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Use 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 used to exchange data.

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 the 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 we 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. Use content negotiation based on the URL, based on a request parameter, or based on HTTP headers.


Tasks

  1. Configure the development environment.

    1. Before starting developing JAX-RS applications, we must set up the development environment by adding the JAX-RS libraries on the classpath.

  2. Define the resources in JAX-RS web applications.

    1. 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 the application, we can make the service more useful and easier to develop.

  3. Configure the JAX-RS application.

    We can configure JAX-RS applications in multiple . To take advantage of the Java EE 6 functionality, we can use the annotation scanning capabilities. By using annotation scanning, we can omit a JAX-RS javax.ws.rs.core.Application subclass or have a minimally defined javax.ws.rs.core.Application subclass. Alternatively, we can specify the IBM JAX-RS servlet or filter to use the functionality available in the IBM JAX-RS servlet and filter.

    Using one of the JAX-RS Version 1.1 configuration methods, we can omit a javax.ws.rs.core.Application subclass in the 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. We might want to use this method when we 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, we 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 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, to specify security constraints or roles, or we want to take advantage of other features enabled using a web.xml file, specify the information in a web.xml file.

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

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

      Use this method to use the annotation scanning capabilities or to use the JAX-RS 1.1 configuration methods. 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 to specify features enabled using servlet initialization parameters to change the behavior and ensure that we get the IBM JAX-RS servlet. When using servlets, we 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 to use the filter when we have JSPs, other servlets and filters, and JAX-RS resources with a mix of URL patterns. We 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. We can implement content negotiation based on URL patterns, request parameters, or HTTP headers.

  5. Assemble JAX-RS web applications.

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

  6. Deploy JAX-RS web applications.

    1. After assembling the JAX-RS web application, we need to deploy your Web archive (WAR) package or the EAR package onto the application server.

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

  • Implement content negotiation based on URL patterns
  • Implement content negotiation based on HTTP headers
  • Implement content negotiation based on request parameters
  • Web services specifications and APIs