Test for ByteBuffer-to-ByteBuffer conversion (fresh copy)

ByteBufferConverter also defensively returns the rewind result now.

Issue: SPR-13031

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

@@ -97,6 +97,7 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 	private Object convertFromByteBuffer(ByteBuffer source, TypeDescriptor targetType) {
 		byte[] bytes = new byte[source.remaining()];
 		source.get(bytes);
+
 		if (targetType.isAssignableTo(BYTE_ARRAY_TYPE)) {
 			return bytes;
 		}
@@ -113,9 +114,7 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 		// Extra cast necessary for compiling on JDK 9 plus running on JDK 8, since
 		// otherwise the overridden ByteBuffer-returning rewind method would be chosen
 		// which isn't available on JDK 8.
-		((Buffer) byteBuffer).rewind();
-
-		return byteBuffer;
+		return ((Buffer) byteBuffer).rewind();
 	}
 
 }

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

@@ -49,8 +49,8 @@ public class ByteBufferConverterTests {
 	public void byteArrayToByteBuffer() throws Exception {
 		byte[] bytes = new byte[] { 1, 2, 3 };
 		ByteBuffer convert = this.conversionService.convert(bytes, ByteBuffer.class);
-		assertThat(bytes, not(sameInstance(convert.array())));
-		assertThat(bytes, equalTo(convert.array()));
+		assertThat(convert.array(), not(sameInstance(bytes)));
+		assertThat(convert.array(), equalTo(bytes));
 	}
 
 	@Test
@@ -58,8 +58,8 @@ public class ByteBufferConverterTests {
 		byte[] bytes = new byte[] { 1, 2, 3 };
 		ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
 		byte[] convert = this.conversionService.convert(byteBuffer, byte[].class);
-		assertThat(bytes, not(sameInstance(convert)));
-		assertThat(bytes, equalTo(convert));
+		assertThat(convert, not(sameInstance(bytes)));
+		assertThat(convert, equalTo(bytes));
 	}
 
 	@Test
@@ -67,8 +67,8 @@ public class ByteBufferConverterTests {
 		byte[] bytes = new byte[] { 1, 2, 3 };
 		ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
 		OtherType convert = this.conversionService.convert(byteBuffer, OtherType.class);
-		assertThat(bytes, not(sameInstance(convert.bytes)));
-		assertThat(bytes, equalTo(convert.bytes));
+		assertThat(convert.bytes, not(sameInstance(bytes)));
+		assertThat(convert.bytes, equalTo(bytes));
 	}
 
 	@Test
@@ -76,8 +76,17 @@ public class ByteBufferConverterTests {
 		byte[] bytes = new byte[] { 1, 2, 3 };
 		OtherType otherType = new OtherType(bytes);
 		ByteBuffer convert = this.conversionService.convert(otherType, ByteBuffer.class);
-		assertThat(bytes, not(sameInstance(convert.array())));
-		assertThat(bytes, equalTo(convert.array()));
+		assertThat(convert.array(), not(sameInstance(bytes)));
+		assertThat(convert.array(), equalTo(bytes));
+	}
+
+	@Test
+	public void byteBufferToByteBuffer() throws Exception {
+		byte[] bytes = new byte[] { 1, 2, 3 };
+		ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+		ByteBuffer convert = this.conversionService.convert(byteBuffer, ByteBuffer.class);
+		assertThat(convert, not(sameInstance(byteBuffer.rewind())));
+		assertThat(convert, equalTo(byteBuffer.rewind()));
 	}