Spring RestTemplate：同时发布图像和对象

Question

我的用户可以在我的服务器上发布食物的照片和食物的相关信息。

例如，假设有人看到好吃的东西，拍了一张照片，然后写下“好吃！”图片下方。照片被发送到服务器，消息“好吃！”包括用户名、日期、位置等在内的一个名为“Post”的对象使用一个 api 调用发送到我的服务器。

我在我的android端写了以下代码：

    final String url = Constants.POST_PICS;
    RestTemplate restTemplate = RestClientConfig.getRestTemplate(context, true);
    //adding StringHttpMessageConverter, formHttpMessageConverter and MappingJackson2HttpMessageConverter to restTemplate
    restTemplate.getMessageConverters().add(new StringHttpMessageConverter());
    FormHttpMessageConverter formHttpMessageConverter = new FormHttpMessageConverter();
    restTemplate.getMessageConverters().add(formHttpMessageConverter);
    restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
    //putting both objects into a map
    MultiValueMap<String, Object> map = new LinkedMultiValueMap<String, Object>();
    map.add("image", new FileSystemResource(file));
    map.add("post", post);
    HttpHeaders imageHeaders = new HttpHeaders();
    //setting content type to multipart as the image is a multipart file
    imageHeaders.setContentType(MediaType.MULTIPART_FORM_DATA);
    HttpEntity<MultiValueMap<String, Object>> imageEntity = new HttpEntity<MultiValueMap<String, Object>>(map, imageHeaders);
    ResponseEntity<Post> response = restTemplate.exchange(url, HttpMethod.POST, imageEntity, Post.class);
    return response.getBody();

这是Spring端的代码：

        @RequestMapping(value = "/uploadpostpic", method = RequestMethod.POST)
public Post uploadPostWithPic(@RequestParam("image") MultipartFile srcFile,
                                  @RequestParam("post") Post post) {
    return serviceGateway.uploadPostWithPic(srcFile, post);
}

我收到一个错误：

请求网络执行期间发生异常：无法 写请求：没有找到适合请求类型的 HttpMessageConverter [模型.帖子]

org.springframework.http.converter.HttpMessageNotWritableException： 无法写入请求：找不到合适的 HttpMessageConverter 请求类型 [Model.Post]

我怀疑这与设置为 MULTIPART_FORM_DATA 的内容类型有关，但我需要将其设置为此，因为我需要将图片传输到服务器。

是否可以同时使用 restTemplate 向上游传输多部分文件和另一个对象？

编辑：

我看过这些帖子：

Resttemplate form/multipart: image + JSON in POST

Sending Multipart File as POST parameters with RestTemplate requests

并根据他们的指导尝试了这段代码：

    final String url = Constants.POST_PIC;
    RestTemplate restTemplate = new RestTemplate();
    restTemplate.getMessageConverters().add(new StringHttpMessageConverter());
    restTemplate.getMessageConverters().add(new ByteArrayHttpMessageConverter());
    restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
    restTemplate.getMessageConverters().add(new ResourceHttpMessageConverter());

    FormHttpMessageConverter formHttpMessageConverter = new FormHttpMessageConverter();
    formHttpMessageConverter.addPartConverter(new MappingJackson2HttpMessageConverter());
    formHttpMessageConverter.addPartConverter(new ResourceHttpMessageConverter()); // This is hope driven programming
    formHttpMessageConverter.addPartConverter(new ByteArrayHttpMessageConverter());

    restTemplate.getMessageConverters().add(formHttpMessageConverter);

    MultiValueMap<String, Object> multipartRequest = new LinkedMultiValueMap<>();

    byte[] bFile = new byte[(int) imageFile.length()];
    FileInputStream fileInputStream;

    //convert file into array of bytes
    fileInputStream = new FileInputStream(imageFile);
    fileInputStream.read(bFile);
    fileInputStream.close();

    ByteArrayResource bytes = new ByteArrayResource(bFile) {
        @Override
        public String getFilename() {
            return "file.jpg";
        }
    };

