解决java.lang.IllegalStateException: getOutputStream() has already been called for this response

问题：下载word文档的时候报错了

在我操作导出word文档的时候，报出了如下 错误代码.

// An highlighted block
十一月 26, 2018 9:05:54 上午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [springMVC] in context with path [/ssm-demo] threw exception [Request processing failed; nested exception is java.lang.IllegalStateException: getOutputStream() has already been called for this response] with root cause
java.lang.IllegalStateException: getOutputStream() has already been called for this response
	at org.apache.catalina.connector.Response.getWriter(Response.java:624)
	at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:211)
	at com.core.util.ResponseUtil.write(ResponseUtil.java:13)
	at com.core.admin.TimeCaseReportController.exportWord(TimeCaseReportController.java:164)
	at com.core.admin.TimeCaseReportController$$FastClassBySpringCGLIB$$76c5edce.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:708)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
	at com.core.admin.TimeCaseReportController$$EnhancerBySpringCGLIB$$6dd5b0d9.exportWord(<generated>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:175)
	at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
	at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	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:493)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
	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:800)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
	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)

报错原因分析

由于我在响应前台的请求时写了一个响应的工具类ResponseUtil，在我调用下载word文档的时候需要用到response，这个时候response就被占用了，当下载完成的时候调用ResponseUtil.write(response, result);，这个时候的response已经被占用，所以就报了以上错误

解决方案

根据报错定位到我写了一个ResponseUtil类用于返回给前台响应信息详见下面的代码，还有一个是定位到了Controller中，我调用ResponseUtil.write(response, result);的地方，直接将ResponseUtil.write(response, result);注释掉，运行，不报错了，解决了。总结：其实只要找到错误产生原因（我这里是response.getWriter()和response.getOutputStream()等接口在调用时发生了资源占用)，定位到对应的位置，就可以解决的。

下面我贴上ResponseUtil类代码：

import java.io.PrintWriter;
import javax.servlet.http.HttpServletResponse;


public class ResponseUtil {

    public static void write(HttpServletResponse response, Object o) throws Exception {
    	
        response.setContentType("text/html;charset=utf-8");
        response.addHeader("Access-Control-Allow-Origin", "*");
        PrintWriter out = response.getWriter();
        // 清空response
        response.reset();
        out.println(o.toString());
        out.flush();
        out.close();
    }
}