title: Access all @RequestHeader key value as Map in our Spring controller
body: <p>I am trying to find way through which, I can populate all Key values from @RequestHeader annotation to a Map.
  I tried to Google it but all I can find is a way to map each key value to one parameter.</p>
  
  <pre><code>import org.springframework.stereotype.Controller;
  import org.springframework.web.bind.annotation.RequestHeader;
  import org.springframework.web.bind.annotation.RequestMapping;
  
  @Controller
  public class HelloController {
  
      @RequestMapping(value = "/hello.htm")
      public String hello(@RequestHeader(value="User-Agent") String userAgent)
  
          //..
      }
  }
  </code></pre>
  
  <p>But I want to achieve something like this.</p>
  
  <p>@RequestHeader Map headerParam;</p>
  
  <p>So that I can traverse the Map and use all header values as required.</p>