Tolerate absolute URLs in manifest's Class-Path attribute

Closes gh-10268

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/ChangeableUrls.java

@@ -143,7 +143,10 @@ final class ChangeableUrls implements Iterable<URL> {
 		List<File> nonExistentEntries = new ArrayList<File>();
 		for (String entry : entries) {
 			try {
-				File referenced = new File(parent, entry);
+				File referenced = new File(entry);
+				if (!referenced.isAbsolute()) {
+					referenced = new File(parent, entry);
+				}
 				if (referenced.exists()) {
 					urls.add(referenced.toURI().toURL());
 				}

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/ChangeableUrlsTests.java

@@ -75,9 +75,11 @@ public class ChangeableUrlsTests {
 	@Test
 	public void urlsFromJarClassPathAreConsidered() throws Exception {
 		File relative = this.temporaryFolder.newFolder();
+		File absolute = this.temporaryFolder.newFolder();
 		File jarWithClassPath = makeJarFileWithUrlsInManifestClassPath(
 				"project-core/target/classes/", "project-web/target/classes/",
-				"does-not-exist/target/classes", relative.getName() + "/");
+				"does-not-exist/target/classes", relative.getName() + "/",
+				absolute.getAbsolutePath() + "/");
 		new File(jarWithClassPath.getParentFile(), "project-core/target/classes")
 				.mkdirs();
 		new File(jarWithClassPath.getParentFile(), "project-web/target/classes").mkdirs();
@@ -87,7 +89,7 @@ public class ChangeableUrlsTests {
 		assertThat(urls.toList()).containsExactly(
 				new URL(jarWithClassPath.toURI().toURL(), "project-core/target/classes/"),
 				new URL(jarWithClassPath.toURI().toURL(), "project-web/target/classes/"),
-				relative.toURI().toURL());
+				relative.toURI().toURL(), absolute.toURI().toURL());
 	}
 
 	private URL makeUrl(String name) throws IOException {