Chapter 9. @FormParam

When the input request body is of the type application/x-www-form-urlencoded (that is, an HTML form), you can inject individual form parameters from the request body into method parameter values. 
<form method="POST" action="/resources/service">
First name: 
<input type="text" name="firstname">
<br>
Last name: 
<input type="text" name="lastname">
</form>
If you post using this form, the service would look as follows: 
@Path("/")
public class NameRegistry {

   @Path("/resources/service")
   @POST
   public void addName(@FormParam("firstname") String first, @FormParam("lastname") String last) {...}
You cannot combine @FormParam with the default application/x-www-form-urlencoded that unmarshalls to a MultivaluedMap<String, String> That is, the following would be illegal: 
@Path("/")
public class NameRegistry {

   @Path("/resources/service")
   @POST
   @Consumes("application/x-www-form-urlencoded")
   public void addName(@FormParam("firstname") String first, MultivaluedMap<String, String> form) {...}