oscache源代码阅读(四) -- JSP/Servlet缓存CacheFilter

oscache对于jsp/servlet的缓存是使用Filter来实现的，对应的类是 com.opensymphony.oscache.web.filter.CacheFilter，既然是Filter那么要看的自然主要有三个方 法：init、doFilter和destroy，这里#destroy()并没有具体实现，只关注前两个即可，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());

         //  此变量用于防治请求被重复的缓存
        requestFiltered  =  REQUEST_FILTERED  +  config.getFilterName();
        log.info( " Request filter attribute is  "   +  requestFiltered);

         //  读取配置文件
        Properties props  =   null ;
         try   {
             //  首先按照Filter参数指定的地方读取配置文件，否则读取默认位置的
            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. " );
        }

         //  实例化ServletCacheAdministrator，ServletCacheAdministrator只有一个实例，这里需要关注一下
        admin  =  ServletCacheAdministrator.getInstance(config.getServletContext(), props);

         //  缓存超时时间
        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());
            }
        }

         //  缓存范围
        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"计划任务"表达式来处理超时时间
        setCron(config.getInitParameter( " cron " ));

         //  是否处理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'. " );
            }
        }

         //  是否处理URL里包括session id的请求
        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'. " );
            }
        }

         //  是否处理写入到response中的header属性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'. " );
            }
        }

         //  是否处理写入到response中的header属性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'. " );
            }
        }

         //  是否处理写入到response中的header属性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的实例，用于创建缓存的key
        ICacheKeyProvider cacheKeyProviderParam  =  (ICacheKeyProvider) instantiateFromInitParam(
                 " ICacheKeyProvider " , ICacheKeyProvider. class ,  this .getClass().getName());
         if  (cacheKeyProviderParam  !=   null )  {
            setCacheKeyProvider(cacheKeyProviderParam);
        }

         //  ICacheGroupsProvider的实例，用于创建缓存的group名字
        ICacheGroupsProvider cacheGroupsProviderParam  =  (ICacheGroupsProvider) instantiateFromInitParam(
                 " ICacheGroupsProvider " , ICacheGroupsProvider. class ,  this .getClass().getName());
         if  (cacheGroupsProviderParam  !=   null )  {
            setCacheGroupsProvider(cacheGroupsProviderParam);
        }

         //  EntryRefreshPolicy的实例，用于指定缓存过期策略
        EntryRefreshPolicy expiresRefreshPolicyParam  =  (EntryRefreshPolicy) instantiateFromInitParam(
                 " EntryRefreshPolicy " , EntryRefreshPolicy. class , ExpiresRefreshPolicy. class .getName());
         if  (expiresRefreshPolicyParam  !=   null )  {
            setExpiresRefreshPolicy(expiresRefreshPolicyParam);
        }   else   {
            setExpiresRefreshPolicy( new  ExpiresRefreshPolicy(time));
        }

         //  指定哪些请求方式不去缓存，如GET，POST等
        String disableCacheOnMethodsParam  =  config.getInitParameter( " disableCacheOnMethods " );
         if  (StringUtil.hasLength(disableCacheOnMethodsParam))  {
            disableCacheOnMethods  =  StringUtil.split(disableCacheOnMethodsParam,  ' , ' );
        }

    }

这个方法主要是对Filter的init-param的载入还有缓存管理器类实例的创建(里面会包括一个Application Scope的Cache的创建还有oscache配置文件的读取)。其中的这句调用时需要关注一下的，admin = ServletCacheAdministrator.getInstance(config.getServletContext(), props)，也就是ServletCacheAdministrator类实例的创建。

     public   synchronized   static  ServletCacheAdministrator getInstance(ServletContext context, Properties p)  {
         //  Cache在ServletContext中的属性名
        String adminKey  =   null ;
         if  (p  !=   null )  {
             //  这里是oscache配置文件中的cache.key属性
            adminKey  =  p.getProperty(CACHE_KEY_KEY);
        }
         if  (adminKey  ==   null )  {
            adminKey  =  DEFAULT_CACHE_KEY;
        }
         //  ServletCacheAdministrator在ServletContext中的键值要加上"_admin"这个后缀
        adminKey  +=  CACHE_ADMINISTRATOR_KEY_SUFFIX;

         //  先尝试在ServletContext中找Cache，当然，第一次初始化时是不会找到的
        ServletCacheAdministrator adm