Support Part/MultiPartFile arrays in ArgumentResolvers

Prior to this commit, parts of a multipart HTTP request could be
injected in @RequestPart and @RequestParam annotated arguments, when
using types:
* MultipartFile, Collection<MultiPartFile>
* javax.servlet.Part, Collection<Part>

This commits updates @RequestParam and @RequestPart argument resolvers
and now allows the array versions of those types:
* Part[]
* MultiPartFile[]

Note that the MockHtpServletRequest backing tests for standard
Servlets implementations now uses a MultiValueMap to store parts
(versus a simple hashmap).

Issue: SPR-11353

spring-web/src/main/java/org/springframework/web/method/annotation/RequestParamMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import java.util.List;
 import java.util.Map;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.Part;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
@@ -69,6 +70,7 @@ import org.springframework.web.util.WebUtils;
  *
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
+ * @author Brian Clozel
  * @since 3.1
  * @see RequestParamMapMethodArgumentResolver
  */
@@ -174,6 +176,11 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethod
 			Assert.notNull(multipartRequest, "Expected MultipartHttpServletRequest: is a MultipartResolver configured?");
 			arg = multipartRequest.getFiles(name);
 		}
+		else if(isMultipartFileArray(parameter)) {
+			assertIsMultipartRequest(servletRequest);
+			Assert.notNull(multipartRequest, "Expected MultipartHttpServletRequest: is a MultipartResolver configured?");
+			arg = multipartRequest.getFiles(name).toArray(new MultipartFile[0]);
+		}
 		else if ("javax.servlet.http.Part".equals(parameter.getParameterType().getName())) {
 			assertIsMultipartRequest(servletRequest);
 			arg = servletRequest.getPart(name);
@@ -182,6 +189,10 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethod
 			assertIsMultipartRequest(servletRequest);
 			arg = new ArrayList<Object>(servletRequest.getParts());
 		}
+		else if (isPartArray(parameter)) {
+			assertIsMultipartRequest(servletRequest);
+			arg = RequestPartResolver.resolvePart(servletRequest);
+		}
 		else {
 			arg = null;
 			if (multipartRequest != null) {
@@ -218,6 +229,16 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethod
 		return ((collectionType != null) && "javax.servlet.http.Part".equals(collectionType.getName()));
 	}
 
+	private boolean isPartArray(MethodParameter parameter) {
+		Class<?> paramType = parameter.getParameterType().getComponentType();
+		return ((paramType != null) && "javax.servlet.http.Part".equals(paramType.getName()));
+	}
+
+	private boolean isMultipartFileArray(MethodParameter parameter) {
+		Class<?> paramType = parameter.getParameterType().getComponentType();
+		return ((paramType != null) && MultipartFile.class.equals(paramType));
+	}
+
 	private Class<?> getCollectionParameterType(MethodParameter parameter) {
 		Class<?> paramType = parameter.getParameterType();
 		if (Collection.class.equals(paramType) || List.class.isAssignableFrom(paramType)){
@@ -277,4 +298,11 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethod
 		}
 	}
 
+	private static class RequestPartResolver {
+
+		public static Object resolvePart(HttpServletRequest servletRequest) throws Exception {
+			return servletRequest.getParts().toArray(new Part[servletRequest.getParts().size()]);
+		}
+	}
+
 }