Interface MultipartResolver

public interface MultipartResolver

A strategy interface for multipart file upload resolution in accordance with RFC 1867. Implementations are typically usable both within an application context and standalone.

There are two concrete implementations included in Spring, as of Spring 3.1:

• CommonsMultipartResolver for Apache Commons FileUpload
• StandardServletMultipartResolver for the Servlet 3.0+ Part API

There is no default resolver implementation used for Spring DispatcherServlets, as an application might choose to parse its multipart requests itself. To define an implementation, create a bean with the id "multipartResolver" in a DispatcherServlet's application context. Such a resolver gets applied to all requests handled by that DispatcherServlet.

If a DispatcherServlet detects a multipart request, it will resolve it via the configured MultipartResolver and pass on a wrapped HttpServletRequest. Controllers can then cast their given request to the MultipartHttpServletRequest interface, which allows for access to any MultipartFiles. Note that this cast is only supported in case of an actual multipart request.

 public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
   MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
   MultipartFile multipartFile = multipartRequest.getFile("image");
   ...
 }

Instead of direct access, command or form controllers can register a ByteArrayMultipartFileEditor or StringMultipartFileEditor with their data binder, to automatically apply multipart content to form bean properties.

As an alternative to using a MultipartResolver with a DispatcherServlet, a MultipartFilter can be registered in web.xml. It will delegate to a corresponding MultipartResolver bean in the root application context. This is mainly intended for applications that do not use Spring's own web MVC framework.

Note: There is hardly ever a need to access the MultipartResolver itself from application code. It will simply do its work behind the scenes, making MultipartHttpServletRequests available to controllers.