Class ExpiresFilter
- All Implemented Interfaces:
- Filter
 ExpiresFilter is a Java Servlet API port of Apache
 mod_expires to add 'Expires' and 'Cache-Control: max-age=' headers to HTTP response according to
 its 'Content-Type'.
 
Following documentation is inspired by mod_expires
Summary
 This filter controls the setting of the Expires HTTP header and the max-age directive of the
 Cache-Control HTTP header in server responses. The expiration date can set to be relative to either the time
 the source file was last modified, or to the time of the client access.
 
These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.
 To modify Cache-Control directives other than max-age (see
 RFC 2616 section 14.9), you can use
 other servlet filters or Apache Httpd
 mod_headers module.
 
Filter Configuration
Basic configuration to add 'Expires' and 'Cache-Control: max-age=' headers to images, CSS and
 JavaScript
 
 
 <web-app ...>
    ...
    <filter>
       <filter-name>ExpiresFilter</filter-name>
       <filter-class>org.apache.catalina.filters.ExpiresFilter</filter-class>
       <init-param>
          <param-name>ExpiresByType image</param-name>
          <param-value>access plus 10 minutes</param-value>
       </init-param>
       <init-param>
          <param-name>ExpiresByType text/css</param-name>
          <param-value>access plus 10 minutes</param-value>
       </init-param>
       <init-param>
          <param-name>ExpiresByType text/javascript</param-name>
          <param-value>access plus 10 minutes</param-value>
       </init-param>
    </filter>
    ...
    <filter-mapping>
       <filter-name>ExpiresFilter</filter-name>
       <url-pattern>/*</url-pattern>
       <dispatcher>REQUEST</dispatcher>
    </filter-mapping>
    ...
 </web-app>
 
 
 Configuration Parameters
ExpiresByType <content-type>
 
 This directive defines the value of the Expires header and the max-age directive of the
 Cache-Control header generated for documents of the specified type (e.g., text/html). The
 second argument sets the number of seconds that will be added to a base time to construct the expiration date. The
 Cache-Control: max-age is calculated by subtracting the request time from the expiration date and expressing
 the result in seconds.
 
 The base time is either the last modification time of the file, or the time of the client's access to the
 document. Which should be used is specified by the <code> field; M means that the
 file's last modification time should be used as the base time, and
 A means the client's access time should be used. The duration
 is expressed in seconds. A2592000 stands for
 access plus 30 days in alternate syntax.
 
 The difference in effect is subtle. If M (modification in
 alternate syntax) is used, all current copies of the document in all caches
 will expire at the same time, which can be good for something like a weekly
 notice that's always found at the same URL. If A (
 access or now in alternate syntax) is used, the date of
 expiration is different for each client; this can be good for image files
 that don't change very often, particularly for a set of related
 documents that all refer to the same images (i.e., the images will be
 accessed repeatedly within a relatively short timespan).
 
Example:
 
 <init-param>
    <param-name>ExpiresByType text/html</param-name>
    <param-value>access plus 1 month 15 days 2 hours</param-value>
 </init-param>
 <init-param>
    <!-- 2592000 seconds = 30 days -->
    <param-name>ExpiresByType image/gif</param-name>
    <param-value>A2592000</param-value>
 </init-param>
 
 
 
 Note that this directive only has effect if ExpiresActive On has
 been specified. It overrides, for the specified MIME type only, any
 expiration date set by the ExpiresDefault directive.
 
You can also specify the expiration time calculation using an alternate syntax, described earlier in this document.
 ExpiresExcludedResponseStatusCodes
 
 This directive defines the http response status codes for which the
 ExpiresFilter will not generate expiration headers. By default, the
 304 status code ("Not modified") is skipped. The
 value is a comma separated list of http status codes.
 
 This directive is useful to ease usage of ExpiresDefault directive.
 Indeed, the behavior of 304 Not modified (which does specify a
 Content-Type header) combined with Expires and
 Cache-Control:max-age= headers can be unnecessarily tricky to
 understand.
 
Configuration sample :
 
 <init-param>
    <param-name>ExpiresExcludedResponseStatusCodes</param-name>
    <param-value>302, 500, 503</param-value>
 </init-param>
 
 
 ExpiresDefault
 This directive sets the default algorithm for calculating the expiration time
 for all documents in the affected realm. It can be overridden on a
 type-by-type basis by the ExpiresByType directive. See the
 description of that directive for details about the syntax of the argument,
 and the "alternate syntax" description as well.
 
