Spring Security3源码分析-authentication-manager标签解析

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。