Annotations for Field and Bean Properties of Resource Classes

JAX-RS annotations for resource classes let you extract specific parts or values from a Uniform Resource Identifier (URI) or request header.

JAX-RS provides the annotations listed in Table 32-1.

Table 32-1 Advanced JAX-RS Annotations

Annotation

Description

@Context

Injects information into a class field, bean property, or method parameter

@CookieParam

Extracts information from cookies declared in the cookie request header

@FormParam

Extracts information from a request representation whose content type is application/x-www-form-urlencoded

@HeaderParam

Extracts the value of a header

@MatrixParam

Extracts the value of a URI matrix parameter

@PathParam

Extracts the value of a URI template parameter

@QueryParam

Extracts the value of a URI query parameter

Extracting Path Parameters

URI path templates are URIs with variables embedded within the URI syntax. The @PathParam annotation lets you use variable URI path fragments when you call a method.

The following code snippet shows how to extract the last name of an employee when the employee’s email address is provided:

@Path("/employees/{firstname}.{lastname}@{domain}.com")
public class EmpResource {

    @GET
    @Produces("text/xml")
    public String getEmployeelastname(@PathParam("lastname") String lastName) {
      ...
    }
}

In this example, the @Path annotation defines the URI variables (or path parameters) {firstname}, {lastname}, and {domain}. The @PathParam in the method parameter of the request method extracts the last name from the email address.

If your HTTP request is GET /employees/john.doe@example.com, the value “doe” is injected into {lastname}.

You can specify several path parameters in one URI.

You can declare a regular expression with a URI variable. For example, if it is required that the last name must consist only of lowercase and uppercase characters, you can declare the following regular expression:

@Path("/employees/{firstname}.{lastname[a-zA-Z]*}@{domain}.com")

If the last name does not match the regular expression, a 404 response is returned.

Extracting Query Parameters

Use the @QueryParam annotation to extract query parameters from the query component of the request URI.

For instance, to query all employees who have joined within a specific range of years, use a method signature like the following:

@Path("/employees/")
@GET
public Response getEmployees(
        @DefaultValue("2003") @QueryParam("minyear") int minyear,
        @DefaultValue("2013") @QueryParam("maxyear") int maxyear)
    {...}

This code snippet defines two query parameters, minyear and maxyear. The following HTTP request would query for all employees who have joined between 2003 and 2013:

GET /employees?maxyear=2013&minyear=2003

The @DefaultValue annotation defines a default value, which is to be used if no values are provided for the query parameters. By default, JAX-RS assigns a null value for Object values and zero for primitive data types. You can use the @DefaultValue annotation to eliminate null or zero values and define your own default values for a parameter.

Extracting Form Data

Use the @FormParam annotation to extract form parameters from HTML forms. For example, the following form accepts the name, address, and manager’s name of an employee:

<FORM action="http://example.com/employees/" method="post">
  <p>
    <fieldset>
      Employee name: <INPUT type="text" name="empname" tabindex="1">
      Employee address: <INPUT type="text" name="empaddress" tabindex="2">
      Manager name: <INPUT type="text" name="managername" tabindex="3">
    </fieldset>
  </p>
</FORM>

Use the following code snippet to extract the manager name from this HTML form:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(@FormParam("managername") String managername) {
    // Store the value
    ...
}

To obtain a map of form parameter names to values, use a code snippet like the following:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(MultivaluedMap<String, String> formParams) {
    // Store the message
}

Extracting the Java Type of a Request or Response

The javax.ws.rs.core.Context annotation retrieves the Java types related to a request or response.

The javax.ws.rs.core.UriInfo interface provides information about the components of a request URI. The following code snippet shows how to obtain a map of query and path parameter names to values:

@GET
public String getParams(@Context UriInfo ui) {
    MultivaluedMap<String, String> queryParams = ui.getQueryParameters();
    MultivaluedMap<String, String> pathParams = ui.getPathParameters();
}

The javax.ws.rs.core.HttpHeaders interface provides information about request headers and cookies. The following code snippet shows how to obtain a map of header and cookie parameter names to values:

@GET
public String getHeaders(@Context HttpHeaders hh) {
    MultivaluedMap<String, String> headerParams = hh.getRequestHeaders();
    MultivaluedMap<String, Cookie> pathParams = hh.getCookies();
}