http://www.cnblogs.com/hzhuxin/archive/2011/12/19/2293730.html

使用過springSecurity的朋友都知道，首先需要在web.xml進行以下配置，

<filter>
??<filter-name>springSecurityFilterChain</filter-name>
??<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
?</filter>

<filter-mapping>
??<filter-name>springSecurityFilterChain</filter-name>
??<url-pattern>/*</url-pattern>

?</filter-mapping>

從這個配置中，可能會給我們造成一個錯覺，以為DelegatingFilterProxy類就是springSecurity的入口，但其實這個類位于spring-web-3.0.5.RELEASE.jar這個jar下面，說明這個類本身是和springSecurity無關。DelegatingFilterProxy類繼承于抽象類GenericFilterBean,間接地implement 了javax.servlet.Filter接口，Servlet容器在啟動時，首先會調用Filter的init方法,GenericFilterBean的作用主要是可以把Filter的初始化參數自動地set到繼承于GenericFilterBean類的Filter中去。在其init方法的如下代碼就是做了這個事：

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PropertyValues pvs = new FilterConfigPropertyValues(filterConfig, this.requiredProperties); BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this); ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext()); bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader)); initBeanWrapper(bw); bw.setPropertyValues(pvs, true);

?另外在init方法中調用了initFilterBean()方法，該方法是GenericFilterBean類是特地留給子類擴展用的，

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protected void initFilterBean() throws ServletException { ????????// If no target bean name specified, use filter name. ????????if (this.targetBeanName == null) { ????????????this.targetBeanName = getFilterName(); ????????} ?? ????????// Fetch Spring root application context and initialize the delegate early, ????????// if possible. If the root application context will be started after this ????????// filter proxy, we'll have to resort to lazy initialization. ????????synchronized (this.delegateMonitor) { ????????????WebApplicationContext wac = findWebApplicationContext(); ????????????if (wac != null) { ????????????????this.delegate = initDelegate(wac); ????????????} ????????} ????}

?可以看出上述代碼首先看Filter是否提供了targetBeanName初始化參數，如果沒有提供則直接使用filter的name做為beanName,產生了beanName后，由于我們在web.xml的filter的name是springSecurityFilterChain,從spring的IOC容器中取出bean的代碼是initDelegate方法，下面是該方法代碼：

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protected Filter initDelegate(WebApplicationContext wac) throws ServletException { ????????Filter delegate = wac.getBean(getTargetBeanName(), Filter.class); ????????if (isTargetFilterLifecycle()) { ????????????delegate.init(getFilterConfig()); ????????} ????????return delegate; }

?通過跟蹤代碼，發現取出的bean是org.springframework.security.FilterChainProxy，該類也是繼承于GenericFilterBean,取出bean后，判斷targetFilterLifecycle屬性是false還是true,決定是否調用該類的init方法。這個FilterChainProxy bean實例最終被保存在DelegatingFilterProxy類的delegate屬性里,

下面看一下DelegatingFilterProxy類的doFilter方法

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public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) ????????????throws ServletException, IOException { ?? ????????// Lazily initialize the delegate if necessary. ????????Filter delegateToUse = null; ????????synchronized (this.delegateMonitor) { ????????????if (this.delegate == null) { ????????????????WebApplicationContext wac = findWebApplicationContext(); ????????????????if (wac == null) { ????????????????????throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?"); ????????????????} ????????????????this.delegate = initDelegate(wac); ????????????} ????????????delegateToUse = this.delegate; ????????} ?? ????????// Let the delegate perform the actual doFilter operation. ????????invokeDelegate(delegateToUse, request, response, filterChain); ????}

?真正要關注invokeDelegate(delegateToUse, request, response, filterChain);這句代碼,在下面可以看出DelegatingFilterProxy類實際是用其delegate屬性即org.springframework.security.FilterChainProxy實例的doFilter方法來響應請求。

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protected void invokeDelegate( ????????????Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain) ????????????throws ServletException, IOException { ?? ????????delegate.doFilter(request, response, filterChain); ????}

?

以上就是DelegatingFilterProxy類的一些內部運行機制，其實主要作用就是一個代理模式的應用,可以把servlet 容器中的filter同spring容器中的bean關聯起來。

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