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Use JAX-RS context objects to obtain more information about requests

Java API for RESTful Web Services (JAX-RS) provides different types of context to resource classes and providers. Use context objects to access request information such as discovering the HTTP headers sent as part of the request. Context objects also provide convenience methods for evaluating a request and building an appropriate response.

Representational State Transfer (REST) application resources might have a need to inspect some application context data upon invocation. For example, a resource method that processes an HTTP GET query might want to inspect the HTTP headers of the request for the Accept-Language HTTP header so that the method can output a response in the language specified by the request.

JAX-RS defines a simple way to retrieve this data within the scope of the application resource. By declaring the @Context annotation with the appropriate object as a parameter to a resource method or as a field within the resource class, the data that we want is injected into the resource. The JAX-RS implementation populates the parameter or field with the contextual data, and the resource method has access to all the contextual data it needs.

Use the following interface types injectable by the JAX-RS runtime environment:

Interface types Description
javax.ws.rs.core.UriInfo The UriInfo interface provides the complete URI specified by the request. This interface can also inspect which resource(s) matched the request URI.
javax.ws.rs.core.Request The Request interface provides information about the request, such as POST or GET. This interface can also evaluate preconditions based on request entity tags.
javax.ws.rs.core.HttpHeaders The HttpHeaders interface provides read-only access to all HTTP headers.
javax.ws.rs.core.SecurityContext The SecurityContext interface provides read-only information about security, such as authentication scheme or security principal.
javax.ws.rs.ext.Providers The Providers interface enables retrieval of ContextResolver, ExceptionMapper, MessageBodyWriter, or MessageBodyReader implementations.

In addition to the JAX-RS interface types, we can inject web container types, such as javax.servlet.http.HttpServletRequest, using the @Context annotation as described in the JAX-RS specification.


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. Add context fields and parameters to obtain information about requests. We can obtain information about requests using HttpHeaders objects, UriInfo objects, Request objects, or SecurityContext objects.

  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 context objects to learn more about requests to the JAX-RS web application.

  • Obtain HTTP headers using HttpHeaders objects
  • Obtain information about URIs using UriInfo objects
  • Evaluating request preconditions using Request objects
  • Determining security information using SecurityContext objects
  • Web services specifications and APIs