是因为web.xml中struts2的filter没有配置处理forward请求的参数改成这样就可以了
<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>/*</url-pattern>
[color=red]<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>[/color]
</filter-mapping>
<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>/*</url-pattern>
[color=red]<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>[/color]
</filter-mapping>