Add ConversionService support for ByteBuffers

Add ByteBufferConverter that is registered by default with the
DefaultConversionService. Allows conversion from/to a ByteBuffer and
byte[] or to any type that can be converted via a byte[].

Issue: SPR-10712

spring-core/src/main/java/org/springframework/core/convert/support/ByteBufferConverter.java

@@ -0,0 +1,114 @@
+/*
+ * Copyright 2002-2013 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.convert.support;
+
+import java.nio.ByteBuffer;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.ConditionalGenericConverter;
+
+/**
+ * Converts a {@link ByteBuffer} directly to and from {@code byte[]}s and indirectly to
+ * any type that the {@link ConversionService} support via {@code byte[]}.
+ *
+ * @author Phillip Webb
+ */
+public class ByteBufferConverter implements ConditionalGenericConverter {
+
+	private static final TypeDescriptor BYTE_BUFFER_TYPE = TypeDescriptor.valueOf(ByteBuffer.class);
+
+	private static final TypeDescriptor BYTE_ARRAY_TYPE = TypeDescriptor.valueOf(byte[].class);
+
+	private static final Set<ConvertiblePair> CONVERTIBLE_PAIRS;
+	static {
+		Set<ConvertiblePair> convertiblePairs = new HashSet<ConvertiblePair>();
+		convertiblePairs.add(new ConvertiblePair(ByteBuffer.class, Object.class));
+		convertiblePairs.add(new ConvertiblePair(Object.class, ByteBuffer.class));
+		CONVERTIBLE_PAIRS = Collections.unmodifiableSet(convertiblePairs);
+	}
+
+
+	private ConversionService conversionService;
+
+
+	public ByteBufferConverter(ConversionService conversionService) {
+		this.conversionService = conversionService;
+	}
+
+
+	@Override
+	public Set<ConvertiblePair> getConvertibleTypes() {
+		return CONVERTIBLE_PAIRS;
+	}
+
+	@Override
+	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+		if (sourceType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+			return matchesFromByteBuffer(targetType);
+		}
+		if (targetType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+			return matchesToByteBuffer(sourceType);
+		}
+		return false;
+	}
+
+	private boolean matchesFromByteBuffer(TypeDescriptor targetType) {
+		return (targetType.isAssignableTo(BYTE_ARRAY_TYPE) || this.conversionService.canConvert(
+				BYTE_ARRAY_TYPE, targetType));
+	}
+
+	private boolean matchesToByteBuffer(TypeDescriptor sourceType) {
+		return (sourceType.isAssignableTo(BYTE_ARRAY_TYPE) || this.conversionService.canConvert(
+				sourceType, BYTE_ARRAY_TYPE));
+	}
+
+	@Override
+	public Object convert(Object source, TypeDescriptor sourceType,
+			TypeDescriptor targetType) {
+		if (sourceType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+			return convertFromByteBuffer((ByteBuffer) source, targetType);
+		}
+		if (targetType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+			return convertToByteBuffer(source, sourceType);
+		}
+		// Should not happen
+		throw new IllegalStateException("Unexpected source/target types");
+	}
+
+	private Object convertFromByteBuffer(ByteBuffer source, TypeDescriptor targetType) {
+		byte[] bytes = new byte[source.remaining()];
+		source.get(bytes);
+		if (targetType.isAssignableTo(BYTE_ARRAY_TYPE)) {
+			return bytes;
+		}
+		return this.conversionService.convert(bytes, BYTE_ARRAY_TYPE, targetType);
+	}
+
+	private Object convertToByteBuffer(Object source, TypeDescriptor sourceType) {
+		byte[] bytes = (byte[]) (source instanceof byte[] ? source
+				: this.conversionService.convert(source, sourceType, BYTE_ARRAY_TYPE));
+		ByteBuffer byteBuffer = ByteBuffer.allocate(bytes.length);
+		byteBuffer.put(bytes);
+		byteBuffer.rewind();
+		return byteBuffer;
+	}
+
+}

spring-core/src/main/java/org/springframework/core/convert/support/DefaultConversionService.java

@@ -53,6 +53,7 @@ public class DefaultConversionService extends GenericConversionService {
 	public static void addDefaultConverters(ConverterRegistry converterRegistry) {
 		addScalarConverters(converterRegistry);
 		addCollectionConverters(converterRegistry);
+		addBinaryConverters(converterRegistry);
 		addFallbackConverters(converterRegistry);
 	}
 
@@ -109,6 +110,11 @@ public class DefaultConversionService extends GenericConversionService {
 		converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));
 	}
 
+	private static void addBinaryConverters(ConverterRegistry converterRegistry) {
+		ConversionService conversionService = (ConversionService) converterRegistry;
+		converterRegistry.addConverter(new ByteBufferConverter(conversionService));
+	}
+
 	private static void addFallbackConverters(ConverterRegistry converterRegistry) {
 		ConversionService conversionService = (ConversionService) converterRegistry;
 		converterRegistry.addConverter(new ObjectToObjectConverter());