HTTP Caching
HTTP caching can significantly improve the performance of a web application. HTTP caching
revolves around the Cache-Control
response header and subsequent conditional request
headers, such as Last-Modified
and ETag
. Cache-Control
advises private (for example, browser)
and public (for example, proxy) caches 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 available in Spring WebFlux.
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, as the following example shows:
-
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()
Controllers
Controllers can add explicit support for HTTP caching. We recommend 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
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 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(ServerWebExchange exchange, Model model) {
long eTag = ... (1)
if (exchange.checkNotModified(eTag)) {
return null; (2)
}
model.addAttribute(...); (3)
return "myViewName";
}
1 | Application-specific calculation. |
2 | Response has been set to 304 (NOT_MODIFIED). No further processing. |
3 | Continue with request processing. |
@RequestMapping
fun myHandleMethod(exchange: ServerWebExchange, model: Model): String? {
val eTag: Long = ... (1)
if (exchange.checkNotModified(eTag)) {
return null(2)
}
model.addAttribute(...) (3)
return "myViewName"
}
1 | Application-specific calculation. |
2 | Response has been set to 304 (NOT_MODIFIED). No further processing. |
3 | Continue with 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.