AVRO-1425: [Java] prioritise thread context ClassLoader over context class ClassLoader

lang/java/avro/src/main/java/org/apache/avro/specific/SpecificData.java

@@ -389,7 +389,7 @@ public Class getClass(Schema schema) {
         return null;
       Class<?> c = classCache.computeIfAbsent(name, n -> {
         try {
-          return ClassUtils.forName(getClassLoader(), getClassName(schema));
+          return ClassUtils.forName(getClassName(schema));
         } catch (ClassNotFoundException e) {
           // This might be a nested namespace. Try using the last tokens in the
           // namespace as an enclosing class by progressively replacing period
@@ -399,7 +399,7 @@ public Class getClass(Schema schema) {
           while (lastDot != -1) {
             nestedName.setCharAt(lastDot, '$');
             try {
-              return ClassUtils.forName(getClassLoader(), nestedName.toString());
+              return ClassUtils.forName(nestedName.toString());
             } catch (ClassNotFoundException ignored) {
             }
             lastDot = n.lastIndexOf('.', lastDot - 1);

lang/java/avro/src/main/java/org/apache/avro/specific/SpecificDatumReader.java

@@ -157,7 +157,7 @@ private Class getPropAsClass(Schema schema, String prop) {
       return null;
     try {
       checkSecurity(name);
-      Class clazz = ClassUtils.forName(getData().getClassLoader(), name);
+      Class clazz = ClassUtils.forName(name);
       return clazz;
     } catch (ClassNotFoundException e) {
       throw new AvroRuntimeException(e);

lang/java/avro/src/main/java/org/apache/avro/util/ClassUtils.java

@@ -45,34 +45,11 @@ public static Class<?> forName(String className) throws ClassNotFoundException {
    */
   public static Class<?> forName(Class<?> contextClass, String className) throws ClassNotFoundException {
     Class<?> c = null;
-    if (contextClass.getClassLoader() != null) {
-      c = forName(className, contextClass.getClassLoader());
-    }
-    if (c == null && Thread.currentThread().getContextClassLoader() != null) {
+    if (Thread.currentThread().getContextClassLoader() != null) {
       c = forName(className, Thread.currentThread().getContextClassLoader());
     }
-    if (c == null) {
-      throw new ClassNotFoundException("Failed to load class" + className);
-    }
-    return c;
-  }
-
-  /**
-   * Loads a class using the class loader. 1. The class loader of the context
-   * class is being used. 2. The thread context class loader is being used. If
-   * both approaches fail, returns null.
-   *
-   * @param classLoader The classloader to use.
-   * @param className   The name of the class to load
-   * @return The class or null if no class loader could load the class.
-   */
-  public static Class<?> forName(ClassLoader classLoader, String className) throws ClassNotFoundException {
-    Class<?> c = null;
-    if (classLoader != null) {
-      c = forName(className, classLoader);
-    }
-    if (c == null && Thread.currentThread().getContextClassLoader() != null) {
-      c = forName(className, Thread.currentThread().getContextClassLoader());
+    if (c == null && contextClass.getClassLoader() != null) {
+      c = forName(className, contextClass.getClassLoader());
     }
     if (c == null) {
       throw new ClassNotFoundException("Failed to load class" + className);
@@ -84,9 +61,9 @@ public static Class<?> forName(ClassLoader classLoader, String className) throws
    * Loads a {@link Class} from the specified {@link ClassLoader} without throwing
    * {@link ClassNotFoundException}.
    *
-   * @param className
-   * @param classLoader
-   * @return
+   * @param className   The name of the class to load
+   * @param classLoader The classloader to use.
+   * @return The class or null if no class loader could load the class.
    */
   private static Class<?> forName(String className, ClassLoader classLoader) {
     Class<?> c = null;

lang/java/protobuf/src/main/java/org/apache/avro/protobuf/ProtobufData.java

@@ -404,7 +404,7 @@ private Conversion getConversionByDescriptor(Descriptor descriptor) {
     String dot = namespace.endsWith("$") ? "" : "."; // back-compatibly handle $
 
     try {
-      Class clazz = ClassUtils.forName(getClassLoader(), namespace + dot + name);
+      Class clazz = ClassUtils.forName(namespace + dot + name);
       return getConversionByClass(clazz);
     } catch (ClassNotFoundException e) {
       return null;