Package org.springframework.web.filter

Class ShallowEtagHeaderFilter

java.lang.Object

org.springframework.web.filter.GenericFilterBean

org.springframework.web.filter.OncePerRequestFilter

org.springframework.web.filter.ShallowEtagHeaderFilter

All Implemented Interfaces:

Filter, Aware, BeanNameAware, DisposableBean, InitializingBean, EnvironmentAware, EnvironmentCapable, ServletContextAware

public class ShallowEtagHeaderFilter
extends OncePerRequestFilter

Filter that generates an ETag value based on the content on the response. This ETag is compared to the If-None-Match header of the request. If these headers are equal, the response content is not sent, but rather a 304 "Not Modified" status instead.

Since the ETag is based on the response content, the response (e.g. a View) is still rendered. As such, this filter only saves bandwidth, not server performance.

Since:

3.0

Author:

Arjen Poutsma, Rossen Stoyanchev, Brian Clozel, Juergen Hoeller

Field Summary

Fields inherited from class org.springframework.web.filter.OncePerRequestFilter

ALREADY_FILTERED_SUFFIX

Fields inherited from class org.springframework.web.filter.GenericFilterBean

logger

Constructor Summary

Constructors

Constructor	Description
ShallowEtagHeaderFilter()

Method Summary

Modifier and Type	Method	Description
static void	disableContentCaching(ServletRequest request)	This method can be used to suppress the content caching response wrapper of the ShallowEtagHeaderFilter.
protected void	doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)	Same contract as for doFilter, but guaranteed to be just invoked once per request within a single request thread.
protected String	generateETagHeaderValue(InputStream inputStream, boolean isWeak)	Generate the ETag header value from the given response body byte array.
protected boolean	isEligibleForEtag(HttpServletRequest request, HttpServletResponse response, int responseStatusCode, InputStream inputStream)	Whether an ETag should be calculated for the given request and response exchange.
boolean	isWriteWeakETag()	Return whether the ETag value written to the response should be weak, as per RFC 7232.
void	setWriteWeakETag(boolean writeWeakETag)	Set whether the ETag value written to the response should be weak, as per RFC 7232.
protected boolean	shouldNotFilterAsyncDispatch()	The default value is false so that the filter may delay the generation of an ETag until the last asynchronously dispatched thread.

Methods inherited from class org.springframework.web.filter.OncePerRequestFilter

doFilter, doFilterNestedErrorDispatch, getAlreadyFilteredAttributeName, isAsyncDispatch, isAsyncStarted, shouldNotFilter, shouldNotFilterErrorDispatch

Methods inherited from class org.springframework.web.filter.GenericFilterBean

addRequiredProperty, afterPropertiesSet, createEnvironment, destroy, getEnvironment, getFilterConfig, getFilterName, getServletContext, init, initBeanWrapper, initFilterBean, setBeanName, setEnvironment, setServletContext

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ShallowEtagHeaderFilter

public ShallowEtagHeaderFilter()

Method Details

setWriteWeakETag

public void setWriteWeakETag(boolean writeWeakETag)

Set whether the ETag value written to the response should be weak, as per RFC 7232.

Should be configured using an <init-param> for parameter name "writeWeakETag" in the filter definition in web.xml.

Since:

4.3

See Also:

• RFC 7232 section 2.3

isWriteWeakETag

public boolean isWriteWeakETag()

Return whether the ETag value written to the response should be weak, as per RFC 7232.

Since:

4.3

shouldNotFilterAsyncDispatch

protected boolean shouldNotFilterAsyncDispatch()

The default value is false so that the filter may delay the generation of an ETag until the last asynchronously dispatched thread.

Overrides:

shouldNotFilterAsyncDispatch in class OncePerRequestFilter

doFilterInternal

protected void doFilterInternal(HttpServletRequest request,
 HttpServletResponse response,
 FilterChain filterChain)
                         throws ServletException,
IOException

Description copied from class: OncePerRequestFilter

Same contract as for doFilter, but guaranteed to be just invoked once per request within a single request thread. See OncePerRequestFilter.shouldNotFilterAsyncDispatch() for details.

Provides HttpServletRequest and HttpServletResponse arguments instead of the default ServletRequest and ServletResponse ones.

Specified by:

doFilterInternal in class OncePerRequestFilter

Throws:

ServletException

IOException

isEligibleForEtag

protected boolean isEligibleForEtag(HttpServletRequest request,
 HttpServletResponse response,
 int responseStatusCode,
 InputStream inputStream)

Whether an ETag should be calculated for the given request and response exchange. By default, this is true if all the following match:

• Response is not committed.
• Response status codes is in the 2xx series.
• Request method is a GET.
• Response Cache-Control header does not contain "no-store" (or is not present at all).

Parameters:

request - the HTTP request

response - the HTTP response

responseStatusCode - the HTTP response status code

inputStream - the response body

Returns:

true if eligible for ETag generation, false otherwise

generateETagHeaderValue

protected String generateETagHeaderValue(InputStream inputStream,
 boolean isWeak)
                                  throws IOException

Generate the ETag header value from the given response body byte array.

The default implementation generates an MD5 hash.

Parameters:

inputStream - the response body as an InputStream

isWeak - whether the generated ETag should be weak

Returns:

the ETag header value

Throws:

IOException

See Also:

• DigestUtils

disableContentCaching

public static void disableContentCaching(ServletRequest request)

This method can be used to suppress the content caching response wrapper of the ShallowEtagHeaderFilter. The main reason for this is streaming scenarios which are not to be cached and do not need an eTag.

Note: This method must be called before the response is written to in order for the entire response content to be written without caching.

Since:

4.2