问题描述：
严重: Servlet.service() for servlet [default] in context with path [/AttendanceManager] threw exception
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
严重: Servlet.service() for servlet [default] in context with path [/AttendanceManager] threw exception
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:456)
at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:753)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:504)
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
然后发现在Chrome上， 出现一个error，
net::ERR_INCOMPLETE_CHUNKED_ENCODING
于是网上各种搜解决办法，有大佬说是Tomcat的header的缓存区大小不够，于是找到了在Tomcat的conf中把server.xml中增加maxHttpHeaderSize的字段或者是把maxHttpHeaderSize的数值调大了，都没有解决这个异常；
终于，今天发现了问题所在，看了另一个大佬的问题描述，大佬是这样分析的；
问题分析：
从提示错误的字面意思判断“Cannotcall sendError() after the response has been committed”，“当response被提交后不能调用sendError()”。
出现这个错误，应该是多次response导致的，可以这么理解，http server发送response后就关闭了socket，这个时候再次发送response给http client就会出现这个问题。
【原文链接：blog.csdn.net/u012377333/…】
于是我就去找；发现了CheckImg.java中，原来多次response提交;
如下是我的解决办法：
