How do I retrieve the URL before @Controller @RequestMapping goes into action?

Question

I have inherited a JAVA Spring MVC web app. I'm totally new to Spring MVC and very much a novice at JAVA. But my first task is to add the application's URL into an email that is already generated through code.

It is basically a way for the user to click the link and go directly to a specific page. But when I try all the various things I have seen on here that involve HttpServletRequest and more importantly getRequestURL().

I can only get the URL after the Controller takes over. What I need is the what I will refer to as the referring URL--the application URL I see in the browser.

The Controller is a REST service and returns localhost:8181/etc/etc which doesn't even include the domain for the site. I have tried the various methods like getHeader("Referer") etc. Again, they just return the post-Controller URL. I've tried added the code to get the correct URL pre-Controller and then pass it to the Controller method. Still gives me the post-Controller URL.

Answer 1

You need some kind of HandlerInterceptorAdapter / HandlerInterceptor.
Inside the preHandle method, you can get a hold on the HttpServletRequest object.

@Override
public boolean preHandle(
        final HttpServletRequest request,
        final HttpServletResponse response,
        final Object handler
) throws Exception {
   // Obtain only the hostname, with the associated port
   final String hostOnly = request.getHeader("Host");

   // Obtain the request URL, excluding query parameters
   final String completeUrl = request.getRequestURL().toString();

   // ... Continue towards the method handler
}

request.getRequestURL() returns a StringBuffer, which you can use to manipulate the URL, before building a String from it.

---

The same URL retrieval concept can be applied to a @Controller/@RestController handler method, if you need it there. Just insert an HttpServletRequest as input parameter.

@GetMapping
public ResponseEntity<?> myHandlerMethod(
          final HttpServletRequest request, 
          /* other parameters */) {
   ... 
}

You can even accept a WebRequest or NativeWebRequest

@GetMapping
public ResponseEntity<?> myHandlerMethod(
          final WebRequest request, 
          /* other parameters */) {
   final String host = request.getHeader("host");
   ...
}

@GetMapping
public ResponseEntity<?> myHandlerMethod(
          final NativeWebRequest request, 
          /* other parameters */) {
   final HttpServletRequest nativeRequest = request.getNativeRequest(HttpServletRequest.class);
   final String host = request.getHeader("host");
   ...
}

---

Edit, based on your comment.

@PostMapping(value = "myurl/{x}/(y)", produces = ...")
public ResponseEntity<String> doSomething(
         final HttpServletRequest request,
         @PathVariable("x") final String x,
         @PathVariable("y") final String y) {
   final String hostOnly = request.getHeader("Host");  // http://yourdomain.com:80

   if (service.sendEmail(x, y, hostOnly)) {
      return new ResponseEntity<>("...");
   } 

   ...

Answer 2

Pass a parameter of type UriComponentsBuilder into your controller method, and it will be pre-populated with the base context that the user originally used to make the request. Then you can do this:

String uri = MvcUriComponentsBuilder.relativeTo(uriBuilder)
        .withMethodName(MyController.class, "someMethod", parameterValue)
        .toUriString();