ByteBufferConverter explicitly declares applicability to byte[]

Includes an optimization for simple ByteBuffer duplication.

Issue: SPR-13056

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

@@ -31,6 +31,7 @@ import org.springframework.core.convert.converter.ConditionalGenericConverter;
  * to any type that the {@link ConversionService} support via {@code byte[]}.
  *
  * @author Phillip Webb
+ * @author Juergen Hoeller
  * @since 4.0
  */
 final class ByteBufferConverter implements ConditionalGenericConverter {
@@ -40,8 +41,11 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 	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>();
+		Set<ConvertiblePair> convertiblePairs = new HashSet<ConvertiblePair>(4);
+		convertiblePairs.add(new ConvertiblePair(ByteBuffer.class, byte[].class));
+		convertiblePairs.add(new ConvertiblePair(byte[].class, ByteBuffer.class));
 		convertiblePairs.add(new ConvertiblePair(ByteBuffer.class, Object.class));
 		convertiblePairs.add(new ConvertiblePair(Object.class, ByteBuffer.class));
 		CONVERTIBLE_PAIRS = Collections.unmodifiableSet(convertiblePairs);
@@ -63,13 +67,11 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 
 	@Override
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+		boolean byteBufferTarget = targetType.isAssignableTo(BYTE_BUFFER_TYPE);
 		if (sourceType.isAssignableTo(BYTE_BUFFER_TYPE)) {
-			return matchesFromByteBuffer(targetType);
+			return (byteBufferTarget || matchesFromByteBuffer(targetType));
-		}
-		if (targetType.isAssignableTo(BYTE_BUFFER_TYPE)) {
-			return matchesToByteBuffer(sourceType);
 		}
-		return false;
+		return (byteBufferTarget && matchesToByteBuffer(sourceType));
 	}
 
 	private boolean matchesFromByteBuffer(TypeDescriptor targetType) {
@@ -84,10 +86,12 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 
 	@Override
 	public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
-		if (sourceType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+		boolean byteBufferTarget = targetType.isAssignableTo(BYTE_BUFFER_TYPE);
-			return convertFromByteBuffer((ByteBuffer) source, targetType);
+		if (source instanceof ByteBuffer) {
+			ByteBuffer buffer = (ByteBuffer) source;
+			return (byteBufferTarget ? buffer.duplicate() : convertFromByteBuffer(buffer, targetType));
 		}
-		if (targetType.isAssignableTo(BYTE_BUFFER_TYPE)) {
+		if (byteBufferTarget) {
 			return convertToByteBuffer(source, sourceType);
 		}
 		// Should not happen

spring-core/src/test/java/org/springframework/core/convert/support/ByteBufferConverterTests.java

@@ -30,6 +30,7 @@ import static org.junit.Assert.*;
  * Tests for {@link ByteBufferConverter}.
  *
  * @author Phillip Webb
+ * @author Juergen Hoeller
  */
 public class ByteBufferConverterTests {
 
@@ -38,8 +39,7 @@ public class ByteBufferConverterTests {
 
 	@Before
 	public void setup() {
-		this.conversionService = new GenericConversionService();
+		this.conversionService = new DefaultConversionService();
-		this.conversionService.addConverter(new ByteBufferConverter(conversionService));
 		this.conversionService.addConverter(new ByteArrayToOtherTypeConverter());
 		this.conversionService.addConverter(new OtherTypeToByteArrayConverter());
 	}
@@ -87,6 +87,8 @@ public class ByteBufferConverterTests {
 		ByteBuffer convert = this.conversionService.convert(byteBuffer, ByteBuffer.class);
 		assertThat(convert, not(sameInstance(byteBuffer.rewind())));
 		assertThat(convert, equalTo(byteBuffer.rewind()));
+		assertThat(convert, equalTo(ByteBuffer.wrap(bytes)));
+		assertThat(convert.array(), equalTo(bytes));
 	}