在请求的Mapping上加上produces = { “application/json;charset=UTF-8” }，例如：

@GetMapping(value = "/user-instance", produces = { "application/json;charset=UTF-8" })
以下是json和xml 
@GetMapping(value = "/user-instance", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
@GetMapping(value = "/user-instance", produces = MediaType.APPLICATION_XML_VALUE)

有时项目需求两种返回格式，这时候我们只要加上jackson xml的依赖就可以了

<dependency>
  <groupId>com.fasterxml.jackson.jaxrs</groupId>
  <artifactId>jackson-jaxrs-xml-provider</artifactId>
</dependency>