Jaxb2Marshaller has non-synchronized access to the JAXBContext once initialized

Also backporting "checkForXmlRootElement" property from 3.2 M2

Issue: SPR-9867
Issue: SPR-9757

org.springframework.oxm/src/main/java/org/springframework/oxm/jaxb/Jaxb2Marshaller.java

@@ -101,11 +101,12 @@ import org.springframework.util.xml.StaxUtils;
 /**
  * Implementation of the <code>Marshaller</code> interface for JAXB 2.0.
  *
- * <p>The typical usage will be to set either the <code>contextPath</code> or the <code>classesToBeBound</code> property
+ * <p>The typical usage will be to set either the "contextPath" or the "classesToBeBound"
- * on this bean, possibly customize the marshaller and unmarshaller by setting properties, schemas, adapters, and
+ * property on this bean, possibly customize the marshaller and unmarshaller by setting
- * listeners, and to refer to it.
+ * properties, schemas, adapters, and listeners, and to refer to it.
  *
  * @author Arjen Poutsma
+ * @author Juergen Hoeller
  * @since 3.0
  * @see #setContextPath(String)
  * @see #setClassesToBeBound(Class[])
@@ -125,9 +126,7 @@ public class Jaxb2Marshaller
 	private static final String CID = "cid:";
 
 
-	/**
+	/** Logger available to subclasses */
-	 * Logger available to subclasses.
-	 */
 	protected final Log logger = LogFactory.getLog(getClass());
 
 	private String contextPath;
@@ -154,21 +153,25 @@ public class Jaxb2Marshaller
 
 	private String schemaLanguage = XMLConstants.W3C_XML_SCHEMA_NS_URI;
 
+	private LSResourceResolver schemaResourceResolver;
+
 	private boolean mtomEnabled = false;
 
-	private ClassLoader beanClassLoader;
-
-	private ResourceLoader resourceLoader;
-
-	private JAXBContext jaxbContext;
-
-	private Schema schema;
-
 	private boolean lazyInit = false;
 
 	private boolean supportJaxbElementClass = false;
 
-	private LSResourceResolver schemaResourceResolver;
+	private boolean checkForXmlRootElement = true;
+
+	private ClassLoader beanClassLoader;
+
+	private ResourceLoader resourceLoader;
+
+	private final Object jaxbContextMonitor = new Object();
+
+	private volatile JAXBContext jaxbContext;
+
+	private Schema schema;
 
 
 	/**
@@ -358,6 +361,21 @@ public class Jaxb2Marshaller
 		this.supportJaxbElementClass = supportJaxbElementClass;
 	}
 
+	/**
+	 * Specify whether the {@link #supports(Class)} should check for
+	 * {@link XmlRootElement @XmlRootElement} annotations.
+	 * <p>Default is {@code true}, meaning that {@code supports(Class)} will check for
+	 * this annotation. However, some JAXB implementations (i.e. EclipseLink MOXy) allow
+	 * for defining the bindings in an external definition file, thus keeping the classes
+	 * annotations free. Setting this property to {@code false} supports these
+	 * JAXB implementations.
+	 * @see #supports(Class)
+	 * @see #supports(Type)
+	 */
+	public void setCheckForXmlRootElement(boolean checkForXmlRootElement) {
+		this.checkForXmlRootElement = checkForXmlRootElement;
+	}
+
 	public void setBeanClassLoader(ClassLoader classLoader) {
 		this.beanClassLoader = classLoader;
 	}
@@ -388,24 +406,29 @@ public class Jaxb2Marshaller
 		}
 	}
 
-	protected synchronized JAXBContext getJaxbContext() {
+	protected JAXBContext getJaxbContext() {
-		if (this.jaxbContext == null) {
+		if (this.jaxbContext != null) {
-			try {
+			return this.jaxbContext;
-				if (StringUtils.hasLength(this.contextPath)) {
+		}
-					this.jaxbContext = createJaxbContextFromContextPath();
+		synchronized (this.jaxbContextMonitor) {
-				}
+			if (this.jaxbContext == null) {
-				else if (!ObjectUtils.isEmpty(this.classesToBeBound)) {
+				try {
-					this.jaxbContext = createJaxbContextFromClasses();
+					if (StringUtils.hasLength(this.contextPath)) {
-				}
+						this.jaxbContext = createJaxbContextFromContextPath();
-				else if (!ObjectUtils.isEmpty(this.packagesToScan)) {
+					}
-					this.jaxbContext = createJaxbContextFromPackages();
+					else if (!ObjectUtils.isEmpty(this.classesToBeBound)) {
-				}
+						this.jaxbContext = createJaxbContextFromClasses();
-			}
+					}
-			catch (JAXBException ex) {
+					else if (!ObjectUtils.isEmpty(this.packagesToScan)) {
-				throw convertJaxbException(ex);
+						this.jaxbContext = createJaxbContextFromPackages();
-			}
+					}
+				}
+				catch (JAXBException ex) {
+					throw convertJaxbException(ex);
+				}
+			}
+			return this.jaxbContext;
 		}
-		return this.jaxbContext;
 	}
 
 	private JAXBContext createJaxbContextFromContextPath() throws JAXBException {
@@ -417,7 +440,9 @@ public class Jaxb2Marshaller
 				return JAXBContext.newInstance(this.contextPath, this.beanClassLoader, this.jaxbContextProperties);
 			}
 			else {
-				return JAXBContext.newInstance(this.contextPath, ClassUtils.getDefaultClassLoader(), this.jaxbContextProperties);
+				// analogous to the JAXBContext.newInstance(String) implementation
+				return JAXBContext.newInstance(this.contextPath, Thread.currentThread().getContextClassLoader(),
+						this.jaxbContextProperties);
 			}
 		}
 		else {
@@ -492,7 +517,7 @@ public class Jaxb2Marshaller
 		if (this.supportJaxbElementClass && JAXBElement.class.isAssignableFrom(clazz)) {
 			return true;
 		}
-		return supportsInternal(clazz, true);
+		return supportsInternal(clazz, this.checkForXmlRootElement);
 	}
 
 	public boolean supports(Type genericType) {
@@ -521,7 +546,7 @@ public class Jaxb2Marshaller
 		}
 		else if (genericType instanceof Class) {
 			Class<?> clazz = (Class<?>) genericType;
-			return supportsInternal(clazz, true);
+			return supportsInternal(clazz, this.checkForXmlRootElement);
 		}
 		return false;
 	}