The Struts dispatcher cannot be found.
错误：The Struts dispatcher cannot be found. This is usually caused by using Struts tags without the associated filter.
异常信息：The Struts dispatcher cannot be found. This is usually caused by using Struts tags without the associated filter. Struts tags are only usable when the request has passed through its servlet filter, which initializes the Struts dispatcher needed for this tag.
环境：tomcat5.5.0
struts.xml信息
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>*.action</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
struts.xml 信息：
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<include file="struts-default.xml"/>
<package name="ygn.action" extends="struts-default">
<action name="HelloWorld" class="ygn.action.HelloWorld">
<result>HelloWorld.jsp</result>
</action>
</package>
</struts>
SayHello.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Say Hello</title>
</head>
<body>
<h3>Say "Hello" to :</h3>
<s:form action="HelloWorld">
Name:<s:textfield name="name"/>
<s:submit/>
</s:form>
</body>
</html>
异常分析：以上的配置及文件中，如果采用 http://ip:port/SayHello.jsp，那么会出现前面所提到的异常。如果采用http://ip:port/SayHello.action 进行访问，那么正常。
原因：如果想要在jsp文件中，采用 struts的tag，那么必须通过web.xml所配置的过滤器访问文件，否则会有异常，即 之前所出现的异常。
解决方案：
方案一：
采用 http://ip:port/SayHello.action 访问
方案二：
将web.xml 的过滤器，从 *.action 修改为： /*
方案三：
修改SayHello.jsp 文件，不使用 struts 的标签
异常信息：The Struts dispatcher cannot be found. This is usually caused by using Struts tags without the associated filter. Struts tags are only usable when the request has passed through its servlet filter, which initializes the Struts dispatcher needed for this tag.
环境：tomcat5.5.0
struts.xml信息
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>*.action</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
struts.xml 信息：
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<include file="struts-default.xml"/>
<package name="ygn.action" extends="struts-default">
<action name="HelloWorld" class="ygn.action.HelloWorld">
<result>HelloWorld.jsp</result>
</action>
</package>
</struts>
SayHello.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Say Hello</title>
</head>
<body>
<h3>Say "Hello" to :</h3>
<s:form action="HelloWorld">
Name:<s:textfield name="name"/>
<s:submit/>
</s:form>
</body>
</html>
异常分析：以上的配置及文件中，如果采用 http://ip:port/SayHello.jsp，那么会出现前面所提到的异常。如果采用http://ip:port/SayHello.action 进行访问，那么正常。
原因：如果想要在jsp文件中，采用 struts的tag，那么必须通过web.xml所配置的过滤器访问文件，否则会有异常，即 之前所出现的异常。
解决方案：
方案一：
采用 http://ip:port/SayHello.action 访问
方案二：
将web.xml 的过滤器，从 *.action 修改为： /*
方案三：
修改SayHello.jsp 文件，不使用 struts 的标签