Spring Security3中的-authentication-manager标签详解

讲解完http标签的解析过程，authentication-manager标签解析部分就很容易理解了 
authentication-manager标签在spring的配置文件中的定义一般如下

 <authentication-manager alias="authenticationManager">
     <authentication-provider user-service-ref="userDetailsManager"/>
 </authentication-manager>   

authentication-manager标签的解析类是： 
org.springframework.security.config.authentication.AuthenticationManagerBeanDefinitionParser 
具体解析方法parse的代码为

 public BeanDefinition parse(Element element, ParserContext pc) {
         Assert.state(!pc.getRegistry().containsBeanDefinition(BeanIds.AUTHENTICATION_MANAGER),
                 "AuthenticationManager has already been registered!");
         pc.pushContainingComponent(new CompositeComponentDefinition(element.getTagName(), pc.extractSource(element)));
         //构造ProviderManager的BeanDefinition
         BeanDefinitionBuilder providerManagerBldr = BeanDefinitionBuilder.rootBeanDefinition(ProviderManager.class);
         //获取alias属性
         String alias = element.getAttribute(ATT_ALIAS);
         //检查session-controller-ref属性，提示通过标签<concurrent-session-control>取代
         checkForDeprecatedSessionControllerRef(element, pc);
         List<BeanMetadataElement> providers = new ManagedList<BeanMetadataElement>();
         NamespaceHandlerResolver resolver = pc.getReaderContext().getNamespaceHandlerResolver();
         //获取authentication-manager的子节点
         NodeList children = element.getChildNodes();
         //循环节点，一般子节点主要是authentication-provider或者
          //ldap-authentication-provider
         for (int i = 0; i < children.getLength(); i++) {
             Node node = children.item(i);
             if (node instanceof Element) {
                 Element providerElt = (Element)node;
                 //判断子标签是否有ref属性，如果有，则直接将ref属性
                    //引用的bean id添加到providers集合中
                 if (StringUtils.hasText(providerElt.getAttribute(ATT_REF))) {
                     providers.add(new RuntimeBeanReference(providerElt.getAttribute(ATT_REF)));
                 } else {
                     //如果没有ref属性，则通过子标签的解析类完成标签解析
                        //如子标签：authentication-provider,解析过程在后面
                     BeanDefinition provider = resolver.resolve(providerElt.getNamespaceURI()).parse(providerElt, pc);
                     Assert.notNull(provider, "Parser for " + providerElt.getNodeName() + " returned a null bean definition");
                     String id = pc.getReaderContext().generateBeanName(provider);
                     //注册provider的BeanDefinition
                     pc.registerBeanComponent(new BeanComponentDefinition(provider, id));
                     //添加注册过的bean到provider集合中
                     providers.add(new RuntimeBeanReference(id));
                 }
             }
         }  

         if (providers.isEmpty()) {
             providers.add(new RootBeanDefinition(NullAuthenticationProvider.class));
         }  

         providerManagerBldr.addPropertyValue("providers", providers);
         //添加默认的事件发布类
         BeanDefinition publisher = new RootBeanDefinition(DefaultAuthenticationEventPublisher.class);
         String id = pc.getReaderContext().generateBeanName(publisher);
         pc.registerBeanComponent(new BeanComponentDefinition(publisher, id));
         //将事件发布类的bean注入到ProviderManager的
          //authenticationEventPublisher属性中
         providerManagerBldr.addPropertyReference("authenticationEventPublisher", id);
         //注册ProviderManager的bean
         pc.registerBeanComponent(
                 new BeanComponentDefinition(providerManagerBldr.getBeanDefinition(), BeanIds.AUTHENTICATION_MANAGER));  

         if (StringUtils.hasText(alias)) {
             pc.getRegistry().registerAlias(BeanIds.AUTHENTICATION_MANAGER, alias);
             pc.getReaderContext().fireAliasRegistered(BeanIds.AUTHENTICATION_MANAGER, alias, pc.extractSource(element));
         }  

         pc.popAndRegisterContainingComponent();  

         return null;
     }  

通过上面的代码片段，能够知道authentication-manager标签解析的步骤是

1.构造ProviderManager的BeanDefinition

2.循环authentication-manager的子标签，构造provider的BeanDefinition，并添加到providers集合中

3.将第2步的providers设置为ProviderManager的providers属性

4.构造异常事件发布类DefaultAuthenticationEventPublisher的BeanDefinition，并设置为ProviderManager的属性authenticationEventPublisher

