如何在使用RestTemplate进行post时添加/设置文件内容

import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.FileSystemResource;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;

public class RestTemplateExample {
    public static void main(String[] args) {
        // 创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();

        // 创建MultiValueMap对象
        MultiValueMap<String, Object> map = new LinkedMultiValueMap<>();

        // 创建文件资源对象
        FileSystemResource fileResource = new FileSystemResource("/path/to/file.txt");

        // 将文件资源对象添加到MultiValueMap中
        map.add("file", fileResource);

        // 创建HttpHeaders对象
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.MULTIPART_FORM_DATA);

        // 创建HttpEntity对象
        HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(map, headers);

        // 发送POST请求
        String url = "http://example.com/upload";
        String response = restTemplate.postForObject(url, requestEntity, String.class);

        // 处理响应结果
        System.out.println(response);
    }
}