在spring中，filter都默認繼承OncePerRequestFilter，但為什么要這樣呢？?
OncePerRequestFilter顧名思義，他能夠確保在一次請求只通過一次filter，而不需要重復執行。

/** * 過濾器基類，旨在確保每個請求調度在任何servlet容器上執行一次執行。? * 它提供了一個帶有HttpServletRequest和HttpServletResponse參數的{@link #doFilterInternal}方法。 */ public abstract class OncePerRequestFilter extends GenericFilterBean {//附加到“已過濾”請求屬性的過濾器名稱的后綴。public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";?//這個doFilter實現存儲“已經過濾”的請求屬性，如果該屬性已經存在，則不進行再次過濾。//@see #getAlreadyFilteredAttributeName@Overridepublic final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)throws ServletException, IOException {if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {throw new ServletException("OncePerRequestFilter just supports HTTP requests");}HttpServletRequest httpRequest = (HttpServletRequest) request;HttpServletResponse httpResponse = (HttpServletResponse) response;String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null;if (hasAlreadyFilteredAttribute || skipDispatch(httpRequest) || shouldNotFilter(httpRequest)) {// 繼續而不調用此過濾器...filterChain.doFilter(request, response);}else {// 調用這個過濾器…request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);try {doFilterInternal(httpRequest, httpResponse, filterChain);}finally {// 刪除此請求的“已過濾”請求屬性。request.removeAttribute(alreadyFilteredAttributeName);}}}/*** 返回表明請求已被過濾的請求屬性的名稱。*/protected String getAlreadyFilteredAttributeName() {// 如果沒有可用的過濾器名，則為{@code null}String name = getFilterName();if (name == null) {name = getClass().getName();}return name + ALREADY_FILTERED_SUFFIX;}private boolean skipDispatch(HttpServletRequest request) {if (isAsyncDispatch(request) && shouldNotFilterAsyncDispatch()) {return true;}if (request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE) != null && shouldNotFilterErrorDispatch(){return true;}return false;}/*** 在Servlet 3.0中引入的調度器類型{@code javax.servlet.DispatcherType.ASYNC}意味著一個過濾器可以在一個請求過程中在多個線* 程中被調用。 如果過濾器當前在異步分派中執行，則此方法返回{true}。*/protected boolean isAsyncDispatch(HttpServletRequest request) {return WebAsyncUtils.getAsyncManager(request).hasConcurrentResult();}/*** 請求處理是否處于異步模式，意味著退出當前線程后不會提交響應。*/protected boolean isAsyncStarted(HttpServletRequest request) {return WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted();}/*** 可以在子類中覆蓋自定義過濾控件，返回{true}以避免過濾給定的請求。 默認實現總是返回{@code false}。*/protected boolean shouldNotFilter(HttpServletRequest request) throws ServletException {return false;}protected boolean shouldNotFilterAsyncDispatch() {return true;}protected boolean shouldNotFilterErrorDispatch() {return true;}/*** 與{@code doFilter}相同的合同，但保證在單個請求線程中每個請求只調用一次。* /protected abstract void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)throws ServletException, IOException;}

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? ? // GenericFilterBean.class//使這個過濾器的名稱對子類可用。類似于GenericServlet的{@code getServletName()}。<p>默認使用FilterConfig的過濾器名稱。//如果在Spring應用程序上下文中初始化為bean，那么它將返回到bean工廠中定義的bean名稱。@Nullableprotected String getFilterName() {return (this.filterConfig != null ? this.filterConfig.getFilterName() : this.beanName);}?

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作者：Pazz楓?
來源：CSDN?
原文：https://blog.csdn.net/baidu_36327010/article/details/80538491?utm_source=copy?
版權聲明：本文為博主原創文章，轉載請附上博文鏈接！

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