Make GroovyWebConfiguration conditional on spring-webmvc's availability

GroovyWebConfiguration creates a GroovyTemplateViewResolver which is
a UrlBasedViewResolver sub-class. UrlBasedViewResolver is provided
by spring-webmvc. Previously, if a user configured a web application
but did not have spring-webmvc on the classpath, the application
would fail to start with a NoClassDefFoundError for
UrlBasedViewResolver.

This commit makes GroovyWebConfiguration conditional on
UrlBasedViewResolver being on the classpath so that it backs of in
the absence of spring-webmvc.

Fixes gh-1793

Author: wilkinsona

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/groovy/template/GroovyTemplateAutoConfiguration.java

@@ -47,13 +47,15 @@
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
+import org.springframework.web.servlet.view.UrlBasedViewResolver;
 
 /**
  * Autoconfiguration support for Groovy templates in MVC. By default creates a
  * {@link MarkupTemplateEngine} configured from {@link GroovyTemplateProperties}, but you
  * can override that by providing a {@link TemplateEngine} of a different type.
  *
  * @author Dave Syer
+ * @author Andy Wilkinson
  * @since 1.1.0
  */
 @Configuration
@@ -144,7 +146,8 @@ public TemplateEngine groovyTemplateEngine() throws Exception {
 	}
 
 	@Configuration
-	@ConditionalOnClass({ Servlet.class, LocaleContextHolder.class })
+	@ConditionalOnClass({ Servlet.class, LocaleContextHolder.class,
+			UrlBasedViewResolver.class })
 	@ConditionalOnWebApplication
 	public static class GroovyWebConfiguration {