Web应用部署描述符（Deploy Descriptor）中Filter的执行顺序
J2EE Web应用的部署描述符DD对于Web开发人员通常都不会陌生，不过某些细节的问题，不好好研究一下Servlet的规范，就可能有些模糊了。
今天遇到个问题：当一个被请求的Web资源符合多个Filter配置的mapping规则时，这些Filter执行的顺序是怎样的？是根据filter标签本身在web.xml中定义的顺序执行，还是根据filter-mapping标签在web.xml中定义的顺序执行呢？
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这个问题网上很多人的说法非常模糊，并没有清楚区分两者的顺序区别（其实在绝大部分场景中，两者的顺序通常是一致的）。终于在Sun当年给出的web.xml的XSD文件中，找到问题比较清楚的说明。
<xsd:complexType name="filter-mappingType"> <xsd:annotation> <xsd:documentation>Declaration of the filter mappings in this webapplication is done by using filter-mappingType.The container uses the filter-mappingdeclarations to decide which filters to apply to a request,and in what order. The container matches the request URI toa Servlet in the normal way. To determine which filters toapply it matches filter-mapping declarations either onservlet-name, or on url-pattern for each filter-mappingelement, depending on which style is used. The order inwhich filters are invoked is the order in whichfilter-mapping declarations that match a request URI for aservlet appear in the list of filter-mapping elements.Thefilter-name value must be the value of the filter-namesub-elements of one of the filter declarations in thedeployment descriptor. </xsd:documentation> </xsd:annotation> <xsd:sequence> <xsd:element name="filter-name" type="javaee:filter-nameType"/> <xsd:choice minOccurs="1" maxOccurs="unbounded"><xsd:element name="url-pattern" type="javaee:url-patternType"/><xsd:element name="servlet-name" type="javaee:servlet-nameType"/> </xsd:choice> <xsd:element name="dispatcher" type="javaee:dispatcherType" minOccurs="0" maxOccurs="4"/> </xsd:sequence> <xsd:attribute name="id" type="xsd:ID"/> </xsd:complexType>这里主要看上面的documentation部分的描述，可以看到， filter的触发顺序是按照filter-mapping的定义顺序执行的，而并非filter定义在web.xml中的顺序。
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