在使用velocityLayout时只能POST显示，在GET无效？ ：报错

不可能吧，贴点代码来看看是什么问题。

<servlet>  
         <servlet-name>velocity</servlet-name>  
         <servlet-class>VelocityServlet</servlet-class>   
         <init-param>  
             <param-name>org.apache.velocity.toolbox</param-name>  
             <param-value>/WEB-INF/cfg/velocity-toolbox.xml</param-value>  
         </init-param>           
         <init-param>  
             <param-name>org.apache.velocity.properties</param-name>  
             <param-value>/WEB-INF/cfg/velocity.properties</param-value>  
         </init-param>  
         <load-on-startup>1</load-on-startup>  
     </servlet> 
     <servlet-mapping>  
         <servlet-name>velocity</servlet-name>  
         <url-pattern>*.vm</url-pattern>  
     </servlet-mapping>

这是web.xml其中URLMappingServlet照抄,没作改变

public class VelocityServlet extends VelocityLayoutServlet{
    public final static String CURRENT_URI = "current_uri"; //{index}  
    public final static String REQUEST_URI = "request_uri"; //{/index} 
 protected void processTemplate(HttpServletRequest request,
 HttpServletResponse response, boolean isPost) {
     String CUR_URI = (String) request.getAttribute(CURRENT_URI);
     String REQ_URI =(String) request.getAttribute(REQUEST_URI);
     log.info("#####>>>> VelocityServlet:"+REQ_URI);
     log.info(RequestUtils.getParam(request, "p1", "welcome"));
     log.info(RequestUtils.getParam(request, "page", 1));
     
 }
    public void doGet(HttpServletRequest request,
            HttpServletResponse response)
 throws IOException, ServletException
 {
     log.info("#####>>>> VelocityServlet: doGet"); 
     processTemplate(request,response, false);
 }
 public void doPost(HttpServletRequest request,
            HttpServletResponse response)
 throws IOException, ServletException
 {
     log.info("#####>>>> VelocityServlet: doPost"); 
     processTemplate(request,response, true);
 }
}

这里只有doPost会用到layout,可以使用layout.vm

velocity.properties

input.encoding = UTF-8
output.encoding = UTF-8
tools.view.servlet.error.template = error.vm
file.resource.loader.class = org.apache.velocity.tools.view.WebappResourceLoader
tools.view.servlet.layout.directory = /WEB-INF/layout/
tools.view.servlet.layout.default.template =  layout.vm

代码看不出来有问题，是不是页面没指定 #set($layout="layout.vm") 啊？