Support data binding for multipart requests in WebFlux

Issue: SPR-14546

spring-web/src/main/java/org/springframework/http/codec/multipart/FilePart.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2002-2017 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.http.codec.multipart;
+
+import java.io.File;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * Specialization of {@link Part} for a file upload.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0
+ */
+public interface FilePart extends Part {
+
+	/**
+	 * Return the name of the file selected by the user in a browser form.
+	 */
+	String getFilename();
+
+
+	/**
+	 * Transfer the file in this part to the given file destination.
+	 * @param dest the target file
+	 * @return completion {@code Mono} with the result of the file transfer,
+	 * possibly {@link IllegalStateException} if the part isn't a file
+	 */
+	Mono<Void> transferTo(File dest);
+
+}

spring-web/src/main/java/org/springframework/http/codec/multipart/FormFieldPart.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2002-2017 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.http.codec.multipart;
+
+/**
+ * Specialization of {@link Part} for a form field.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0
+ */
+public interface FormFieldPart extends Part {
+
+	/**
+	 * Return the form field value.
+	 */
+	String getValue();
+
+}

spring-web/src/main/java/org/springframework/http/codec/multipart/Part.java

@@ -16,11 +16,7 @@
 
 package org.springframework.http.codec.multipart;
 
-import java.io.File;
-import java.util.Optional;
-
 import reactor.core.publisher.Flux;
-import reactor.core.publisher.Mono;
 
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.http.HttpHeaders;
@@ -29,9 +25,10 @@ import org.springframework.http.HttpHeaders;
  * Representation for a part in a "multipart/form-data" request.
  *
  * <p>The origin of a multipart request may a browser form in which case each
- * part represents a text-based form field or a file upload. Multipart requests
- * may also be used outside of browsers to transfer data with any content type
- * such as JSON, PDF, etc.
+ * part is either a {@link FormFieldPart} or a {@link FilePart}.
+ *
+ * <p>Multipart requests may also be used outside of a browser for data of any
+ * content type (e.g. JSON, PDF, etc).
  *
  * @author Sebastien Deleuze
  * @author Rossen Stoyanchev
@@ -53,30 +50,9 @@ public interface Part {
 	 */
 	HttpHeaders getHeaders();
 
-	/**
-	 *
-	 * Return the name of the file selected by the user in a browser form.
-	 * @return the filename if defined and available
-	 */
-	Optional<String> getFilename();
-
-	/**
-	 * Return the part content converted to a String with the charset from the
-	 * {@code Content-Type} header or {@code UTF-8} by default.
-	 */
-	Mono<String> getContentAsString();
-
 	/**
 	 * Return the part raw content as a stream of DataBuffer's.
 	 */
 	Flux<DataBuffer> getContent();
 
-	/**
-	 * Transfer the file in this part to the given file destination.
-	 * @param destination the target file
-	 * @return completion {@code Mono} with the result of the file transfer,
-	 * possibly {@link IllegalStateException} if the part isn't a file
-	 */
-	Mono<Void> transferTo(File destination);
-
 }

spring-web/src/main/java/org/springframework/http/codec/multipart/SynchronossPartHttpMessageReader.java

@@ -52,8 +52,6 @@ import org.springframework.http.MediaType;
 import org.springframework.http.ReactiveHttpInputMessage;
 import org.springframework.http.codec.HttpMessageReader;
 import org.springframework.util.Assert;
-import org.springframework.util.MimeType;
-import org.springframework.util.StreamUtils;
 
 /**
  * {@code HttpMessageReader} for parsing {@code "multipart/form-data"} requests
@@ -71,6 +69,8 @@ import org.springframework.util.StreamUtils;
  */
 public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part> {
 
+	private final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
+
 
 	@Override
 	public List<MediaType> getReadableMediaTypes() {
@@ -88,7 +88,7 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 	public Flux<Part> read(ResolvableType elementType, ReactiveHttpInputMessage message,
 			Map<String, Object> hints) {
 
-		return Flux.create(new SynchronossPartGenerator(message));
+		return Flux.create(new SynchronossPartGenerator(message, this.bufferFactory));
 	}
 
 
@@ -109,9 +109,12 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 
 		private final ReactiveHttpInputMessage inputMessage;
 
