JavaServer Pages, 3rd Edition

Request Methods

As described earlier, GET is the most commonly used request method, intended to retrieve a resource without causing anything else to happen on the server. The POST method is almost as common as GET; it requests some kind of processing on the server, for instance, updating a database or processing a purchase order.

The way parameters are transferred is one of the most obvious differences between the GET and POST request methods. A GET request always uses a query string to send parameter values, while a POST request always sends them as part of the body (additionally, it can send some parameters as a query string, just to make life interesting). If you insert a link in an HTML page using an <a> element, clicking on the link results in a GET request being sent to the server. Since the GET request uses a query string to pass parameters, you can include hardcoded parameter values in the link URI:

<a href="/forecast?city=Hermosa+Beach&state=CA">
  Hermosa Beach weather forecast
</a>

When you use a form to send user input to the server, you can specify whether to use the GET or POST method with the method attribute, as shown here:

<form action="/forecast" method="POST">
  City: <input name="city" type="text">
  State: <input name="state" type="text">
  <p>
  <input type="SUBMIT">
</form>

If the user enters “Hermosa Beach” and “CA” in the form fields and clicks on the Submit button, the browser sends a request message like this to the server:

POST /forecast HTTP/1.1 Host: www.gefionsoftware.com ...