SpringBoot RestTemplate upload file

 @Test
    public void testUpload() throws Exception {
        String url = "http://127.0.0.1/file/upload";
        String filePath = "C:\\temp\\1.png";

        RestTemplate rest = new RestTemplate();
        FileSystemResource resource = new FileSystemResource(new File(filePath));
        MultiValueMap<String, Object> param = new LinkedMultiValueMap<>();
        param.add("file", resource);
        param.add("fid", "1");

        String string = rest.postForObject(url, param, String.class);

        System.out.println(string);
    }

or

    @Test
    public void testUpload2() throws Exception {

        String url = "http://127.0.0.1/file/upload";
        String filePath = "C:\\temp\\1.png";

        RestTemplate rest = new RestTemplate();
        FileSystemResource resource = new FileSystemResource(new File(filePath));
        MultiValueMap<String, Object> param = new LinkedMultiValueMap<>();
        param.add("file", resource);
        param.add("fid", "1");

        HttpEntity<MultiValueMap<String, Object>> httpEntity = new HttpEntity<MultiValueMap<String, Object>>(param);
        ResponseEntity<String> responseEntity = rest.exchange(url, HttpMethod.POST, httpEntity, String.class);

        System.out.println(responseEntity.getBody());

    }

SpringBoot project front and back end separated ajax attachment upload and download, refer to SpringBoot project front and back end separated ajax attachment upload and download