+		private final DataBufferFactory bufferFactory;
+
 
-		SynchronossPartGenerator(ReactiveHttpInputMessage inputMessage) {
+		SynchronossPartGenerator(ReactiveHttpInputMessage inputMessage, DataBufferFactory factory) {
 			this.inputMessage = inputMessage;
+			this.bufferFactory = factory;
 		}
 
 
@@ -119,7 +122,7 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 		public void accept(FluxSink<Part> emitter) {
 
 			MultipartContext context = createMultipartContext();
-			NioMultipartParserListener listener = new FluxSinkAdapterListener(emitter);
+			NioMultipartParserListener listener = new FluxSinkAdapterListener(emitter, this.bufferFactory);
 			NioMultipartParser parser = Multipart.multipart(context).forNIO(listener);
 
 			this.inputMessage.getBody().subscribe(buffer -> {
@@ -167,11 +170,14 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 
 		private final FluxSink<Part> sink;
 
+		private final DataBufferFactory bufferFactory;
+
 		private final AtomicInteger terminated = new AtomicInteger(0);
 
 
-		FluxSinkAdapterListener(FluxSink<Part> sink) {
+		FluxSinkAdapterListener(FluxSink<Part> sink, DataBufferFactory bufferFactory) {
 			this.sink = sink;
+			this.bufferFactory = bufferFactory;
 		}
 
 
@@ -179,14 +185,17 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 		public void onPartFinished(StreamStorage storage, Map<String, List<String>> headers) {
 			HttpHeaders httpHeaders = new HttpHeaders();
 			httpHeaders.putAll(headers);
-			this.sink.next(new SynchronossPart(httpHeaders, storage));
+			Part part = MultipartUtils.getFileName(httpHeaders) != null ?
+					new SynchronossFilePart(httpHeaders, storage, this.bufferFactory) :
+					new DefaultSynchronossPart(httpHeaders, storage, this.bufferFactory);
+			this.sink.next(part);
 		}
 
 		@Override
 		public void onFormFieldPartFinished(String name, String value, Map<String, List<String>> headers) {
 			HttpHeaders httpHeaders = new HttpHeaders();
 			httpHeaders.putAll(headers);
-			this.sink.next(new SynchronossPart(httpHeaders, value));
+			this.sink.next(new SynchronossFormFieldPart(httpHeaders, this.bufferFactory, value));
 		}
 
 		@Override
@@ -213,31 +222,18 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 	}
 
 
-	private static class SynchronossPart implements Part {
+	private static abstract class AbstractSynchronossPart implements Part {
 
 		private final HttpHeaders headers;
 
-		private final StreamStorage storage;
-
-		private final String content;
-
-		private final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
-
+		private final DataBufferFactory bufferFactory;
 
-		SynchronossPart(HttpHeaders headers, StreamStorage storage) {
-			Assert.notNull(headers, "HttpHeaders is required");
-			Assert.notNull(storage, "'storage' is required");
-			this.headers = headers;
-			this.storage = storage;
-			this.content = null;
-		}
 
-		SynchronossPart(HttpHeaders headers, String content) {
+		AbstractSynchronossPart(HttpHeaders headers, DataBufferFactory bufferFactory) {
 			Assert.notNull(headers, "HttpHeaders is required");
-			Assert.notNull(content, "'content' is required");
+			Assert.notNull(bufferFactory, "'bufferFactory' is required");
 			this.headers = headers;
-			this.storage = null;
-			this.content = content;
+			this.bufferFactory = bufferFactory;
 		}
 
 
@@ -251,52 +247,53 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 			return this.headers;
 		}
 
-		@Override
-		public Optional<String> getFilename() {
-			return Optional.ofNullable(MultipartUtils.getFileName(this.headers));
+		protected DataBufferFactory getBufferFactory() {
+			return this.bufferFactory;
 		}
+	}
 
-		@Override
-		public Mono<String> getContentAsString() {
-			if (this.content != null) {
-				return Mono.just(this.content);
-			}
-			try {
-				InputStream inputStream = this.storage.getInputStream();
-				Charset charset = getCharset();
-				return Mono.just(StreamUtils.copyToString(inputStream, charset));
-			}
-			catch (IOException e) {
-				return Mono.error(new IllegalStateException(
-						"Error while reading part content as a string", e));
-			}
-		}
+	private static class DefaultSynchronossPart extends AbstractSynchronossPart {
 
