Using content negotiation to serve multiple content types in JAX-RS applications

One of the advantages of RESTful applications is the ability to return different representations of resources. With Representational State Transfer (REST), clients and servers can exchange resources of the same media type or use differing media types. Content negotiation enables clients and servers to agree on the content format that is used to exchange data.

About this task

Resources are represented by many different formats. XML, JavaScript Object Notation (JSON), Atom, plain text, PNG, JPEG, GIF, and custom or proprietary formats are used to represent resources. Representational State Transfer (REST) provides the flexibility to represent a single resource in multiple formats.

Depending on the requirements of your application, resources can return representations in a single format or in different formats, depending on the request. For example, resources accessed using JavaScript clients might prefer JSON representations because JSON is easy to consume. However, other clients prefer XML.

Use content negotiation if you want to serve multiple formats to clients. Content negotiation is the method in which the client and server agree on the response content type to use. There are three types of content negotiation that affect the response. You can use content negotiation that is based on the URL, based on a request parameter, or based on HTTP headers.

Procedure

  1. Configure the development environment. Set up your development environment by adding the JAX-RS libraries on the classpath.
  2. Define the resources in JAX-RS web applications.

    Resources are the basic building block of a RESTful service. Resources can contain static or dynamically updated data. Examples of resources from an online book store application include a book, an order from a store, and a collection of users. By identifying the resources in your application, you can make the service more useful and easier to develop. The following topics describe how to define resources:

  3. Configure the JAX-RS application.

    You can configure JAX-RS applications in multiple ways depending on your needs. To take advantage of the Java Platform, Enterprise Edition (Java EE) 6 functionality, you can use the annotation scanning capabilities. By using annotation scanning, you can omit a JAX-RS javax.ws.rs.core.Application subclass or have a minimally defined javax.ws.rs.core.Application subclass. Alternatively, you can specify the IBM® JAX-RS servlet or filter if you want to use the functionality available in the IBM JAX-RS servlet and filter.

    Using one of the JAX-RS Version 1.1 configuration methods, you can omit a javax.ws.rs.core.Application subclass in your application or have a javax.ws.rs.core.Application subclass that returns an empty set of classes to inform the JAX-RS runtime environment to find and use all the JAX-RS classes in the application. You might want to use this method when you do not want to have to manually add every relevant JAX-RS class to a javax.ws.rs.core.Application subclass as you develop the application.

    By specifying the specific IBM JAX-RS servlet and filter, you can take advantage of and ensure specific IBM JAX-RS behavior. For example, using the IBM JAX-RS filter can be helpful in developing a web application with a mix of JAX-RS resources and JavaServer Pages (JSP) files with the same URL patterns.

    Even though there is a JAX-RS V1.1 configuration method that supports the use of an optional web.xml file, if you want to specify security constraints or roles, or you want to take advantage of other features enabled using a web.xml file, you must specify the information in a web.xml file.

    Choose one of the following three methods to configure your JAX-RS application:

    • Configure JAX-RS applications using JAX-RS 1.1 methods

      Use this method if you want to use the annotation scanning capabilities or to use the JAX-RS 1.1 configuration methods. You can use the annotation scanning capabilities to promote application portability, to minimize the amount of configuration code, or to dynamically modify the application without changes to the application code.

    • Configure the web.xml file for JAX-RS servlets

      Use this method if you want to specify features that are enabled using servlet initialization parameters to change the behavior and ensure that you get the IBM JAX-RS servlet. When using servlets, you can define a servlet path in the web.xml file that is appended to the base URL.

    • Configure the web.xml file for JAX-RS filters

      Use this method if you want to use the filter when you have JSPs, other servlets and filters, and JAX-RS resources with a mix of URL patterns. You can configure the web.xml file to define filters that indicate the possible URLs on which the filter can be invoked.

  4. Implement content negotiation to serve multiple content types.
    Use content negotiation to determine the best resource representation for the server to return to the client. You can implement content negotiation based on URL patterns, request parameters, or HTTP headers.
  5. Assemble JAX-RS web applications.

    After you develop the Java class files for your JAX-RS web application and edit the web.xml file to enable the JAX-RS servlet, you are ready to assemble the application. Assemble the web application into a web application archive (WAR) package. You can assemble the WAR package into an enterprise archive (EAR) package, if required.

  6. Deploy JAX-RS web applications.

    Deploy your web archive (WAR) package or the enterprise archive (EAR) package onto the application server.

Results

You have implemented content negotiation to determine the formats for resources to represent data.