JavaServer Pages, 3rd Edition

Requests in Detail

Let’s take a closer look at requests. A user sends a request to the server by clicking a link on a web page, submitting a form, or typing in a web page address in the browser’s address field. To send a request, the browser needs to know which server to talk to and which resource to ask for. This information is specified by an HTTP Uniform Resource Locator (URL):

http://www.gefionsoftware.com/index.html

The first part of the URL shown specifies that the request is made using the HTTP protocol. This is followed by the name of the server, in this case www.gefionsoftware.com. The web server waits for requests to come in on a specific TCP/IP port. Port number 80 is the standard port for HTTP requests. If the web server uses another port, the URL must specify the port number in addition to the server name. For example:

http://www.gefionsoftware.com:8080/index.html

This request is sent to a server that uses port 8080 instead of 80. The last part of the URL, /index.html, identifies the resource that the client is requesting.

A URL is actually a specialization of a Uniform Resource Identifier (URI, defined in the RFC-2396^[1] specification). A URL identifies a resource partly by its location, for instance the server that contains the resource. Another type of URI is a Uniform Resource Name (URN), which is a globally unique identifier that is valid no matter where the resource is located. HTTP deals only with the URL variety. The terms URI and URL are often used interchangeable, ...