Java Servlet Programming

Status Codes

Until now, our servlet examples have not set HTTP response status codes. We’ve been taking advantage of the fact that if a servlet doesn’t specifically set the status code, the server steps in and sets its value to the default 200 “OK” status code. That’s a useful convenience when we are returning normal successful responses. However, by using status codes, a servlet can do more with its response. For example, it can redirect a request or report a problem.

The most common status code numbers are defined as mnemonic constants (public final static int fields) in the HttpServletResponse class. A few of these are listed in Table 5.1. The full list is available in Appendix C.

Table 5-1. HTTP Status Codes

Mnemonic Constant	Code	Default Message	Meaning
SC_OK	200	OK	The client’s request was successful, and the server’s response contains the requested data. This is the default status code.
SC_NO_CONTENT	204	No Content	The request succeeded, but there was no new response body to return. Browsers receiving this code should retain their current document view. This is a useful code for a servlet to use when it accepts data from a form but wants the browser view to stay at the form, as it avoids the “Document contains no data” error message.
SC_MOVED_PERMANENTLY	301	Moved Permanently	The requested resource has permanently moved to a new location. Future references should use the new URL in requests. The new location is given by the Location header. Most browsers automatically ...