Spring boot 项目中进行下载文件的时候出现的异常，当前异常出现之后，文件还是能够下载，这就很奇怪，所有我们得去解决这个问题，不能看着问题不管，接下来我们来看看完整的异常：

org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:308) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:181) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:123) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90) ~[shiro-core-1.4.0.jar:1.4.0]
	at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83) ~[shiro-core-1.4.0.jar:1.4.0]
	at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387) ~[shiro-core-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125) ~[shiro-web-1.4.0.jar:1.4.0]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:97) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123) ~[druid-1.0.29.jar:1.0.29]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.boot.actuate.web.trace.servlet.HttpTraceFilter.doFilterInternal(HttpTraceFilter.java:88) ~[spring-boot-actuator-2.1.16.RELEASE.jar:2.1.16.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:94) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:114) ~[spring-boot-actuator-2.1.16.RELEASE.jar:2.1.16.RELEASE]
	at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:104) ~[spring-boot-actuator-2.1.16.RELEASE.jar:2.1.16.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.17.RELEASE.jar:5.1.17.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.37.jar:9.0.37]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]

在进行dug之后，我发现文件下载是没有一点问题的，主要问题在于控制层下载文件之后放回了数据出去，然后就出现了异常，
怀疑是 handler处理时发生异常：
在这里插入图片描述
发现是这里出现了异常，放回值不为null的时候就抛出这个异常，看下我们的代码
在这里插入图片描述
问题就在于放回了对象出去，我们把返回值修改成 viod 就可以解决这一个问题了

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