request.read(Person.class).as(Json.class);

at("/test").serve(TestPage.class);

public class TestPage {

    private String param;

    @Get
    public Reply<?> get() {
        // request get param "param" is already mapped in param
    }

    @Post
    public Reply<?> post() {
        // request post param "param" is already mapped in param
    }


    public void setParam(String param) {
        this.param = param;
    }

    public String getParam() {
        return this.param;
    }

}

public class TestPage {
   @Inject Json json;

   @Post
   public void post(Request request) {
     String data = request.param("data");
     Person p = json.in(new ByteArrayInputStream(data.getBytes()), Person.class);

     ...
   }
}