Remove assumption that a file URI can be turned into a File

Closes gh-13493

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/server/StaticResourceJars.java

@@ -78,15 +78,24 @@ class StaticResourceJars {
 			throw new IllegalStateException(
 					"Failed to create File from URL '" + url + "'");
 		}
+		catch (IllegalArgumentException ex) {
+			return null;
+		}
 	}
 
 	private void addUrl(List<URL> urls, URL url) {
 		try {
-			if ("file".equals(url.getProtocol())) {
-				addUrlFile(urls, url, toFile(url));
+			if (!"file".equals(url.getProtocol())) {
+				addUrlConnection(urls, url, url.openConnection());
 			}
 			else {
-				addUrlConnection(urls, url, url.openConnection());
+				File file = toFile(url);
+				if (file != null) {
+					addUrlFile(urls, url, file);
+				}
+				else {
+					addUrlConnection(urls, url, url.openConnection());
+				}
 			}
 		}
 		catch (IOException ex) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/servlet/server/StaticResourceJarsTests.java

@@ -74,6 +74,14 @@ public class StaticResourceJarsTests {
 		assertThat(staticResourceJarUrls).hasSize(0);
 	}
 
+	@Test
+	public void uncPathsAreTolerated() throws Exception {
+		File jarFile = createResourcesJar("test-resources.jar");
+		List<URL> staticResourceJarUrls = new StaticResourceJars().getUrlsFrom(
+				jarFile.toURI().toURL(), new URL("file://unc.example.com/test.jar"));
+		assertThat(staticResourceJarUrls).hasSize(1);
+	}
+
 	private File createResourcesJar(String name) throws IOException {
 		return createJar(name, (output) -> {
 			JarEntry jarEntry = new JarEntry("META-INF/resources");