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132

Chapter 6 Generating the Server Response: HTTP Status Codes

404 (Not Found)

The infamous 404 (

SC_NOT_FOUND

) status tells the client that no 

resource could be found at that address. This value is the standard  no 

such page  response. It is such a common and useful response that 

there is a special method for it in the 

HttpServletResponse

 class: 

sendError("message")

. The advantage of 

sendError

 over 

setSta 

tus

 is that, with 

sendError

, the server automatically generates an error 

page showing the error message. Unfortunately, however, the default 

behavior of Internet Explorer 5 is to ignore the error page you send 

back and displays its own, even though doing so contradicts the HTTP 

specification. To turn off this setting, go to the Tools menu, select Inter 

net Options, choose the Advanced tab, and make sure  Show friendly 

HTTP error messages  box is not checked. Unfortunately, however, few 

users are aware of this setting, so this  feature  prevents most users of 

Internet Explorer version 5 from seeing any informative messages you 

return. Other major browsers and version 4 of Internet Explorer prop 

erly display server generated error pages. See Figures 6 3 and 6 4 for 

an example.

Core Warning

By default, Internet Explorer version 5 ignores server generated error pages.

405 (Method Not Allowed)

A 405 (

SC_METHOD_NOT_ALLOWED

) value indicates that the request 

method (

GET

, 

POST

, 

HEAD

, 

PUT

, 

DELETE

, etc.) was not allowed for this 

particular resource. This status code is new in HTTP 1.1. 

406 (Not Acceptable)

A value of 406 (

SC_NOT_ACCEPTABLE

) signifies that the requested 

resource has a MIME type incompatible with the types specified 

by the client in its 

Accept

 header. See Table 7.1 in Section 7.2 

(HTTP 1.1 Response Headers and Their Meaning) for the names 

and meanings of the common MIME types. The 406 value is new in 

HTTP 1.1. 

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