    //post portion of the multipartRequest
    HttpHeaders xHeader = new HttpHeaders();
    xHeader.setContentType(MediaType.APPLICATION_JSON);
    HttpEntity<Post> xPart = new HttpEntity<>(post, xHeader);
    multipartRequest.add("post", xPart);

    //picture portion of the multipartRequest
    HttpHeaders pictureHeader = new HttpHeaders();
    pictureHeader.setContentType(MediaType.IMAGE_JPEG);
    HttpEntity<ByteArrayResource> picturePart = new HttpEntity<>(bytes, pictureHeader);
    multipartRequest.add("srcFile", picturePart);

    //adding both the post and picture portion to one httpentity for transmitting to server
    HttpHeaders header = new HttpHeaders();
    header.setContentType(MediaType.MULTIPART_FORM_DATA); 
    HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity(multipartRequest, header);
    return restTemplate.postForObject(url, requestEntity, Post.class);

另一方面，post = null，我不确定为什么它是 null。

这就是我想要在服务器端做的所有事情：

public Post uploadPostPic(MultipartFile srcFile, Post post) {
    Post savedPost = repo.save(post);
 }

我将它保存到我的存储库中，错误是：

java.lang.IllegalArgumentException: Entity must not be null!

Answer 1

试试这样的： 在此处发送 jsonString，稍后使用 objectwriter 将其转换为对象。如果您需要更多解释，请告诉我。

@RequestMapping(value = "/uploadMultipleFile", method = RequestMethod.POST)
    public @ResponseBody
    String uploadMultipleFileHandler(@RequestParam("name") String[] names,
            @RequestParam("file") MultipartFile[] files) {

        if (files.length != names.length)
            return "Mandatory information missing";

        String message = "";
        for (int i = 0; i < files.length; i++) {
            MultipartFile file = files[i];
            String name = names[i];
            try {
                byte[] bytes = file.getBytes();

                // Creating the directory to store file
                String rootPath = System.getProperty("catalina.home");
                File dir = new File(rootPath + File.separator + "tmpFiles");
                if (!dir.exists())
                    dir.mkdirs();

                // Create the file on server
                File serverFile = new File(dir.getAbsolutePath()
                        + File.separator + name);
                BufferedOutputStream stream = new BufferedOutputStream(
                        new FileOutputStream(serverFile));
                stream.write(bytes);
                stream.close();

                logger.info("Server File Location="
                        + serverFile.getAbsolutePath());

                message = message + "You successfully uploaded file=" + name
                        + "<br />";
            } catch (Exception e) {
                return "You failed to upload " + name + " => " + e.getMessage();
            }
        }
        return message;
    }
}

已编辑：

最终，我不得不使用 jsonString 来解决我的问题。这并不理想，因为网址最终会变得很长，但这是解决我的问题的最快方法：

请查看 mykong 关于如何将对象转换为 jsonString 并将它们重新转换回对象的建议：

ObjectMapper mapper = new ObjectMapper();
Staff obj = new Staff();

//Object to JSON in String
String jsonInString = mapper.writeValueAsString(obj);

//JSON from String to Object
Staff obj = mapper.readValue(jsonInString, Staff.class);

http://www.mkyong.com/java/jackson-2-convert-java-object-to-from-json/

Answer 2

我用这个做了类似的东西：

  HttpHeaders headers = new HttpHeaders();
  headers.add("Accept","application/json");     
  headers.setContentType(MediaType.MULTIPART_FORM_DATA);
  MultiValueMap<String, Object> map =  new LinkedMultiValueMap<String, Object>();
  map.add("image", new FileSystemResource(file));
  map.add("post", post);
  HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<MultiValueMap<String, Object>>(map, headers);
  RestTemplate restTemplate = RestClientConfig.getRestTemplate(context, true);
  restTemplate.getMessageConverters().add(new FormHttpMessageConverter());
  ResponseEntity<Post> response = restTemplate.postForObject(url, requestEntity, Post.class);

