Merge multipart and query param values

DefaultMultipartHttpServletRequest always returned mulitpart parameter
values only rather than aggregating with query parameters, which
contradicts with Servlet spec, section 3.1, and is inconsistent with
StandardMultipartHttpServletRequest.

Issue: SPR-16590

spring-web/src/test/java/org/springframework/web/multipart/support/DefaultMultipartHttpServletRequestTests.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2002-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.multipart.support;
+
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+import org.springframework.mock.web.test.MockHttpServletRequest;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+
+import static org.junit.Assert.*;
+
+/**
+ * Unit tests for {@link DefaultMultipartHttpServletRequest}.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class DefaultMultipartHttpServletRequestTests {
+
+	private final MockHttpServletRequest servletRequest = new MockHttpServletRequest();
+
+	private final Map<String, String[]> multipartParams = new LinkedHashMap<>();
+
+	private final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<>();
+
+
+	@Test // SPR-16590
+	public void parameterValues() {
+
+		this.multipartParams.put("key", new String[] {"p"});
+		this.queryParams.add("key", "q");
+
+		String[] values = createMultipartRequest().getParameterValues("key");
+
+		assertArrayEquals(new String[] {"p", "q"}, values);
+	}
+
+	@Test // SPR-16590
+	public void parameterMap() {
+
+		this.multipartParams.put("key1", new String[] {"p1"});
+		this.multipartParams.put("key2", new String[] {"p2"});
+
+		this.queryParams.add("key1", "q1");
+		this.queryParams.add("key3", "q3");
+
+		Map<String, String[]> map = createMultipartRequest().getParameterMap();
+
+		assertEquals(3, map.size());
+		assertArrayEquals(new String[] {"p1", "q1"}, map.get("key1"));
+		assertArrayEquals(new String[] {"p2"}, map.get("key2"));
+		assertArrayEquals(new String[] {"q3"}, map.get("key3"));
+	}
+
+	private DefaultMultipartHttpServletRequest createMultipartRequest() {
+		insertQueryParams();
+		return new DefaultMultipartHttpServletRequest(this.servletRequest, new LinkedMultiValueMap<>(),
+				this.multipartParams, new HashMap<>());
+	}
+
+	private void insertQueryParams() {
+		StringBuilder query = new StringBuilder();
+		for (String key : this.queryParams.keySet()) {
+			for (String value : this.queryParams.get(key)) {
+				this.servletRequest.addParameter(key, value);
+				query.append(query.length() > 0 ? "&" : "").append(key).append("=").append(value);
+			}
+		}
+		this.servletRequest.setQueryString(query.toString());
+	}
+
+}