5.通过registerBeanComponent方法完成bean的注册任务

authentication-provider标签的解析类为 
org.springframework.security.config.authentication.AuthenticationProviderBeanDefinitionParser

 public BeanDefinition parse(Element element, ParserContext parserContext) {
     //首先构造DaoAuthenticationProvider的BeanDefinition
     RootBeanDefinition authProvider = new RootBeanDefinition(DaoAuthenticationProvider.class);
     authProvider.setSource(parserContext.extractSource(element));
     //获取password-encoder子标签
     Element passwordEncoderElt = DomUtils.getChildElementByTagName(element, Elements.PASSWORD_ENCODER);  

     if (passwordEncoderElt != null) {
         //如果有password-encoder子标签，把解析任务交给
           //PasswordEncoderParser完成
         PasswordEncoderParser pep = new PasswordEncoderParser(passwordEncoderElt, parserContext);
         authProvider.getPropertyValues().addPropertyValue("passwordEncoder", pep.getPasswordEncoder());
         //如果有salt-source标签，将值注入到saltSource属性中
         if (pep.getSaltSource() != null) {
             authProvider.getPropertyValues().addPropertyValue("saltSource", pep.getSaltSource());
         }
     }
     //下面获取子标签user-service、jdbc-user-service、ldap-user-service
     Element userServiceElt = DomUtils.getChildElementByTagName(element, Elements.USER_SERVICE);
     Element jdbcUserServiceElt = DomUtils.getChildElementByTagName(element, Elements.JDBC_USER_SERVICE);
     Element ldapUserServiceElt = DomUtils.getChildElementByTagName(element, Elements.LDAP_USER_SERVICE);  

     String ref = element.getAttribute(ATT_USER_DETAILS_REF);  

     if (StringUtils.hasText(ref)) {
         if (userServiceElt != null || jdbcUserServiceElt != null || ldapUserServiceElt != null) {
             parserContext.getReaderContext().error("The " + ATT_USER_DETAILS_REF + " attribute cannot be used in combination with child" +
                     "elements '" + Elements.USER_SERVICE + "', '" + Elements.JDBC_USER_SERVICE + "' or '" +
                     Elements.LDAP_USER_SERVICE + "'", element);
         }
     } else {
         // Use the child elements to create the UserDetailsService
         AbstractUserDetailsServiceBeanDefinitionParser parser = null;
         Element elt = null;
         //下面的if语句，主要是根据子标签的不同，选择子标签对应的解析器处理
         if (userServiceElt != null) {
             elt = userServiceElt;
             parser = new UserServiceBeanDefinitionParser();
         } else if (jdbcUserServiceElt != null) {
             elt = jdbcUserServiceElt;
             parser = new JdbcUserServiceBeanDefinitionParser();
         } else if (ldapUserServiceElt != null) {
             elt = ldapUserServiceElt;
             parser = new LdapUserServiceBeanDefinitionParser();
         } else {
             parserContext.getReaderContext().error("A user-service is required", element);
         }  

         parser.parse(elt, parserContext);
         ref = parser.getId();
         String cacheRef = elt.getAttribute(AbstractUserDetailsServiceBeanDefinitionParser.CACHE_REF);  

         if (StringUtils.hasText(cacheRef)) {
             authProvider.getPropertyValues().addPropertyValue("userCache", new RuntimeBeanReference(cacheRef));
         }
     }
     //将解析后的bean id注入到userDetailsService属性中
     authProvider.getPropertyValues().addPropertyValue("userDetailsService", new RuntimeBeanReference(ref));
     return authProvider;
 }  

如果学习过acegi的配置，应该知道，acegi有这么一段配置

 <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
    <property name="providers">
       <list>
          <ref local="daoAuthenticationProvider"/>
         <ref local="anonymousAuthenticationProvider"/>
       </list>
    </property>
 </bean>  

实际上authentication-manager标签所要达到的目标就是构造上面的bean。其中anonymousAuthenticationProvider是在http解析过程添加的。

其实可以完全像acegi那样自定义每个bean。

 <authentication-manager alias="authenticationManager">
     <authentication-provider user-service-ref="userDetailsManager"/>
 </authentication-manager>  

上面的标签如果用bean来定义，则可以完全由下面的xml来替代。

 <bean id="org.springframework.security.authenticationManager" class="org.springframework.security.authentication.ProviderManager">
         <property name="authenticationEventPublisher" ref="defaultAuthenticationEventPublisher"></property>
         <property name="providers">
             <list>
                 <ref local="daoAuthenticationProvider"/>
                 <ref local="anonymousAuthenticationProvider"/>
             </list>
         </property>
     </bean>  

     <bean id="defaultAuthenticationEventPublisher" class="org.springframework.security.authentication.DefaultAuthenticationEventPublisher"></bean>  

     <bean id="anonymousAuthenticationProvider" class="org.springframework.security.authentication.AnonymousAuthenticationProvider">
         <property name="key"><value>work</value></property>
     </bean>  

     <bean id="daoAuthenticationProvider" class="org.springframework.security.authentication.dao.DaoAuthenticationProvider">
         <property name="userDetailsService" ref="userDetailsManager"></property>
     </bean>  

需要注意的是anonymousAuthenticationProvider的bean中，需要增加key属性。如果采用authentication-manager标签的方式，key虽然没有定义，在增加AnonymousAuthenticationFilter过滤器中，是通过java.security.SecureRandom.nextLong()来生成的。

显而易见，如果采用bean的方式来定义，非常复杂，而且需要了解底层的组装过程才行，不过能够提高更大的扩展性。采用authentication-manager标签的方式，很简洁，只需要提供UserDetailsService即可。