struts2報錯The Struts dispatcher cannot be found

轉載自：今天學習struts2的驗證，突然出現了下面這個異常鬱悶死了

org.apache.jasper.JasperException: 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. - [unknown location]
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

root cause

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. - [unknown location]
	org.apache.struts2.views.jsp.TagUtils.getStack(TagUtils.java:60)
	org.apache.struts2.views.jsp.StrutsBodyTagSupport.getStack(StrutsBodyTagSupport.java:44)
	org.apache.struts2.views.jsp.ComponentTagSupport.doStartTag(ComponentTagSupport.java:48)
	org.apache.jsp.validation.signup_jsp._jspx_meth_s_005ffielderror_005f0(signup_jsp.java:109)
	org.apache.jsp.validation.signup_jsp._jspService(signup_jsp.java:76)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.37 logs.

  #原來是要將web.xml文件的filter配置改成下面這樣：
    <filter>
        <filter-name>StrutsPrepareAndExecuteFilter</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>StrutsPrepareAndExecuteFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

  #也有可能是沒有導進標籤庫,導入標籤：

      <%@taglib uri="/struts-tags" prefix="s"%>