Add DataBuffer::toString(Charset)

Closes gh-23317

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

@@ -355,4 +355,28 @@ public interface DataBuffer {
 	 */
 	OutputStream asOutputStream();
 
+	/**
+	 * Return this buffer's data a String using the specified charset. Default implementation
+	 * delegates to {@code toString(readPosition(), readableByteCount(), charset)}.
+	 *
+	 * @param charset the character set to use
+	 * @return a string representation of all this buffers data
+	 * @since 5.2
+	 */
+	default String toString(Charset charset) {
+		Assert.notNull(charset, "Charset must not be null");
+		return toString(readPosition(), readableByteCount(), charset);
+	}
+
+	/**
+	 * Return a part of this buffer's data as a String using the specified charset.
+	 *
+	 * @param index the index at which to start the string
+	 * @param length the number of bytes to use for the string
+	 * @param charset the charset to use
+	 * @return a string representation of a part of this buffers data
+	 * @since 5.2
+	 */
+	String toString(int index, int length, Charset charset);
+
 }

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

@@ -21,6 +21,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.Buffer;
 import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
 import java.util.Arrays;
 import java.util.function.IntPredicate;
 
@@ -381,6 +382,28 @@ public class DefaultDataBuffer implements DataBuffer {
 	}
 
 
+	@Override
+	public String toString(int index, int length, Charset charset) {
+		checkIndex(index, length);
+		Assert.notNull(charset, "Charset must not be null");
+
+		byte[] bytes;
+		int offset;
+
+		if (this.byteBuffer.hasArray()) {
+			bytes = this.byteBuffer.array();
+			offset = this.byteBuffer.arrayOffset() + index;
+		}
+		else {
+			bytes = new byte[length];
+			offset = 0;
+			ByteBuffer duplicate = this.byteBuffer.duplicate();
+			duplicate.clear().position(index).limit(index + length);
+			duplicate.get(bytes, 0, length);
+		}
+		return new String(bytes, offset, length, charset);
+	}
+
 	/**
 	 * Calculate the capacity of the buffer.
 	 * @see io.netty.buffer.AbstractByteBufAllocator#calculateNewCapacity(int, int)

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

@@ -293,6 +293,18 @@ public class NettyDataBuffer implements PooledDataBuffer {
 		return new ByteBufOutputStream(this.byteBuf);
 	}
 
+	@Override
+	public String toString(Charset charset) {
+		Assert.notNull(charset, "Charset must not be null");
+		return this.byteBuf.toString(charset);
+	}
+
+	@Override
+	public String toString(int index, int length, Charset charset) {
+		Assert.notNull(charset, "Charset must not be null");
+		return this.byteBuf.toString(index, length, charset);
+	}
+
 	@Override
 	public boolean isAllocated() {
 		return this.byteBuf.refCnt() > 0;

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

@@ -235,6 +235,44 @@ public class DataBufferTests extends AbstractDataBufferAllocatingTestCase {
 		release(buffer);
 	}
 
+	@Test
+	public void toStringNullCharset() {
+		DataBuffer buffer = createDataBuffer(1);
+		try {
+			assertThatIllegalArgumentException().isThrownBy(() ->
+					buffer.toString(null));
+		}
+		finally {
+			release(buffer);
+		}
+	}
+
+	@Test
+	public void toStringUtf8() {
+		String spring = "Spring";
+		byte[] bytes = spring.getBytes(StandardCharsets.UTF_8);
+		DataBuffer buffer = createDataBuffer(bytes.length);
+		buffer.write(bytes);
+
+		String result = buffer.toString(StandardCharsets.UTF_8);
+
+		assertThat(result).isEqualTo(spring);
+		release(buffer);
+	}
+
+	@Test
+	public void toStringSection() {
+		String spring = "Spring";
+		byte[] bytes = spring.getBytes(StandardCharsets.UTF_8);
+		DataBuffer buffer = createDataBuffer(bytes.length);
+		buffer.write(bytes);
+
+		String result = buffer.toString(1, 3, StandardCharsets.UTF_8);
+
+		assertThat(result).isEqualTo("pri");
+		release(buffer);
+	}
+
 	@Test
 	public void inputStream() throws IOException {
 		DataBuffer buffer = createDataBuffer(4);