Add ServerRequest::multipartData in WebMvc.fn

This commit adds the multipartData method to ServerRequest in WebMvc.fn,
returning a MultiValueMap<String, Part>.

Closes gh-24909

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequest.java

@@ -44,6 +44,7 @@ import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
+import javax.servlet.http.Part;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpHeaders;
@@ -85,6 +86,9 @@ class DefaultServerRequest implements ServerRequest {
 
 	private final Map<String, Object> attributes;
 
+	@Nullable
+	private MultiValueMap<String, Part> parts;
+
 
 	public DefaultServerRequest(HttpServletRequest servletRequest, List<HttpMessageConverter<?>> messageConverters) {
 		this.serverHttpRequest = new ServletServerHttpRequest(servletRequest);
@@ -228,6 +232,19 @@ class DefaultServerRequest implements ServerRequest {
 		return this.params;
 	}
 
+	@Override
+	public MultiValueMap<String, Part> multipartData() throws IOException, ServletException {
+		MultiValueMap<String, Part> result = this.parts;
+		if (result == null) {
+			result = servletRequest().getParts().stream()
+					.collect(Collectors.groupingBy(Part::getName,
+							LinkedMultiValueMap::new,
+							Collectors.toList()));
+			this.parts = result;
+		}
+		return result;
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	public Map<String, String> pathVariables() {

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequestBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -30,6 +30,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Consumer;
+import java.util.stream.Collectors;
 
 import javax.servlet.ReadListener;
 import javax.servlet.ServletException;
@@ -37,6 +38,7 @@ import javax.servlet.ServletInputStream;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpSession;
+import javax.servlet.http.Part;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpHeaders;
@@ -199,6 +201,14 @@ class DefaultServerRequestBuilder implements ServerRequest.Builder {
 			return this.methodName;
 		}
 
+		@Override
+		public MultiValueMap<String, Part> multipartData() throws IOException, ServletException {
+			return servletRequest().getParts().stream()
+					.collect(Collectors.groupingBy(Part::getName,
+							LinkedMultiValueMap::new,
+							Collectors.toList()));
+		}
+
 		@Override
 		public URI uri() {
 			return this.uri;

spring-webmvc/src/main/java/org/springframework/web/servlet/function/RequestPredicates.java

@@ -40,6 +40,7 @@ import javax.servlet.ServletException;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpSession;
+import javax.servlet.http.Part;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -994,6 +995,16 @@ public abstract class RequestPredicates {
 			return this.request.params();
 		}
 
+		@Override
+		public MultiValueMap<String, Part> multipartData() throws IOException, ServletException {
+			return this.request.multipartData();
+		}
+
+		@Override
+		public String pathVariable(String name) {
+			return this.request.pathVariable(name);
+		}
+
 		@Override
 		@SuppressWarnings("unchecked")
 		public Map<String, String> pathVariables() {

spring-webmvc/src/main/java/org/springframework/web/servlet/function/ServerRequest.java

@@ -33,6 +33,7 @@ import javax.servlet.ServletException;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpSession;
+import javax.servlet.http.Part;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.io.buffer.DataBuffer;
@@ -186,6 +187,17 @@ public interface ServerRequest {
 	 */
 	MultiValueMap<String, String> params();
 
+	/**
+	 * Get the parts of a multipart request, provided the Content-Type is
+	 * {@code "multipart/form-data"}, or an exception otherwise.
+	 * @return the multipart data, mapping from name to part(s)
+	 * @throws IOException           if an I/O error occurred during the retrieval
+	 * @throws ServletException      if this request is not of type {@code "multipart/form-data"}
+	 * @since 5.3
+	 * @see HttpServletRequest#getParts()
+	 */
+	MultiValueMap<String, Part> multipartData() throws IOException, ServletException;
+
 	/**
 	 * Get the path variable with the given name, if present.
 	 * @param name the variable name

spring-webmvc/src/test/java/org/springframework/web/servlet/function/DefaultServerRequestTests.java

@@ -33,6 +33,7 @@ import java.util.Optional;
 import java.util.OptionalLong;
 
 import javax.servlet.http.Cookie;
+import javax.servlet.http.Part;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -53,6 +54,7 @@ import org.springframework.web.HttpMediaTypeNotSupportedException;
 import org.springframework.web.testfixture.server.MockServerWebExchange;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 import org.springframework.web.testfixture.servlet.MockHttpSession;
+import org.springframework.web.testfixture.servlet.MockPart;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -129,6 +131,25 @@ public class DefaultServerRequestTests {
 		assertThat(request.param("foo")).isEqualTo(Optional.of("bar"));
 	}
 
+	@Test
+	public void multipartData() throws Exception {
+		MockPart formPart = new MockPart("form", "foo".getBytes(UTF_8));
+		MockPart filePart = new MockPart("file", "foo.txt", "foo".getBytes(UTF_8));
+
+		MockHttpServletRequest servletRequest = new MockHttpServletRequest("POST", "/");
+		servletRequest.addPart(formPart);
+		servletRequest.addPart(filePart);
+
+		DefaultServerRequest request =
+				new DefaultServerRequest(servletRequest, this.messageConverters);
+
+		MultiValueMap<String, Part> result = request.multipartData();
+
+		assertThat(result).hasSize(2);
+		assertThat(result.get("form")).containsExactly(formPart);
+		assertThat(result.get("file")).containsExactly(filePart);
+	}
+
 	@Test
 	public void emptyQueryParam() {
 		MockHttpServletRequest servletRequest = new MockHttpServletRequest("GET", "/");