FileUpload.java

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface FileUpload {

}

FileUploadReturnValueHandler.java

import org.springframework.core.MethodParameter;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;

public class FileUploadReturnValueHandler implements HandlerMethodReturnValueHandler {

	public static final String MSIE_USER_AGENT_IDENTIFIER = "MSIE";
	public static final String USER_AGENT_HEADER = "user-agent";
	public static final String REQUESTED_WITH = "X-Requested-With";
	public static final String AJAX_IDENTIFIER = "XMLHttpRequest";

	private final HandlerMethodReturnValueHandler delegate;

	public FileUploadReturnValueHandler(HandlerMethodReturnValueHandler delegate) {
		this.delegate = delegate;
	}

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
		if (returnType.getMethodAnnotation(FileUpload.class) != null) {
			return true;
		} else {
			return delegate.supportsReturnType(returnType);
		}
	}

	@Override
	public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
			throws Exception {
		if (returnType.getMethodAnnotation(FileUpload.class) != null) {
			HttpHeaders httpHeaders = new HttpHeaders();
			browserSpecificActions(webRequest, httpHeaders);
			returnValue = new ResponseEntity(
					returnValue,
					httpHeaders,
					HttpStatus.OK
			);
		}
		delegate.handleReturnValue(returnValue, returnType, mavContainer, webRequest);

	}

	private void browserSpecificActions(NativeWebRequest webRequest, HttpHeaders httpHeaders) {
		String header = webRequest.getHeader(USER_AGENT_HEADER);
		if (isInternetExplorer(header) && !isAjax(webRequest)) {
			// IE downloads JSON as a file if its not requested with ajax.
			// If we set text/plain mime type it is shown as a text in a browser
			httpHeaders.setContentType(MediaType.TEXT_PLAIN);
		}
	}

	private boolean isInternetExplorer(String header) {
		return header.indexOf(MSIE_USER_AGENT_IDENTIFIER) != -1;
	}

	private boolean isAjax(NativeWebRequest webRequest) {
		return AJAX_IDENTIFIER.equalsIgnoreCase(webRequest.getHeader(REQUESTED_WITH));
	}
}

FileUploadSupportFactoryBean.java

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;

import java.util.List;


@Component
public class FileUploadSupportFactoryBean implements InitializingBean {

	private static final Logger logger = LoggerFactory.getLogger(FileUploadSupportFactoryBean.class);

	@Autowired
	private RequestMappingHandlerAdapter adapter;

	@Override
	public void afterPropertiesSet() throws Exception {
		List<HandlerMethodReturnValueHandler> handlers = Lists.newArrayList(adapter.getReturnValueHandlers());
		decorateHandlers(handlers);
		adapter.setReturnValueHandlers(handlers);
	}

	private void decorateHandlers(List<HandlerMethodReturnValueHandler> handlers) {
		for (HandlerMethodReturnValueHandler handler : handlers) {
			if (handler instanceof HttpEntityMethodProcessor) {
				FileUploadReturnValueHandler decorator = new FileUploadReturnValueHandler(handler);
				int index = handlers.indexOf(handler);
				handlers.set(index, decorator);
				logger.info("HttpEntityMethodProcessor was decorated with FileUploadReturnValueHandler");
				break;
			}
		}
	}
}

ImportController.java

@RestController
public class ImportController

  @RequestMapping(value = "/api/import", method = RequestMethod.POST, produces = "application/json")
  public CustomResponse<ImportResult> importData(@RequestParam(value = "file") final MultipartFile file,	Parameters parameters) {
      // some processing  
    return new CustomResponse(data);
  }
}