Polishing external contribution

Change position and limit on duplicate, rather than source.

See gh-30967
Closes gh-32009

spring-core/src/main/java/org/springframework/core/io/buffer/DefaultDataBuffer.java

@@ -37,7 +37,6 @@ import org.springframework.util.ObjectUtils;
  * @author Arjen Poutsma
  * @author Juergen Hoeller
  * @author Brian Clozel
- * @author Injae Kim
  * @since 5.0
  * @see DefaultDataBufferFactory
  */
@@ -81,14 +80,16 @@ public class DefaultDataBuffer implements DataBuffer {
 
 	/**
 	 * Directly exposes the native {@code ByteBuffer} that this buffer is based
-	 * on also updating the {@code ByteBuffer's} position and limit to match
-	 * the current {@link #readPosition()} and {@link #writePosition()}.
+	 * on. The {@linkplain ByteBuffer#position() position} of the returned
+	 * {@code ByteBuffer} is set to the {@linkplain #readPosition() read
+	 * position}, and the {@linkplain ByteBuffer#limit()} to the
+	 * {@linkplain #writePosition() write position}.
 	 * @return the wrapped byte buffer
 	 */
 	public ByteBuffer getNativeBuffer() {
-		this.byteBuffer.position(this.readPosition);
-		this.byteBuffer.limit(this.writePosition);
-		return this.byteBuffer;
+		return this.byteBuffer.duplicate()
+				.position(this.readPosition)
+				.limit(this.writePosition);
 	}
 
 	private void setNativeBuffer(ByteBuffer byteBuffer) {

spring-core/src/test/java/org/springframework/core/io/buffer/DefaultDataBufferTests.java

@@ -36,20 +36,23 @@ class DefaultDataBufferTests {
 
 	@Test // gh-30967
 	void getNativeBuffer() {
-		DefaultDataBuffer buffer = bufferFactory.allocateBuffer(256);
-		buffer.write("0123456789", StandardCharsets.UTF_8);
+		DefaultDataBuffer dataBuffer = this.bufferFactory.allocateBuffer(256);
+		dataBuffer.write("0123456789", StandardCharsets.UTF_8);
 
 		byte[] result = new byte[7];
-		buffer.read(result);
+		dataBuffer.read(result);
 		assertThat(result).isEqualTo("0123456".getBytes(StandardCharsets.UTF_8));
 
-		ByteBuffer nativeBuffer = buffer.getNativeBuffer();
+		ByteBuffer nativeBuffer = dataBuffer.getNativeBuffer();
 		assertThat(nativeBuffer.position()).isEqualTo(7);
-		assertThat(buffer.readPosition()).isEqualTo(7);
+		assertThat(dataBuffer.readPosition()).isEqualTo(7);
 		assertThat(nativeBuffer.limit()).isEqualTo(10);
-		assertThat(buffer.writePosition()).isEqualTo(10);
+		assertThat(dataBuffer.writePosition()).isEqualTo(10);
+		assertThat(nativeBuffer.capacity()).isEqualTo(256);
+		assertThat(dataBuffer.capacity()).isEqualTo(256);
 
-		release(buffer);
+
+		release(dataBuffer);
 	}
 
 }