MultipartResolver

MultipartResolver from the org.springframework.web.multipart package is a strategy for parsing multi-part requests, including file uploads. There is one implementation based on FileUpload from the Commons project, and another based on multipart query parsing Servlet 3.0.

To enable multipart processing, you must declare a MultipartResolver bean in the DispatcherServlet configuration from Spring under the name multipartResolver. DispatcherServlet will detect it and apply it to the incoming request. Upon receiving a POST with content type multipart/form-data, the resolver parses the content by wrapping the current HttpServletRequest as MultipartHttpServletRequest to provide access to recognized files in addition to exposing components as query parameters.

FileUpload from Apache Commons

To use FileUpload from Apache Commons, you can configure a bean of type CommonsMultipartResolver called multipartResolver. You also need to have the commons-fileupload jar file as a dependency in your classpath.

This resolver variant delegates authority to a local library within the application, providing maximum cross-platform portability between servlet containers. Alternatively, you can use standard multi-part servlet recognition through the container's own parser, as described below.

Servlet 3.0

Multipart parsing according to the Servlet 3.0 specification must be enabled in the servlet container configuration. To do this:

• In Java, set MultipartConfigElement to register servlets.

• In web.xml, add a "<multipart-config>" section to the servlet declaration.

The following example shows how to configure MultipartConfigElement to register servlets:

public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    // ...
    @Override
    protected void customizeRegistration(ServletRegistration.Dynamic registration) {
        // Optionally also sets maxFileSize, maxRequestSize, fileSizeThreshold
        registration.setMultipartConfig(new MultipartConfigElement("/tmp"));
    }
}

class AppInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {
    // ...
    override fun customizeRegistration(registration: ServletRegistration.Dynamic) {
        // Optionally also sets maxFileSize, maxRequestSize, fileSizeThreshold
        registration.setMultipartConfig(MultipartConfigElement("/tmp"))
    }
}

Once the Servlet 3.0 configuration is created, you can add a bean of type StandardServletMultipartResolver called multipartResolver.