Use fast exceptions in findResource(s)

Some libraries like aspectj are using findResource to see the raw
bytecode of a class. It will even call findResource for every method of
every class of beans that are post processed. This can be significant
performance hit on startup when LaunchedURLClassLoader and there are a
lot of nested jars.

See gh-3640
Fixes gh-4557

spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java

@@ -76,7 +76,13 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 			if (name.equals("") && hasURLs()) {
 				return getURLs()[0];
 			}
-			return super.findResource(name);
+			Handler.setUseFastConnectionExceptions(true);
+			try {
+				return super.findResource(name);
+			}
+			finally {
+				Handler.setUseFastConnectionExceptions(false);
+			}
 		}
 		catch (IllegalArgumentException ex) {
 			return null;
@@ -88,7 +94,13 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 		if (name.equals("") && hasURLs()) {
 			return Collections.enumeration(Arrays.asList(getURLs()));
 		}
-		return super.findResources(name);
+		Handler.setUseFastConnectionExceptions(true);
+		try {
+			return super.findResources(name);
+		}
+		finally {
+			Handler.setUseFastConnectionExceptions(false);
+		}
 	}
 
 	private boolean hasURLs() {
@@ -100,33 +112,8 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 		if (this.rootClassLoader == null) {
 			return findResources(name);
 		}
-
-		final Enumeration<URL> rootResources = this.rootClassLoader.getResources(name);
-		final Enumeration<URL> localResources = findResources(name);
-
-		return new Enumeration<URL>() {
-
-			@Override
-			public boolean hasMoreElements() {
-				try {
-					Handler.setUseFastConnectionExceptions(true);
-					return rootResources.hasMoreElements()
-							|| localResources.hasMoreElements();
-				}
-				finally {
-					Handler.setUseFastConnectionExceptions(false);
-				}
-			}
-
-			@Override
-			public URL nextElement() {
-				if (rootResources.hasMoreElements()) {
-					return rootResources.nextElement();
-				}
-				return localResources.nextElement();
-			}
-
-		};
+		return new ResourceEnumeration(this.rootClassLoader.getResources(name),
+				findResources(name));
 	}
 
 	/**
@@ -162,6 +149,7 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 			}
 		}
 		catch (Exception ex) {
+
 		}
 
 		// 2) Try to find locally
@@ -171,6 +159,7 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 			return cls;
 		}
 		catch (Exception ex) {
+
 		}
 
 		// 3) Use standard loading
@@ -265,4 +254,41 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 
 	}
 
+	/**
+	 * {@link Enumeration} implementation used for {@code getResources()}.
+	 */
+	private static class ResourceEnumeration implements Enumeration<URL> {
+
+		private final Enumeration<URL> rootResources;
+
+		private final Enumeration<URL> localResources;
+
+		ResourceEnumeration(Enumeration<URL> rootResources,
+				Enumeration<URL> localResources) {
+			this.rootResources = rootResources;
+			this.localResources = localResources;
+		}
+
+		@Override
+		public boolean hasMoreElements() {
+			try {
+				Handler.setUseFastConnectionExceptions(true);
+				return this.rootResources.hasMoreElements()
+						|| this.localResources.hasMoreElements();
+			}
+			finally {
+				Handler.setUseFastConnectionExceptions(false);
+			}
+		}
+
+		@Override
+		public URL nextElement() {
+			if (this.rootResources.hasMoreElements()) {
+				return this.rootResources.nextElement();
+			}
+			return this.localResources.nextElement();
+		}
+
+	}
+
 }