NettyDataBufferFactory.join returns single-element buffer as-is

Issue: SPR-17560

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

@@ -31,6 +31,7 @@ import org.springframework.util.Assert;
  * Netty {@link ByteBufAllocator}.
  *
  * @author Arjen Poutsma
+ * @author Juergen Hoeller
  * @since 5.0
  * @see io.netty.buffer.PooledByteBufAllocator
  * @see io.netty.buffer.UnpooledByteBufAllocator
@@ -47,7 +48,7 @@ public class NettyDataBufferFactory implements DataBufferFactory {
 	 * @see io.netty.buffer.UnpooledByteBufAllocator
 	 */
 	public NettyDataBufferFactory(ByteBufAllocator byteBufAllocator) {
-		Assert.notNull(byteBufAllocator, "'byteBufAllocator' must not be null");
+		Assert.notNull(byteBufAllocator, "ByteBufAllocator must not be null");
 		this.byteBufAllocator = byteBufAllocator;
 	}
 
@@ -97,8 +98,12 @@ public class NettyDataBufferFactory implements DataBufferFactory {
 	 */
 	@Override
 	public DataBuffer join(List<? extends DataBuffer> dataBuffers) {
-		Assert.notNull(dataBuffers, "'dataBuffers' must not be null");
-		CompositeByteBuf composite = this.byteBufAllocator.compositeBuffer(dataBuffers.size());
+		Assert.notEmpty(dataBuffers, "DataBuffer List must not be empty");
+		int bufferCount = dataBuffers.size();
+		if (bufferCount == 1) {
+			return dataBuffers.get(0);
+		}
+		CompositeByteBuf composite = this.byteBufAllocator.compositeBuffer(bufferCount);
 		for (DataBuffer dataBuffer : dataBuffers) {
 			Assert.isInstanceOf(NettyDataBuffer.class, dataBuffer);
 			composite.addComponent(true, ((NettyDataBuffer) dataBuffer).getNativeBuffer());
@@ -107,11 +112,11 @@ public class NettyDataBufferFactory implements DataBufferFactory {
 	}
 
 	/**
-	 * Return the given Netty {@link DataBuffer} as a {@link ByteBuf}. Returns the
-	 * {@linkplain NettyDataBuffer#getNativeBuffer() native buffer} if {@code buffer} is
-	 * a {@link NettyDataBuffer}; returns {@link Unpooled#wrappedBuffer(ByteBuffer)}
-	 * otherwise.
-	 * @param buffer the {@code DataBuffer} to return a {@code ByteBuf} for.
+	 * Return the given Netty {@link DataBuffer} as a {@link ByteBuf}.
+	 * <p>Returns the {@linkplain NettyDataBuffer#getNativeBuffer() native buffer}
+	 * if {@code buffer} is a {@link NettyDataBuffer}; returns
+	 * {@link Unpooled#wrappedBuffer(ByteBuffer)} otherwise.
+	 * @param buffer the {@code DataBuffer} to return a {@code ByteBuf} for
 	 * @return the netty {@code ByteBuf}
 	 */
 	public static ByteBuf toByteBuf(DataBuffer buffer) {

spring-test/src/test/java/org/springframework/test/web/reactive/server/samples/bind/HttpServerTests.java

@@ -26,8 +26,8 @@ import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.web.reactive.function.server.RouterFunctions;
 import org.springframework.web.reactive.function.server.ServerResponse;
 
-import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
-import static org.springframework.web.reactive.function.server.RouterFunctions.route;
+import static org.springframework.web.reactive.function.server.RequestPredicates.*;
+import static org.springframework.web.reactive.function.server.RouterFunctions.*;
 
 /**
  * Sample tests demonstrating live server integration tests.
@@ -43,11 +43,9 @@ public class HttpServerTests {
 
 
 	@Before
-	public void setUp() throws Exception {
-
+	public void start() throws Exception {
 		HttpHandler httpHandler = RouterFunctions.toHttpHandler(
-				route(GET("/test"), request ->
-						ServerResponse.ok().syncBody("It works!")));
+				route(GET("/test"), request -> ServerResponse.ok().syncBody("It works!")));
 
 		this.server = new ReactorHttpServer();
 		this.server.setHandler(httpHandler);
@@ -60,7 +58,7 @@ public class HttpServerTests {
 	}
 
 	@After
-	public void tearDown() {
+	public void stop() {
 		this.server.stop();
 	}