Dinesh on Java

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

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/dinesh.rajput@example.com, the value “rajput” 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 lower and upper case 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("2002") @QueryParam("minyear") int minyear,
        @DefaultValue("2010") @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 1999 and 2009:

GET /employees?maxyear=2009&minyear=1999
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">

<fieldset>
Employee name: <input name="empname" tabindex="1" type="text" />  
Employee address: <input name="empaddress" tabindex="2" type="text" /> 
Manager name: <input name="managername" tabindex="3" type="text" /> </fieldset>
</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();
}

References
1. JAVA REST Web Services
2. Wikipedia for REST Web Service