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
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