-		private Charset getCharset() {
-			return Optional.ofNullable(this.headers.getContentType())
-					.map(MimeType::getCharset).orElse(StandardCharsets.UTF_8);
+		private final StreamStorage storage;
+
+
+		DefaultSynchronossPart(HttpHeaders headers, StreamStorage storage, DataBufferFactory factory) {
+			super(headers, factory);
+			Assert.notNull(storage, "'storage' is required");
+			this.storage = storage;
 		}
 
+
 		@Override
 		public Flux<DataBuffer> getContent() {
-			if (this.content != null) {
-				DataBuffer buffer = this.bufferFactory.allocateBuffer(this.content.length());
-				buffer.write(this.content.getBytes());
-				return Flux.just(buffer);
-			}
 			InputStream inputStream = this.storage.getInputStream();
-			return DataBufferUtils.read(inputStream, this.bufferFactory, 4096);
+			return DataBufferUtils.read(inputStream, getBufferFactory(), 4096);
+		}
+
+		protected StreamStorage getStorage() {
+			return this.storage;
+		}
+	}
+
+	private static class SynchronossFilePart extends DefaultSynchronossPart implements FilePart {
+
+
+		public SynchronossFilePart(HttpHeaders headers, StreamStorage storage, DataBufferFactory factory) {
+			super(headers, storage, factory);
+		}
+
+
+		@Override
+		public String getFilename() {
+			return MultipartUtils.getFileName(getHeaders());
 		}
 
 		@Override
 		public Mono<Void> transferTo(File destination) {
-			if (this.storage == null || !getFilename().isPresent()) {
-				return Mono.error(new IllegalStateException("The part does not represent a file."));
-			}
 			ReadableByteChannel input = null;
 			FileChannel output = null;
 			try {
-				input = Channels.newChannel(this.storage.getInputStream());
+				input = Channels.newChannel(getStorage().getInputStream());
 				output = new FileOutputStream(destination).getChannel();
 
 				long size = (input instanceof FileChannel ? ((FileChannel) input).size() : Long.MAX_VALUE);
@@ -332,4 +329,34 @@ public class SynchronossPartHttpMessageReader implements HttpMessageReader<Part>
 		}
 	}
 
+	private static class SynchronossFormFieldPart extends AbstractSynchronossPart implements FormFieldPart {
+
+		private final String content;
+
+
+		SynchronossFormFieldPart(HttpHeaders headers, DataBufferFactory bufferFactory, String content) {
+			super(headers, bufferFactory);
+			this.content = content;
+		}
+
+
+		@Override
+		public String getValue() {
+			return this.content;
+		}
+
+		@Override
+		public Flux<DataBuffer> getContent() {
+			byte[] bytes = this.content.getBytes(getCharset());
+			DataBuffer buffer = getBufferFactory().allocateBuffer(bytes.length);
+			buffer.write(bytes);
+			return Flux.just(buffer);
+		}
+
+		private Charset getCharset() {
+			return Optional.ofNullable(MultipartUtils.getCharEncoding(getHeaders()))
+					.map(Charset::forName).orElse(StandardCharsets.UTF_8);
+		}
+	}
+
 }

spring-web/src/main/java/org/springframework/web/bind/support/WebExchangeDataBinder.java

@@ -19,10 +19,12 @@ package org.springframework.web.bind.support;
 import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
+import java.util.stream.Collectors;
 
 import reactor.core.publisher.Mono;
 
 import org.springframework.beans.MutablePropertyValues;
+import org.springframework.http.codec.multipart.FormFieldPart;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.MultiValueMap;
@@ -105,6 +107,9 @@ public class WebExchangeDataBinder extends WebDataBinder {
 
 	private static void addBindValue(Map<String, Object> params, String key, List<?> values) {
 		if (!CollectionUtils.isEmpty(values)) {
+			values = values.stream()
+					.map(value -> value instanceof FormFieldPart ? ((FormFieldPart) value).getValue() : value)
+					.collect(Collectors.toList());
 			params.put(key, values.size() == 1 ? values.get(0) : values);
 		}
 	}

spring-web/src/test/java/org/springframework/http/codec/multipart/MultipartHttpMessageWriterTests.java

@@ -39,7 +39,10 @@ import org.springframework.mock.http.server.reactive.test.MockServerHttpResponse
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
 
