返回前端数据 重复$ref解决

String json = JSON.toJSONString(r,
SerializerFeature.DisableCircularReferenceDetect);

       r = JSON.parseObject(json, new TypeReference<R>(){});

or

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    FastJsonHttpMessageConverter4 converter = new FastJsonHttpMessageConverter4();
    FastJsonConfig config = new FastJsonConfig();
    config.setSerializerFeatures(SerializerFeature.WriteMapNullValue,//保留空的字段
            SerializerFeature.WriteNullStringAsEmpty,//String null -> ""
            SerializerFeature.DisableCircularReferenceDetect //关闭循环引用
    );//Number null -> 0 SerializerFeature.WriteNullNumberAsZero
    converter.setFastJsonConfig(config);
    converter.setDefaultCharset(Charset.forName("UTF-8"));
    converters.add(converter);
}