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Support conditional updates in ServletWebRequest

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Prior to this commit, `ServletWebRequest.checkNotModified` would only
support conditional GET/HEAD requests with "If-Modified-Since" and/or
"If-None-Match" request headers. In those cases, the server would return
"HTTP 304 Not Modified" responses if the resource didn't change.

This commit adds support for conditional update requests, such as
POST/PUT/DELETE requests with "If-Unmodified-Since" request headers.
If the underlying resource has been modified since the specified date,
the server will return a "409 Precondition failed" response status
to prevent concurrent updates.

Even if the modification status of the resource is reversed here
(modified vs. not modified), we're keeping here the same intent for the
return value, which signals if the response requires more processing or
if the handler method can return immediately:

```
if (request.checkNotModified(lastModified)) {
  // shortcut exit - no further processing necessary
  return null;
}
```

Issue: SPR-13863
This commit is contained in:
Brian Clozel
2016-03-01 14:37:29 +01:00
parent b3abd3b809
commit 0d6f80052d
4 changed files with 115 additions and 41 deletions
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15
src/asciidoc/web-mvc.adoc
View File

@@ -4449,17 +4449,24 @@ This can be achieved as follows:
----
There are two key elements here: calling `request.checkNotModified(lastModified)` and
returning `null`. The former sets the response status to 304 before it returns `true`.
returning `null`. The former sets the appropriate response status and headers
before it returns `true`.
The latter, in combination with the former, causes Spring MVC to do no further
processing of the request.
Note that there are 3 variants for this:
* `request.checkNotModified(lastModified)` compares lastModified with the
`'If-Modified-Since'` request header
* `request.checkNotModified(eTag)` compares eTag with the `'ETag'` request header
`'If-Modified-Since'` or `'If-Unmodified-Since'` request header
* `request.checkNotModified(eTag)` compares eTag with the `'If-None-Match'` request header
* `request.checkNotModified(eTag, lastModified)` does both, meaning that both
conditions should be valid for the server to issue an `HTTP 304 Not Modified` response
conditions should be valid
When receiving conditional `'GET'`/`'HEAD'` requests, `checkNotModified` will check
that the resource has not been modified and if so, it will result in a `HTTP 304 Not Modified`
response. In case of conditional `'POST'`/`'PUT'`/`'DELETE'` requests, `checkNotModified`
will check that the resource has not been modified and if it has been, it will result in a
`HTTP 409 Precondition Failed` response to prevent concurrent modifications.
[[mvc-httpcaching-shallowetag]]