Make EmbeddedVelocityToolboxView work in servlet container deployments

EmbeddedVelocityToolboxView is used with both embedded containers and
when a Spring Boot application is deployed to a servlet container. It
process the ServletContext to intercept calls to getResource so that it
can load Velocity’s toolbox.xml file from within an executable jar.
Previously, when it created the proxy, it didn’t specify the ClassLoader
to use. This resulted in the proxy being created using the ClassLoader
that loaded the Class that is being proxied. This fails when the
application is deployed to a ServletContainer as the ClassLoader that
loaded the ServletContext implementation is the container’s ClassLoader
and it cannot see the classes that are specific to the web application.

This commit updates EmbeddedVelocityToolboxView to specify the
ClassLoader to use when creating the proxy. It specifies its own
ClassLoader thereby ensuring that the proxy creation can load
application-specific classes.

Fixes gh-4967

Author: wilkinsona

spring-boot/src/main/java/org/springframework/boot/web/servlet/view/velocity/EmbeddedVelocityToolboxView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -34,10 +34,11 @@
 
 /**
  * Extended version of {@link VelocityToolboxView} that can load toolbox locations from
- * the classpath as well as the servlet context. This is useful when run an embedded web
- * server.
+ * the classpath as well as the servlet context. This is useful when running in an
+ * embedded web server.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @since 1.2.5
  */
 @SuppressWarnings("deprecation")
@@ -69,7 +70,7 @@ private ServletContext getToolboxConfigFileAwareServletContext() {
 		ProxyFactory factory = new ProxyFactory();
 		factory.setTarget(getServletContext());
 		factory.addAdvice(new GetResourceMethodInterceptor(getToolboxConfigLocation()));
-		return (ServletContext) factory.getProxy();
+		return (ServletContext) factory.getProxy(getClass().getClassLoader());
 	}
 
 	/**