Align classloader used to create the JAXBContext

This commit makes sure that JAXBContext.newInstance consistently use
the target class classloader to detect the necessary resources.

Previously, the current thread's context classloader was used, which
could lead to not finding the required JAXB components.

Closes gh-33158

Author: snicoll

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,7 +51,7 @@ public Unmarshaller createUnmarshaller(Class<?> clazz) throws CodecException, JA
 	private JAXBContext getJaxbContext(Class<?> clazz) throws CodecException {
 		return this.jaxbContexts.computeIfAbsent(clazz, key -> {
 			try {
-				return JAXBContext.newInstance(clazz);
+				return createJaxbContext(clazz);
 			}
 			catch (JAXBException ex) {
 				throw new CodecException(
@@ -60,4 +60,20 @@ private JAXBContext getJaxbContext(Class<?> clazz) throws CodecException {
 		});
 	}
 
+	/**
+	 * Create a {@link JAXBContext} for the given type, exposing the class
+	 * ClassLoader as current thread context ClassLoader for the time of
+	 * creating the context.
+	 */
+	private JAXBContext createJaxbContext(Class<?> clazz) throws JAXBException {
+		ClassLoader currentClassLoader = Thread.currentThread().getContextClassLoader();
+		try {
+			Thread.currentThread().setContextClassLoader(clazz.getClassLoader());
+			return JAXBContext.newInstance(clazz);
+		}
+		finally {
+			Thread.currentThread().setContextClassLoader(currentClassLoader);
+		}
+	}
+
 }