Web使用部署描述符（Deploy Descriptor）中Filter的执行顺序

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？

 

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 web
	application is done by using filter-mappingType.
	The container uses the filter-mapping
	declarations to decide which filters to apply to a request,
	and in what order. The container matches the request URI to
	a Servlet in the normal way. To determine which filters to
	apply it matches filter-mapping declarations either on
	servlet-name, or on url-pattern for each filter-mapping
	element, depending on which style is used. The order in
	which filters are invoked is the order in which
	filter-mapping declarations that match a request URI for a
	servlet appear in the list of filter-mapping elements.The
	filter-name value must be the value of the filter-name
	sub-elements of one of the filter declarations in the
	deployment 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。