fix(convention): WW-5593 handle NoClassDefFoundError in action class scanning (#1469)

The PackageBasedActionConfigBuilder now catches NoClassDefFoundError in
addition to ClassNotFoundException when scanning for action classes.
This prevents application startup failures when classes have missing
optional dependencies (e.g., test classes depending on JUnit).

Changes:
- Add NoClassDefFoundError to catch block in getActionClassTest()
- Improve error message to suggest missing dependencies
- Add unit tests for both exception types

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: lukaszlenart

plugins/convention/src/main/java/org/apache/struts2/convention/PackageBasedActionConfigBuilder.java

@@ -682,8 +682,9 @@ public boolean test(ClassFinder.ClassInfo classInfo) {
 
                 try {
                     return inPackage && (nameMatches || (checkImplementsAction && org.apache.struts2.action.Action.class.isAssignableFrom(classInfo.get())));
-                } catch (ClassNotFoundException ex) {
-                    LOG.error("Unable to load class [{}]", classInfo.getName(), ex);
+                } catch (ClassNotFoundException | NoClassDefFoundError ex) {
+                    LOG.error("Unable to load class [{}]. Perhaps it exists but certain dependencies are not available?",
+                            classInfo.getName(), ex);
                     return false;
                 }
             }

plugins/convention/src/test/java/org/apache/struts2/convention/PackageBasedActionConfigBuilderTest.java

@@ -18,6 +18,10 @@
  */
 package org.apache.struts2.convention;
 
+import org.apache.struts2.result.ActionChainResult;
+import org.apache.struts2.util.finder.ClassFinder;
+import org.apache.struts2.util.finder.Test;
+
 import jakarta.servlet.ServletContext;
 import junit.framework.TestCase;
 import org.apache.commons.lang3.StringUtils;
@@ -131,6 +135,120 @@ public void setUp() throws Exception {
                 .bind();
     }
 