Alternate Syntax
 The ExpiresDefault and ExpiresByType directives can also be
 defined in a more readable syntax of the form:
 
 
 <init-param>
    <param-name>ExpiresDefault</param-name>
    <param-value><base> [plus] (<num> <type>)*</param-value>
 </init-param>
 <init-param>
    <param-name>ExpiresByType type/encoding</param-name>
    <param-value><base> [plus] (<num> <type>)*</param-value>
 </init-param>
 
 
 
 where <base> is one of:
 
- access
- now(equivalent to '- access')
- modification
 The plus keyword is optional. <num> should be an
 integer value (acceptable to Integer.parseInt()), and
 <type> is one of:
 
- years
- months
- weeks
- days
- hours
- minutes
- seconds
For example, any of the following directives can be used to make documents expire 1 month after being accessed, by default:
 
 <init-param>
    <param-name>ExpiresDefault</param-name>
    <param-value>access plus 1 month</param-value>
 </init-param>
 <init-param>
    <param-name>ExpiresDefault</param-name>
    <param-value>access plus 4 weeks</param-value>
 </init-param>
 <init-param>
    <param-name>ExpiresDefault</param-name>
    <param-value>access plus 30 days</param-value>
 </init-param>
 
 
 
 The expiry time can be fine-tuned by adding several '
 <num> <type>' clauses:
 
 
 <init-param>
    <param-name>ExpiresByType text/html</param-name>
    <param-value>access plus 1 month 15 days 2 hours</param-value>
 </init-param>
 <init-param>
    <param-name>ExpiresByType image/gif</param-name>
    <param-value>modification plus 5 hours 3 minutes</param-value>
 </init-param>
 
 
 
 Note that if you use a modification date based setting, the Expires
 header will not be added to content that does not come from
 a file on disk. This is due to the fact that there is no modification time
 for such content.
 
Expiration headers generation eligibility
 A response is eligible to be enriched by ExpiresFilter if :
 
- no expiration header is defined (Expiresheader or themax-agedirective of theCache-Controlheader),
- the response status code is not excluded by the directive
 ExpiresExcludedResponseStatusCodes,
- the Content-Typeof the response matches one of the types defined the inExpiresByTypedirectives or theExpiresDefaultdirective is defined.
Note :
- If Cache-Controlheader contains other directives thanmax-age, they are concatenated with themax-agedirective that is added by theExpiresFilter.
Expiration configuration selection
The expiration configuration if elected according to the following algorithm:
- ExpiresByTypematching the exact content-type returned by- HttpServletResponse.getContentType()possibly including the charset (e.g. '- text/xml;charset=UTF-8'),
- ExpiresByTypematching the content-type without the charset if- HttpServletResponse.getContentType()contains a charset (e.g. '- text/xml;charset=UTF-8' -> '- text/xml'),
- ExpiresByTypematching the major type (e.g. substring before '- /') of- HttpServletResponse.getContentType()(e.g. '- text/xml;charset=UTF-8' -> '- text'),
- ExpiresDefault
Implementation Details
When to write the expiration headers ?
 The ExpiresFilter traps the 'on before write response
 body' event to decide whether it should generate expiration headers or
 not.
 
 To trap the 'before write response body' event, the
 ExpiresFilter wraps the http servlet response's writer and
 outputStream to intercept calls to the methods write(),
 print(), close() and flush(). For empty response
 body (e.g. empty files), the write(), print(),
 close() and flush() methods are not called; to handle this
 case, the ExpiresFilter, at the end of its doFilter()
 method, manually triggers the onBeforeWriteResponseBody() method.
 
Configuration syntax
 The ExpiresFilter supports the same configuration syntax as Apache
 Httpd mod_expires.
 
 A challenge has been to choose the name of the <param-name>
 associated with ExpiresByType in the <filter>
 declaration. Indeed, Several ExpiresByType directives can be
 declared when web.xml syntax does not allow to declare several
 <init-param> with the same name.
 
 The workaround has been to declare the content type in the
 <param-name> rather than in the <param-value>.
 
Designed for extension : the open/close principle
 The ExpiresFilter has been designed for extension following the
 open/close principle.
 
Key methods to override for extension are :
- 
 isEligibleToExpirationHeaderGeneration(HttpServletRequest, XHttpServletResponse)
- 
 getExpirationDate(HttpServletRequest, XHttpServletResponse)
Troubleshooting
 To troubleshoot, enable logging on the
 org.apache.catalina.filters.ExpiresFilter.
 
