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128
Chapter 6 Generating the Server Response: HTTP Status Codes
204 (No Content)
A status code of 204 (
SC_NO_CONTENT
) stipulates that the browser
should continue to display the previous document because no new doc
ument is available. This behavior is useful if the user periodically
reloads a page by pressing the Reload button, and you can determine
that the previous page is already up to date. For example, a servlet
might do something like this:
int pageVersion =
Integer.parseInt(request.getParameter("pageVersion"));
if (pageVersion >= currentVersion) {
response.setStatus(response.SC_NO_CONTENT);
} else {
// Create regular page
}
However, this approach does not work for pages that are automatically
reloaded via the
Refresh
response header or the equivalent
HTTP EQUIV="Refresh" ...>
HTML entry, since returning a 204 sta
tus code stops future reloading. JavaScript based automatic reloading
could still work in such a case, though. See the discussion of
Refresh
in
Section 7.2 (HTTP 1.1 Response Headers and Their Meaning) for
details.
205 (Reset Content)
A value of 205 (
SC_RESET_CONTENT
) means that there is no new docu
ment, but the browser should reset the document view. This status
code is used to force browsers to clear form fields. It is new in HTTP
1.1.
206 (Partial Content)
A status code of 206 (
SC_PARTIAL_CONTENT
) is sent when the server
fulfills a partial request that includes a
Range
header. This value is new
in HTTP 1.1.
300 (Multiple Choices)
A value of 300 (
SC_MULTIPLE_CHOICES
) signifies that the requested
document can be found several places, which will be listed in the
returned document. If the server has a preferred choice, it should be
listed in the
Location
response header.
Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.
Servlet and JSP training courses by book's author: courses.coreservlets.com.
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