关于spring security自定义sessionRegistry不工作的原因简析

最近调了一下spring security的集群session共享，用到了自定义的SessionRegistry，却发现怎么也不工作，翻了翻stackoverfllow，也没找到靠谱的办法，最后自己debug，找到了问题所在
本文基于 Spring3.1.5,Spring security 2.0.4
最开始配置如下：

<beans:bean id="sessionRegistry"
class="com.shop.core.security.support.SessionRegistryImpl" scope="singleton">
<beans:property name="cacheManager" ref="cacheManager" />
</beans:bean>
<bean:http auto-config="false" entry-point-ref="loginUrlEntryPoint">
...
<bean:concurrent-session-control max-sessions="200000"
exception-if-maximum-exceeded="false" expired-url="/outline.htm"
session-registry-alias="sessionRegistry"  />
...
</bean:http>

debug发现自定义的SessionRegistryImpl类也有载入，但是最终系统调用的仍然是原来的

org.springframework.security.concurrent.SessionRegistryImpl

通过阅读源代码发现了其中原因，解释见注释：

public class ConcurrentSessionsBeanDefinitionParser implements BeanDefinitionParser {

static final String ATT_EXPIRY_URL = "expired-url";
static final String ATT_MAX_SESSIONS = "max-sessions";
static final String ATT_EXCEPTION_IF_MAX_EXCEEDED = "exception-if-maximum-exceeded";
static final String ATT_SESSION_REGISTRY_ALIAS = "session-registry-alias";
static final String ATT_SESSION_REGISTRY_REF = "session-registry-ref";

public BeanDefinition parse(Element element, ParserContext parserContext) {
CompositeComponentDefinition compositeDef =
new CompositeComponentDefinition(element.getTagName(), parserContext.extractSource(element));
parserContext.pushContainingComponent(compositeDef);

BeanDefinitionRegistry beanRegistry = parserContext.getRegistry();
//这里通过session-registry-ref 去获取自定义的sessionregistry，
String sessionRegistryId = element.getAttribute(ATT_SESSION_REGISTRY_REF);

if (!StringUtils.hasText(sessionRegistryId)) {
RootBeanDefinition sessionRegistry = new RootBeanDefinition(SessionRegistryImpl.class);
beanRegistry.registerBeanDefinition(BeanIds.SESSION_REGISTRY, sessionRegistry);
parserContext.registerComponent(new BeanComponentDefinition(sessionRegistry, BeanIds.SESSION_REGISTRY));
sessionRegistryId = BeanIds.SESSION_REGISTRY;
} else {
//注册默认ID
// Register the default ID as an alias so that things like session fixation filter can access it
beanRegistry.registerAlias(sessionRegistryId, BeanIds.SESSION_REGISTRY);
}

String registryAlias = element.getAttribute(ATT_SESSION_REGISTRY_ALIAS);
if (StringUtils.hasText(registryAlias)) {
beanRegistry.registerAlias(sessionRegistryId, registryAlias);
}

BeanDefinitionBuilder filterBuilder =
BeanDefinitionBuilder.rootBeanDefinition(ConcurrentSessionFilter.class);
filterBuilder.addPropertyValue("sessionRegistry", new RuntimeBeanReference(sessionRegistryId));

也即是说sessionRegistry在做初始化的时候，spring security用了beanRegistry去管理了自身默认的bean的实现，如果你要使用自定义的，就需要给出相应的配置以取代默认，在BeanIds抽象类里面定义了默认的实现别名，如果获取不到就去获取默认。

public abstract class BeanIds {

/** External alias for FilterChainProxy bean, for use in web.xml files */
public static final String SPRING_SECURITY_FILTER_CHAIN = "springSecurityFilterChain";

/** Package protected as end users shouldn't really be using this BFPP directly */
static final String INTERCEPT_METHODS_BEAN_FACTORY_POST_PROCESSOR = "_interceptMethodsBeanfactoryPP";
static final String CONTEXT_SOURCE_SETTING_POST_PROCESSOR = "_contextSettingPostProcessor";
static final String ENTRY_POINT_INJECTION_POST_PROCESSOR = "_entryPointInjectionBeanPostProcessor";
static final String USER_DETAILS_SERVICE_INJECTION_POST_PROCESSOR = "_userServiceInjectionPostProcessor";
static final String SESSION_REGISTRY_INJECTION_POST_PROCESSOR = "_sessionRegistryInjectionPostProcessor";
static final String FILTER_CHAIN_POST_PROCESSOR = "_filterChainProxyPostProcessor";
static final String FILTER_LIST = "_filterChainList";

public static final String JDBC_USER_DETAILS_MANAGER = "_jdbcUserDetailsManager";
public static final String USER_DETAILS_SERVICE = "_userDetailsService";
public static final String ANONYMOUS_PROCESSING_FILTER = "_anonymousProcessingFilter";
public static final String ANONYMOUS_AUTHENTICATION_PROVIDER = "_anonymousAuthenticationProvider";
public static final String BASIC_AUTHENTICATION_FILTER = "_basicAuthenticationFilter";
public static final String BASIC_AUTHENTICATION_ENTRY_POINT = "_basicAuthenticationEntryPoint";
public static final String SESSION_REGISTRY = "_sessionRegistry";
public static final String CONCURRENT_SESSION_FILTER = "_concurrentSessionFilter";
所以我的配置里面只需要加上session-registry-ref就好了。。
<beans:bean id="sessionRegistry"
class="com.shop.core.security.support.SessionRegistryImpl" scope="singleton">
<beans:property name="cacheManager" ref="cacheManager" />
</beans:bean>
<bean:http auto-config="false" entry-point-ref="loginUrlEntryPoint">
...
<bean:concurrent-session-control max-sessions="200000"
exception-if-maximum-exceeded="false" expired-url="/outline.htm"
session-registry-alias="sessionRegistry"  session-registry-ref="sessionRegistry"/>
...
</bean:http>