Also, sort far less often; there's no need to sort on every access, o…

…nly after mutations.

 This does leave the possibility that custom subclasses are adding to
 the list and not sorting afterwards, but there is an "addLoader" method
 available that behaves appropriately. Ideally, loaders could be made
 private. .

JCL2/core/src/main/java/org/xeustechnologies/jcl/AbstractClassLoader.java

@@ -40,7 +40,11 @@
 @SuppressWarnings("unchecked")
 public abstract class AbstractClassLoader extends ClassLoader {
 
-	protected final List<ProxyClassLoader> loaders = new ArrayList<ProxyClassLoader>();
+	// we could use concurrent sorted set like ConcurrentSkipListSet here instead, which would be automatically sorted
+	// and wouldn't require the lock.
+	// But that was added in 1.6, and according to Maven we're targeting 1.5+.
+	/** Note that all iterations over this list *must* synchronize on it first! */
+	protected final List<ProxyClassLoader> loaders = Collections.synchronizedList(new ArrayList<ProxyClassLoader>());
 
 	private final ProxyClassLoader systemLoader = new SystemLoader();
 	private final ProxyClassLoader parentLoader = new ParentLoader();
@@ -66,14 +70,20 @@ public AbstractClassLoader() {
 	}
 
 	protected void addDefaultLoader() {
-		loaders.add(systemLoader);
-		loaders.add(parentLoader);
-		loaders.add(currentLoader);
-		loaders.add(threadLoader);
+		synchronized (loaders) {
+			loaders.add(systemLoader);
+			loaders.add(parentLoader);
+			loaders.add(currentLoader);
+			loaders.add(threadLoader);
+			Collections.sort(loaders);
+		}
 	}
 
 	public void addLoader(ProxyClassLoader loader) {
-		loaders.add(loader);
+		synchronized (loaders) {
+			loaders.add(loader);
+			Collections.sort(loaders);
+		}
 	}
 
 	/*
@@ -98,8 +108,6 @@ public Class loadClass(String className, boolean resolveIt) throws ClassNotFound
 		if (className == null || className.trim().equals(""))
 			return null;
 
-		Collections.sort(loaders);
-
 		Class clazz = null;
 
 		// Check osgi boot delegation
@@ -108,11 +116,13 @@ public Class loadClass(String className, boolean resolveIt) throws ClassNotFound
 		}
 
 		if (clazz == null) {
-			for (ProxyClassLoader l : loaders) {
-				if (l.isEnabled()) {
-					clazz = l.loadClass(className, resolveIt);
-					if (clazz != null)
-						break;
+			synchronized (loaders) {
+				for (ProxyClassLoader l : loaders) {
+					if (l.isEnabled()) {
+						clazz = l.loadClass(className, resolveIt);
+						if (clazz != null)
+							break;
+					}
 				}
 			}
 		}
@@ -135,8 +145,6 @@ public URL getResource(String name) {
 		if (name == null || name.trim().equals(""))
 			return null;
 
-		Collections.sort(loaders);
-
 		URL url = null;
 
 		// Check osgi boot delegation
@@ -145,11 +153,13 @@ public URL getResource(String name) {
 		}
 
 		if (url == null) {
-			for (ProxyClassLoader l : loaders) {
-				if (l.isEnabled()) {
-					url = l.findResource(name);
-					if (url != null)
-						break;
+			synchronized (loaders) {
+				for (ProxyClassLoader l : loaders) {
+					if (l.isEnabled()) {
+						url = l.findResource(name);
+						if (url != null)
+							break;
+					}
 				}
 			}
 		}
@@ -170,8 +180,6 @@ public InputStream getResourceAsStream(String name) {
 		if (name == null || name.trim().equals(""))
 			return null;
 
-		Collections.sort(loaders);
-
 		InputStream is = null;
 
 		// Check osgi boot delegation
@@ -180,11 +188,13 @@ public InputStream getResourceAsStream(String name) {
 		}
 
 		if (is == null) {
-			for (ProxyClassLoader l : loaders) {
-				if (l.isEnabled()) {
-					is = l.loadResource(name);
-					if (is != null)
-						break;
+			synchronized (loaders) {
+				for (ProxyClassLoader l : loaders) {
+					if (l.isEnabled()) {
+						is = l.loadResource(name);
+						if (is != null)
+							break;
+					}
 				}
 			}
 		}

JCL2/core/src/main/java/org/xeustechnologies/jcl/JarClassLoader.java

@@ -62,7 +62,7 @@ public JarClassLoader() {
      * 
      */
     public void initialize() {
-        loaders.add( localLoader );
+        addLoader( localLoader );
     }
 
     /**