oscache對于jsp/servlet的緩存是使用Filter來實現的，對應的類是 com.opensymphony.oscache.web.filter.CacheFilter，既然是Filter那么要看的自然主要有三個方 法：init、doFilter和destroy，這里#destroy()并沒有具體實現，只關注前兩個即可，首先看一下#init()方法，

???? public ? void ?init(FilterConfig?filterConfig)? {
????????config? = ?filterConfig;

????????log.info( " OSCache:?Initializing?CacheFilter?with?filter?name? " ? + ?config.getFilterName());

???????? // ?此變量用于防治請求被重復的緩存
????????requestFiltered? = ?REQUEST_FILTERED? + ?config.getFilterName();
????????log.info( " Request?filter?attribute?is? " ? + ?requestFiltered);

???????? // ?讀取配置文件
????????Properties?props? = ? null ;
???????? try ? {
???????????? // ?首先按照Filter參數指定的地方讀取配置文件，否則讀取默認位置的
????????????String?propertiesfile? = ?config.getInitParameter( " oscache-properties-file " );

???????????? if ?(propertiesfile? != ? null ? && ?propertiesfile.length()? > ? 0 )? {
????????????????props? = ?Config.loadProperties(propertiesfile,
???????????????????????? " CacheFilter?with?filter?name?' " ? + ?config.getFilterName()? + ? " ' " );
????????????}
????????} ? catch ?(Exception?e)? {
????????????log.info( " OSCache:?Init?parameter?'oscache-properties-file'?not?set,?using?default. " );
????????}

???????? // ?實例化ServletCacheAdministrator，ServletCacheAdministrator只有一個實例，這里需要關注一下
????????admin? = ?ServletCacheAdministrator.getInstance(config.getServletContext(),?props);

???????? // ?緩存超時時間
????????String?timeParam? = ?config.getInitParameter( " time " );
???????? if ?(timeParam? != ? null )? {
???????????? try ? {
????????????????setTime(Integer.parseInt(timeParam));
????????????} ? catch ?(NumberFormatException?nfe)? {
????????????????log.error( " OSCache:?Unexpected?value?for?the?init?parameter?'time',?defaulting?to?one?hour.?Message= "
???????????????????????? + ?nfe.getMessage());
????????????}
????????}

???????? // ?緩存范圍
????????String?scopeParam? = ?config.getInitParameter( " scope " );
???????? if ?(scopeParam? != ? null )? {
???????????? if ?( " session " .equalsIgnoreCase(scopeParam))? {
????????????????setCacheScope(PageContext.SESSION_SCOPE);
????????????} ? else ? if ?( " application " .equalsIgnoreCase(scopeParam))? {
????????????????setCacheScope(PageContext.APPLICATION_SCOPE);
????????????} ? else ? {
????????????????log.error( " OSCache:?Wrong?value?' " ? + ?scopeParam
???????????????????????? + ? " '?for?init?parameter?'scope',?defaulting?to?'application'. " );
????????????}

????????}

???????? // ?利用"計劃任務"表達式來處理超時時間
????????setCron(config.getInitParameter( " cron " ));

???????? // ?是否處理include
????????String?fragmentParam? = ?config.getInitParameter( " fragment " );
???????? if ?(fragmentParam? != ? null )? {
???????????? if ?( " no " .equalsIgnoreCase(fragmentParam))? {
????????????????setFragment(FRAGMENT_NO);
????????????} ? else ? if ?( " yes " .equalsIgnoreCase(fragmentParam))? {
????????????????setFragment(FRAGMENT_YES);
????????????} ? else ? if ?( " auto " .equalsIgnoreCase(fragmentParam))? {
????????????????setFragment(FRAGMENT_AUTODETECT);
????????????} ? else ? {
????????????????log.error( " OSCache:?Wrong?value?' " ? + ?fragmentParam
???????????????????????? + ? " '?for?init?parameter?'fragment',?defaulting?to?'auto?detect'. " );
????????????}
????????}

???????? // ?是否處理URL里包括session?id的請求
????????String?nocacheParam? = ?config.getInitParameter( " nocache " );
???????? if ?(nocacheParam? != ? null )? {
???????????? if ?( " off " .equalsIgnoreCase(nocacheParam))? {
????????????????nocache? = ?NOCACHE_OFF;
????????????} ? else ? if ?( " sessionIdInURL " .equalsIgnoreCase(nocacheParam))? {
????????????????nocache? = ?NOCACHE_SESSION_ID_IN_URL;
????????????} ? else ? {
????????????????log.error( " OSCache:?Wrong?value?' " ? + ?nocacheParam
???????????????????????? + ? " '?for?init?parameter?'nocache',?defaulting?to?'off'. " );
????????????}
????????}

???????? // ?是否處理寫入到response中的header屬性Last-Modified
????????String?lastModifiedParam? = ?config.getInitParameter( " lastModified " );
???????? if ?(lastModifiedParam? != ? null )? {
???????????? if ?( " off " .equalsIgnoreCase(lastModifiedParam))? {
????????????????lastModified? = ?LAST_MODIFIED_OFF;
????????????} ? else ? if ?( " on " .equalsIgnoreCase(lastModifiedParam))? {
????????????????lastModified? = ?LAST_MODIFIED_ON;
????????????} ? else ? if ?( " initial " .equalsIgnoreCase(lastModifiedParam))? {
????????????????lastModified? = ?LAST_MODIFIED_INITIAL;
????????????} ? else ? {
????????????????log.error( " OSCache:?Wrong?value?' " ? + ?lastModifiedParam
???????????????????????? + ? " '?for?init?parameter?'lastModified',?defaulting?to?'initial'. " );
????????????}
????????}

