我正在尝试将一个文件从我的服务器上传到另一个服务器。在执行此操作时，我遇到了以下错误：`Resolved [org.springframework.web.multipart.support.MissingServletRequestPartException: Required request part 'file' is not present]`
我已经在请求体中放置了'file'键。我无法弄清楚为什么会发生这种情况。
上传服务器：
```java
String url = "http://localhost:8441/api/jar/solve";
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.MULTIPART_FORM_DATA);
MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
body.add("file", Paths.get("pathToFile").toFile());
HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(body, headers);
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<String> response = restTemplate.postForEntity(url, requestEntity, String.class);

@RequestMapping(value = "/api", method = RequestMethod.POST, consumes = MediaType.ALL_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<ResponseDTO> solveUsingJar(@RequestParam("file") MultipartFile file) {
}

<details>
<summary>英文:</summary>
I am trying to upload a file on my server to another server. While doing this 
I am getting this error : `Resolved [org.springframework.web.multipart.support.MissingServletRequestPartException: Required request part &#39;file&#39; is not present]
`
I have put the &#39;file&#39; key in my body. I am unable to figure out why this is hapenning.
Uploading Server:
``` String url = &quot;http://localhost:8441/api/jar/solve&quot;;
                HttpHeaders headers = new HttpHeaders();
                headers.setContentType(MediaType.MULTIPART_FORM_DATA);
                MultiValueMap&lt;String, Object&gt; body
                        = new LinkedMultiValueMap&lt;&gt;();
                body.add(&quot;file&quot;, Paths.get(&quot;pathToFile&quot;).toFile());
                HttpEntity&lt;MultiValueMap&lt;String, Object&gt;&gt; requestEntity
                        = new HttpEntity&lt;&gt;(body, headers);
                RestTemplate restTemplate = new RestTemplate();
                ResponseEntity&lt;String&gt; response = restTemplate
                        .postForEntity(url, requestEntity, String.class);

@RequestMapping(value = "/api", method = RequestMethod.POST, consumes = MediaType.ALL_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<ResponseDTO> solveUsingJar(@RequestParam("file") MultipartFile file) {
}

STEP-1 : 在服务器 Server-1 上上传文件：
    @PostMapping("/upload/profile")
    public UploadFileResponse uploadProfileImg(@RequestPart("file") MultipartFile file)
    {		
    	return fileService.uploadProfileImg(file);
    }
STEP-2 : 使用 RestTemplate 在服务器 Server-2 上上传该文件。
    public String upload(MultipartFile file) throws IOException 
    {
    	ResponseEntity<UploadFileResponse> response = null;
    	 
    	try
    	{
    		File convFile = new File(file.getOriginalFilename());		    
    		
    		convFile.createNewFile();		
    		
    		FileOutputStream fos = new FileOutputStream(convFile);		    
    		fos.write(file.getBytes());
    		fos.close();
    		
    		LinkedMultiValueMap<String, Object> map = new LinkedMultiValueMap<>();
    		 
    		String uploadURI = KeyConstant.FILE_UPLOAD_API_URI+"/file";		// Server-2（文件目录）FILE_UPLOAD_API_URI ：http://27.34.2.33:28181/upload/file
    			
    		map.add("file",  new FileSystemResource(convFile));
    		
    		HttpHeaders headers = new HttpHeaders();
    		
    		headers.setContentType(MediaType.MULTIPART_FORM_DATA);
    		
    		HttpEntity<LinkedMultiValueMap<String, Object>> requestEntity = new HttpEntity<>(map, headers);
    		
    		RestTemplate restTemplate = new RestTemplate();
    		
    		response = restTemplate.exchange(uploadURI, HttpMethod.POST, requestEntity, UploadFileResponse.class);		
    	}
    	catch(Exception e) {e.printStackTrace();}
    	
    	return response.getBody();
    }
STEP-3 : 服务器 Server-2 文件上传 Rest 控制器：
    @PostMapping("/upload/file")
    public UploadFileResponse uploadFileByDirectory(@RequestPart(value = "file") MultipartFile file)
    {
    	return this.amazonClient.uploadFilebyDirectory(KeyConstant.AMAZON_S3_PATH, file);
    }