Fixed a Sonarqube finding and added more unit tests to ensure all available classes are loaded

Author: subhash686

powertools-common/src/main/java/software/amazon/lambda/powertools/common/internal/ClassPreLoader.java

@@ -68,15 +68,24 @@ private static void preloadClassesFromStream(InputStream is) {
                 }
                 final String className = line.stripTrailing();
                 if (!className.isBlank()) {
-                    try {
-                        Class.forName(className, true, ClassPreLoader.class.getClassLoader());
-                    } catch (ClassNotFoundException e) {
-                        // No action is required if a class listed in the file cannot be found
-                    }
+                    loadClassIfFound(className);
                 }
             }
         } catch (Exception ignored) {
             // No action is required if preloading fails for any reason
         }
     }
+
+    /**
+     * Initializes the class with given name if found, ignores otherwise
+     *
+     * @param className
+     */
+    private static void loadClassIfFound(String className) {
+        try {
+            Class.forName(className, true, ClassPreLoader.class.getClassLoader());
+        } catch (ClassNotFoundException e) {
+            // No action is required if the class with given name cannot be found
+        }
+    }
 }

powertools-common/src/test/java/software/amazon/lambda/powertools/common/internal/ClassPreLoaderTest.java

@@ -6,9 +6,29 @@
 
 class ClassPreLoaderTest {
 
+    // Making this volatile so the Thread Context doesn't need any special handling
+    static volatile boolean dummyClassLoaded = false;
+
+    /**
+     * Dummy class to be loaded by ClassPreLoader in test.
+     * <b>The class name is referenced in <i>powertools-common/src/test/resources/classesloaded.txt</i></b>
+     * This class is used to verify that the ClassPreLoader can load valid classes.
+     * The static block sets a flag to indicate that the class has been loaded.
+     */
+    static class DummyClass {
+        static {
+            dummyClassLoaded = true;
+        }
+    }
     @Test
     void preloadClasses_shouldIgnoreInvalidClassesAndLoadValidClasses() {
+
+        dummyClassLoaded = false;
+        // powertools-common/src/test/resources/classesloaded.txt has a class that does not exist
         // Verify that the missing class did not throw any exception
         assertDoesNotThrow(ClassPreLoader::preloadClasses);
+
+        // When the classloaded.txt is a mixed bag of valid and invalid classes, Valid class must load
+        assertTrue(dummyClassLoaded, "DummyClass should be loaded");
     }
 }

powertools-common/src/test/resources/classesloaded.txt

@@ -1 +1,2 @@
-software.amazon.lambda.powertools.common.internal.NonExistingClass
+software.amazon.lambda.powertools.common.internal.NonExistingClass
+software.amazon.lambda.powertools.common.internal.ClassPreLoaderTest$DummyClass