Servlet.service() for servlet default threw exception java.lang.IllegalStateException a

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严重: Servlet.service() for servlet default threw exceptionjava.lang.IllegalStateExceptionat org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:407)at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:819)at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:519)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:235)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)at java.lang.Thread.run(Unknown Source)

深层原理 1.Servlet规范说明，不能既调用 response.getOutputStream()，又调用response.getWriter()，无论先调用哪一个，在调用第二个时候应会抛出 IllegalStateException.2.servlet代码中有out.write(””)，这个和JSP中缺省调用的response.getOutputStream()产生冲突.因为在jsp中，out变量是通过response.getWriter得到的，在程序中既用了 response.getOutputStream，又用了out变量，故出现以上错误。 解决: 法一:在JSP文件中,加入下面两句 <%out.clear();out = pageContext.pushBody();%> 此法的缺陷:很多开发项目并不是JSP前端,如freemarker,velocity等造成问题的"response.getOutputStream()"并未被写在JSP里,而是写在servlet/action里法二: 在action中,不要return 回具体的result文件,而是return null  //return SUCCESS; return null;   很好的解决了问题，同时也明白了相应的原理。

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