Code refactor based on review comments

Author: shreyas-gopalakrishna

src/main/java/com/microsoft/azure/functions/worker/reflect/EnhancedClassLoaderProvider.java

@@ -19,21 +19,19 @@ public EnhancedClassLoaderProvider() {
      */
     @Override
     public ClassLoader createClassLoader() {
-        URL[] urlsForClassLoader = new URL[urls.size()];
-        urls.toArray(urlsForClassLoader);
-
-        URLClassLoader classLoader = getURLClassLoaderInstance(urlsForClassLoader);
-        return classLoader;
+        return getURLClassLoaderInstance();
     }
 
     /**
-     * @param urlsForClassLoader Array of URLs to construct a new URLClassLoader
-     * @return single instance of URLClassLoader
+     * Create and return a singleton URL classloader
+     * @return instance of URLClassLoader
      */
-    private URLClassLoader getURLClassLoaderInstance(URL[] urlsForClassLoader) {
+    private URLClassLoader getURLClassLoaderInstance() {
         if (classLoaderInstance == null) {
-            synchronized (URLClassLoader.class) {
+            synchronized (lock) {
                 if (classLoaderInstance == null) {
+                    URL[] urlsForClassLoader = new URL[urls.size()];
+                    urls.toArray(urlsForClassLoader);
                     classLoaderInstance = new URLClassLoader(urlsForClassLoader);
                     loadDrivers(classLoaderInstance);
                 }
@@ -88,5 +86,6 @@ public void addUrl(URL url) throws IOException {
         urls.add(url);
     }
     private final Set<URL> urls;
+    private final Object lock = new Object();
     private static volatile URLClassLoader classLoaderInstance;
 }