Extract of logging.properties
 org.apache.catalina.filters.ExpiresFilter.level = FINE
 
 Sample of initialization log message :
 Mar 26, 2010 2:01:41 PM org.apache.catalina.filters.ExpiresFilter init
 FINE: Filter initialized with configuration ExpiresFilter[
    excludedResponseStatusCode=[304],
    default=null,
    byType={
       image=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]],
       text/css=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]],
       text/javascript=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]]}]
 
 
 Sample of per-request log message where ExpiresFilter adds an expiration date
 
 Mar 26, 2010 2:09:47 PM org.apache.catalina.filters.ExpiresFilter onBeforeWriteResponseBody
 FINE: Request "/tomcat.gif" with response status "200" content-type "image/gif", set expiration date 3/26/10 2:19 PM
 
 
 Sample of per-request log message where ExpiresFilter does not add an expiration date
 
 Mar 26, 2010 2:10:27 PM org.apache.catalina.filters.ExpiresFilter onBeforeWriteResponseBody
 FINE: Request "/docs/config/manager.html" with response status "200" content-type "text/html", no expiration configured
 - 
Nested Class SummaryNested ClassesModifier and TypeClassDescriptionprotected static classDuration composed of anExpiresFilter.Duration.amountand aExpiresFilter.Duration.unitprotected static enumDuration unitprotected static classMain piece of configuration of the filter.protected static enumExpiration configuration starting point.classWrapping extension of theHttpServletResponseto yrap the "Start Write Response Body" event.classWrapping extension ofPrintWriterto trap the "Start Write Response Body" event.classWrapping extension ofServletOutputStreamto trap the "Start Write Response Body" event.
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Field SummaryFields inherited from class org.apache.catalina.filters.FilterBasesm
- 
Constructor SummaryConstructors
- 
Method SummaryModifier and TypeMethodDescriptionprotected static int[]commaDelimitedListToIntArray(String commaDelimitedInts) Convert a comma delimited list of numbers into anint[].protected static String[]commaDelimitedListToStringArray(String commaDelimitedStrings) Deprecated.Unused.protected static booleanvoiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain) ThedoFiltermethod of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain.int[]protected DategetExpirationDate(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) Returns the expiration date of the givenExpiresFilter.XHttpServletResponseornullif no expiration date has been configured for the declared content type.protected DategetExpirationDate(ExpiresFilter.ExpiresConfiguration configuration, ExpiresFilter.XHttpServletResponse response) Returns the expiration date of the givenExpiresFilter.ExpiresConfiguration,HttpServletRequestandExpiresFilter.XHttpServletResponse.protected Logvoidinit(FilterConfig filterConfig) Iterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.protected static StringintsToCommaDelimitedString(int[] ints) Convert an array of ints into a comma delimited stringprotected booleanisEligibleToExpirationHeaderGeneration(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) protectedfor extension.protected static booleanprotected static booleanisNotEmpty(String str) voidonBeforeWriteResponseBody(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) If no expiration header has been set by the servlet and an expiration has been defined in theExpiresFilterconfiguration, sets the 'Expires' header and the attribute 'max-age' of the 'Cache-Control' header.protected ExpiresFilter.ExpiresConfigurationparseExpiresConfiguration(String inputLine) Parse configuration lines like 'access plus 1 month 15 days 2 hours' or 'modification 1 day 2 hours 5 seconds'voidsetDefaultExpiresConfiguration(ExpiresFilter.ExpiresConfiguration defaultExpiresConfiguration) voidsetExcludedResponseStatusCodes(int[] excludedResponseStatusCodes) voidsetExpiresConfigurationByContentType(Map<String, ExpiresFilter.ExpiresConfiguration> expiresConfigurationByContentType) protected static booleanstartsWithIgnoreCase(String string, String prefix) protected static StringsubstringBefore(String str, String separator) toString()Methods inherited from class org.apache.catalina.filters.FilterBaseisConfigProblemFatal
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Constructor Details- 
ExpiresFilterpublic ExpiresFilter()
 
- 
- 
Method Details- 
commaDelimitedListToIntArrayConvert a comma delimited list of numbers into anint[].- Parameters:
- commaDelimitedInts- can be- null
- Returns:
- never nullarray
 
- 
commaDelimitedListToStringArrayDeprecated.Unused. Will be removed in Tomcat 11.Convert a given comma delimited list of strings into an array of String- Parameters:
- commaDelimitedStrings- the string to be split
- Returns:
- array of patterns (non null)
 
- 
contains- Parameters:
- str- String that will be searched
- searchStr- The substring to search
- Returns:
- trueif the given- strcontains the given- searchStr.
 
- 
intsToCommaDelimitedStringConvert an array of ints into a comma delimited string- Parameters:
- ints- The int array
- Returns:
- a comma separated string
 
- 
isEmpty- Parameters:
- str- The String to check
- Returns:
- trueif the given- stris- nullor has a zero characters length.
 
