.wadlto.jaxrs.JAXRSContainer class shipped with the cxf-tools-wadlto-jaxrs module:

Please see CXF source for more details and org.apache.cxf.tools.wadlto.jaxrs.JAXRSContainerTest in particular.

External WADL documents and JAXRS endpoints.

External WADL documents can be linked to from jaxrs:server endpoints using newly introduced "docLocation" attribute, for example:

If external WADL documents include external schemas and jaxrs endpoints need to have the schema validation enabled, then those schemas can be referenced in the jaxrs:schemaLocations section as well.

WADL Auto Generation

Note that in CXF 3.0.0 WADL Generator code has been moved to

CXF JAX-RS supports the auto-generation of WADL for JAX-RS endpoints.
Note that JAX-RS subresources are late-resolved by default, so using annotated interfaces for subresources and a staticSubresourceResolution=true property will let the whole resource tree/graph be described in a generated instance. Schemas will be generated for JAXB-annotated types. See below for the information on how to get auto-generated WADL instances reference existing schemas.

CXF 2.4.0: org.apache.cxf.jaxrs.ext.Description and org.apache.cxf.jaxrs.ext.xml.XMLName have been moved to org.apache.cxf.jaxrs.model.wadl package given that their purpose is to improve the WADL generation. Also, org.apache.cxf.jaxrs.model.wadl.WadlElement has been renamed to 'ElementClass'.

Documenting resource classes and methods in generated WADL

WADL documents can include doc fragments.

Users may want to use Description annotations which can be attached to resource classes and methods.

Note that starting from CXF 2.4.0, Description annotations can be applied to input parameters. Additionally, a method-level Descriptions annotation can have a collection of categorized Description annotations, with each Description targeting a specific WADL element by setting its 'target' property to one of the DocTarget values. For example, one can use a Descriptions annotation to document the response representation of a particular resource method, as well as add documentation fragments to WADL wadl:method/wadl:request and wadl:method/wadl:response elements:

Every unique @Path value adds a new 'resource' element to the generated WADL, thus the last Description annotation in the @Descriptions array ensures the doc extension is also added to the 'resource' element. Note that multiple resource methods having different HTTP methods but sharing the same @Path value will have the same parent 'resource' element representing this shared path fragment, in this case a Description with the DocTarget.RESOURCE target will be ignored unless it is added to the first resource method with this shared @Path:

Customizing WADL Generation

One can register a custom WadlGenerator as a jaxrs:provider. The custom generator can extend the default
org.apache.cxf.jaxrs.model.wadl.WadlGenerator or register a default one with one of the following properties set.

  • wadlNamespace: default is "http://wadl.dev.java.net/2009/02", the earlier one is "http://research.sun.com/wadl/2006/10".
  • singleResourceMultipleMethods: default is 'true', for example, if a resource class has multiple methods supported at the same path such as "/" (GET, POST, etc) then WADL will list them all as the child nodes of a single resource element.
  • useSingleSlashResource: default is false, for example, if you have a root resource class with a path "root" and a resource method with a path "" or "/" then a WADL resource representing the root will not have a child resource representing this resource method (it would do if a resource method had a more specific path such as "bar").

Starting from CXF 2.4.1 and 2.3.5 the following properties are also supported:

  • applicationTitle: can be used to create an application title.
  • namespacePrefix: defaut is 'prefix', it can be set to other value such as 'ns'.
  • ignoreForwardSlash: can be used to enforce that resource path values do not start from '/'
  • addResourceAndMethodIds: WadlGenerator will add "id" attributes to wadl:resource and wadl:method elements

An ElementClass annotation can help with representing JAX-RS Response elements in the generated WADL.

Representing explicit JAXB collections

Starting from CXF 2.5.5 and 2.6.2 it is possible to get explicit collections represented in generated WADL grammar sections and have WADL representations linking to these schema elements. Note it is only possible for JAXB collections, for example:

Given the above example, WADLGenerator will attempt to add a 'books' element to the generated schema with the targetNamespace set to "http://books". This 'books' element will have a sequence of elements linking to a type representing the "Book" class.

Representing external schemas and non JAXB types

By default, the WADL grammar section will be properly generated if resource methods accept or return JAXB types.

