系统要集群，使用SNA方案。
一、 缓存的处理
缓存要使用统一的缓存服务器，集中式缓存。
原先的实现采用ehcache。
在spring里的配置，以资源缓存为例：
<!-- EhCache Manager -->
<bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean">
<property name="configLocation">
<value>classpath:ehcache.xml</value>
</property>
</bean>
<bean id="resourceCacheBackend"
class="org.springframework.cache.ehcache.EhCacheFactoryBean">
<property name="cacheManager" ref="cacheManager"/>
<property name="cacheName" value="resourceCache"/>
</bean>
<bean id="resourceCache"
class="com.framework.extcomponent.security.authentication.services.acegi.cache.EhCacheBasedResourceCache"
autowire="byName">
<property name="cache" ref="resourceCacheBackend"/>
</bean>
cacheManager负责对ehcache进行管理，初始化、启动、停止。
resourceCacheBackend负责实际执行缓存操作，put 、get、remove。
resourceCache实现具有业务语义的业务应用层面的缓存操作，内部调用resourceCacheBackend操作。
现在采用memcached。
关于客户端，采用文初封装的客户端，地址在http://code.google.com/p/memcache-client-forjava/。
使用spring的FactoryBean进行二次封装。同理：
memcachedManager负责对memcached进行管理，初始化、启动、停止。
代码：
/** *//**
* Date: 2008-10-14
* Time: 10:36:30
* 管理Memcached 的CacheManager
*/
public class MemcachedCacheManagerFactoryBean implements FactoryBean, InitializingBean, DisposableBean 
{
protected final Log logger = LogFactory.getLog(getClass());
private ICacheManager<IMemcachedCache> cacheManager;
public Object getObject() throws Exception {
return cacheManager;
}
public Class getObjectType() {
return this.cacheManager.getClass();
}
public boolean isSingleton() {
return true;
}
public void afterPropertiesSet() throws Exception {
logger.info("Initializing Memcached CacheManager");
cacheManager = CacheUtil.getCacheManager(IMemcachedCache.class,
MemcachedCacheManager.class.getName());
cacheManager.start();
}
public void destroy() throws Exception {
logger.info("Shutting down Memcached CacheManager");
cacheManager.stop();
}
}
配置：
<bean id="memcachedManager"
class="com.framework.extcomponent.cache.MemcachedCacheManagerFactoryBean"/>
resourceCacheBackend负责实际执行缓存操作，put 、get、remove。
代码：
/** *//**
* Date: 2008-10-14
* Time: 10:37:16
* 返回 MemcachedCache
*/
public class MemcachedCacheFactoryBean implements FactoryBean, BeanNameAware, InitializingBean {
protected final Log logger = LogFactory.getLog(getClass());
private ICacheManager<IMemcachedCache> cacheManager;
private String cacheName;
private String beanName;
private IMemcachedCache cache;
public void setCacheManager(ICacheManager<IMemcachedCache> cacheManager) {
this.cacheManager = cacheManager;
}
public void setCacheName(String cacheName) {
this.cacheName = cacheName;
}
public Object getObject() throws Exception {
return cache;
}
public Class getObjectType() {
return this.cache.getClass();
}
public boolean isSingleton() {
return true;
}
public void setBeanName(String name) {
this.beanName=name;
}
public void afterPropertiesSet() throws Exception {
// If no cache name given, use bean name as cache name.
if (this.cacheName == null) {
this.cacheName = this.beanName;
}
cache = cacheManager.getCache(cacheName);
}
}
配置：
<bean id="resourceCacheBackend"
class="com.framework.extcomponent.cache.MemcachedCacheFactoryBean">
<property name="cacheManager" ref="memcachedManager"/>
<property name="cacheName" value="memcache"/>
</bean>
resourceCache同上，替换新的实现类MemcachedBasedResourceCache即可。
二、 Session失效的处理
采用memcached作为httpsession的存储，并不直接保存httpsession对象，自定义SessionMap，SessionMap直接继承HashMap，保存SessionMap。
会话胶粘：未失败转发的情况下没必要在memcached保存的SessionMap和httpsession之间复制来复制去，眉来眼去。
利用memcached计数器保存在线人数。
系统权限采用了acegi，在acegi的拦截器链里配置snaFilter
<bean id="filterChainProxy"
class="org.acegisecurity.util.FilterChainProxy">
<property name="filterInvocationDefinitionSource">
<value>
CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
PATTERN_TYPE_APACHE_ANT
/**=snaFilter,httpSessionContextIntegrationFilter,logoutFilter,authenticationProcessingFilter,basicProcessingFilter,securityContextHolderAwareRequestFilter,exceptionTranslationFilter,filterInvocationInterceptor
</value>
</property>
</bean>
注意需要配置在第一个。
snaFilter的职责：
1、 没有HttpSession时，创建HttpSession;
2、 创建Cookie保存HttpSession id;
3、 如果Cookie保存的HttpSession id与当前HttpSession id一致，说明是正常请求；
4、 如果Cookie保存的HttpSession id与当前HttpSession id不一致，说明是失败转发；失败转发的处理：
4.1、根据Cookie保存的HttpSession id从memcached获取SessionMap；
4.2、SessionMap属性复制到当前HttpSession；
4.3、memcached删除SessionMap。
5、 判断当前请求url是否是登出url，是则删除SessionMap，在线人数减1.
