Support for decoding @RequestPart content

Issue: SPR-15515

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

@@ -17,6 +17,7 @@
 package org.springframework.http.codec;
 
 import org.springframework.core.codec.Decoder;
+import org.springframework.core.codec.Encoder;
 
 /**
  * Helps to configure a list of client-side HTTP message readers and writers
@@ -55,6 +56,13 @@ public interface ClientCodecConfigurer extends CodecConfigurer {
 	 */
 	interface ClientDefaultCodecsConfigurer extends DefaultCodecsConfigurer {
 
+		/**
+		 * Configure encoders or writers for use with
+		 * {@link org.springframework.http.codec.multipart.MultipartHttpMessageWriter
+		 * MultipartHttpMessageWriter}.
+		 */
+		MultipartCodecsConfigurer multipartCodecs();
+
 		/**
 		 * Configure the {@code Decoder} to use for Server-Sent Events.
 		 * <p>By default the {@link #jackson2Decoder} override is used for SSE.
@@ -63,5 +71,25 @@ public interface ClientCodecConfigurer extends CodecConfigurer {
 		void serverSentEventDecoder(Decoder<?> decoder);
 	}
 
+	/**
+	 * Registry and container for multipart HTTP message writers.
+	 */
+	interface MultipartCodecsConfigurer {
+
+		/**
+		 * Add a Part {@code Encoder}, internally wrapped with
+		 * {@link EncoderHttpMessageWriter}.
+		 * @param encoder the encoder to add
+		 */
+		MultipartCodecsConfigurer encoder(Encoder<?> encoder);
+
+		/**
+		 * Add a Part {@link HttpMessageWriter}. For writers of type
+		 * {@link EncoderHttpMessageWriter} consider using the shortcut
+		 * {@link #encoder(Encoder)} instead.
+		 * @param writer the writer to add
+		 */
+		MultipartCodecsConfigurer writer(HttpMessageWriter<?> writer);
+	}
 
 }

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

@@ -108,7 +108,7 @@ public interface CodecConfigurer {
 		void reader(HttpMessageReader<?> reader);
 
 		/**
-		 * Add a custom {@link HttpMessageWriter}. For readers of type
+		 * Add a custom {@link HttpMessageWriter}. For writers of type
 		 * {@link EncoderHttpMessageWriter} consider using the shortcut
 		 * {@link #encoder(Encoder)} instead.
 		 * @param writer the writer to add

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

@@ -16,9 +16,11 @@
 
 package org.springframework.http.codec;
 
+import java.util.ArrayList;
 import java.util.List;
 
 import org.springframework.core.codec.Decoder;
+import org.springframework.core.codec.Encoder;
 import org.springframework.core.codec.StringDecoder;
 import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.http.codec.multipart.MultipartHttpMessageWriter;
@@ -48,6 +50,17 @@ class DefaultClientCodecConfigurer extends DefaultCodecConfigurer implements Cli
 			extends AbstractDefaultCodecsConfigurer
 			implements ClientCodecConfigurer.ClientDefaultCodecsConfigurer {
 
+		private DefaultMultipartCodecsConfigurer multipartCodecs;
+
+
+		@Override
+		public MultipartCodecsConfigurer multipartCodecs() {
+			if (this.multipartCodecs == null) {
+				this.multipartCodecs = new DefaultMultipartCodecsConfigurer();
+			}
+			return this.multipartCodecs;
+		}
+
 		@Override
 		public void serverSentEventDecoder(Decoder<?> decoder) {
 			HttpMessageReader<?> reader = new ServerSentEventHttpMessageReader(decoder);
@@ -58,7 +71,10 @@ class DefaultClientCodecConfigurer extends DefaultCodecConfigurer implements Cli
 		protected void addTypedWritersTo(List<HttpMessageWriter<?>> result) {
 			super.addTypedWritersTo(result);
 			addWriterTo(result, FormHttpMessageWriter::new);
-			addWriterTo(result, MultipartHttpMessageWriter::new);
+			addWriterTo(result, () -> findWriter(MultipartHttpMessageWriter.class,
+					() -> this.multipartCodecs != null ?
+							new MultipartHttpMessageWriter(this.multipartCodecs.getWriters()) :
+							new MultipartHttpMessageWriter()));
 		}
 
 		@Override
@@ -89,7 +105,28 @@ class DefaultClientCodecConfigurer extends DefaultCodecConfigurer implements Cli
 			addReaderTo(result,
 					() -> new DecoderHttpMessageReader<>(StringDecoder.allMimeTypes(false)));
 		}
+	}
 
+	private static class DefaultMultipartCodecsConfigurer implements MultipartCodecsConfigurer {
+
+		private final List<HttpMessageWriter<?>> writers = new ArrayList<>();
+
+
+		@Override
+		public MultipartCodecsConfigurer encoder(Encoder<?> encoder) {
+			writer(new EncoderHttpMessageWriter<>(encoder));
+			return this;
+		}
+
+		@Override
+		public MultipartCodecsConfigurer writer(HttpMessageWriter<?> writer) {
+			this.writers.add(writer);
+			return this;
+		}
+
+		public List<HttpMessageWriter<?>> getWriters() {
+			return this.writers;
+		}
 	}
 
 }