当session中用户名不存在时转向login页面怎么做（使用Struts1标签）
我直接使用forward标签结果报如下异常：

ServletException in:/page/jsp/template/template2.jsp] javax.servlet.jsp.JspException: Exception forwarding for name GotoLoginPageWhenSessionFailed: java.lang.IllegalStateException: Error: Attempt to clear a buffer that's already been flushed' javax.servlet.ServletException: javax.servlet.jsp.JspException: Exception forwarding for name GotoLoginPageWhenSessionFailed: java.lang.IllegalStateException: Error: Attempt to clear a buffer that's already been flushed at org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:855) at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:784) at org.apache.jsp.page.jsp.template.template2_jsp._jspService(template2_jsp.java:234) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:687) at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:590) at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:505) at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968) at org.apache.jasper.runtime.PageContextImpl.include(PageContextImpl.java:614) at org.apache.struts.tiles.TilesUtilImpl.doInclude(TilesUtilImpl.java:138) at org.apache.struts.tiles.TilesUtil.doInclude(TilesUtil.java:152) at org.apache.struts.tiles.TilesUtil.doInclude(TilesUtil.java:138) at org.apache.struts.taglib.tiles.InsertTag.doInclude(InsertTag.java:756) at org.apache.struts.taglib.tiles.InsertTag$InsertHandler.doEndTag(InsertTag.java:881) at org.apache.struts.taglib.tiles.InsertTag.doEndTag(InsertTag.java:473) at org.apache.jsp.page.jsp.task.tododone.index_jsp._jspx_meth_tiles_005finsert_005f0(index_jsp.java:128) at org.apache.jsp.page.jsp.task.tododone.index_jsp._jspService(index_jsp.java:68) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:687) at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:469) at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:403) at org.apache.catalina.core.ApplicationDispatcher.for