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Filters
The spring-web
module provides some useful filters:
Form Data
Browsers can submit form data only through HTTP GET or HTTP POST but non-browser clients can also
use HTTP PUT, PATCH, and DELETE. The Servlet API requires ServletRequest.getParameter*()
methods to support form field access only for HTTP POST.
The spring-web
module provides FormContentFilter
to intercept HTTP PUT, PATCH, and DELETE
requests with a content type of application/x-www-form-urlencoded
, read the form data from
the body of the request, and wrap the ServletRequest
to make the form data
available through the ServletRequest.getParameter*()
family of methods.
Forwarded Headers
As a request goes through proxies (such as load balancers) the host, port, and scheme may change, and that makes it a challenge to create links that point to the correct host, port, and scheme from a client perspective.
RFC 7239 defines the Forwarded
HTTP header
that proxies can use to provide information about the original request. There are other
non-standard headers, too, including X-Forwarded-Host
, X-Forwarded-Port
,
X-Forwarded-Proto
, X-Forwarded-Ssl
, and X-Forwarded-Prefix
.
ForwardedHeaderFilter
is a Servlet filter that modifies the request in order to
a) change the host, port, and scheme based on Forwarded
headers, and b) to remove those
headers to eliminate further impact. The filter relies on wrapping the request, and
therefore it must be ordered ahead of other filters, such as RequestContextFilter
, that
should work with the modified and not the original request.
There are security considerations for forwarded headers since an application cannot know
if the headers were added by a proxy, as intended, or by a malicious client. This is why
a proxy at the boundary of trust should be configured to remove untrusted Forwarded
headers that come from the outside. You can also configure the ForwardedHeaderFilter
with removeOnly=true
, in which case it removes but does not use the headers.
In order to support asynchronous requests and error dispatches this
filter should be mapped with DispatcherType.ASYNC
and also DispatcherType.ERROR
.
If using Spring Framework’s AbstractAnnotationConfigDispatcherServletInitializer
(see Servlet Config) all filters are automatically registered for all dispatch
types. However if registering the filter via web.xml
or in Spring Boot via a
FilterRegistrationBean
be sure to include DispatcherType.ASYNC
and
DispatcherType.ERROR
in addition to DispatcherType.REQUEST
.
Shallow ETag
The ShallowEtagHeaderFilter
filter creates a “shallow” ETag by caching the content
written to the response and computing an MD5 hash from it. The next time a client sends,
it does the same, but it also compares the computed value against the If-None-Match
request header and, if the two are equal, returns a 304 (NOT_MODIFIED).
This strategy saves network bandwidth but not CPU, as the full response must be computed for each request.
State-changing HTTP methods and other HTTP conditional request headers such as If-Match
and
If-Unmodified-Since
are outside the scope of this filter. Other strategies at the controller level
can avoid the computation and have a broader support for HTTP conditional requests.
See HTTP Caching.
This filter has a writeWeakETag
parameter that configures the filter to write weak ETags
similar to the following: W/"02a2d595e6ed9a0b24f027f2b63b134d6"
(as defined in
RFC 7232 Section 2.3).
In order to support asynchronous requests this filter must be mapped
with DispatcherType.ASYNC
so that the filter can delay and successfully generate an
ETag to the end of the last async dispatch. If using Spring Framework’s
AbstractAnnotationConfigDispatcherServletInitializer
(see Servlet Config)
all filters are automatically registered for all dispatch types. However if registering
the filter via web.xml
or in Spring Boot via a FilterRegistrationBean
be sure to include
DispatcherType.ASYNC
.
CORS
Spring MVC provides fine-grained support for CORS configuration through annotations on
controllers. However, when used with Spring Security, we advise relying on the built-in
CorsFilter
that must be ordered ahead of Spring Security’s chain of filters.
See the sections on CORS and the CORS Filter for more details.