See, setContentType() allow servlet to response to the client by sending exact type of data is reverting back to client system. That allows client system to validate data on the basis of it for further process. In short, try to look into browser's dev tool -> network....... there you will find request sent to server and the data received by by the broswser..... after expanding request you will se Content-type= text/html........... this something Servlet sets with the help of above answer