Chapter 44. Introduction to RESTful Web Services

Representational State Transfer (REST) is an architectural style first described in a doctoral dissertation by a researcher named Roy Fielding. In RESTful systems, servers expose resources using a URI, and clients access these resources using the four HTTP verbs. As clients receive representations of a resource they are placed in a state. When they access a new resource, typically by following a link, they change, or transition, their state. In order to work, REST assumes that resources are capable of being represented using a pervasive standard grammar.

The World Wide Web is the most ubiquitous example of a system designed on REST principles. Web browsers act as clients accessing resources hosted on Web servers. The resources are represented using HTML or XML grammars that all Web browsers can consume. The browsers can also easily follow the links to new resources.

The advantages of RESTful systems is that they are highly scalable and highly flexible. Because the resources are accessed and manipulated using the four HTTP verbs, the resources are exposed using a URIs, and the resources are represented using standard grammars, clients are not as affected by changes to the servers. Also, RESTful systems can take full advantage of the scalability features of HTTP such as caching and proxies.

RESTful architectures adhere to the following basic principles:

Resources are central to REST. A resource is a source of information that can be addressed using a URI. In the early days of the Web, resources were largely static documents. In the modern Web, a resource can be any source of information. For example a Web service can be a resource if it can be accessed using a URI.

RESTful endpoints exchange representations of the resources they address. A representation is a document containing the data provided by the resource. For example, the method of a Web service that provides access to a customer record would be a resource, the copy of the customer record exchanged between the service and the consumer is a representation of the resource.

When designing RESTful Web services it is helpful to keep in mind the following:

Regardless of the framework you use to implement a RESTful Web service, there are a number of steps that should be followed:

Once you have defined the service, you can implement it using Apache CXF.

Apache CXF provides an implementation of the Java API for RESTFul Web Services(JAX-RS). JAX-RS provides a standardized way to map POJOs to resources using annotations.

When moving from the abstract service definition to a RESTful Web service implemented using JAX-RS, you need to do the following:

By default, Apache CXF uses Java Architecture for XML Binding (JAXB) objects to map the resources and their representations to Java objects. Provides clean, well defined mappings between Java objects and XML elements.

The Apache CXF JAX-RS implementation also supports exchanging data using JavaScript Object Notation (JSON). JSON is a popular data format used by Ajax developers. The marshaling of data between JSON and JAXB is handled by the Apache CXF runtime.