How to send response before actions in spring mvc

You can of course do processing after sending the response. The more general way would be to use the afterCompletion method of a HandlerInterceptor. By construction, it will be executed after the response have been sent to client, but it forces you to split you logic in 2 components the before part in controller, and the after part in the interceptor.

The alternative way is to forget Spring MVC machinery and manually commit the response in the controller:

@RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method = RequestMethod.POST)
public void doSomething(@RequestBody List<Message> messages, HttpServletResponse response) {
    int code = (messages!=null && !messages.isEmpty()) ? HttpServletResponse.SC_OK
            : HttpServletResponse.SC_NOT_FOUND;
    if (code != HttpServletResponse.SC_OK) {
        response.sendError(code, res);
        return;
    }
    java.io.PrintWriter wr = response.getWriter();
    response.setStatus(code);
    wr.print(res);
    wr.flush();
    wr.close();

    // Now it it time to do the long processing
    ...
}

Note the void return code to notify Spring that the response have been committed in the controller.

As a side advantage, the processing still occurs in the same thread, so you have full access to session scoped attributes or any other thread local variables used by Spring MVC or Spring Security...

I guess you mau use the async mechanism of spring Async methods have been introduced in servlet 3.0 and Spring offers some support to them Basically... you make a request; the request is handled by the server and then, in background, a new thread manages the requesta data Here a useful link (at least i hope :) ) http://spring.io/blog/2012/05/10/spring-mvc-3-2-preview-making-a-controller-method-asynchronous/

You can use @Async

@RequestMapping(value = Connectors.CONNECTOR_HEARTBEAT, method = 
      RequestMethod.POST)
public ResponseEntity<String> doSomething(@RequestBody List<Message> 
      messages) {
    do();
    HttpStatus code = (messages!=null && !messages.isEmpty()) ? HttpStatus.OK
        : HttpStatus.NOT_FOUND;
     return new ResponseEntity<String>(res, code);

}

@Async 
void do(){
   //your code
}

this work in java 8