Fix memory leak for Jaxb2XmlEncoder

This commit fixes a memory leak in Jaxb2XmlEncoder that occurs when
the input stream contains an error. Test added as well.

Issue: SPR-17419

Author: poutsma

spring-web/src/main/java/org/springframework/http/codec/xml/Jaxb2XmlEncoder.java

@@ -34,6 +34,7 @@
 import org.springframework.core.codec.Hints;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
+import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.core.log.LogFormatUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
@@ -78,27 +79,38 @@ public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType
 	@Override
 	protected Flux<DataBuffer> encode(Object value, DataBufferFactory dataBufferFactory,
 			ResolvableType type, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
+
+		if (!Hints.isLoggingSuppressed(hints)) {
+			LogFormatUtils.traceDebug(logger, traceOn -> {
+				String formatted = LogFormatUtils.formatValue(value, !traceOn);
+				return Hints.getLogPrefix(hints) + "Encoding [" + formatted + "]";
+			});
+		}
+
+		boolean release = true;
+		DataBuffer buffer = dataBufferFactory.allocateBuffer(1024);
+		OutputStream outputStream = buffer.asOutputStream();
+		Class<?> clazz = ClassUtils.getUserClass(value);
+
 		try {
-			if (!Hints.isLoggingSuppressed(hints)) {
-				LogFormatUtils.traceDebug(logger, traceOn -> {
-					String formatted = LogFormatUtils.formatValue(value, !traceOn);
-					return Hints.getLogPrefix(hints) + "Encoding [" + formatted + "]";
-				});
-			}
-			DataBuffer buffer = dataBufferFactory.allocateBuffer(1024);
-			OutputStream outputStream = buffer.asOutputStream();
-			Class<?> clazz = ClassUtils.getUserClass(value);
 			Marshaller marshaller = this.jaxbContexts.createMarshaller(clazz);
 			marshaller.setProperty(Marshaller.JAXB_ENCODING, StandardCharsets.UTF_8.name());
 			marshaller.marshal(value, outputStream);
+			release = false;
 			return Flux.just(buffer);
 		}
 		catch (MarshalException ex) {
-			return Flux.error(new EncodingException("Could not marshal " + value.getClass() + " to XML", ex));
+			return Flux.error(new EncodingException(
+					"Could not marshal " + value.getClass() + " to XML", ex));
 		}
 		catch (JAXBException ex) {
 			return Flux.error(new CodecException("Invalid JAXB configuration", ex));
 		}
+		finally {
+			if (release) {
+				DataBufferUtils.release(buffer);
+			}
+		}
 	}
 
 }

spring-web/src/test/java/org/springframework/http/codec/xml/Jaxb2XmlEncoderTests.java

@@ -20,6 +20,9 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlElements;
+import javax.xml.bind.annotation.XmlRootElement;
 
 import org.junit.Test;
 import reactor.core.publisher.Flux;
@@ -34,15 +37,9 @@
 import org.springframework.http.MediaType;
 import org.springframework.http.codec.Pojo;
 
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertThat;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 import static org.xmlunit.matchers.CompareMatcher.isSimilarTo;
 
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlElements;
-import javax.xml.bind.annotation.XmlRootElement;
-
 /**
  * @author Sebastien Deleuze
  * @author Arjen Poutsma
@@ -94,6 +91,18 @@ public void encode() {
 				.verifyComplete();
 	}
 
+	@Test
+	public void encodeError() {
+		Flux<Pojo> source = Flux.error(RuntimeException::new);
+		Flux<DataBuffer> output = this.encoder.encode(source, this.bufferFactory,
+				ResolvableType.forClass(Pojo.class),
+				MediaType.APPLICATION_XML, Collections.emptyMap());
+
+		StepVerifier.create(output)
+				.expectError(RuntimeException.class)
+				.verify();
+	}
+
 	@Test
 	public void encodeElementsWithCommonType() {
 		Mono<Container> source = Mono.just(new Container());