Servlet doOptions() For CORS Preflight Check

The following code sample adds a doOptions method within a servlet and sends the appropriate headers in response to a CORS preflight request.

A CORS preflight request is a HTTP OPTIONS request that most browsers send prior to making an AJAX-JSONP call. The browser expects a series of access control headers stating if the server allows cross-domain information sharing. The settings in the code below will fit the needs of the vast majority of AJAX-JSONP applications.

public void doOptions(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
    //The following are CORS headers. Max age informs the 
    //browser to keep the results of this call for 1 day.
    resp.setHeader("Access-Control-Allow-Origin", "*");
    resp.setHeader("Access-Control-Allow-Methods", "GET, POST");
    resp.setHeader("Access-Control-Allow-Headers", "Content-Type");
    resp.setHeader("Access-Control-Max-Age", "86400");
    //Tell the browser what requests we allow.
    resp.setHeader("Allow", "GET, HEAD, POST, TRACE, OPTIONS");