Even when you do use JAXB, the JAXB types may have been generated from the external schema so having WadlGenerator attempting to recreate the original schema may not work well. To have a generated WADL referencing the original schema(s) please set a 'schemaLocations' list property (programmatically or from Spring) :

In this case the grammar section will have the 'book.xsd' schema inlined. If this schema imports other schemas then the imports with relative URIs will be replaced by the absolute URIs based on the current endpoint's base address. For example, if the endpoint address is "http://somehost/bar" and the 'book.xsd' imports "foo/book1.xsd" then the published WADL will contain an "http://somehost/bar/foo/book1.xsd". At the moment a custom RequestHandler filter will have to be registered to serve resources such as "http://somehost/bar/foo/book1.xsd" which can 'calculate' which resource is required get the absolute request URI and comparing it with the base URI, possibly with the help of the injected JAXRS UriInfo context. Alternatively, resources such as book1.xsd may be served by CXFServlet itself (see the Redirection with CXFServlet)

TODO : add ignoreImports flag so that users can list root and imported schemas in "schemaLocations" and have them all inlined.

Note that the root schema such as "book.xsd" is inlined - you can have it referenced only by setting an 'externalLinks' list property. This will work very well when the "book.xsd" is indeed available at the external URI, but this property can also be used to avoid the local schemas being inlined. Moreover, the use of JAXB will not be required. The result will look like this:

Note that "schemaLocations" and "externalLinks" properties differ in that the schemas referenced by the former one are inlined.

You can also customize the way schema elements are referenced. When WadlGenerator creates WADL representation elements (representing resource method input or output types) it will be able to link to schema elements provided a given type is actually a JAXB one, so the result may look like this :

If no JAXB is used then you can attach an XMLName annotation to method input or output types. Alternatively, you can register an instance of ElementQNameResolver with the WadlGenerator which will be used for creating wadl:representation/@element values.

Changing the base address

Starting from CXF 2.6.2 it is possible to affect the base address specified in the auto-generated WADL (in wadl:resources/@base attribute).
WADLGenerator can be indirectly configured by setting a jaxrs:server/@publishedEndpointUrl attribute, similarly to the way CXF WSDL generator can be configured by setting a jaxws:endpoint/@publishedEndpointUrl attribute.

Service listings and WADL queries

Links to WADL instances for RESTful endpoints are available from {base endpointaddress}/services, in addition to SOAP endpoints if any.

For example, given

and visiting

> http://localhost:8080/store/books
> http://localhost:8080/store/books/services

will let you see all the WADL links.

Note that you can override the location at which listings are provided (in case you would like '/services' be available to your resources) using 'service-list-path' CXFServlet parameter, example:

> 'service-list-path' = '/listings'

Going to the service listings page is not the only way to see WADL instances, one can also get it using a ?_wadl query.

> http://localhost:8080/store/books/orders?_wadl

will give you the description of all the root resource classes registered
with a given jaxrs:server endpoint.

For example, if the following 2 root resource classes has been registered with this endpoint:

then WADL will contain the description of both FictionBookOrders and SportBookOrders resources.

> http://localhost:8080/store/books/orders/fiction?_wadl
> http://localhost:8080/store/books/orders/sport?_wadl

will give you all the info for FictionBookOrders and SportBookOrders respectively.

Note that WadlGenerator will return an existing WADL document instead of auto-generating a new one if jaxrs:server/@docLocation attribute has been set.

By default, starting from CXF 2.5.1 and 2.4.5, the media type for a ?_wadl response is set to application/xml which is to do with the fact that Firefox does not really like 'application/vnd.sun.wadl+xml' unless some wadl plugin is registered. If HTTP Content-Type is set to 'application/xml' then Firefox will show it with no problems.

You can easily customize what Content-Type is set by either using a WadlGenerator 'defaultMediaType' property or using the extension mappings and adding a .wadl at the end of request URI instead of using a _wadl query: "http://localhost:8080/store/books/orders/fiction.wadl", where extensions will map a 'wadl' to 'application/vnd.sun.wadl+xml' or indeed to 'application/xml'.

WADL in JSON format

Use a "?_wadl&_type=json" or something like "fiction.wadl", where extensions will map a 'wadl' to 'application/json' in order to get a WADL JSON representations, please see this blog entry for more information.

Hiding links to JAXRS endpoints from the services page

In some cases you may not want the users to see the links to some JAXRS endpoints. For example, if you have an AtomPullServer endpoint collecting the log entries for a number of application endpoints, you may not want to see AtomPullServer endpoint being listed among the endpoints representing the actual application and which users are actually interested in. If so then adding an "org.apache.cxf.endpoint.private" boolean property with a value "true" will do the trick; note the same property can be used by jaxws endpoints.