Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Developer's Guide

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### Request Handling

When a request is made, the Application Server hands the incoming data to the servlet engine. The servlet engine processes the request’s input data, such as form data, cookies, session information, and URL name-value pairs, into an `HttpServletRequest` request object type.

The servlet engine also creates an `HttpServletResponse` response object type. The engine then passes both as parameters to the servlet’s `service()` method.

In an HTTP servlet, the default `service()` method routes requests to another method based on the HTTP transfer method: `POST`, `GET`, `DELETE`, `HEAD`, `OPTIONS`, `PUT`, or `TRACE`. For example, HTTP `POST` requests are sent to the `doPost()` method, HTTP `GET` requests are sent to the `doGet()` method, and so on. This enables the servlet to process request data differently, depending on which transfer method is used. Since the routing takes place in the service method, you generally do not override `service()` in an HTTP servlet. Instead, override `doGet()`, `doPost()`, and so on, depending on the request type you expect.

To perform the tasks to answer a request, override the `service()` method for generic servlets, and the `doGet()` or `doPost()` methods for HTTP servlets. Very often, this means accessing EJB components to perform business transactions, then collating the information in the request object or in a JDBC `ResultSet` object.

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