 /**
  * @author Sebastien Deleuze
@@ -114,37 +117,39 @@ public class MultipartHttpMessageWriterTests {
 		assertEquals(5, requestParts.size());
 
 		Part part = requestParts.getFirst("name 1");
+		assertTrue(part instanceof FormFieldPart);
 		assertEquals("name 1", part.getName());
-		assertEquals("value 1", part.getContentAsString().block());
-		assertFalse(part.getFilename().isPresent());
+		assertEquals("value 1", ((FormFieldPart) part).getValue());
 
-		List<Part> part2 = requestParts.get("name 2");
-		assertEquals(2, part2.size());
-		part = part2.get(0);
+		List<Part> parts2 = requestParts.get("name 2");
+		assertEquals(2, parts2.size());
+		part = parts2.get(0);
+		assertTrue(part instanceof FormFieldPart);
 		assertEquals("name 2", part.getName());
-		assertEquals("value 2+1", part.getContentAsString().block());
-		part = part2.get(1);
+		assertEquals("value 2+1", ((FormFieldPart) part).getValue());
+		part = parts2.get(1);
+		assertTrue(part instanceof FormFieldPart);
 		assertEquals("name 2", part.getName());
-		assertEquals("value 2+2", part.getContentAsString().block());
+		assertEquals("value 2+2", ((FormFieldPart) part).getValue());
 
 		part = requestParts.getFirst("logo");
+		assertTrue(part instanceof FilePart);
 		assertEquals("logo", part.getName());
-		assertTrue(part.getFilename().isPresent());
-		assertEquals("logo.jpg", part.getFilename().get());
+		assertEquals("logo.jpg", ((FilePart) part).getFilename());
 		assertEquals(MediaType.IMAGE_JPEG, part.getHeaders().getContentType());
 		assertEquals(logo.getFile().length(), part.getHeaders().getContentLength());
 
 		part = requestParts.getFirst("utf8");
+		assertTrue(part instanceof FilePart);
 		assertEquals("utf8", part.getName());
-		assertTrue(part.getFilename().isPresent());
-		assertEquals("Hall\u00F6le.jpg", part.getFilename().get());
+		assertEquals("Hall\u00F6le.jpg", ((FilePart) part).getFilename());
 		assertEquals(MediaType.IMAGE_JPEG, part.getHeaders().getContentType());
 		assertEquals(utf8.getFile().length(), part.getHeaders().getContentLength());
 
 		part = requestParts.getFirst("json");
 		assertEquals("json", part.getName());
 		assertEquals(MediaType.APPLICATION_JSON_UTF8, part.getHeaders().getContentType());
-		assertEquals("{\"bar\":\"bar\"}", part.getContentAsString().block());
+		assertEquals("{\"bar\":\"bar\"}", ((FormFieldPart) part).getValue());
 	}
 
 

spring-web/src/test/java/org/springframework/http/codec/multipart/SynchronossPartHttpMessageReaderTests.java

@@ -18,7 +18,6 @@ package org.springframework.http.codec.multipart;
 
 import java.io.IOException;
 import java.util.Map;
-import java.util.Optional;
 
 import org.junit.Test;
 import reactor.core.publisher.Flux;
@@ -88,10 +87,9 @@ public class SynchronossPartHttpMessageReaderTests {
 
 		assertTrue(parts.containsKey("fooPart"));
 		Part part = parts.getFirst("fooPart");
+		assertTrue(part instanceof FilePart);
 		assertEquals("fooPart", part.getName());
-		Optional<String> filename = part.getFilename();
-		assertTrue(filename.isPresent());
-		assertEquals("foo.txt", filename.get());
+		assertEquals("foo.txt", ((FilePart) part).getFilename());
 		DataBuffer buffer = part.getContent().reduce(DataBuffer::write).block();
 		assertEquals(12, buffer.readableByteCount());
 		byte[] byteContent = new byte[12];
@@ -100,10 +98,9 @@ public class SynchronossPartHttpMessageReaderTests {
 
 		assertTrue(parts.containsKey("barPart"));
 		part = parts.getFirst("barPart");
+		assertTrue(part instanceof FormFieldPart);
 		assertEquals("barPart", part.getName());
-		filename = part.getFilename();
-		assertFalse(filename.isPresent());
-		assertEquals("bar", part.getContentAsString().block());
+		assertEquals("bar", ((FormFieldPart) part).getValue());
 	}
 
