Understanding ServletRequest

Question

I'm trying to understand how the ServletRequest works.

For example: http://docs.oracle.com/javaee/6/api/javax/servlet/ServletRequest.html#getParameterNames()

States "Returns an Enumeration of String objects containing the names of the parameters contained in this request"

I have seen an instance of this as such

Enumeration test_enum = request.getParameterNames();
            StringBuilder sb = new StringBuilder();
            while (test_enum.hasMoreElements()) {
                String paramName = cleanString((String)test_enum.nextElement());
                String paramValue = cleanString(request.getParameter(paramName));
                if (alteredValues.containsKey(paramName)) paramValue = alteredValues.get(paramName);
                try {
                    paramValue = URLEncoder.encode(paramValue, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                }
                sb.append("&").append(paramName).append("=").append(paramValue);
            }

So I understand that the goal of this is to find all parameters and list them out in URL format.

The thing I don't understand is how getParameterNames() finds the parameters on the page, does it just look for any element with a name attribute and counts that as a parameter?

What qualifies as a parameter in this case?

It gets the parameters from the request. HTTP requests are a known format. "The page" is ancillary; requests don't have to come from a web page. — Dave Newton, May 08 '13 at 00:22
http://stackoverflow.com/questions/2793150/how-to-use-java-net-urlconnection-to-fire-and-handle-http-requests may be helpful in understanding how web browsers work "under the covers". — BalusC, May 08 '13 at 00:34

score 1 · Accepted Answer · answered May 08 '13 at 10:49

When you make a HTTP GET or HTTP POST request to a resource on a server, your browser creates a request package. That request package has certain body parts. In 1 of the body parts, it has all the form fields you entered before making a request.

For ex, this image is a sample HTTP GET request package:

enter image description here

In the above image, you can see bookId=1234&author=Tan+Ah+Teck line. This line is the Parameter line. So in the servlet, you can use request.getParameterNames() which will give you the enumeration of all parameters.

Thanks for pointing this out. It really does say in the javadoc "names of the parameters contained in _this request_" — RenaissanceProgrammer, May 08 '13 at 16:22

Understanding ServletRequest

1 Answers1