spring boot 原生错误处理ErrorController

最近开始使用springboot，发现一个奇怪的现象，一个url报错

使用浏览器地址请求返回一个html界面

Whitelabel Error Page

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Tue Nov 29 10:48:26 CST 2016
There was an unexpected error (type=Bad Request, status=400).
Required String parameter 'fileName' is not present

使用postman请求返回一个json格式的响应

{
    "timestamp": 1480388264722,
    "status": 400,
    "error": "Bad Request",
    "exception": "org.springframework.web.bind.MissingServletRequestParameterException",
    "message": "Required String parameter 'fileName' is not present",
    "path": "/file/delete"
}

究竟spring boot怎么来区分这种请求返回不同格式的数据的呢。经过一步步跟进。精髓在BasicErrorController这个类上

@RequestMapping(
        value = {"${error.path:/error}"},
        produces = {"text/html"}
    )
    public ModelAndView errorHtml(HttpServletRequest request) {
        return new ModelAndView("error", this.getErrorAttributes(request, false));
    }

    @RequestMapping({"${error.path:/error}"})
    @ResponseBody
    public ResponseEntity> error(HttpServletRequest request) {
        Map body = this.getErrorAttributes(request, this.getTraceParameter(request));
        HttpStatus status = this.getStatus(request);
        return new ResponseEntity(body, status);
    }

spring boot 根据Accept头的内容，输出不同格式的错误响应。比如针对浏览器的请求生成html页面，针对其它请求生成json格式的返回。字段为accept的text/html的内容来判断