- 
isNotEmpty- Parameters:
- str- The String to check
- Returns:
- trueif the given- strhas at least one character (can be a whitespace).
 
- 
startsWithIgnoreCase- Parameters:
- string- can be- null
- prefix- can be- null
- Returns:
- trueif the given- stringstarts with the given- prefixignoring case.
 
- 
substringBefore- Parameters:
- str- can be- null
- separator- can be- null
- Returns:
- the subset of the given strthat is before the first occurrence of the givenseparator. Returnnullif the givenstror the givenseparatoris null. Return and empty string if theseparatoris empty.
 
- 
doFilterpublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException Description copied from interface:jakarta.servlet.FilterThedoFiltermethod of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this method allows the Filter to pass on the request and response to the next entity in the chain.A typical implementation of this method would follow the following pattern:- 
 1. Examine the request
 2. Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
 3. Optionally wrap the response object with a custom implementation to filter content or headers for output filtering
 4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()),
 4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
 5. Directly set headers on the response after invocation of the next entity in the filter chain.- Parameters:
- request- The request to process
- response- The response associated with the request
- chain- Provides access to the next filter in the chain for this filter to pass the request and response to for further processing
- Throws:
- IOException- if an I/O error occurs during this filter's processing of the request
- ServletException- if the processing fails for any other reason
 
- 
getDefaultExpiresConfiguration
- 
getExcludedResponseStatusCodes
- 
getExcludedResponseStatusCodesAsIntspublic int[] getExcludedResponseStatusCodesAsInts()
- 
getExpirationDateprotected Date getExpirationDate(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) Returns the expiration date of the givenExpiresFilter.XHttpServletResponseornullif no expiration date has been configured for the declared content type.protectedfor extension.- Parameters:
- request- The HTTP request
- response- The wrapped HTTP response
- Returns:
- the expiration date
- See Also:
 
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getExpirationDateprotected Date getExpirationDate(ExpiresFilter.ExpiresConfiguration configuration, ExpiresFilter.XHttpServletResponse response) Returns the expiration date of the given ExpiresFilter.ExpiresConfiguration,HttpServletRequestandExpiresFilter.XHttpServletResponse.protectedfor extension.- Parameters:
- configuration- The parsed expires
- response- The Servlet response
- Returns:
- the expiration date
 
- 
getExpiresConfigurationByContentType
- 
getLogger- Specified by:
- getLoggerin class- FilterBase
 
- 
initDescription copied from class:FilterBaseIterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.- Specified by:
- initin interface- Filter
- Overrides:
- initin class- FilterBase
- Parameters:
- filterConfig- The configuration information associated with the filter instance being initialised
- Throws:
- ServletException- if- FilterBase.isConfigProblemFatal()returns- trueand a configured parameter does not have a matching setter
 
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isEligibleToExpirationHeaderGenerationprotected boolean isEligibleToExpirationHeaderGeneration(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) protectedfor extension.- Parameters:
- request- The Servlet request
- response- The Servlet response
- Returns:
- trueif an expire header may be added
 
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onBeforeWriteResponseBodypublic void onBeforeWriteResponseBody(HttpServletRequest request, ExpiresFilter.XHttpServletResponse response) If no expiration header has been set by the servlet and an expiration has been defined in the ExpiresFilterconfiguration, sets the 'Expires' header and the attribute 'max-age' of the 'Cache-Control' header.Must be called on the "Start Write Response Body" event. Invocations to Logger.debug(...)are guarded byLog.isDebugEnabled()becauseHttpServletRequest.getRequestURI()andServletResponse.getContentType()costsStringobjects instantiations (as of Tomcat 7).- Parameters:
- request- The Servlet request
- response- The Servlet response
 
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parseExpiresConfigurationParse configuration lines like 'access plus 1 month 15 days 2 hours' or 'modification 1 day 2 hours 5 seconds'- Parameters:
- inputLine- the input
- Returns:
- the parsed expires
 
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setDefaultExpiresConfigurationpublic void setDefaultExpiresConfiguration(ExpiresFilter.ExpiresConfiguration defaultExpiresConfiguration) 
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setExcludedResponseStatusCodespublic void setExcludedResponseStatusCodes(int[] excludedResponseStatusCodes) 
- 
setExpiresConfigurationByContentTypepublic void setExpiresConfigurationByContentType(Map<String, ExpiresFilter.ExpiresConfiguration> expiresConfigurationByContentType) 
- 
toString
 
-