Chapter 52. Getting and Using Context Information

When a class field or method parameter that is a UriInfo object is decorated with the @Context annotation, the URI context for the current request is injected into the UriInfo object.

Injecting the URI context into a class field shows a class with a field populated by injecting the URI context.

import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.Path;
...
@Path("/monstersforhire/")
public class MonsterService
{
  @Context
  UriInfo requestURI;
  ...
}

One of the main advantages of using the URI context is that it provides access to the base URI of the service and the path segment of the URI for the selected resource. This information can be useful for a number of purposes such as making processing decisions based on the URI or calculating URIs to return as part of the response. For example if the base URI of the request contains a .com extension the service may decide to use US dollars and if the base URI contains a .co.uk extension is may decide to us British Pounds.

The UriInfo interface provides methods for accessing the parts of the URI:

The base URI is the root URI on which the service is published. It does not contain any portion of the URI specified in any of the service’s @Path annotations. For example if a service implementing the resource defined in Example 47.5, “Disabling URI decoding” were published to http://fusesource.org and a request was made on http://fusesource.org/montersforhire/nightstalker?12 the base URI would be http://fusesource.org.

Table 52.2, “Methods for accessing a resource’s base URI” describes the methods that return the base URI.

The path portion of the request URI is the portion of the URI that was used to select the current resource. It does not include the base URI, but does include any URI template variable and matrix parameters included in the URI.

The value of the path depends on the resource selected. For example, the paths for the resources defined in Getting a resource’s path would be:

@Path("/monstersforhire/")
public class MonsterService
{
  @Context
  UriInfo rootUri;

  ...

  @GET
  public List<Monster> getMonsters(@Context UriInfo getUri)
  {
    String rootPath = rootUri.getPath();
    ...
  }

  @GET
  @Path("/{type}")
  public Monster getMonster(@PathParam("type") String type,
                            @Context UriInfo getUri)
  {
    String getterPath = getUri.getPath();
    ...
  }

  @PUT
  @Path("/{id}")
  public void addMonster(@Encoded @PathParam("type") String type,
                         @Context UriInfo putUri)
  {
    String putterPath = putUri.getPath();
    ...
  }
  ...
}

Table 52.3, “Methods for accessing a resource’s path” describes the methods that return the resource path.

Table 52.4, “Methods for accessing the full request URI” describes the methods that return the full request URI. You have the option of returning the request URI or the absolute path of the resource. The difference is that the request URI includes the any query parameters appended to the URI and the absolute path does not include the query parameters.

For a request made using the URI http://fusesource.org/montersforhire/nightstalker?12, the getRequestUri() methods would return http://fusesource.org/montersforhire/nightstalker?12. The getAbsolutePath() method would return http://fusesource.org/montersforhire/nightstalker.

As described in the section called “Setting the path”, resource paths can contain variable segments that are bound to values dynamically. Often these variable path segments are used as parameters to a resource method as described in the section called “Getting data from the URI’s path”. You can, however, also access them through the URI context.

The UriInfo interface provides two methods, shown in Example 52.1, “Methods for returning path parameters from the URI context”, that return a list of the path parameters.

The getPathParameters() method that does not take any parameters automatically decodes the path parameters. If you want to disable URI decoding use getPathParameters(false).

The values are stored in the map using their template identifiers as keys. For example if the URI template for the resource is /{color}/box/{note} the returned map will have two entries with the keys color and note.

Example 52.2, “Extracting path parameters from the URI context” shows code for retrieving the path parameters using the URI context.

import javax.ws.rs.Path;
import javax.ws.rs.Get;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.core.MultivaluedMap;

@Path("/monstersforhire/")
public class MonsterService

  @GET
  @Path("/{type}/{size}")
  public Monster getMonster(@Context UriInfo uri)
  {
    MultivaluedMap paramMap = uri.getPathParameters();
    String type = paramMap.getFirst("type");
    String size = paramMap.getFirst("size");
  }
}