+    /**
+     * Tests that NoClassDefFoundError is properly caught and handled
+     * when scanning action classes with missing dependencies.
+     * <p>
+     * This is a regression test for WW-5593: Convention plugin fails with
+     * NoClassDefFoundError when classes have missing optional dependencies.
+     *
+     * @see <a href="https://issues.apache.org/jira/browse/WW-5593">WW-5593</a>
+     */
+    public void testNoClassDefFoundErrorHandling() throws Exception {
+        // Setup minimal configuration
+        ResultTypeConfig defaultResult = new ResultTypeConfig.Builder("dispatcher",
+                ServletDispatcherResult.class.getName()).defaultResultParam("location").build();
+        PackageConfig strutsDefault = makePackageConfig("struts-default", null, null, "dispatcher",
+                new ResultTypeConfig[]{defaultResult}, null, null, null, true);
+
+        final DummyContainer mockContainer = new DummyContainer();
+        Configuration configuration = new DefaultConfiguration() {
+            @Override
+            public Container getContainer() {
+                return mockContainer;
+            }
+        };
+        configuration.addPackageConfig("struts-default", strutsDefault);
+
+        ActionNameBuilder actionNameBuilder = new SEOActionNameBuilder("true", "-");
+        ObjectFactory of = new ObjectFactory();
+        of.setContainer(mockContainer);
+
+        mockContainer.setActionNameBuilder(actionNameBuilder);
+        mockContainer.setConventionsService(new ConventionsServiceImpl(""));
+
+        // Create the builder with a package that will trigger NoClassDefFoundError simulation
+        PackageBasedActionConfigBuilder builder = new PackageBasedActionConfigBuilder(
+                configuration, mockContainer, of, "false", "struts-default", "false");
+        builder.setActionPackages("org.apache.struts2.convention.actions.noclass");
+        builder.setActionSuffix("Action");
+
+        DefaultFileManagerFactory fileManagerFactory = new DefaultFileManagerFactory();
+        fileManagerFactory.setContainer(ActionContext.getContext().getContainer());
+        fileManagerFactory.setFileManager(new DefaultFileManager());
+        builder.setFileManagerFactory(fileManagerFactory);
+        builder.setProviderAllowlist(new ProviderAllowlist());
+
+        // The getActionClassTest() method returns a Test that should catch NoClassDefFoundError
+        Test<ClassFinder.ClassInfo> actionClassTest = builder.getActionClassTest();
+
+        // Create a mock ClassInfo that throws NoClassDefFoundError when get() is called
+        // Note: Class name must NOT end with "Action" suffix to ensure classInfo.get() is actually called
+        // (otherwise nameMatches=true and the condition short-circuits without calling get())
+        ClassFinder.ClassInfo mockClassInfo = EasyMock.createMock(ClassFinder.ClassInfo.class);
+        EasyMock.expect(mockClassInfo.getName()).andReturn("org.apache.struts2.convention.actions.noclass.MissingDependency").anyTimes();
+        EasyMock.expect(mockClassInfo.get()).andThrow(new NoClassDefFoundError("junit/framework/TestCase"));
+        EasyMock.replay(mockClassInfo);
+
+        // This should return false (class excluded) instead of throwing NoClassDefFoundError
+        boolean result = actionClassTest.test(mockClassInfo);
+        assertFalse("NoClassDefFoundError should be caught and class should be excluded", result);
+    }
+
+    /**
+     * Tests that ClassNotFoundException is still properly handled.
+     * This is a companion test to testNoClassDefFoundErrorHandling() to ensure
+     * the existing ClassNotFoundException handling still works.
+     */
+    public void testClassNotFoundExceptionHandling() throws Exception {
+        // Setup minimal configuration
+        ResultTypeConfig defaultResult = new ResultTypeConfig.Builder("dispatcher",
+                ServletDispatcherResult.class.getName()).defaultResultParam("location").build();
+        PackageConfig strutsDefault = makePackageConfig("struts-default", null, null, "dispatcher",
+                new ResultTypeConfig[]{defaultResult}, null, null, null, true);
+
+        final DummyContainer mockContainer = new DummyContainer();
+        Configuration configuration = new DefaultConfiguration() {
+            @Override
+            public Container getContainer() {
+                return mockContainer;
+            }
+        };
+        configuration.addPackageConfig("struts-default", strutsDefault);
+
+        ActionNameBuilder actionNameBuilder = new SEOActionNameBuilder("true", "-");
+        ObjectFactory of = new ObjectFactory();
+        of.setContainer(mockContainer);
+
+        mockContainer.setActionNameBuilder(actionNameBuilder);
+        mockContainer.setConventionsService(new ConventionsServiceImpl(""));
+
+        PackageBasedActionConfigBuilder builder = new PackageBasedActionConfigBuilder(
+                configuration, mockContainer, of, "false", "struts-default", "false");
+        builder.setActionPackages("org.apache.struts2.convention.actions.noclass");
+        builder.setActionSuffix("Action");
+
+        DefaultFileManagerFactory fileManagerFactory = new DefaultFileManagerFactory();
+        fileManagerFactory.setContainer(ActionContext.getContext().getContainer());
+        fileManagerFactory.setFileManager(new DefaultFileManager());
+        builder.setFileManagerFactory(fileManagerFactory);
+        builder.setProviderAllowlist(new ProviderAllowlist());
+
+        Test<ClassFinder.ClassInfo> actionClassTest = builder.getActionClassTest();
+
+        // Create a mock ClassInfo that throws ClassNotFoundException when get() is called
+        // Note: Class name must NOT end with "Action" suffix to ensure classInfo.get() is actually called
+        // (otherwise nameMatches=true and the condition short-circuits without calling get())
+        ClassFinder.ClassInfo mockClassInfo = EasyMock.createMock(ClassFinder.ClassInfo.class);
+        EasyMock.expect(mockClassInfo.getName()).andReturn("org.apache.struts2.convention.actions.noclass.MissingClass").anyTimes();
+        EasyMock.expect(mockClassInfo.get()).andThrow(new ClassNotFoundException("org.example.MissingClass"));
+        EasyMock.replay(mockClassInfo);
+
+        // This should return false (class excluded) instead of throwing ClassNotFoundException
+        boolean result = actionClassTest.test(mockClassInfo);
+        assertFalse("ClassNotFoundException should be caught and class should be excluded", result);
+    }
+
     public void testActionPackages() throws MalformedURLException {
         run("org.apache.struts2.convention.actions", null, null);
     }