This commit improves HTTP caching defaults and flexibility in
Spring MVC.
1) Better default caching headers
The `WebContentGenerator` abstract class has been updated with
better HTTP defaults for HTTP caching, in line with current
browsers and proxies implementation (wide support of HTTP1.1, etc);
depending on the `setCacheSeconds` value:
* sends "Cache-Control: max-age=xxx" for caching responses and
do not send a "must-revalidate" value by default.
* sends "Cache-Control: no-store" or "Cache-Control: no-cache"
in order to prevent caching
Other methods used to set specific header such as
`setUseExpiresHeader` or `setAlwaysMustRevalidate` are now deprecated
in favor of `setCacheControl` for better flexibility.
Using one of the deprecated methods re-enables previous HTTP caching
behavior.
This change is applied in many Handlers, since
`WebContentGenerator` is extended by `AbstractController`,
`WebContentInterceptor`, `ResourceHttpRequestHandler` and others.
2) New CacheControl builder class
This new class brings more flexibility and allows developers
to set custom HTTP caching headers.
Several strategies are provided:
* `CacheControl.maxAge(int)` for caching responses with a
"Cache-Control: max-age=xxx" header
* `CacheControl.noStore()` prevents responses from being cached
with a "Cache-Control: no-store" header
* `CacheControl.noCache()` forces caches to revalidate the cached
response before reusing it, with a "Cache-Control: no-store" header.
From that point, it is possible to chain method calls to craft a
custom CacheControl instance:
```
CacheControl cc = CacheControl.maxAge(1, TimeUnit.HOURS)
.cachePublic().noTransform();
```
3) Configuring HTTP caching in Resource Handlers
On top of the existing ways of configuring caching mechanisms,
it is now possible to use a custom `CacheControl` to serve
resources:
```
@Configuration
public class MyWebConfig extends WebMvcConfigurerAdapter {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
CacheControl cc = CacheControl.maxAge(1, TimeUnit.HOURS);
registry.addResourceHandler("/resources/**)
.addResourceLocations("classpath:/resources/")
.setCacheControl(cc);
}
}
```
or
```
<mvc:resources mapping="/resources/**" location="classpath:/resources/">
<mvc:cachecontrol max-age="3600" cache-public="true"/>
</mvc:resources>
```
Issue: SPR-2779, SPR-6834, SPR-7129, SPR-9543, SPR-10464
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