 	@Test

spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java

@@ -30,6 +30,8 @@ import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
+import org.springframework.http.codec.multipart.FilePart;
+import org.springframework.http.codec.multipart.FormFieldPart;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -99,12 +101,11 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 
 		private void assertFooPart(Part part) {
 			assertEquals("fooPart", part.getName());
-			Optional<String> filename = part.getFilename();
-			assertTrue(filename.isPresent());
-			assertEquals("foo.txt", filename.get());
+			assertTrue(part instanceof FilePart);
+			assertEquals("foo.txt", ((FilePart) part).getFilename());
 			DataBuffer buffer = part
 					.getContent()
-					.reduce((s1, s2) -> s1.write(s2))
+					.reduce(DataBuffer::write)
 					.block();
 			assertEquals(12, buffer.readableByteCount());
 			byte[] byteContent = new byte[12];
@@ -114,9 +115,8 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 
 		private void assertBarPart(Part part) {
 			assertEquals("barPart", part.getName());
-			Optional<String> filename = part.getFilename();
-			assertFalse(filename.isPresent());
-			assertEquals("bar", part.getContentAsString().block());
+			assertTrue(part instanceof FormFieldPart);
+			assertEquals("bar", ((FormFieldPart) part).getValue());
 		}
 	}
 

spring-web/src/test/java/org/springframework/web/bind/support/WebExchangeDataBinderTests.java

@@ -17,15 +17,22 @@
 package org.springframework.web.bind.support;
 
 import java.beans.PropertyEditorSupport;
-import java.io.UnsupportedEncodingException;
-import java.net.URLEncoder;
 import java.time.Duration;
-import java.util.Iterator;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
 
 import org.junit.Before;
 import org.junit.Test;
+import reactor.core.publisher.Mono;
 
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
+import org.springframework.http.codec.FormHttpMessageWriter;
+import org.springframework.http.codec.multipart.FilePart;
+import org.springframework.http.codec.multipart.MultipartHttpMessageWriter;
+import org.springframework.mock.http.client.reactive.test.MockClientHttpRequest;
 import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
 import org.springframework.tests.sample.beans.ITestBean;
 import org.springframework.tests.sample.beans.TestBean;
@@ -34,9 +41,12 @@ import org.springframework.util.MultiValueMap;
 import org.springframework.web.server.ServerWebExchange;
 
 import static junit.framework.TestCase.assertFalse;
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.springframework.core.ResolvableType.forClass;
+import static org.springframework.core.ResolvableType.forClassWithGenerics;
 
 /**
  * Unit tests for {@link WebExchangeDataBinder}.
@@ -177,39 +187,60 @@ public class WebExchangeDataBinderTests {
 		assertEquals("test", this.testBean.getSpouse().getName());
 	}
 
-
-	private String generateForm(MultiValueMap<String, String> form) {
-		StringBuilder builder = new StringBuilder();
-		try {
-			for (Iterator<String> names = form.keySet().iterator(); names.hasNext();) {
-				String name = names.next();
-				for (Iterator<String> values = form.get(name).iterator(); values.hasNext();) {
-					String value = values.next();
-					builder.append(URLEncoder.encode(name, "UTF-8"));
-					if (value != null) {
-						builder.append('=');
-						builder.append(URLEncoder.encode(value, "UTF-8"));
-						if (values.hasNext()) {
-							builder.append('&');
-						}
-					}
-				}
-				if (names.hasNext()) {
-					builder.append('&');
-				}
-			}
-		}
-		catch (UnsupportedEncodingException ex) {
-			throw new IllegalStateException(ex);
-		}
-		return builder.toString();
+	@Test
+	public void testMultipart() throws Exception {
+
+		MultipartBean bean = new MultipartBean();
+		WebExchangeDataBinder binder = new WebExchangeDataBinder(bean);
+
+		MultiValueMap<String, Object> data = new LinkedMultiValueMap<>();
+		data.add("name", "bar");
+		data.add("someList", "123");
+		data.add("someList", "abc");
+		data.add("someArray", "dec");
+		data.add("someArray", "456");
+		data.add("part", new ClassPathResource("org/springframework/http/codec/multipart/foo.txt"));
+		data.add("somePartList", new ClassPathResource("org/springframework/http/codec/multipart/foo.txt"));
+		data.add("somePartList", new ClassPathResource("org/springframework/http/server/reactive/spring.png"));
+		binder.bind(exchangeMultipart(data)).block(Duration.ofMillis(5000));
+
+		assertEquals("bar", bean.getName());
+		assertEquals(Arrays.asList("123", "abc"), bean.getSomeList());
+		assertArrayEquals(new String[] {"dec", "456"}, bean.getSomeArray());
+		assertEquals("foo.txt", bean.getPart().getFilename());
+		assertEquals(2, bean.getSomePartList().size());
+		assertEquals("foo.txt", bean.getSomePartList().get(0).getFilename());
+		assertEquals("spring.png", bean.getSomePartList().get(1).getFilename());
 	}
 
