spring - 如果多部分文件参数为 null，则 ModelAttribute 的多部分/表单数据绑定(bind)失败

Question

我有一个映射的 Controller 用于处理上传的文件

Controller

  @RequestMapping(value = "/careers/pursue", method = RequestMethod.POST)
  public Callable<String> pursue(
      final @RequestParam("g-recaptcha-response") String captchaResponse,
      final @RequestParam("file") MultipartFile file,
      final @ModelAttribute("jobapplication") @Valid JobApplication application, final BindingResult bindingResult,
      final Model model)  

表单

<form name="jobsForm" id="jobsForm" novalidate="novalidate" action="#" th:action="@{/careers/pursue}"
                    th:object="${jobapplication}" method="post" enctype="multipart/form-data">
    <div class="control-group form-group">
        <div class="controls">
            <label>First Name:</label>
            <input type="text" class="form-control" id="firstName" th:field="*{firstName}" required="required" data-validation-required-message="Please enter your name." />
            <p class="help-block"></p>
        </div>
    </div>
    <div class="control-group form-group">
        <div class="controls">
            <label>Last Name:</label>
            <input type="text" class="form-control" id="lastName" th:field="*{lastName}" required="required" data-validation-required-message="Please enter your name." />
            <p class="help-block"></p>
        </div>
    </div>                    
    <div class="control-group form-group">
        <div class="controls">
            <label>Phone Number:</label>
            <input type="tel" class="form-control" id="phone" th:field="*{phone}" required="required" data-validation-required-message="Please enter your phone number." />
        </div>
    </div>
    <div class="control-group form-group">
        <div class="controls">
            <label>Email Address:</label>
            <input type="email" class="form-control" id="email" th:field="*{email}" required="required" data-validation-required-message="Please enter your email address."/>
        </div>
    </div>
    <div class="control-group form-group">
        <div class="controls">
            <label>Role:</label>
            <input type="email" class="form-control" id="role" th:field="*{role}" required="required" data-validation-required-message="Please enter your email address."/>
        </div>
    </div>                    
    <div class=" control-group form-group">
                            <div class="g-recaptcha" data-sitekey="ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ"></div>                    
    </div>
    <div class=" control-group form-group">
         <span class="btn btn-primary btn-file">
                                Add your Resumé <input type="file" name="file" id="file" required="required"/>
                         </span>
    </div>
    <div id="success"></div>
    <!-- For success/fail messages -->
    <button type="submit" class="btn btn-primary">Apply!</button>
</form>

现在，如果有人在提交之前错过将文件附加到表单，

-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="firstName"

Anadi
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="lastName"

Misra
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="phone"

9845420420
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="email"

foo@bar.com
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="role"

open.project
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="g-recaptcha-response"

03AHJ_Vuv9i7WQ_4zCipfnyrLNl6467l_cZgGIhkdpLjS1M0YmWvwQMOWQeRcrAHFh8s3-jO13NQs7019lzI7UobwNeHKIhBmcLMiVGPk38Iy8BjrEi2glI4QGjE4VTvRhV_-WWYsmlzV_7PRPE5Y8L0NboPXYoG9JSabMOL8V958w74pOzkxabsoR4wouCSa0gzo0EbOsLiCWjd0MAvZiCcKJGdwIlMp0WIjxcufB-RfG2F0rwv65yrgL-By0bdMewkWULY_aRvC-FRSqOEM9X5Qg4gviA-cvc5IY2XnRtaUALOPlR_QbwjgUKl2mJEFNab6Pks3MlsivuEZFkba4isDFlrJ4jXwBBQ
-----------------------------749526091303082321866336941
Content-Disposition: form-data; name="file"; filename=""
Content-Type: application/octet-stream


-----------------------------749526091303082321866336941--

或者尝试在不验证验证码的情况下提交，我收到此异常

Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of processor 'org.thymeleaf.spring4.processor.attr.SpringInputGeneralFieldAttrProcessor' (jobs:91)
....
....
Caused by: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'jobapplication' available as request attribute
at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:144)
at org.thymeleaf.spring4.util.FieldUtils.getBindStatusFromParsedExpression(FieldUtils.java:396)
at org.thymeleaf.spring4.util.FieldUtils.getBindStatus(FieldUtils.java:323)
at org.thymeleaf.spring4.util.FieldUtils.getBindStatus(FieldUtils.java:289)
at org.thymeleaf.spring4.processor.attr.AbstractSpringFieldAttrProcessor.processAttribute(AbstractSpringFieldAttrProcessor.java:98)
at org.thymeleaf.processor.attr.AbstractAttrProcessor.doProcess(AbstractAttrProcessor.java:87)
at org.thymeleaf.processor.AbstractProcessor.process(AbstractProcessor.java:212)
... 66 common frames omitted