Answer 3

您需要告诉 Spring 如何将请求参数映射到您的对象。您可以通过像 Alexander 建议的那样实现自定义 HttpMessageConterter 来做到这一点，但我有一个更简单的方法：使用命令对象（有时称为表单支持对象）：

public class PostWithPicCommand() {
   public PostWithPic() {}; //Default constructor is required

   //name the variables like the request parameters!
   private Post post;
   private MultipartFile image;

   Getter and Setter!
}

@RequestMapping(value = "/uploadpostpic", method = RequestMethod.POST)
public Post uploadPostWithPic(PostWithPicCommand postWithPicCommand
      /*no @Param attribte for postWithPicCommand*/) {    
    ....
}

并且你需要配置/注册springs Multipart Resolver，并且需要将请求作为多部分请求发送。

Answer 4

好吧，几周前我遇到了同样的问题。首先要明确multipart/form-data content-type 是什么意思：

“multipart/form-data”消息包含一系列部分，每个部分 代表一个成功的控制。

成功的控件对于提交是“有效的”。每一个成功的 控件的控件名称与其当前值配对，作为 提交的表单数据集

简单来说，使用多部分表单数据，您可以将不同内容类型的数据发送到服务器。这是一个示例：

POST / HTTP/1.1
Host: localhost:8000
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:29.0) Gecko/20100101 Firefox/29.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: __atuvc=34%7C7; permanent=0; _gitlab_session=226ad8a0be43681acf38c2fab9497240; __profilin=p%3Dt; request_method=GET
Connection: keep-alive
Content-Type: multipart/form-data; boundary=---------------------------9051914041544843365972754266
Content-Length: 554

-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="text"

text default
-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file1"; filename="a.txt"
Content-Type: text/plain

Content of a.txt.

-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file2"; filename="a.html"
Content-Type: text/html

<!DOCTYPE html><title>Content of a.html.</title>

-----------------------------9051914041544843365972754266--

这里是发送三个不同集合的示例 - 第一个是binary data，第二个是plain text，第三个是html，它们由边界分隔。

现在Spring's RestTemplate 工作得怎么样了？

当您将请求标头设置为 multipart/form-data 时，resttemplate 将从注册的消息转换器中获取适当的 HttpMessageConverter，对于 multipart/form-data 将是 FormHttpMessageConverter，请参阅文档 here。

但是FormHttpMessageConverter 具有partConverters 的属性，它们是为FormHttpMessageConverter 注册的转换器，默认情况下它们是（字符串、字节数组和资源）。这是构造函数的源代码；）

public FormHttpMessageConverter() {
    this.supportedMediaTypes.add(MediaType.APPLICATION_FORM_URLENCODED);
    this.supportedMediaTypes.add(MediaType.MULTIPART_FORM_DATA);

    this.partConverters.add(new ByteArrayHttpMessageConverter());
    StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
    stringHttpMessageConverter.setWriteAcceptCharset(false);
    this.partConverters.add(stringHttpMessageConverter);
    this.partConverters.add(new ResourceHttpMessageConverter());
} 

简单地说，FormHttpMessageConverter 找不到正确的消息转换器来写入对象Post。如果您希望将Post 写为 JSON，您应该将MappingJackson2HttpMessageConverter 添加到partConverters。

@Produces
    public RestTemplate getRestTemplate() {
        RestTemplate template = new RestTemplate();
        template.getMessageConverters().add(0,createFormHttpConverter());
        return template;
    }
 private static HttpMessageConverter<?> createFormHttpConverter(){

        FormHttpMessageConverter formHttpMessageConverter = new FormHttpMessageConverter();
        formHttpMessageConverter.setPartConverters(getPartConverters());
        return formHttpMessageConverter;
    }

private static List<HttpMessageConverter<?>> getPartConverters(){
    RestTemplate template = new RestTemplate();
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    List<HttpMessageConverter<?>> messageConverters = template.getMessageConverters();
    messageConverters.add(0,converter);
    return messageConverters;
}

Answer 5

我没有为您的 Post 类看到已注册的 HttpMessageConverter。您可能需要为 MultiValueMap 注册一个 HttpMessageConverter。