ResourceUrlProvider handles sanitizes double slashes

Issue: SPR-16296

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

@@ -34,6 +34,7 @@ import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.lang.Nullable;
 import org.springframework.util.AntPathMatcher;
 import org.springframework.util.PathMatcher;
+import org.springframework.util.StringUtils;
 import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
 import org.springframework.web.util.UrlPathHelper;
 
@@ -217,6 +218,14 @@ public class ResourceUrlProvider implements ApplicationListener<ContextRefreshed
 	 */
 	@Nullable
 	public final String getForLookupPath(String lookupPath) {
+
+		// Clean duplicate slashes or pathWithinPattern won't match lookupPath
+		String previous;
+		do {
+			previous = lookupPath;
+			lookupPath = StringUtils.replace(lookupPath, "//", "/");
+		} while (!lookupPath.equals(previous));
+
 		if (logger.isTraceEnabled()) {
 			logger.trace("Getting resource URL for lookup path \"" + lookupPath + "\"");
 		}

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

@@ -35,6 +35,9 @@ import org.springframework.web.context.support.AnnotationConfigWebApplicationCon
 import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
 
 import static org.junit.Assert.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 
 /**
@@ -136,6 +139,25 @@ public class ResourceUrlProviderTests {
 		assertFalse(urlProviderBean.isAutodetect());
 	}
 
+	@Test // SPR-16296
+	public void getForLookupPathShouldNotFailIfPathContainsDoubleSlashes() {
+		// given
+		ResourceResolver mockResourceResolver = mock(ResourceResolver.class);
+		when(mockResourceResolver.resolveUrlPath(any(), any(), any())).thenReturn("some-path");
+
+		ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();
+		handler.getResourceResolvers().add(mockResourceResolver);
+
+		ResourceUrlProvider provider = new ResourceUrlProvider();
+		provider.getHandlerMap().put("/some-pattern/**", handler);
+
+		// when
+		String lookupForPath = provider.getForLookupPath("/some-pattern/some-lib//some-resource");
+
+		// then
+		assertEquals("/some-pattern/some-path", lookupForPath);
+	}
+
 
 	@Configuration
 	@SuppressWarnings({"unused", "WeakerAccess"})