org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation

at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:238) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:218) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:119) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver.doResolveHandlerMethodException(ExceptionHandlerExceptionResolver.java:405) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.handler.AbstractHandlerMethodExceptionResolver.doResolveException(AbstractHandlerMethodExceptionResolver.java:61) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:140) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.handler.HandlerExceptionResolverComposite.resolveException(HandlerExceptionResolverComposite.java:78) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1255) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]

解决：

 标注 produces = MediaType.TEXT_PLAIN_VALUE

改成返回 String 就好了