如何让spring boot rest api发送混合内容作为响应(结构化内容加上附件)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

@RestController
public class MyController {

    @GetMapping("/api")
    public ResponseEntity<Object> getMixedContent() {
        // 创建一个响应体对象
        MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();

        // 添加结构化内容
        body.add("data", "Hello, World!");

        // 添加附件
        Resource file = new FileSystemResource("path/to/file");
        body.add("attachment", file);

        // 创建响应头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.MULTIPART_MIXED);

        // 创建响应实体
        ResponseEntity<Object> responseEntity = new ResponseEntity<>(body, headers, HttpStatus.OK);
        return responseEntity;
    }
}