Upgrade to Tomcat 8.0.30 and continue to use absolute redirects

Tomcat 8.0.30 has changed to using relative URIs in its redirects
by default. To avoid any problems that this behaviour change may
causes we override the default and configure Tomcat to continue to
use absolute URIs.

Closes gh-4715

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -134,7 +134,7 @@
 		<thymeleaf-extras-conditionalcomments.version>2.1.1.RELEASE</thymeleaf-extras-conditionalcomments.version>
 		<thymeleaf-layout-dialect.version>1.2.9</thymeleaf-layout-dialect.version>
 		<thymeleaf-extras-data-attribute.version>1.3</thymeleaf-extras-data-attribute.version>
-		<tomcat.version>8.0.28</tomcat.version>
+		<tomcat.version>8.0.30</tomcat.version>
 		<undertow.version>1.1.9.Final</undertow.version>
 		<velocity.version>1.7</velocity.version>
 		<velocity-tools.version>2.0</velocity-tools.version>

spring-boot/src/main/java/org/springframework/boot/context/embedded/tomcat/TomcatEmbeddedServletContainerFactory.java

@@ -167,6 +167,12 @@ protected void prepareContext(Host host, ServletContextInitializer[] initializer
 		context.setParentClassLoader(
 				this.resourceLoader != null ? this.resourceLoader.getClassLoader()
 						: ClassUtils.getDefaultClassLoader());
+		try {
+			context.setUseRelativeRedirects(false);
+		}
+		catch (NoSuchMethodError ex) {
+			// Tomcat is < 8.0.30. Continue
+		}
 		SkipPatternJarScanner.apply(context, this.tldSkip);
 		WebappLoader loader = new WebappLoader(context.getParentClassLoader());
 		loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());