It takes me almost half a day , but I haven't solve it ,I don't know why . I would be much appreciate for your help...
$(document).ready(function(){ alert("can show"); $("#button").click(function(){ alert("when click button , can show "); $.post("AddComment",null,function(data){ // AddComment is a servlet name alert("here can't show"); },"json"); }); }); servlet ,root ,"servlets/AddComment", public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("here can't show,that is ,the method $.post does not work"); } servlet config in web.xml: <servlet> <servlet-name>AddComment</servlet-name> <servlet-class>servlets.AddComment</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>AddComment</servlet-name> <url-pattern>/servlets/AddComment</url-pattern> </servlet-mapping>