Spring 3.0 MultipartFile upload

问题:

I am converting Java web application to Spring framework and appreciate some advice on the issues I am facing with the file upload. Original code was written using org.apache.commons.fileupload.

1. Does Spring MultipartFile wraps org.apache.commons.fileupload or I can exclude this dependency from my POM file?

2. I have seen following example:

   @RequestMapping(value = "/form", method = RequestMethod.POST)
   public String handleFormUpload(@RequestParam("file") MultipartFile file) {
   
       if (!file.isEmpty()) {
           byte[] bytes = file.getBytes();
           // store the bytes somewhere
          return "redirect:uploadSuccess";
       } else {
           return "redirect:uploadFailure";
       }
   }
   

   Originally I tried to follow this example but was always getting an error as it couldn't find this request param. So, in my controller I have done the following:

   @RequestMapping(value = "/upload", method = RequestMethod.POST)
   public @ResponseBody
   ExtResponse upload(HttpServletRequest request, HttpServletResponse response)
   {
      // Create a JSON response object.
      ExtResponse extResponse = new ExtResponse();
      try {
          if (request instanceof MultipartHttpServletRequest)
          {
              MultipartHttpServletRequest multipartRequest =
                           (MultipartHttpServletRequest) request;
              MultipartFile file = multipartRequest.getFiles("file");
              InputStream input = file.getInputStream();
              // do the input processing
              extResponse.setSuccess(true);
           }
       } catch (Exception e) {
           extResponse.setSuccess(false);
           extResponse.setMessage(e.getMessage());
       }
       return extResponse;
   }
   

and it is working. If someone can tell me why @RequestParam did not work for me, I will appreciate. BTW I do have

    <bean id="multipartResolver"
        class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="2097152"/>
    </bean>

in my servlet context file.

回答1:

1. spring does not have a dependency on commons-fileupload, so you'll need it. If it's not there spring will use its internal mechanism
2. You should pass a MultipartFile as a method parameter, rather than @RequestParam(..)

回答2:

I had to

1. add commons-fileupload dependency to my pom,
2. add multipartResolver bean (mentioned in the question),
3. use @RequestParam("file") MultipartFile file in the handleFormUpload method and
4. add enctype in my jsp : <form:form method="POST" action="/form" enctype="multipart/form-data" >

to get it to work.

回答3:

This works for me.

@RequestMapping(value = "upload.spr", method = RequestMethod.POST)
public ModelAndView upload(@RequestParam("file") MultipartFile file, HttpServletResponse response)
{
    //  handle file here
}

回答4:

The General sysntax for request param is this @RequestParam(value="Your value", required=true), mode over request param is used to get a value frm the Url.

回答5:

In a POST you will only send the params in the request body, not in the URL (for which you use @RequestParams)

Thats why your second method worked.

回答6:

In Spring MVC 3.2 support for Servet 3.0 was introduced. So you need to include commons-file upload if you use earlier versions of Spring.