+
+
 	private ServerWebExchange exchange(MultiValueMap<String, String> formData) {
+
+		MockClientHttpRequest request = new MockClientHttpRequest(HttpMethod.POST, "/");
+
+		new FormHttpMessageWriter().write(Mono.just(formData),
+				forClassWithGenerics(MultiValueMap.class, String.class, String.class),
+				MediaType.APPLICATION_FORM_URLENCODED, request, Collections.emptyMap()).block();
+
 		return MockServerHttpRequest
 				.post("/")
 				.contentType(MediaType.APPLICATION_FORM_URLENCODED)
-				.body(generateForm(formData))
+				.body(request.getBody())
+				.toExchange();
+	}
+
+	private ServerWebExchange exchangeMultipart(MultiValueMap<String, ?> multipartData) {
+
+		MockClientHttpRequest request = new MockClientHttpRequest(HttpMethod.POST, "/");
+
+		new MultipartHttpMessageWriter().write(Mono.just(multipartData), forClass(MultiValueMap.class),
+				MediaType.MULTIPART_FORM_DATA, request, Collections.emptyMap()).block();
+
+		return MockServerHttpRequest
+				.post("/")
+				.contentType(request.getHeaders().getContentType())
+				.body(request.getBody())
 				.toExchange();
 	}
 
@@ -222,4 +253,58 @@ public class WebExchangeDataBinderTests {
 		}
 	}
 
+	private static class MultipartBean {
+
+		private String name;
+
+		private List<?> someList;
+
+		private String[] someArray;
+
+		private FilePart part;
+
+		private List<FilePart> somePartList;
+
+
+		public String getName() {
+			return this.name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public List<?> getSomeList() {
+			return this.someList;
+		}
+
+		public void setSomeList(List<?> someList) {
+			this.someList = someList;
+		}
+
+		public String[] getSomeArray() {
+			return this.someArray;
+		}
+
+		public void setSomeArray(String[] someArray) {
+			this.someArray = someArray;
+		}
+
+		public FilePart getPart() {
+			return this.part;
+		}
+
+		public void setPart(FilePart part) {
+			this.part = part;
+		}
+
+		public List<FilePart> getSomePartList() {
+			return this.somePartList;
+		}
+
+		public void setSomePartList(List<FilePart> somePartList) {
+			this.somePartList = somePartList;
+		}
+	}
+
 }

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolver.java

@@ -237,7 +237,7 @@ public class ModelAttributeMethodArgumentResolver extends HandlerMethodArgumentR
 	private boolean hasErrorsArgument(MethodParameter parameter) {
 		int i = parameter.getParameterIndex();
 		Class<?>[] paramTypes = parameter.getMethod().getParameterTypes();
-		return (paramTypes.length > i && Errors.class.isAssignableFrom(paramTypes[i + 1]));
+		return (paramTypes.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
 	}
 
 	private void validateIfApplicable(WebExchangeDataBinder binder, MethodParameter parameter) {

spring-webflux/src/test/java/org/springframework/web/reactive/function/MultipartIntegrationTests.java

@@ -27,6 +27,8 @@ import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.codec.multipart.FilePart;
+import org.springframework.http.codec.multipart.FormFieldPart;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -38,7 +40,6 @@ import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.reactive.function.server.ServerResponse;
 
 import static org.junit.Assert.assertEquals;
-
 import static org.springframework.web.reactive.function.server.RequestPredicates.POST;
 import static org.springframework.web.reactive.function.server.RouterFunctions.route;
 
