No Access-Control-Allow-Origin header is present on the requested resource

Question

I want to access information from same domain but with different port number  To allow this I am adding Access-Control-Allow-Origin with the response header   Servlet Code  present on www example com PORT NUMBER   String json   new Gson   toJson list   response setContentType  application json    response setCharacterEncoding  UTF-8    response setHeader  Access-Control-Allow-Origin          cross domain request CORS response getWriter   write json     jQuery code  present on www example com     post  http   www example com PORT NUMBER MYSERVLET   MyParam   value    done function data        alert data         Several times I am getting this error in console    XMLHttpRequest cannot load  http   www example com PORT NUMBER MYSERVLET  No  Access-Control-Allow-Origin  header is present on the requested resource    This error mostly occures first time when   post gets executed  Second time it allows   My question is that is there missing in servlet or in jQuery code   Any suggestion will be appreciated   Update1  I have changed   response setHeader  Access-Control-Allow-Origin           To   response setHeader  Access-Control-Allow-Origin    http   www example com      Then I am getting this error in console   XMLHttpRequest cannot load http   www example com PORT NUMBER MyServletName The  Access-Control-Allow-Origin  whitelists only  http   www example com  Origin  http   www example com  is not in the list  and is therefore not allowed access     Note  whitelist and origin are same  but still it gives error  It works sometimes  and gives above error sometimes    Let me know if you need anymore information

User · Answer

On your servlet simply override the service method of your servlet so that you can add headers for all your http methods  POST  GET  DELETE  PUT  etc         Override     protected void service HttpServletRequest req  HttpServletResponse res  throws ServletException  IOException            if   http   www example com   equals req getHeader  origin                  res setHeader  Access-Control-Allow-Origin   req getHeader  origin                 res setHeader  Access-Control-Allow-Headers    Authorization                       super service req  res

User · Answer

I find the solution in spring io like this       response setHeader  Access-Control-Allow-Origin             response setHeader  Access-Control-Allow-Methods    POST  GET  OPTIONS  DELETE        response setHeader  Access-Control-Max-Age    3600        response setHeader  Access-Control-Allow-Headers    x-requested-with

User · Answer

You are missing  json  dataType in the   post   method     post  http   www example com PORT NUMBER MYSERVLET   MyParam   value             done function data                     alert data                json               -      -------here     Updates   try with this   response setHeader  Access-Control-Allow-Origin   request getHeader  Origin

User · Answer

Solution  Instead of using setHeader method I have used addHeader   response addHeader  Access-Control-Allow-Origin             in above line will allow access to all domains  For allowing access to specific domain only   response addHeader  Access-Control-Allow-Origin    http   www example com      For issues related to IE lt  9  Please see here

[javascript] No Access-Control-Allow-Origin header is present on the requested resource

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