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6.2 HTTP 1.1 Status Codes and Their Purpose

129

301 (Moved Permanently)

The 301 (

SC_MOVED_PERMANENTLY

) status indicates that the requested 

document is elsewhere; the new URL for the document is given in the 

Location

 response header. Browsers should automatically follow the 

link to the new URL. 

302 (Found)

This value is similar to 301, except that the URL given by the 

Location

header should be interpreted as a temporary replacement, not a perma 

nent one. Note: in HTTP 1.0, the message was 

Moved Temporarily

instead of 

Found

, and the constant in 

HttpServletResponse

 is 

SC_MOVED_TEMPORARILY

, not the expected 

SC_FOUND

. 

Core Note

The constant representing 302 is 

SC_MOVED_TEMPORARILY

, not 

SC_FOUND

.

Status code 302 is very useful because browsers automatically follow 

the reference to the new URL given in the 

Location

 response header. 

It is so useful, in fact, that there is a special method for it, 

sendRedi 

rect

. Using 

response.sendRedirect(url)

 has a couple of advan 

tages over using 

response.setStatus(response.SC_MOVED_TEMPORARILY)

 and 

response.setHeader("Location", url)

. First, it is shorter and 

easier. Second, with 

sendRedirect

, the servlet automatically builds a 

page containing the link to show to older browsers that don't automat 

ically follow redirects. Finally, with version 2.2 of servlets (the version 

in J2EE), 

sendRedirect

 can handle relative URLs, automatically 

translating them into absolute ones. You must use an absolute URL in 

version 2.1, however.

If you redirect the user to another page within your own site, you should 

pass the URL through the 

encodeURL

 method of 

HttpServletRe 

sponse

. Doing so is a simple precaution in case you ever use session 

tracking based on URL rewriting. URL rewriting is a way to track users 

who have cookies disabled while they are at your site. It is implemented 

by adding extra path information to the end of each URL, but the serv 

let session tracking API takes care of the details automatically. Session 

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

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