After adding res.setContentType(text/html); problem resolved :)
Before sending data to client (displayed by Browser on client machine), the Servlet container informs the client browser of what type of data is being sent now. The data that can be sent may be simple plain text, html form, xml form, image form of type gif or jpg, excel sheet etc. To send this information, the Servlet container uses response object with the method setContentType().
Some examples :
response.setContentType("text/html");
response.setContentType("text/plain");
response.setContentType("text/css");
response.setContentType("application/html");
response.setContentType("image/gif");
response.setContentType("application/zip");
response.setContentType("application/pdf");
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…