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:

Aware, BeanNameAware, DisposableBean, InitializingBean, EnvironmentAware, ServletContextAware

public class ShallowEtagHeaderFilter
extends OncePerRequestFilter

javax.servlet.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.

NOTE: As of Spring Framework 5.0, this filter uses request/response decorators built on the Servlet 3.1 API.

Since:

3.0

Author:

Arjen Poutsma, Rossen Stoyanchev, Brian Clozel, Juergen Hoeller

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	ShallowEtagHeaderFilter.HttpStreamingAwareContentCachingResponseWrapper

Field Summary

Fields

Modifier and Type	Field and Description
private static java.lang.String	DIRECTIVE_NO_STORE
private static java.lang.String	HEADER_CACHE_CONTROL
private static java.lang.String	HEADER_ETAG
private static java.lang.String	HEADER_IF_NONE_MATCH
private static java.lang.String	STREAMING_ATTRIBUTE
private boolean	writeWeakETag

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 and Description
ShallowEtagHeaderFilter()

Method Summary

Modifier and Type	Method and Description
static void	disableContentCaching(ServletRequest request) This method can be used to disable 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 java.lang.String	generateETagHeaderValue(java.io.InputStream inputStream, boolean isWeak) Generate the ETag header value from the given response body byte array.
private static boolean	isContentCachingDisabled(HttpServletRequest request)
protected boolean	isEligibleForEtag(HttpServletRequest request, HttpServletResponse response, int responseStatusCode, java.io.InputStream inputStream) Indicates whether the given request and response are eligible for ETag generation.
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.
private void	updateResponse(HttpServletRequest request, HttpServletResponse response)

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

doFilter, getAlreadyFilteredAttributeName, isAsyncDispatch, isAsyncStarted, shouldNotFilter, shouldNotFilterErrorDispatch

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

addRequiredProperty, afterPropertiesSet, destroy, 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

Field Detail

HEADER_ETAG

private static final java.lang.String HEADER_ETAG

See Also:

Constant Field Values

HEADER_IF_NONE_MATCH

private static final java.lang.String HEADER_IF_NONE_MATCH

See Also:

Constant Field Values

HEADER_CACHE_CONTROL

private static final java.lang.String HEADER_CACHE_CONTROL

See Also:

Constant Field Values

DIRECTIVE_NO_STORE

private static final java.lang.String DIRECTIVE_NO_STORE

See Also:

Constant Field Values

STREAMING_ATTRIBUTE

private static final java.lang.String STREAMING_ATTRIBUTE

writeWeakETag

private boolean writeWeakETag

Constructor Detail

ShallowEtagHeaderFilter

public ShallowEtagHeaderFilter()

Method Detail

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,
                                java.io.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

java.io.IOException

updateResponse

private void updateResponse(HttpServletRequest request,
                            HttpServletResponse response)
                     throws java.io.IOException

Throws:

java.io.IOException

isEligibleForEtag

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

Indicates whether the given request and response are eligible for ETag generation.

The default implementation returns true if all conditions match:

• response status codes in the 2xx series
• request method is a GET
• response Cache-Control header is not set or does not contain a "no-store" directive

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 java.lang.String generateETagHeaderValue(java.io.InputStream inputStream,
                                                   boolean isWeak)
                                            throws java.io.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:

java.io.IOException

See Also:

DigestUtils

disableContentCaching

public static void disableContentCaching(ServletRequest request)

This method can be used to disable the content caching response wrapper of the ShallowEtagHeaderFilter. This can be done before the start of HTTP streaming for example where the response will be written to asynchronously and not in the context of a Servlet container thread.

Since:

4.2

isContentCachingDisabled

private static boolean isContentCachingDisabled(HttpServletRequest request)