代码：
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException {
final HttpServletRequest hrequest = (HttpServletRequest) servletRequest;
final HttpServletResponse hresponse = (HttpServletResponse) servletResponse;
String uri = hrequest.getRequestURI();
logger.debug("开始SNA拦截-----------------" + uri);
HttpSession httpSession = hrequest.getSession();
String sessionId = httpSession.getId();
//如果是登出,则直接干掉sessionMap
if (uri.equals(logoutUrl)) {
logger.debug("remove sessionmap:" + sessionId);
//在线人数减1
getCache().addOrDecr("userCount",1);
getCache().remove(sessionId);
} else {
String cookiesessionid = getSessionIdFromCookie(hrequest, hresponse);
if (!sessionId.equals(cookiesessionid)) {
createCookie(sessionId, hresponse);
SessionMap sessionMap = getSessionMap(cookiesessionid);
if (sessionMap != null) {
logger.debug("fail over--------sessionid:" + sessionId + "cookiesessionid:" + cookiesessionid);
initialHttpSession(sessionMap, httpSession);
cache.remove(cookiesessionid);
}
}
}
filterChain.doFilter(hrequest, hresponse);
}
利用HttpSessionAttributeListener监听httpsession的属性变化,同步到memecached中的sessionmap。
public void attributeAdded(HttpSessionBindingEvent event) {
HttpSession httpSession = event.getSession();
String attrName = event.getName();
Object attrValue = event.getValue();
String sessionId = httpSession.getId();
logger.debug("attributeAdded sessionId:" + sessionId + "name:" + attrName + ",value:" + attrValue);
SessionMap sessionMap = getSessionMap(sessionId);
if (sessionMap == null){
//在线人数加1
getCache().addOrIncr("userCount",1);
sessionMap = new SessionMap();
}
logger.debug("name:" + attrName + ",value:" + attrValue);
sessionMap.put(attrName, attrValue);
getCache().put(sessionId, sessionMap);
}
public void attributeRemoved(HttpSessionBindingEvent event) {
HttpSession httpSession = event.getSession();
String attrName = event.getName();
String sessionId = httpSession.getId();
logger.debug("attributeRemoved sessionId:" + sessionId + "name:" + attrName);
SessionMap sessionMap = getSessionMap(sessionId);
if (sessionMap != null) {
logger.debug("remove:" + attrName);
sessionMap.remove(attrName);
getCache().put(sessionId, sessionMap);
}
}
public void attributeReplaced(HttpSessionBindingEvent event) {
attributeAdded(event);
}
利用HttpSessionListener，sessionDestroyed事件时根据sessionid删除memcached里的sessionMap（如果存在）。不再担心httpsession的过期问题。
public void sessionDestroyed(HttpSessionEvent event) {
HttpSession httpSession = event.getSession();
String sessionId = httpSession.getId();
logger.debug("session Removed sessionId:" + sessionId);
SessionMap sessionMap = getSessionMap(sessionId);
if (sessionMap != null) {
logger.debug("remove sessionmap:" + sessionId);
//在线人数减1
getCache().addOrDecr("userCount",1);
getCache().remove(sessionId);
}
}
三、 文件保存的处理
和缓存类似，采用集中式的文件服务。对于linux，采用nfs。参考文档
http://linux.vbird.org/linux_server/0330nfs.php#What_NFS_perm。关键在于对权限的分配。
应用程序本身不用修改。