Struts中错误:Can't get definitions factory from context
tiles-def.xml
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE tiles-definitions PUBLIC
"-//Apache Software Foundation//DTD Tiles Configuration 1.1//EN"
"http://struts.apache.org/dtds/tiles-config_1_1.dtd">
<tiles-definitions>
<definition name="first.mainLayout" path="/template/layouts/xmlLayout.jsp">
<put name="header" value="/template/header.jsp"/>
<put name="menu" value="/template/menu.jsp" />
<put name="footer" value="/common/footer.jsp" />
<put name="body" value="/template/body.jsp" />
</definition>
</tiles-definitions>
struts-config.xml
...
<plug-in className="org.apache.struts.tiles.TilesPlugin">
<set-property
property="definitions-config"
value="/WEB-INF/tiles-defs.xml"/>
<set-property
property="definitions-parser-validate"
value="true"/>
<set-property
property="moduleAware"
value="true"/>
</plug-in>
...
请大家帮忙分析原因.