报错：java.lang.IllegalStateException: Cannot call sendError() after the response has been committed(待解答)

严重: Servlet.service() for servlet [default] in context with path [/20161101-struts2-1] threw exception
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:462)
at org.apache.catalina.servlets.DefaultServlet.serveResource(DefaultServlet.java:726)
at org.apache.catalina.servlets.DefaultServlet.doGet(DefaultServlet.java:398)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at com.tt.struts2.helloworld.FilterDispatcher.doFilter(FilterDispatcher.java:44)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1100)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:687)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2508)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2497)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

代码如下：

分析：不知道为什么，还需要研究

解决办法：请求转发之后加上return