protected void doResponseHeaders(final HttpServletResponse response, final String mimeType) {
        if (mimeType != null) {
            response.setContentType(mimeType);
        }
    }
Set the response headers. This method is called to set the response
headers such as content type and content length. May be extended to add
additional headers.

@param response
@param resource
@param mimeType
metamorphosis-server-wrapper/src/main/java/com/taobao/metamorphosis/http/processor/MetamorphosisOnJettyProcessor.java