Fixed resource name and added unit tests and javadoc comments

Author: subhash686

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

@@ -22,32 +22,37 @@
 import java.net.URLConnection;
 import java.util.Enumeration;
 
+/**
+ * Used to preload classes to support automatic priming for SnapStart
+ */
 public class ClassPreLoader {
     public static final String CLASSES_FILE = "classesloaded.txt";
-    public static void preloadClass(String classname, boolean initialize) {
-        try {
-            Class.forName(classname, initialize, ClassPreLoader.class.getClassLoader());
-        } catch (Throwable ignored) {
-        }
-    }
-    public static void preloadClasses(boolean initialize) {
+
+    /**
+     * Initializes the classes listed in the classesloaded resource
+     */
+    public static void preloadClasses() {
         try {
             Enumeration<URL> files = ClassPreLoader.class.getClassLoader().getResources(CLASSES_FILE);
+            // If there are multiple files, preload classes from all of them
             while (files.hasMoreElements()) {
                 URL url = files.nextElement();
                 URLConnection conn = url.openConnection();
                 conn.setUseCaches(false);
                 InputStream is = conn.getInputStream();
-                preloadClassesFromStream(is, initialize);
+                preloadClassesFromStream(is);
             }
         } catch (IOException ignored) {
+            // No action is required if preloading fails for any reason
         }
-        InputStream is = ClassPreLoader.class
-                .getResourceAsStream( CLASSES_FILE);
-        if (is != null)
-            preloadClassesFromStream(is, initialize);
     }
-    public static void preloadClassesFromStream(InputStream is, boolean initialize) {
+
+    /**
+     * Loads the list of classes passed as a stream
+     *
+     * @param is
+     */
+    private static void preloadClassesFromStream(InputStream is) {
         try (is;
              InputStreamReader isr = new InputStreamReader(is, StandardCharsets.UTF_8);
              BufferedReader reader = new BufferedReader(isr)) {
@@ -59,13 +64,11 @@ public static void preloadClassesFromStream(InputStream is, boolean initialize)
                 }
                 final String className = line.stripTrailing();
                 if (!className.isBlank()) {
-                    preloadClass(className, initialize);
+                    Class.forName(className, true, ClassPreLoader.class.getClassLoader());
                 }
             }
         } catch (Exception ignored) {
+            // No action is required if preloading fails for any reason
         }
     }
-    public void invokePreloadClasses(boolean initialize) {
-        preloadClasses(initialize);
-    }
 }

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

@@ -0,0 +1,53 @@
+package software.amazon.lambda.powertools.common.internal;
+
+import static org.mockito.Mockito.*;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.Collections;
+
+import org.junit.jupiter.api.Test;
+
+class ClassPreLoaderTest {
+
+    @Test
+    void preloadClasses_shouldIgnoreInvalidClassesAndLoadValidClasses() throws Exception {
+        // Mock the class loader with no resources
+        ClassLoader classLoader = mock(ClassLoader.class);
+        URL mockUrl = mock(URL.class);
+        URLConnection mockConnection = mock(URLConnection.class);
+        InputStream mockInputStream = new ByteArrayInputStream("java.lang.String\nInvalid.Class".getBytes());
+
+        when(mockUrl.openConnection()).thenReturn(mockConnection);
+        when(mockConnection.getInputStream()).thenReturn(mockInputStream);
+        when(classLoader.getResources(ClassPreLoader.CLASSES_FILE))
+                .thenReturn(Collections.enumeration(Collections.singletonList(mockUrl)));
+
+        // Inject the mocked class loader
+        Thread.currentThread().setContextClassLoader(classLoader);
+        // Call the method under test
+        ClassPreLoader.preloadClasses();
+
+        // Verify that only the valid class was loaded
+        Class.forName("java.lang.String", true, ClassPreLoader.class.getClassLoader());
+    }
+
+    @Test
+    void preloadClasses_shouldHandleEmptyResources() throws Exception {
+        // Mock the class loader with no resources
+        ClassLoader classLoader = mock(ClassLoader.class);
+        when(classLoader.getResources(ClassPreLoader.CLASSES_FILE))
+                .thenReturn(Collections.emptyEnumeration());
+
+        // Inject the mocked class loader
+        Thread.currentThread().setContextClassLoader(classLoader);
+
+        // Call the method under test
+        ClassPreLoader.preloadClasses();
+
+        // Verify no interactions with the class loader
+        verifyNoInteractions(classLoader);
+    }
+}

powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/internal/LambdaMetricsAspect.java

@@ -158,10 +158,9 @@ private void validateMetricsAndRefreshOnFailure(Metrics metrics) {
 
     @Override
     public void beforeCheckpoint(org.crac.Context<? extends Resource> context) throws Exception {
-        System.out.println("before preloading");
-        ClassPreLoader.preloadClasses(true);
-        System.out.println("after preloading");
+        ClassPreLoader.preloadClasses();
     }
+
     @Override
     public void afterRestore(org.crac.Context<? extends Resource> context) throws Exception {
     }