getWriter() has already been called for this response异常（100%解决)

java.lang.IllegalStateException: getWriter() has already been called for this response异常（100%解决）

首先看下抛的异常详情：

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

at org.apache.catalina.connector.Response.getOutputStream(Response.java:585)
at org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:194)
at javax.servlet.ServletResponseWrapper.getOutputStream(ServletResponseWrapper.java:100)
at org.springframework.http.server.ServletServerHttpResponse.getBody(ServletServerHttpResponse.java:89)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:244)
at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:106)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:231)
at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:203)
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:81)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:113)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)

同常我们利用java导出CSV，txt等不同格式文件，会出现这个异常。

对待这个异常，通常有俩种解决办法，本人提供思路和少量代码展示。

思路：

一：查看getWriter（）,outPutStream是否同时存在，这俩个进行文件写入操作只能用一个

二：SpringMvc,springBoot,Servelt中发送Post请求时，会默认取消HttpResponse，正如抛的异常

代码展示（解决办法）：

controller层（servlert，springMvc,Servlet原理都一样）：

具体导出方法：