package com.sample.resources;
 
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.EntityTag;
import javax.ws.rs.core.Request;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.Response.ResponseBuilder;
 
//Root resource class
@Path("/root")
public class Resource {
  //field in which the Request is injected by using the Context annotation
  private @Context Request request;
  //HTTP Entity Tag to be used in the content negotiation
  private EntityTag eTag = new EntityTag("a-resource-status-specific-tag");
 
  //Resource method
  @GET
  public Response getData() {
ResponseBuilder rb = null;
    //perform the content negotiation (evaluation of preconditions)
    //  null if matched with the precondition, if not matched, 
    //  the ResponseBuilder object is acquired in which 
    //  a suitable ETag HTTP header or a status code (412: Precondition Failed) is set
    rb = request.evaluatePreconditions(this.eTag);
    if (rb != null) {
      //if not matched with the precondition, generate an HTTP response 
      // from the ResponseBuilder object and return the response as it is
      return rb.build();
    } else {
      //if matched with the precondition, return the request data
      String data = "Some Information";
      return Response.ok().entity(data).build();
    }
  }
}