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spring之DelegatingFilterProxy
DelegatingFilterProxy是一个标准servlet Filter的代理，代理实现了Filter接口的spring管理的Bean。支持一个在web.xml的init-param定义的"targetBeanName" filter，在spring applicationContext中指定了target bean的名称。
web.xml通常包含一个DelegatingFilterProxy的定义，它在root springContext中指定了filter-name及对应的bean。在springcontext中实现了标准servlet filter接口的bean在调用时都将被代理。
注意：Servlet Filter接口默认定义的lifecycle方法不会被代理到target bean，它依赖spring applicationContext管理target bean的lifecycle。在filter的属性targetFilterLifecycle的init-param中指定为true将强制执行Filter.init()和Filter.destory()方法，让Filter来管理filter的lifecycle。
从spring 3.1开始，DelegatingFilterProxy更新到可以支持servlet 3.0基于实例的filter注册方法来构建，通常和spring 3.1的 org.springframework.web.WebApplicationInitializer spi一起使用。这个类由spring security中Ben Alex 写的FilterToBeanProxy灵感触发而写的。
具体实现如下：
1.初始化方法
@Override protected void initFilterBean() throws ServletException { synchronized (this.delegateMonitor) { if (this.delegate == null) { // 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. WebApplicationContext wac = findWebApplicationContext(); if (wac != null) { this.delegate = initDelegate(wac); } } } }
初始化代理
/** * Initialize the Filter delegate, defined as bean the given Spring * application context. * <p>The default implementation fetches the bean from the application context * and calls the standard {@code Filter.init} method on it, passing * in the FilterConfig of this Filter proxy. * @param wac the root application context * @return the initialized delegate Filter * @throws ServletException if thrown by the Filter * @see #getTargetBeanName() * @see #isTargetFilterLifecycle() * @see #getFilterConfig() * @see javax.servlet.Filter#init(javax.servlet.FilterConfig) */ protected Filter initDelegate(WebApplicationContext wac) throws ServletException { Filter delegate = wac.getBean(getTargetBeanName(), Filter.class); if (isTargetFilterLifecycle()) { delegate.init(getFilterConfig()); } return delegate; }
2. 触发代理方法
@Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException { // Lazily initialize the delegate if necessary. Filter delegateToUse = this.delegate; if (delegateToUse == null) { synchronized (this.delegateMonitor) { if (this.delegate == null) { WebApplicationContext wac = findWebApplicationContext(); if (wac == null) { throw new IllegalStateException("No WebApplicationContext found: " + "no ContextLoaderListener or DispatcherServlet registered?"); } this.delegate = initDelegate(wac); } delegateToUse = this.delegate; } } // Let the delegate perform the actual doFilter operation. invokeDelegate(delegateToUse, request, response, filterChain); }
触发代理
/** * Actually invoke the delegate Filter with the given request and response. * @param delegate the delegate Filter * @param request the current HTTP request * @param response the current HTTP response * @param filterChain the current FilterChain * @throws ServletException if thrown by the Filter * @throws IOException if thrown by the Filter */ protected void invokeDelegate( Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException { delegate.doFilter(request, response, filterChain); }
3.销毁方法
/** * Destroy the Filter delegate. * Default implementation simply calls {@code Filter.destroy} on it. * @param delegate the Filter delegate (never {@code null}) * @see #isTargetFilterLifecycle() * @see javax.servlet.Filter#destroy() */ protected void destroyDelegate(Filter delegate) { if (isTargetFilterLifecycle()) { delegate.destroy(); } }
spring之DelegatingFilterProxy
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