JavaServer Pages, 3rd Edition

Request Parameters

Besides the URI and headers, a request message can contain additional information in the form of parameters. If the URI identifies a server-side program for displaying weather information, for example, request parameters can provide information about the city the user wants to see a forecast for. In an e-commerce application, the URI may identify a program that processes orders, with the user’s customer number and the list of items to be purchased transferred as parameters.

Parameters can be sent in one of two ways: tacked on to the URI in the form of a query string or sent as part of the request message body. This is an example of a URL with a query string:

http://www.weather.com/forecast?city=Hermosa+Beach&state=CA

The query string starts with a question mark (?) and consists of name/value pairs separated by ampersands (&). These names and values must be URL-encoded , meaning that special characters, such as whitespace, question marks, ampersands, and all other nonalphanumeric characters are encoded so that they don’t get confused with characters used to separate name/value pairs and other parts of the URI. In this example, the space between Hermosa and Beach is encoded as a plus sign. Other special characters are encoded as their corresponding hexadecimal ASCII value; for instance, a question mark is encoded as %3F. When parameters are sent as part of the request body, they follow the same syntax; URL encoded name/value pairs separated by ampersands.