使用 RestTemplate 上传 CommonsMultipartFile 文件失败

Question

我正在尝试使用在请求中接受 CommonsMultipartFile 的 Web 服务。因此，我使用 Spring 的 RestTemplate 创建了一个 HTTP 客户端。下面是接受 URI 和 MultipartFile 作为参数的方法。我正在尝试将此文件以 ByteArrayResource 的形式传递给 Web 服务。

public String upload(String uri, MultipartFile file) throws IOException {
    logger.info("URI: " + uri);

    ByteArrayResource fileAsResource = new ByteArrayResource(file.getBytes()) {
        @Override
        public String getFilename() {
            return file.getOriginalFilename();
        }
    };

    MultiValueMap<String, Object> parts = new LinkedMultiValueMap<String, Object>();
    parts.add("file", fileAsResource);
    parts.add("fileName", file.getOriginalFilename());

    HttpHeaders httpHeaders = new HttpHeaders();
    httpHeaders.setContentType(MediaType.MULTIPART_FORM_DATA);

    HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<MultiValueMap<String, Object>>(parts, httpHeaders);

    ResponseEntity<String> responseEntity = rest.exchange(uri, HttpMethod.POST, requestEntity, String.class);

    this.setStatus(responseEntity.getStatusCode());
    return responseEntity.getBody();
}

这就是我创建 CommonsMultipartFile 的方式：

private MultipartFile getCommonsMultipartFile() throws FileNotFoundException, IOException {
    File file = new File("C:\\Dummy_Test.txt");

    DiskFileItemFactory factory = new DiskFileItemFactory();
    FileItem fileItem = factory.createItem( "file", "multipart/form-data", false, "Dummy_Test.txt" );
    IOUtils.copy(new FileInputStream(file), fileItem.getOutputStream());
    MultipartFile commonsMultipartFile = new CommonsMultipartFile(fileItem);

    return commonsMultipartFile;
}

但是每当我运行此客户端以访问 Web 服务时，我都会收到此错误。

 org.springframework.web.client.ResourceAccessException: I/O error: resource loaded from byte array cannot be resolved to absolute file path; nested exception is java.io.FileNotFoundException: resource loaded from byte array cannot be resolved to absolute file path
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:453)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:401)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:377)
    at com.attikala.service.UploaderService.upload(UploaderService.java:118)
    at com.attikala.service.UploaderService.main(UploaderService.java:55)
Caused by: java.io.FileNotFoundException: resource loaded from byte array cannot be resolved to absolute file path
    at org.springframework.core.io.AbstractResource.getFile(AbstractResource.java:107)
    at org.springframework.core.io.AbstractResource.contentLength(AbstractResource.java:116)
    at org.springframework.http.converter.ResourceHttpMessageConverter.getContentLength(ResourceHttpMessageConverter.java:99)
    at org.springframework.http.converter.ResourceHttpMessageConverter.write(ResourceHttpMessageConverter.java:81)
    at org.springframework.http.converter.ResourceHttpMessageConverter.write(ResourceHttpMessageConverter.java:1)
    at org.springframework.http.converter.FormHttpMessageConverter.writePart(FormHttpMessageConverter.java:288)
    at org.springframework.http.converter.FormHttpMessageConverter.writeParts(FormHttpMessageConverter.java:252)
    at org.springframework.http.converter.FormHttpMessageConverter.writeMultipart(FormHttpMessageConverter.java:242)
    at org.springframework.http.converter.FormHttpMessageConverter.write(FormHttpMessageConverter.java:194)
    at org.springframework.http.converter.FormHttpMessageConverter.write(FormHttpMessageConverter.java:1)
    at org.springframework.web.client.RestTemplate$HttpEntityRequestCallback.doWithRequest(RestTemplate.java:588)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:436)
    ... 4 more

有人可以帮我弄清楚这里发生了什么吗？

注意：如果我使用下面的代码上传文件，它工作得很好。

public String upload(String uri) {
    LinkedMultiValueMap<String, Object> map = new LinkedMultiValueMap<>();

    FileSystemResource value = new FileSystemResource(new File("C:\\Dummy_Test.txt"));
    map.add("file", value);
    map.add("fileName", "Dummy_Test.txt");

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.MULTIPART_FORM_DATA);

    HttpEntity<LinkedMultiValueMap<String, Object>> requestEntity = new HttpEntity<>(map, headers);

    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<String> responseEntity = restTemplate.exchange(uri, HttpMethod.POST, requestEntity, String.class);

    return responseEntity.getBody();
}

所以，我在想，我是否需要始终为我上传的文件提供绝对路径？我知道我在这里遗漏了一些东西。不知道是什么。

谢谢。

Answer 1

终于，我发现了发生了什么。我来啦 -

当这个声明

ResponseEntity<String> responseEntity = rest.exchange(uri, HttpMethod.POST, requestEntity, String.class);

被执行，在幕后它试图java.io.File从传递的 MultipartFile 中提取类型的文件，然后获取文件长度。但是 MultipartFile 不是那种类型，因此它抛出了异常。

为了解决这个问题，我还必须contentLength()在创建ByteArrayResource. 达达！

    ByteArrayResource fileAsResource = new ByteArrayResource(file.getBytes()) {

        @Override
        public String getFilename() {
            return file.getOriginalFilename();
        }

        @Override
        public long contentLength() throws IOException {
            return file.getSize();
        }
    };

如果有人遇到同样的问题，希望这会有所帮助。