Only enable full path optimization when there's one DispatcherServlet

Previously, UrlPathHelper's full path optimization was enabled when
there was a dispatcher servlet mapped to /. The UrlPathHelper is used
across Spring MVC and if there are multiple dispatcher servlets they
all share the sample UrlPathHelper. This meant that any additional
dispatcher servlets mapping to locations other than / would not be able
to map requests correctly as the UrlPathHelper would use the full path,
ignoring the url mapping of the dispatcher servlet.

This commit updates the MVC auto-configuration so that use of the full
path is only enabled if there's a single dispatcher servlet
registration.

Fixes gh-22682

Author: wilkinsona

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

@@ -56,6 +56,7 @@
 import org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties.Format;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.convert.ApplicationConversionService;
+import org.springframework.boot.web.servlet.ServletRegistrationBean;
 import org.springframework.boot.web.servlet.filter.OrderedFormContentFilter;
 import org.springframework.boot.web.servlet.filter.OrderedHiddenHttpMethodFilter;
 import org.springframework.boot.web.servlet.filter.OrderedRequestContextFilter;
@@ -191,18 +192,22 @@ public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
 
 		private final ObjectProvider<DispatcherServletPath> dispatcherServletPath;
 
+		private final ObjectProvider<ServletRegistrationBean<?>> servletRegistrations;
+
 		final ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer;
 
 		public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties, WebMvcProperties mvcProperties,
 				ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
 				ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
-				ObjectProvider<DispatcherServletPath> dispatcherServletPath) {
+				ObjectProvider<DispatcherServletPath> dispatcherServletPath,
+				ObjectProvider<ServletRegistrationBean<?>> servletRegistrations) {
 			this.resourceProperties = resourceProperties;
 			this.mvcProperties = mvcProperties;
 			this.beanFactory = beanFactory;
 			this.messageConvertersProvider = messageConvertersProvider;
 			this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
 			this.dispatcherServletPath = dispatcherServletPath;
+			this.servletRegistrations = servletRegistrations;
 		}
 
 		@Override
@@ -234,14 +239,19 @@ public void configurePathMatch(PathMatchConfigurer configurer) {
 					this.mvcProperties.getPathmatch().isUseRegisteredSuffixPattern());
 			this.dispatcherServletPath.ifAvailable((dispatcherPath) -> {
 				String servletUrlMapping = dispatcherPath.getServletUrlMapping();
-				if (servletUrlMapping.equals("/")) {
+				if (servletUrlMapping.equals("/") && singleDispatcherServlet()) {
 					UrlPathHelper urlPathHelper = new UrlPathHelper();
 					urlPathHelper.setAlwaysUseFullPath(true);
 					configurer.setUrlPathHelper(urlPathHelper);
 				}
 			});
 		}
 
+		private boolean singleDispatcherServlet() {
+			return this.servletRegistrations.stream().map(ServletRegistrationBean::getServlet)
+					.filter(DispatcherServlet.class::isInstance).count() == 1;
+		}
+
 		@Override
 		@SuppressWarnings("deprecation")
 		public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {

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

@@ -52,6 +52,7 @@
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.boot.web.server.WebServerFactoryCustomizerBeanPostProcessor;
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
+import org.springframework.boot.web.servlet.ServletRegistrationBean;
 import org.springframework.boot.web.servlet.filter.OrderedFormContentFilter;
 import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
 import org.springframework.context.ApplicationContext;
@@ -84,6 +85,7 @@
 import org.springframework.web.filter.FormContentFilter;
 import org.springframework.web.filter.HiddenHttpMethodFilter;
 import org.springframework.web.filter.RequestContextFilter;
+import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.HandlerAdapter;
 import org.springframework.web.servlet.HandlerExceptionResolver;
 import org.springframework.web.servlet.HandlerMapping;
@@ -866,6 +868,23 @@ void urlPathHelperDoesNotUseFullPathWithServletMapping() {
 		});
 	}
 
+	@Test
+	void urlPathHelperDoesNotUseFullPathWithAdditionalDispatcherServlet() {
+		this.contextRunner.withUserConfiguration(AdditionalDispatcherServletConfiguration.class).run((context) -> {
+			UrlPathHelper urlPathHelper = context.getBean(UrlPathHelper.class);
+			assertThat(urlPathHelper).extracting("alwaysUseFullPath").isEqualTo(false);
+		});
+	}
+
+	@Test
+	void urlPathHelperDoesNotUseFullPathWithAdditionalUntypedDispatcherServlet() {
+		this.contextRunner.withUserConfiguration(AdditionalUntypedDispatcherServletConfiguration.class)
+				.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);
@@ -1248,4 +1267,24 @@ public void addCorsMappings(CorsRegistry registry) {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class AdditionalDispatcherServletConfiguration {
+
+		@Bean
+		ServletRegistrationBean<DispatcherServlet> additionalDispatcherServlet() {
+			return new ServletRegistrationBean<>(new DispatcherServlet());
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class AdditionalUntypedDispatcherServletConfiguration {
+
+		@Bean
+		ServletRegistrationBean<?> additionalDispatcherServlet() {
+			return new ServletRegistrationBean<>(new DispatcherServlet());
+		}
+
+	}
+
 }