ajax 和 servlet参数问题

Question

jquery代码：
var username = $('#username').val();
var pwd = $('#pwd').val();
var param ='{"username":"'+username+'","pwd":"'+pwd+'"}';
$('#login').click(function(){
alert(param);
$.ajax({
type:'post',
url:'MyServlet',
data:param,
success:function(){}
})
})

servlet代码：
protected void doPost(HttpServletRequest request, HttpServletResponse resp)
throws ServletException, IOException {
String aa = request.getParameter("param");
System.out.println(aa);
}
这里获取不到ajax传过来的param的值 调试为空的 为什么 求大神帮忙

Answer 1

 data: {"orderId":orderId,"commant":commant},  

或
data: "orderId=" + orderId + "&commant=" + commant