More Servlets and JavaServer Pages™

2.7. The Server Response: HTTP Status Codes

When a Web server responds to a request from a browser or other Web client, the response typically consists of a status line, some response headers, a blank line, and the document. Here is a minimal example:

HTTP/1.1 200 OK 
Content-Type: text/plain 

Hello World 

The status line consists of the HTTP version (HTTP/1.1 in the example above), a status code (an integer; 200 in the example), and a very short message corresponding to the status code (OK in the example). In most cases, all of the headers are optional except for Content-Type, which specifies the MIME type of the document that follows. Although most responses contain a document, some don’t. For example, responses to HEAD requests should never ...