Validate Resource type in ResourceHttpRequestHandler

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -57,6 +57,7 @@ import org.springframework.util.StringValueResolver;
 import org.springframework.web.HttpRequestHandler;
 import org.springframework.web.accept.ContentNegotiationManager;
 import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.context.support.ServletContextResource;
 import org.springframework.web.cors.CorsConfiguration;
 import org.springframework.web.cors.CorsConfigurationSource;
 import org.springframework.web.servlet.HandlerMapping;
@@ -445,6 +446,12 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 					location = location.substring(endIndex + 1);
 				}
 				Resource resource = applicationContext.getResource(location);
+				if (location.equals("/") && !(resource instanceof ServletContextResource)) {
+					throw new IllegalStateException(
+							"The String-based location \"/\" should be relative to the web application root " +
+									"but resolved to a Resource of type: " + resource.getClass() + ". " +
+									"If this is intentional, please pass it as a pre-configured Resource via setLocations.");
+				}
 				this.locationsToUse.add(resource);
 				if (charset != null) {
 					if (!(resource instanceof UrlResource)) {

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandlerTests.java

@@ -29,6 +29,7 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.UrlResource;
 import org.springframework.http.HttpMethod;
@@ -38,6 +39,7 @@ import org.springframework.util.StringUtils;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.accept.ContentNegotiationManager;
 import org.springframework.web.accept.ContentNegotiationManagerFactoryBean;
+import org.springframework.web.context.support.StaticWebApplicationContext;
 import org.springframework.web.servlet.HandlerMapping;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
@@ -723,6 +725,25 @@ public class ResourceHttpRequestHandlerTests {
 		assertThat(this.response.getContentAsString()).isEqualTo("h1 { color:red; }");
 	}
 
+	@Test
+	public void servletContextRootValidation() {
+		StaticWebApplicationContext context = new StaticWebApplicationContext() {
+			@Override
+			public Resource getResource(String location) {
+				return new FileSystemResource("/");
+			}
+		};
+
+		ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();
+		handler.setLocationValues(Collections.singletonList("/"));
+		handler.setApplicationContext(context);
+
+		assertThatIllegalStateException().isThrownBy(handler::afterPropertiesSet)
+				.withMessage("The String-based location \"/\" should be relative to the web application root but " +
+						"resolved to a Resource of type: class org.springframework.core.io.FileSystemResource. " +
+						"If this is intentional, please pass it as a pre-configured Resource via setLocations.");
+	}
+
 
 	private long resourceLastModified(String resourceName) throws IOException {
 		return new ClassPathResource(resourceName, getClass()).getFile().lastModified();