Allow Tomcat context root redirect to be configured via the environment

This commit adds a new property, server.tomcat.redirect-context-root,
that can be used to configure the Tomcat Context’s 
mapperContextRootRedirectEnabled property. The default is to not apply
any configuration and, therefore, to use Tomcat’s default of true.

Closes gh-6248

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -646,6 +646,12 @@ public class ServerProperties
 		 */
 		private int maxHttpHeaderSize = 0; // bytes
 
+		/**
+		 * Whether requests to the context root should be redirected by appending a / to
+		 * the path.
+		 */
+		private Boolean redirectContextRoot;
+
 		/**
 		 * Character encoding to use to decode the URI.
 		 */
@@ -742,6 +748,14 @@ public class ServerProperties
 			this.portHeader = portHeader;
 		}
 
+		public Boolean getRedirectContextRoot() {
+			return this.redirectContextRoot;
+		}
+
+		public void setRedirectContextRoot(Boolean redirectContextRoot) {
+			this.redirectContextRoot = redirectContextRoot;
+		}
+
 		public String getRemoteIpHeader() {
 			return this.remoteIpHeader;
 		}
@@ -789,6 +803,9 @@ public class ServerProperties
 				customizeConnectionTimeout(factory,
 						serverProperties.getConnectionTimeout());
 			}
+			if (this.redirectContextRoot != null) {
+				customizeRedirectContextRoot(factory, this.redirectContextRoot);
+			}
 		}
 
 		private void customizeConnectionTimeout(
@@ -911,6 +928,19 @@ public class ServerProperties
 			factory.addContextValves(valve);
 		}
 
+		private void customizeRedirectContextRoot(
+				TomcatEmbeddedServletContainerFactory factory,
+				final boolean redirectContextRoot) {
+			factory.addContextCustomizers(new TomcatContextCustomizer() {
+
+				@Override
+				public void customize(Context context) {
+					context.setMapperContextRootRedirectEnabled(redirectContextRoot);
+				}
+
+			});
+		}
+
 		public static class Accesslog {
 
 			/**

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java

@@ -29,6 +29,7 @@ import javax.servlet.ServletException;
 import javax.servlet.SessionCookieConfig;
 import javax.servlet.SessionTrackingMode;
 
+import org.apache.catalina.Context;
 import org.apache.catalina.Valve;
 import org.apache.catalina.valves.RemoteIpValve;
 import org.junit.Before;
@@ -41,6 +42,7 @@ import org.springframework.beans.MutablePropertyValues;
 import org.springframework.boot.bind.RelaxedDataBinder;
 import org.springframework.boot.context.embedded.ConfigurableEmbeddedServletContainer;
 import org.springframework.boot.context.embedded.jetty.JettyEmbeddedServletContainerFactory;
+import org.springframework.boot.context.embedded.tomcat.TomcatContextCustomizer;
 import org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory;
 import org.springframework.boot.context.embedded.undertow.UndertowEmbeddedServletContainerFactory;
 import org.springframework.boot.web.servlet.ServletContextInitializer;
@@ -150,6 +152,30 @@ public class ServerPropertiesTests {
 				.isEqualTo("10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
 	}
 
+	@Test
+	public void redirectContextRootIsNotConfiguredByDefault() throws Exception {
+		bindProperties(new HashMap<String, String>());
+		ServerProperties.Tomcat tomcat = this.properties.getTomcat();
+		assertThat(tomcat.getRedirectContextRoot()).isNull();
+	}
+
+	@Test
+	public void redirectContextRootCanBeConfigured() throws Exception {
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.redirect-context-root", "false");
+		bindProperties(map);
+		ServerProperties.Tomcat tomcat = this.properties.getTomcat();
+		assertThat(tomcat.getRedirectContextRoot()).isEqualTo(false);
+		TomcatEmbeddedServletContainerFactory container = new TomcatEmbeddedServletContainerFactory();
+		this.properties.customize(container);
+		Context context = mock(Context.class);
+		for (TomcatContextCustomizer customizer : container
+				.getTomcatContextCustomizers()) {
+			customizer.customize(context);
+		}
+		verify(context).setMapperContextRootRedirectEnabled(false);
+	}
+
 	@Test
 	public void testTrailingSlashOfContextPathIsRemoved() {
 		new RelaxedDataBinder(this.properties, "server").bind(new MutablePropertyValues(

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -214,6 +214,7 @@ content into your application; rather pick only the properties that you need.
 	server.tomcat.port-header=X-Forwarded-Port # Name of the HTTP header used to override the original port value.
 	server.tomcat.protocol-header= # Header that holds the incoming protocol, usually named "X-Forwarded-Proto".
 	server.tomcat.protocol-header-https-value=https # Value of the protocol header that indicates that the incoming request uses SSL.
+	server.tomcat.redirect-context-root= # Whether requests to the context root should be redirected by appending a / to the path.
 	server.tomcat.remote-ip-header= # Name of the http header from which the remote ip is extracted. For instance `X-FORWARDED-FOR`
 	server.tomcat.uri-encoding=UTF-8 # Character encoding to use to decode the URI.
 	server.undertow.accesslog.dir= # Undertow access log directory.

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

@@ -184,7 +184,6 @@ public class TomcatEmbeddedServletContainerFactory
 						: ClassUtils.getDefaultClassLoader());
 		try {
 			context.setUseRelativeRedirects(false);
-			context.setMapperContextRootRedirectEnabled(true);
 		}
 		catch (NoSuchMethodError ex) {
 			// Tomcat is < 8.0.30. Continue