HTTP Caching
HTTP caching can significantly improve the performance of a web application. HTTP caching
revolves around the Cache-Control
response header and, subsequently, conditional request
headers (such as Last-Modified
and ETag
). Cache-Control
advises private (for example, browser)
and public (for example, proxy) caches on how to cache and re-use responses. An ETag
header is used
to make a conditional request that may result in a 304 (NOT_MODIFIED) without a body,
if the content has not changed. ETag
can be seen as a more sophisticated successor to
the Last-Modified
header.
This section describes the HTTP caching-related options that are available in Spring Web MVC.
CacheControl
CacheControl
provides support for
configuring settings related to the Cache-Control
header and is accepted as an argument
in a number of places:
While RFC 7234 describes all possible
directives for the Cache-Control
response header, the CacheControl
type takes a
use case-oriented approach that focuses on the common scenarios:
-
Java
-
Kotlin
// Cache for an hour - "Cache-Control: max-age=3600"
CacheControl ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS);
// Prevent caching - "Cache-Control: no-store"
CacheControl ccNoStore = CacheControl.noStore();
// Cache for ten days in public and private caches,
// public caches should not transform the response
// "Cache-Control: max-age=864000, public, no-transform"
CacheControl ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS).noTransform().cachePublic();
// Cache for an hour - "Cache-Control: max-age=3600"
val ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS)
// Prevent caching - "Cache-Control: no-store"
val ccNoStore = CacheControl.noStore()
// Cache for ten days in public and private caches,
// public caches should not transform the response
// "Cache-Control: max-age=864000, public, no-transform"
val ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS).noTransform().cachePublic()
WebContentGenerator
also accepts a simpler cachePeriod
property (defined in seconds) that
works as follows:
-
A
-1
value does not generate aCache-Control
response header. -
A
0
value prevents caching by using the'Cache-Control: no-store'
directive. -
An
n > 0
value caches the given response forn
seconds by using the'Cache-Control: max-age=n'
directive.
Controllers
Controllers can add explicit support for HTTP caching. We recommended doing so, since the
lastModified
or ETag
value for a resource needs to be calculated before it can be compared
against conditional request headers. A controller can add an ETag
header and Cache-Control
settings to a ResponseEntity
, as the following example shows:
-
Java
-
Kotlin
@GetMapping("/book/{id}")
public ResponseEntity<Book> showBook(@PathVariable Long id) {
Book book = findBook(id);
String version = book.getVersion();
return ResponseEntity
.ok()
.cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS))
.eTag(version) // lastModified is also available
.body(book);
}
@GetMapping("/book/{id}")
fun showBook(@PathVariable id: Long): ResponseEntity<Book> {
val book = findBook(id);
val version = book.getVersion()
return ResponseEntity
.ok()
.cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS))
.eTag(version) // lastModified is also available
.body(book)
}
The preceding example sends a 304 (NOT_MODIFIED) response with an empty body if the comparison
to the conditional request headers indicates that the content has not changed. Otherwise, the
ETag
and Cache-Control
headers are added to the response.
You can also make the check against conditional request headers in the controller, as the following example shows:
-
Java
-
Kotlin
@RequestMapping
public String myHandleMethod(WebRequest request, Model model) {
long eTag = ... (1)
if (request.checkNotModified(eTag)) {
return null; (2)
}
model.addAttribute(...); (3)
return "myViewName";
}
1 | Application-specific calculation. |
2 | The response has been set to 304 (NOT_MODIFIED) — no further processing. |
3 | Continue with the request processing. |
@RequestMapping
fun myHandleMethod(request: WebRequest, model: Model): String? {
val eTag: Long = ... (1)
if (request.checkNotModified(eTag)) {
return null (2)
}
model[...] = ... (3)
return "myViewName"
}
1 | Application-specific calculation. |
2 | The response has been set to 304 (NOT_MODIFIED) — no further processing. |
3 | Continue with the request processing. |
There are three variants for checking conditional requests against eTag
values, lastModified
values, or both. For conditional GET
and HEAD
requests, you can set the response to
304 (NOT_MODIFIED). For conditional POST
, PUT
, and DELETE
, you can instead set the response
to 412 (PRECONDITION_FAILED), to prevent concurrent modification.
Static Resources
You should serve static resources with a Cache-Control
and conditional response headers
for optimal performance. See the section on configuring Static Resources.
ETag
Filter
You can use the ShallowEtagHeaderFilter
to add “shallow” eTag
values that are computed from the
response content and, thus, save bandwidth but not CPU time. See Shallow ETag.