Retrieve POST parameters only (Java)

Question

Does anyone know of a way to get only POST parameters from an HttpServletRequest object?

IE, PHP has the $_POST superglobal and Perl's CGI.pm will only retrieve POST parameters if the HTTP method is POST (by default).

HttpServletRequest.getParameter(String) will include the GET URL parameters even if the HTTP method is POST.

Answer 1

From my understanding, there are no such things as POST parameters and GET parameters in HTTP, there are POST and GET methods. When a request is made using the POST method, parameters go within the message body. In case of a GET request, parameters go in the URL.

My first thought was that it was an implementation bug in your servlet container. But, since things are not always as you expect, java servlet specification (at least the 2.4 version) does not differentiate between the two kind of parameters. So, there is no way to obtain post or url parameters using the servlet API.

Surely you already have a plan B. But, just in case, I post two alternatives that came to my mind:

1. If you have access to the parameter name definition, you could use a prefix to differentiate between the two when you iterate the getParameterNames() result.

2. You could parse the URL creating an URL object and using getQuery() method to obtain just the parameters. Then, parse the parameters on the query string using some utility class such as ParameterParser in HttpClient library. And finally, subtract that names from the getParameterNames() result.

Answer 2

I guess one way might be to manually parse HttpServletRequest.getQueryString() and check that a parameter is not present in it.

A naive implementation (ignoring url-escaped key values) would go something like this (untested) :

public boolean isInQuery(HttpServletRequest request, String key) {
  String query = request.getQueryString();
  String[] nameValuePairs = query.split("&");
  for(String nameValuePair: nameValuePairs) {
    if(nameValuePair.startsWith(key + "=")) {
      return true;
    }
  }
  return false;
}

Answer 3

Couldn't you just get the parameters from the HttpServletRequest within doPost or doGet in a subclass of HttpServlet?

Anything you grab (via getParemeter) inside of doPost is a POST and anything inside of doGet is a GET.