我期望的是我得到验证码响应和文件的空值，然后我的 Controller 方法应该能够处理它，并将用户发送回带有特定错误消息的表单。它的工作方式与没有多部分数据的表单类似，即我没有收到绑定(bind)错误，但 Controller 参数中出现空值。仅当我使用多部分表单数据时，我才会看到此问题，如果填充了所有数据，即用户验证验证码并附加文件，则绑定(bind)一切正常。

使这些参数可选或使用 RequestPart 也没有帮助(我承认我真的不明白 RequestPart 注释的目的是什么)因此，将 Controller 更改为此(膝跳实验； -))

  @RequestMapping(value = "/careers/pursue", method = RequestMethod.POST)
  public Callable<String> pursue(
      final @RequestPart(value = "g-recaptcha-response", required = false) String captchaResponse,
      final @RequestPart(value = "file", required = false) MultipartFile file,
      final @ModelAttribute("jobapplication") @Valid JobApplication application, final BindingResult bindingResult,
      final Model model) 

也没有帮助。我需要延长 StandardServletMultipartResolver或者是否需要更改/修复 SpringInputGeneralFieldAttrProcessor ，还是我在这里遗漏了一些小细节？

更新

添加 Controller 方法

  @RequestMapping(value = "/careers/pursue", method = RequestMethod.POST)
  public Callable<String> pursue(final @ModelAttribute("jobapplication") @Valid JobApplication application,
      final BindingResult bindingResult, final Model model,
      final @RequestParam(value = "g-recaptcha-response", required = false) String captchaResponse,
      final @RequestPart(value = "file", required = false) MultipartFile file) {
    return new Callable<String>() {
      @Override
      public String call() throws Exception {
        try {
          model.asMap().clear();
          GoogleCaptchaResponseData response = captchaVerifier.isCaptchaResponseValid(captchaResponse).get();
          model.addAttribute("recaptcha", response.isSuccess());
          model.addAttribute("recaptchamessage", response.getErrorCodes());

          if (response.isSuccess() && !file.isEmpty()) {
            byte[] bytes = file.getBytes();

            LOGGER.info("Found file of type {}", file.getOriginalFilename());
            ByteArrayInputStream inputBytes = new ByteArrayInputStream(bytes);
            mailApi.sendMail(mailApi.buildJobApplicationEmail(application, new BufferedInputStream(inputBytes)));
            model.asMap().clear();
            model.addAttribute("uploadsuccess", true);
            model.addAttribute("resource_host", resourceHost);
            model.addAttribute("jobapplication", new JobApplication());
          }
        } catch (InterruptedException | ExecutionException e) {
          LOGGER.error(e.getMessage(), e);
          model.asMap().clear();
          model.addAttribute("jobapplication", application);
          model.addAttribute("resource_host", resourceHost);
          model.addAttribute("uploadsuccess", false);
        }
        return "jobs";
      }
    };
  }

Answer 1

@RequestPart 依赖 HttpMessageConvertors 和 content-type 将多部分数据绑定(bind)到方法参数，而 @RequestParam 依赖注册的转换器来进行转换。 Spring mvc 默认提供某些转换器。您可以使用@RequestParam或@RequestPart来绑定(bind)文件数据。大多数应用程序使用commons file upload来上传文件并注册

org.springframework.web.multipart.commons.CommonsMultipartResolver

用于多部分解析。注册后，spring 检查对多部分数据的每个请求，并使用它将其解析为方法 arg。检查这里

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/mvc.html#mvc-multipart

有几个项目您可以尝试。确保您的验证码和文件参数都是可选的，如下所示在 Controller 中。我切换到 @RequestParam 进行验证码。

@RequestMapping(value = "/careers/pursue", method = RequestMethod.POST)
  public Callable<String> pursue(
      final @RequestParam(value = "g-recaptcha-response", required = false) String captchaResponse,
      final @RequestPart(value = "file", required = false) MultipartFile file,
      final @ModelAttribute("jobapplication") @Valid JobApplication application, final BindingResult bindingResult,
      final Model model) 

希望这有帮助。