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126

Chapter 6 Generating the Server Response: HTTP Status Codes

6.2 HTTP 1.1 Status Codes and 

Their Purpose

The following sections describe each of the status codes available for use in

servlets talking to HTTP 1.1 clients, along with the standard message associ 

ated with each code. A good understanding of these codes can dramatically

increase the capabilities of your servlets, so you should at least skim the

descriptions to see what options are at your disposal. You can come back to

get details when you are ready to make use of some of the capabilities. Note

that Appendix A (Servlet and JSP Quick Reference) presents a brief summary

of these codes in tabular format.

The complete HTTP 1.1 specification is given in RFC 2616, which you can

access on line by going to 

http://www.rfc editor.org/

 and following the

links to the latest RFC archive sites. Codes that are new in HTTP 1.1 are

noted, since many browsers support only HTTP 1.0. You should only send

the new codes to clients that support HTTP 1.1, as verified by checking

request.getRequestProtocol

. 

The rest of this section describes the specific status codes available in

HTTP 1.1. These codes fall into five general categories:

100 199

Codes in the 100s are informational, indicating that the client 

should respond with some other action. 

200 299

Values in the 200s signify that the request was successful. 

300 399

Values in the 300s are used for files that have moved and usually 

include a 

Location

 header indicating the new address. 

400 499

Values in the 400s indicate an error by the client. 

500 599

Codes in the 500s signify an error by the server. 

The constants in 

HttpServletResponse

 that represent the various codes

are derived from the standard messages associated with the codes. In serv 

lets, you usually refer to status codes only by means of these constants. For

example, you would use 

response.setSta 

tus(response.SC_NO_CONTENT)

 rather than 

response.setStatus(204)

,

since the latter is unclear to readers and is prone to typographical errors.

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.