问题
I'was debugging a client-side AJAX problem that is making request to servlet. But the bug turned out to be at server side. You can refer to my original question here. From the discussion with more experienced people, I found out that servlet is using request.getAttribute() method to retrieve parameters from the request instead of getParameter(). So I thought to open a new question to clear my doubt.
Now my question is: If I use GET method to pass parameters from client to server, getAttribute() in Servlet works fine and I can get param values. But when I use POST method, getAttribute() returns null. Why does it work for GET and not for POST?
回答1:
You should always use getParameter, when attribute come from GET or POST method. And use getAttribute when request is forwarded from another servlet/jsp. Such as :
ServletA:
request.setAttribute("test","value")
request.getRequestDispatcher("/ServletB").forward(request, response)
ServletB:
request.getAttribute("test") <-- you can get test attribute by using getAttribute
回答2:
Now my question is: If I use GET method to pass parameters from client to server, getAttribute() in Servlet works fine and I can get param values. But when I use POST method, getAttribute() returns null. Why does it work for GET and not for POST?
Complete nonsense. You're apparently working on an existing project which has a lot of other existing servlets and filters. My cents that there's another filter in the request-response chain which maps request parameters to request attribtues for some unobvious reason.
Please create a blank playground project and create a playground servlet to familarize yourself better with servlets without all that noise in existing projects.
See also:
- Our Servlets wiki page
来源：https://stackoverflow.com/questions/7266338/why-does-getattribute-in-httpservletrequest-works-for-get-method-but-not-for-p