Fix regression in HttpPutFormContentFilter

Re-arrange the checks so that if there is no form parameter, then
immediately and unconditionally delegate to super.getParameterValues().
Or reversely if there is no super.getParameterValues() then return the
form parameter.

So the only remaining case is when combining values present in both.
In that case we'll take both only if a queryString exists.

One extra fix is to not even wrap the request if we did not parse any
form parameters at all which can happen with HttpHiddenMethodFilter.

Issue: SPR-15828, 15835

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/filter/HttpPutFormContentFilter.java

@@ -98,12 +98,14 @@ public InputStream getBody() throws IOException {
 				}
 			};
 			MultiValueMap<String, String> formParameters = this.formConverter.read(null, inputMessage);
-			HttpServletRequest wrapper = new HttpPutFormContentRequestWrapper(request, formParameters);
-			filterChain.doFilter(wrapper, response);
-		}
-		else {
-			filterChain.doFilter(request, response);
+			if (!formParameters.isEmpty()) {
+				HttpServletRequest wrapper = new HttpPutFormContentRequestWrapper(request, formParameters);
+				filterChain.doFilter(wrapper, response);
+				return;
+			}
 		}
+
+		filterChain.doFilter(request, response);
 	}
 
 	private boolean isFormContentType(HttpServletRequest request) {
@@ -162,17 +164,17 @@ public Enumeration<String> getParameterNames() {
 		@Override
 		@Nullable
 		public String[] getParameterValues(String name) {
-			String[] queryParam = (super.getQueryString() != null ? super.getParameterValues(name) : null);
+			String[] parameterValues = super.getParameterValues(name);
 			List<String> formParam = this.formParameters.get(name);
 			if (formParam == null) {
-				return queryParam;
+				return parameterValues;
 			}
-			else if (queryParam == null) {
+			if (parameterValues == null || getQueryString() == null) {
 				return formParam.toArray(new String[formParam.size()]);
 			}
 			else {
-				List<String> result = new ArrayList<>(queryParam.length + formParam.size());
-				result.addAll(Arrays.asList(queryParam));
+				List<String> result = new ArrayList<>(parameterValues.length + formParam.size());
+				result.addAll(Arrays.asList(parameterValues));
 				result.addAll(formParam);
 				return result.toArray(new String[result.size()]);
 			}

spring-web/src/test/java/org/springframework/web/filter/HttpPutFormContentFilterTests.java

@@ -58,7 +58,7 @@ public void setup() {
 
 	@Test
 	public void wrapPutAndPatchOnly() throws Exception {
-		request.setContent("".getBytes("ISO-8859-1"));
+		request.setContent("foo=bar".getBytes("ISO-8859-1"));
 		for (HttpMethod method : HttpMethod.values()) {
 			request.setMethod(method.name());
 			filterChain = new MockFilterChain();
@@ -204,4 +204,13 @@ public void getParameterMap() throws Exception {
 		assertArrayEquals(new String[] {"value4"}, parameters.get("name4"));
 	}
 
+	@Test // SPR-15835
+	public void hiddenHttpMethodFilterFollowedByHttpPutFormContentFilter() throws Exception {
+		request.addParameter("_method", "PUT");
+		request.addParameter("hiddenField", "testHidden");
+		filter.doFilter(request, response, filterChain);
+
+		assertArrayEquals(new String[]{"testHidden"}, filterChain.getRequest().getParameterValues("hiddenField"));
+	}
+
 }