[api] Fix NPE bug in getContextClassLoader().

api/src/main/java/ai/djl/repository/RepositoryFactoryImpl.java

@@ -14,6 +14,7 @@
 
 import ai.djl.repository.zoo.ModelLoader;
 import ai.djl.repository.zoo.ModelZoo;
+import ai.djl.util.ClassLoaderUtils;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URI;
@@ -137,7 +138,7 @@ public Repository newInstance(String name, URI uri) {
             if (p.startsWith("/")) {
                 p = p.substring(1);
             }
-            URL u = Thread.currentThread().getContextClassLoader().getResource(p);
+            URL u = ClassLoaderUtils.getContextClassLoader().getResource(p);
             if (u == null) {
                 throw new IllegalArgumentException("Resource not found: " + uri);
             }

api/src/main/java/ai/djl/repository/zoo/BaseModelLoader.java

@@ -228,7 +228,7 @@ protected TranslatorFactory getTranslatorFactory(
 
         String factoryClass = (String) arguments.get("translatorFactory");
         if (factoryClass != null) {
-            ClassLoader cl = Thread.currentThread().getContextClassLoader();
+            ClassLoader cl = ClassLoaderUtils.getContextClassLoader();
             factory = ClassLoaderUtils.initClass(cl, factoryClass);
         }
         return factory;

api/src/main/java/ai/djl/translate/ServingTranslatorFactory.java

@@ -20,6 +20,7 @@
 import ai.djl.modality.cv.translator.ImageServingTranslator;
 import ai.djl.ndarray.NDList;
 import ai.djl.ndarray.NDManager;
+import ai.djl.util.ClassLoaderUtils;
 import ai.djl.util.Pair;
 import java.io.File;
 import java.io.IOException;
@@ -107,7 +108,7 @@ private ServingTranslator findTranslator(Path path, String className) {
                 urls.add(p.toUri().toURL());
             }
 
-            ClassLoader parentCl = Thread.currentThread().getContextClassLoader();
+            ClassLoader parentCl = ClassLoaderUtils.getContextClassLoader();
             ClassLoader cl = new URLClassLoader(urls.toArray(new URL[0]), parentCl);
             if (className != null && !className.isEmpty()) {
                 return initTranslator(cl, className);

api/src/main/java/ai/djl/util/ClassLoaderUtils.java

@@ -68,7 +68,7 @@ public static <T> T findImplementation(Path path, String className) {
                 urls[index++] = p.toUri().toURL();
             }
 
-            final ClassLoader contextCl = Thread.currentThread().getContextClassLoader();
+            final ClassLoader contextCl = getContextClassLoader();
             ClassLoader cl =
                     AccessController.doPrivileged(
                             (PrivilegedAction<ClassLoader>)
@@ -154,4 +154,17 @@ public static <T> T initClass(ClassLoader cl, String className) {
         }
         return null;
     }
+
+    /**
+     * Returns the context class loader if available.
+     *
+     * @return the context class loader if available
+     */
+    public static ClassLoader getContextClassLoader() {
+        ClassLoader cl = Thread.currentThread().getContextClassLoader();
+        if (cl == null) {
+            return ClassLoaderUtils.class.getClassLoader(); // NOPMD
+        }
+        return cl;
+    }
 }

api/src/main/java/ai/djl/util/Platform.java

@@ -59,7 +59,7 @@ public static Platform detectPlatform(String engine) {
         String nativeProp = "native/lib/" + engine + ".properties";
         Enumeration<URL> urls;
         try {
-            urls = Thread.currentThread().getContextClassLoader().getResources(nativeProp);
+            urls = ClassLoaderUtils.getContextClassLoader().getResources(nativeProp);
         } catch (IOException e) {
             throw new AssertionError("Failed to list property files.", e);
         }

basicdataset/src/main/java/ai/djl/basicdataset/cv/classification/ImageNet.java

@@ -15,6 +15,7 @@
 import ai.djl.modality.cv.transform.ToTensor;
 import ai.djl.training.dataset.Dataset;
 import ai.djl.translate.Pipeline;
+import ai.djl.util.ClassLoaderUtils;
 import ai.djl.util.JsonUtils;
 import ai.djl.util.Progress;
 import java.io.IOException;
@@ -101,7 +102,7 @@ public void prepare(Progress progress) throws IOException {
     }
 
     private void loadSynset() {
-        ClassLoader cl = Thread.currentThread().getContextClassLoader();
+        ClassLoader cl = ClassLoaderUtils.getContextClassLoader();
         try (InputStream classStream = cl.getResourceAsStream("imagenet/classes.json")) {
             if (classStream == null) {
                 throw new AssertionError("Missing imagenet/classes.json in jar resource");

testing/src/main/java/ai/djl/testing/CoverageUtils.java

@@ -12,6 +12,7 @@
  */
 package ai.djl.testing;
 
+import ai.djl.util.ClassLoaderUtils;
 import java.io.File;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
@@ -98,13 +99,13 @@ public static void testGetterSetters(Class<?> baseClass)
 
     private static List<Class<?>> getClasses(Class<?> clazz)
             throws IOException, ReflectiveOperationException, URISyntaxException {
-        ClassLoader appClassLoader = Thread.currentThread().getContextClassLoader();
+        ClassLoader appClassLoader = ClassLoaderUtils.getContextClassLoader();
         Field field = appClassLoader.getClass().getDeclaredField("ucp");
         field.setAccessible(true);
         Object ucp = field.get(appClassLoader);
         Method method = ucp.getClass().getDeclaredMethod("getURLs");
         URL[] urls = (URL[]) method.invoke(ucp);
-        ClassLoader cl = new TestClassLoader(urls, Thread.currentThread().getContextClassLoader());
+        ClassLoader cl = new TestClassLoader(urls, ClassLoaderUtils.getContextClassLoader());
 
         URL url = clazz.getProtectionDomain().getCodeSource().getLocation();
         String path = url.getPath();