Added DataBuffer Encoder/Decoder

This commit adds a DataBuffer Encoder and Decoder, and uses it in
the annotation-based processing model.

Note that these codecs are not used in the functional processing model,
since the BodyInserter/BodyExtractor already have methods for
writing/reading DataBuffers.

Issue: SPR-15148

spring-core/src/main/java/org/springframework/core/codec/DataBufferDecoder.java

@@ -0,0 +1,57 @@
+/*
+ * 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.core.codec;
+
+import java.util.Map;
+
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Flux;
+
+import org.springframework.core.ResolvableType;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.util.MimeType;
+import org.springframework.util.MimeTypeUtils;
+
+/**
+ * Simple pass-through decoder for {@link DataBuffer}s.
+ * <p><strong>Note</strong> that the "decoded" buffers returned by instances of this class should
+ * be released after usage by calling
+ * {@link org.springframework.core.io.buffer.DataBufferUtils#release(DataBuffer)}.
+ *
+ * @author Arjen Poutsma
+ * @since 5.0
+ */
+public class DataBufferDecoder extends AbstractDecoder<DataBuffer> {
+
+	public DataBufferDecoder() {
+		super(MimeTypeUtils.ALL);
+	}
+
+
+	@Override
+	public boolean canDecode(ResolvableType elementType, MimeType mimeType) {
+		Class<?> clazz = elementType.getRawClass();
+		return (super.canDecode(elementType, mimeType) && DataBuffer.class.isAssignableFrom(clazz));
+	}
+
+	@Override
+	public Flux<DataBuffer> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
+			MimeType mimeType, Map<String, Object> hints) {
+		return Flux.from(inputStream);
+	}
+
+}

spring-core/src/main/java/org/springframework/core/codec/DataBufferEncoder.java

@@ -0,0 +1,57 @@
+/*
+ * 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.core.codec;
+
+import java.util.Map;
+
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Flux;
+
+import org.springframework.core.ResolvableType;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferFactory;
+import org.springframework.util.MimeType;
+import org.springframework.util.MimeTypeUtils;
+
+/**
+ * Simple pass-through encoder for {@link DataBuffer}s.
+ *
+ * @author Arjen Poutsma
+ * @since 5.0
+ */
+public class DataBufferEncoder extends AbstractEncoder<DataBuffer> {
+
+	public DataBufferEncoder() {
+		super(MimeTypeUtils.ALL);
+	}
+
+
+	@Override
+	public boolean canEncode(ResolvableType elementType, MimeType mimeType) {
+		Class<?> clazz = elementType.getRawClass();
+		return (super.canEncode(elementType, mimeType) && DataBuffer.class.isAssignableFrom(clazz));
+	}
+
+	@Override
+	public Flux<DataBuffer> encode(Publisher<? extends DataBuffer> inputStream,
+			DataBufferFactory bufferFactory, ResolvableType elementType, MimeType mimeType,
+			Map<String, Object> hints) {
+
+		return Flux.from(inputStream);
+	}
+
+}