How can I set correct Last-Modified header value for Spring Web Service that is cached using Spring Cache?

Question

I have such Spring MVC Controller:

@Controller
@RequestMapping(value = "/user")
public class UserController {
   .....      
   @Cacheable(value = "users", key = "#id")
   @RequestMapping(value = "/get", method = RequestMethod.GET)
   @ResponseBody
   public User getUser(Long id){
       return userService.get(id);
   }
   ....
}

I want to add header Last-Modified to HTTP Response of GetUser web service.
How can I get proper date when cache was added to my store?
How can I add header Last-Modified with this date to response of my Spring Controller Method?

Answer 1

Spring has an already build in support to handle the last-modified and If-Modified-Since header in for driven request handler methods.

It is based on WebRequest.checkNotModified(long lastModifiedTimestamp)

This example is just taken from the java doc:

This will also transparently set the appropriate response headers, for both the modified case and the not-modified case. Typical usage:

 @RequestMapping(value = "/get", method = RequestMethod.GET)
 public String myHandleMethod(WebRequest webRequest, Model model) {
    long lastModified = // application-specific calculation
    if (request.checkNotModified(lastModified)) {
      // shortcut exit - no further processing necessary
      return null;
    }
    // further request processing, actually building content
    model.addAttribute(...);
    return "myViewName";
}

---

But your @Cacheable annotation is a problem, because it prevent that the method is executed (for the second invocation) and therefore the request.checkNotModified is not invoked. - If the caching is important then you could remove the @Cacheable annotation from the controller method and put it on an inner method that is invoked after request.checkNotModified is done.

 //use selfe in order to use annotation driven advices
 @Autowire
 YourController selfe;

 @RequestMapping(value = "/get", method = RequestMethod.GET)
 public String myHandleMethod(WebRequest webRequest, Model model) {
    long lastModified = // application-specific calculation
    if (request.checkNotModified(lastModified)) {
      // shortcut exit - no further processing necessary
      return null;
    } else {  
      return selfe.innerMyHandleMethod(model);
    }
}

@Cacheable(value = "users", key = "#id")
public String innerMyHandleMethod(Model model) {   
    model.addAttribute(...);
    return "myViewName";
}