@@ -57,9 +58,7 @@ public class MultipartIntegrationTests extends AbstractRouterFunctionIntegration
 
 		StepVerifier
 				.create(result)
-				.consumeNextWith(response -> {
-					assertEquals(HttpStatus.OK, response.statusCode());
-				})
+				.consumeNextWith(response -> assertEquals(HttpStatus.OK, response.statusCode()))
 				.verifyComplete();
 	}
 
@@ -90,8 +89,8 @@ public class MultipartIntegrationTests extends AbstractRouterFunctionIntegration
 						Map<String, Part> parts = map.toSingleValueMap();
 						try {
 							assertEquals(2, parts.size());
-							assertEquals("foo.txt", parts.get("fooPart").getFilename().get());
-							assertEquals("bar", parts.get("barPart").getContentAsString().block());
+							assertEquals("foo.txt", ((FilePart) parts.get("fooPart")).getFilename());
+							assertEquals("bar", ((FormFieldPart) parts.get("barPart")).getValue());
 						}
 						catch(Exception e) {
 							return Mono.error(e);

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java

@@ -33,11 +33,13 @@ import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.codec.multipart.FilePart;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.http.server.reactive.AbstractHttpHandlerIntegrationTests;
 import org.springframework.http.server.reactive.HttpHandler;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.bind.annotation.ModelAttribute;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestPart;
@@ -117,6 +119,21 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 				.verifyComplete();
 	}
 
+	@Test
+	public void modelAttribute() {
+		Mono<String> result = webClient
+				.post()
+				.uri("/modelAttribute")
+				.contentType(MediaType.MULTIPART_FORM_DATA)
+				.body(BodyInserters.fromMultipartData(generateBody()))
+				.retrieve()
+				.bodyToMono(String.class);
+
+		StepVerifier.create(result)
+				.consumeNextWith(body -> assertEquals("TestBean[barPart=bar,fooPart=foo.txt]", body))
+				.verifyComplete();
+	}
+
 
 	private MultiValueMap<String, Object> generateBody() {
 		HttpHeaders fooHeaders = new HttpHeaders();
@@ -135,23 +152,58 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 	static class MultipartController {
 
 		@PostMapping("/requestPart")
-		void part(@RequestPart Part fooPart) {
-			assertEquals("foo.txt", fooPart.getFilename().get());
+		void requestPart(@RequestPart Part fooPart) {
+			assertEquals("foo.txt", ((FilePart) fooPart).getFilename());
 		}
 
 		@PostMapping("/requestBodyMap")
-		Mono<String> part(@RequestBody Mono<MultiValueMap<String, Part>> parts) {
+		Mono<String> requestBodyMap(@RequestBody Mono<MultiValueMap<String, Part>> parts) {
 			return parts.map(map -> map.toSingleValueMap().entrySet().stream()
 					.map(Map.Entry::getKey).sorted().collect(Collectors.joining(",", "Map[", "]")));
 		}
 
 		@PostMapping("/requestBodyFlux")
-		Mono<String> part(@RequestBody Flux<Part> parts) {
+		Mono<String> requestBodyFlux(@RequestBody Flux<Part> parts) {
 			return parts.map(Part::getName).collectList()
 					.map(names -> names.stream().sorted().collect(Collectors.joining(",", "Flux[", "]")));
 		}
+
+		@PostMapping("/modelAttribute")
+		String modelAttribute(@ModelAttribute TestBean testBean) {
+			return testBean.toString();
+		}
+	}
+
+	static class TestBean {
+
+		private String barPart;
+
+		private FilePart fooPart;
+
+
+		public String getBarPart() {
+			return this.barPart;
+		}
+
+		public void setBarPart(String barPart) {
+			this.barPart = barPart;
+		}
+
+		public FilePart getFooPart() {
+			return this.fooPart;
+		}
+
+		public void setFooPart(FilePart fooPart) {
+			this.fooPart = fooPart;
+		}
+
+		@Override
+		public String toString() {
+			return "TestBean[barPart=" + getBarPart() + ",fooPart=" + getFooPart().getFilename() + "]";
+		}
 	}
 
+
 	@Configuration
 	@EnableWebFlux
 	@SuppressWarnings("unused")