MarshallingView unwraps JAXBElement value for Marshaller.supports(Class) check

Issue: SPR-11827

spring-webmvc/src/main/java/org/springframework/web/servlet/view/xml/MarshallingView.java

@@ -20,6 +20,7 @@ import java.io.ByteArrayOutputStream;
 import java.util.Map;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
+import javax.xml.bind.JAXBElement;
 import javax.xml.transform.stream.StreamResult;
 
 import org.springframework.oxm.Marshaller;
@@ -55,7 +56,7 @@ public class MarshallingView extends AbstractView {
 
 
 	/**
-	 * Constructs a new {@code MarshallingView} with no {@link Marshaller} set.
+	 * Construct a new {@code MarshallingView} with no {@link Marshaller} set.
 	 * The marshaller must be set after construction by invoking {@link #setMarshaller}.
 	 */
 	public MarshallingView() {
@@ -74,7 +75,7 @@ public class MarshallingView extends AbstractView {
 
 
 	/**
-	 * Sets the {@link Marshaller} to be used by this view.
+	 * Set the {@link Marshaller} to be used by this view.
 	 */
 	public void setMarshaller(Marshaller marshaller) {
 		this.marshaller = marshaller;
@@ -124,23 +125,42 @@ public class MarshallingView extends AbstractView {
 	 */
 	protected Object locateToBeMarshalled(Map<String, Object> model) throws IllegalStateException {
 		if (this.modelKey != null) {
-			Object obj = model.get(this.modelKey);
-			if (obj == null) {
+			Object value = model.get(this.modelKey);
+			if (value == null) {
 				throw new IllegalStateException("Model contains no object with key [" + this.modelKey + "]");
 			}
-			if (!this.marshaller.supports(obj.getClass())) {
-				throw new IllegalStateException("Model object [" + obj + "] retrieved via key [" +
+			if (!isEligibleForMarshalling(this.modelKey, value)) {
+				throw new IllegalStateException("Model object [" + value + "] retrieved via key [" +
 						this.modelKey + "] is not supported by the Marshaller");
 			}
-			return obj;
+			return value;
 		}
-		for (Object obj : model.values()) {
-			if (obj != null && (model.size() == 1 || !(obj instanceof BindingResult)) &&
-					this.marshaller.supports(obj.getClass())) {
-				return obj;
+		for (Map.Entry<String, Object> entry : model.entrySet()) {
+			Object value = entry.getValue();
+			if (value != null && (model.size() == 1 || !(value instanceof BindingResult)) &&
+					isEligibleForMarshalling(entry.getKey(), value)) {
+				return value;
 			}
 		}
 		return null;
 	}
 
+	/**
+	 * Check whether the given value from the current view's model is eligible
+	 * for marshalling through the configured {@link Marshaller}.
+	 * <p>The default implementation calls {@link Marshaller#supports(Class)},
+	 * unwrapping a given {@link JAXBElement} first if applicable.
+	 * @param modelKey the value's key in the model (never {@code null})
+	 * @param value the value to check (never {@code null})
+	 * @return whether the given value is to be considered as eligible
+	 * @see Marshaller#supports(Class)
+	 */
+	protected boolean isEligibleForMarshalling(String modelKey, Object value) {
+		Class<?> classToCheck = value.getClass();
+		if (value instanceof JAXBElement) {
+			classToCheck = ((JAXBElement) value).getDeclaredType();
+		}
+		return this.marshaller.supports(classToCheck);
+	}
+
 }

spring-webmvc/src/test/java/org/springframework/web/servlet/view/xml/MarshallingViewTests.java

@@ -19,6 +19,8 @@ package org.springframework.web.servlet.view.xml;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import javax.xml.bind.JAXBElement;
+import javax.xml.namespace.QName;
 import javax.xml.transform.stream.StreamResult;
 
 import org.junit.Before;
@@ -35,6 +37,7 @@ import static org.mockito.BDDMockito.*;
 
 /**
  * @author Arjen Poutsma
+ * @author Juergen Hoeller
  */
 public class MarshallingViewTests {
 
@@ -84,6 +87,25 @@ public class MarshallingViewTests {
 		assertEquals("Invalid content length", 0, response.getContentLength());
 	}
 
+	@Test
+	public void renderModelKeyWithJaxbElement() throws Exception {
+		String toBeMarshalled = "value";
+		String modelKey = "key";
+		view.setModelKey(modelKey);
+		Map<String, Object> model = new HashMap<String, Object>();
+		model.put(modelKey, new JAXBElement<String>(new QName("model"), String.class, toBeMarshalled));
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+
+		given(marshallerMock.supports(String.class)).willReturn(true);
+		marshallerMock.marshal(eq(toBeMarshalled), isA(StreamResult.class));
+
+		view.render(model, request, response);
+		assertEquals("Invalid content type", "application/xml", response.getContentType());
+		assertEquals("Invalid content length", 0, response.getContentLength());
+	}
+
 	@Test
 	public void renderInvalidModelKey() throws Exception {
 		Object toBeMarshalled = new Object();