???????? // ?是否處理寫入到response中的header屬性Expires
????????String?expiresParam? = ?config.getInitParameter( " expires " );
???????? if ?(expiresParam? != ? null )? {
???????????? if ?( " off " .equalsIgnoreCase(expiresParam))? {
????????????????setExpires(EXPIRES_OFF);
????????????} ? else ? if ?( " on " .equalsIgnoreCase(expiresParam))? {
????????????????setExpires(EXPIRES_ON);
????????????} ? else ? if ?( " time " .equalsIgnoreCase(expiresParam))? {
????????????????setExpires(EXPIRES_TIME);
????????????} ? else ? {
????????????????log.error( " OSCache:?Wrong?value?' " ? + ?expiresParam
???????????????????????? + ? " '?for?init?parameter?'expires',?defaulting?to?'on'. " );
????????????}
????????}

???????? // ?是否處理寫入到response中的header屬性Cache-Control
????????String?cacheControlMaxAgeParam? = ?config.getInitParameter( " max-age " );
???????? if ?(cacheControlMaxAgeParam? != ? null )? {
???????????? if ?(cacheControlMaxAgeParam.equalsIgnoreCase( " no?init " ))? {
????????????????setCacheControlMaxAge(MAX_AGE_NO_INIT);
????????????} ? else ? if ?(cacheControlMaxAgeParam.equalsIgnoreCase( " time " ))? {
????????????????setCacheControlMaxAge(MAX_AGE_TIME);
????????????} ? else ? {
???????????????? try ? {
????????????????????setCacheControlMaxAge(Long.parseLong(cacheControlMaxAgeParam));
????????????????} ? catch ?(NumberFormatException?nfe)? {
????????????????????log.error( " OSCache:?Unexpected?value?for?the?init?parameter?'max-age',?defaulting?to?'60'.?Message= "
???????????????????????????? + ?nfe.getMessage());
????????????????}
????????????}
????????}

???????? // ?ICacheKeyProvider的實例，用于創(chuàng)建緩存的key
????????ICacheKeyProvider?cacheKeyProviderParam? = ?(ICacheKeyProvider)?instantiateFromInitParam(
???????????????? " ICacheKeyProvider " ,?ICacheKeyProvider. class ,? this .getClass().getName());
???????? if ?(cacheKeyProviderParam? != ? null )? {
????????????setCacheKeyProvider(cacheKeyProviderParam);
????????}

???????? // ?ICacheGroupsProvider的實例，用于創(chuàng)建緩存的group名字
????????ICacheGroupsProvider?cacheGroupsProviderParam? = ?(ICacheGroupsProvider)?instantiateFromInitParam(
???????????????? " ICacheGroupsProvider " ,?ICacheGroupsProvider. class ,? this .getClass().getName());
???????? if ?(cacheGroupsProviderParam? != ? null )? {
????????????setCacheGroupsProvider(cacheGroupsProviderParam);
????????}

???????? // ?EntryRefreshPolicy的實例，用于指定緩存過期策略
????????EntryRefreshPolicy?expiresRefreshPolicyParam? = ?(EntryRefreshPolicy)?instantiateFromInitParam(
???????????????? " EntryRefreshPolicy " ,?EntryRefreshPolicy. class ,?ExpiresRefreshPolicy. class .getName());
???????? if ?(expiresRefreshPolicyParam? != ? null )? {
????????????setExpiresRefreshPolicy(expiresRefreshPolicyParam);
????????} ? else ? {
????????????setExpiresRefreshPolicy( new ?ExpiresRefreshPolicy(time));
????????}

???????? // ?指定哪些請求方式不去緩存，如GET，POST等
????????String?disableCacheOnMethodsParam? = ?config.getInitParameter( " disableCacheOnMethods " );
???????? if ?(StringUtil.hasLength(disableCacheOnMethodsParam))? {
????????????disableCacheOnMethods? = ?StringUtil.split(disableCacheOnMethodsParam,? ' , ' );
????????}

????}

這個方法主要是對Filter的init-param的載入還有緩存管理器類實例的創(chuàng)建(里面會包括一個Application Scope的Cache的創(chuàng)建還有oscache配置文件的讀取)。其中的這句調用時需要關注一下的，admin = ServletCacheAdministrator.getInstance(config.getServletContext(), props)，也就是ServletCacheAdministrator類實例的創(chuàng)建。

???? public ? synchronized ? static ?ServletCacheAdministrator?getInstance(ServletContext?context,?Properties?p)? {
???????? // ?Cache在ServletContext中的屬性名
????????String?adminKey? = ? null ;
???????? if ?(p? != ? null )? {
???????????? // ?這里是oscache配置文件中的cache.key屬性
????????????adminKey? = ?p.getProperty(CACHE_KEY_KEY);
????????}
???????? if ?(adminKey? == ? null )? {
????????????adminKey? = ?DEFAULT_CACHE_KEY;
????????}
???????? // ?ServletCacheAdministrator在ServletContext中的鍵值要加上"_admin"這個后綴
????????adminKey? += ?CACHE_ADMINISTRATOR_KEY_SUFFIX;

???????? // ?先嘗試在ServletContext中找Cache，當然，第一次初始化時是不會找到的
????????ServletCacheAdministrator?adm

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oscache源代碼閱讀(四) -- JSP/Servlet緩存CacheFilter