Optimize UrlPathHelper configuration for Spring MVC

Prior to this commit, Spring Boot would auto-configure Spring MVC and
would keep the default `UrlPathHelper` configuration.
Since Spring Boot is in charge of configuring the `DispatcherServlet`
and its mapping, it is in a position to optimally configure the
`UrlPathHelper` depending on the chosen mapping.

This commit sets the `alwaysUseFullPath` property of `UrlPathHelper` if
the Servlet mapping is `"/"`. This is more efficient since this
configuration requires less processing of the request path.

Closes gh-21499

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration.java

@@ -119,6 +119,7 @@ import org.springframework.web.servlet.resource.VersionResourceResolver;
 import org.springframework.web.servlet.view.BeanNameViewResolver;
 import org.springframework.web.servlet.view.ContentNegotiatingViewResolver;
 import org.springframework.web.servlet.view.InternalResourceViewResolver;
+import org.springframework.web.util.UrlPathHelper;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for {@link EnableWebMvc Web MVC}.
@@ -188,16 +189,20 @@ public class WebMvcAutoConfiguration {
 
 		private final ObjectProvider<HttpMessageConverters> messageConvertersProvider;
 
+		private final ObjectProvider<DispatcherServletPath> dispatcherServletPath;
+
 		final ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer;
 
 		public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties, WebMvcProperties mvcProperties,
 				ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
-				ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider) {
+				ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
+				ObjectProvider<DispatcherServletPath> dispatcherServletPath) {
 			this.resourceProperties = resourceProperties;
 			this.mvcProperties = mvcProperties;
 			this.beanFactory = beanFactory;
 			this.messageConvertersProvider = messageConvertersProvider;
 			this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
+			this.dispatcherServletPath = dispatcherServletPath;
 		}
 
 		@Override
@@ -227,6 +232,14 @@ public class WebMvcAutoConfiguration {
 			configurer.setUseSuffixPatternMatch(this.mvcProperties.getPathmatch().isUseSuffixPattern());
 			configurer.setUseRegisteredSuffixPatternMatch(
 					this.mvcProperties.getPathmatch().isUseRegisteredSuffixPattern());
+			this.dispatcherServletPath.ifAvailable((dispatcherPath) -> {
+				String servletUrlMapping = dispatcherPath.getServletUrlMapping();
+				if (servletUrlMapping.equals("/")) {
+					UrlPathHelper urlPathHelper = new UrlPathHelper();
+					urlPathHelper.setAlwaysUseFullPath(true);
+					configurer.setUrlPathHelper(urlPathHelper);
+				}
+			});
 		}
 
 		@Override

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfigurationTests.java

@@ -118,6 +118,7 @@ import org.springframework.web.servlet.resource.VersionResourceResolver;
 import org.springframework.web.servlet.resource.VersionStrategy;
 import org.springframework.web.servlet.view.AbstractView;
 import org.springframework.web.servlet.view.ContentNegotiatingViewResolver;
+import org.springframework.web.util.UrlPathHelper;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
@@ -139,8 +140,9 @@ class WebMvcAutoConfigurationTests {
 	private static final MockServletWebServerFactory webServerFactory = new MockServletWebServerFactory();
 
 	private final WebApplicationContextRunner contextRunner = new WebApplicationContextRunner()
-			.withConfiguration(AutoConfigurations.of(WebMvcAutoConfiguration.class,
-					HttpMessageConvertersAutoConfiguration.class, PropertyPlaceholderAutoConfiguration.class))
+			.withConfiguration(
+					AutoConfigurations.of(WebMvcAutoConfiguration.class, DispatcherServletAutoConfiguration.class,
+							HttpMessageConvertersAutoConfiguration.class, PropertyPlaceholderAutoConfiguration.class))
 			.withUserConfiguration(Config.class);
 
 	@Test
@@ -848,6 +850,22 @@ class WebMvcAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	void urlPathHelperUsesFullPathByDefault() {
+		this.contextRunner.run((context) -> {
+			UrlPathHelper urlPathHelper = context.getBean(UrlPathHelper.class);
+			assertThat(urlPathHelper).extracting("alwaysUseFullPath").isEqualTo(true);
+		});
+	}
+
+	@Test
+	void urlPathHelperDoesNotUseFullPathWithServletMapping() {
+		this.contextRunner.withPropertyValues("spring.mvc.servlet.path=/test/").run((context) -> {
+			UrlPathHelper urlPathHelper = context.getBean(UrlPathHelper.class);
+			assertThat(urlPathHelper).extracting("alwaysUseFullPath").isEqualTo(false);
+		});
+	}
+
 	private void assertCacheControl(AssertableWebApplicationContext context) {
 		Map<String, Object> handlerMap = getHandlerMap(context.getBean("resourceHandlerMapping", HandlerMapping.class));
 		assertThat(handlerMap).hasSize(2);