Add default value to newCheckedInstanceOfProperty

Author: ppkarwasz

log4j-api/src/main/java/org/apache/logging/log4j/util/LoaderUtil.java

@@ -26,6 +26,7 @@
 import java.util.Enumeration;
 import java.util.LinkedHashSet;
 import java.util.Objects;
+import java.util.function.Supplier;
 
 /**
  * <em>Consider this class private.</em> Utility class for ClassLoaders.
@@ -328,11 +329,37 @@ public static <T> T newInstanceOf(final String className) throws ClassNotFoundEx
      * @since 2.5
      */
     public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
-            throws ClassNotFoundException, InvocationTargetException, InstantiationException,
-            IllegalAccessException, NoSuchMethodException {
+            throws ClassNotFoundException, InvocationTargetException, InstantiationException, IllegalAccessException,
+                    NoSuchMethodException {
+        return newCheckedInstanceOfProperty(propertyName, clazz, () -> null);
+    }
+
+    /**
+     * Loads and instantiates a class given by a property name.
+     *
+     * @param propertyName The property name to look up a class name for.
+     * @param clazz        The class to cast it to.
+     * @param defaultSupplier Supplier of a default value if the property is not present.
+     * @param <T>          The type to cast it to.
+     * @return new instance of the class given in the property or {@code null} if the property was unset.
+     * @throws ClassNotFoundException      if the class isn't available to the usual ClassLoaders
+     * @throws ExceptionInInitializerError if an exception was thrown while initializing the class
+     * @throws LinkageError                if the linkage of the class fails for any other reason
+     * @throws ClassCastException          if the class is not compatible with the generic type parameter provided
+     * @throws NoSuchMethodException       if no zero-arg constructor exists
+     * @throws SecurityException           if this class is not allowed to access declared members of the provided class
+     * @throws IllegalAccessException      if the class can't be instantiated through a public constructor
+     * @throws InstantiationException      if the provided class is abstract or an interface
+     * @throws InvocationTargetException   if an exception is thrown by the constructor
+     * @since 2.22
+     */
+    public static <T> T newCheckedInstanceOfProperty(
+            final String propertyName, final Class<T> clazz, final Supplier<T> defaultSupplier)
+            throws ClassNotFoundException, InvocationTargetException, InstantiationException, IllegalAccessException,
+                    NoSuchMethodException {
         final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
         if (className == null) {
-            return null;
+            return defaultSupplier.get();
         }
         return newCheckedInstanceOf(className, clazz);
     }

log4j-core/src/main/java/org/apache/logging/log4j/core/async/DisruptorUtil.java

@@ -84,31 +84,25 @@ static int calculateRingBufferSize(final String propertyName) {
     }
 
     static ExceptionHandler<RingBufferLogEvent> getAsyncLoggerExceptionHandler() {
-        ExceptionHandler<RingBufferLogEvent> handler = null;
         try {
-            handler =
-                    LoaderUtil.newCheckedInstanceOfProperty(LOGGER_EXCEPTION_HANDLER_PROPERTY, ExceptionHandler.class);
+            return LoaderUtil.newCheckedInstanceOfProperty(
+                    LOGGER_EXCEPTION_HANDLER_PROPERTY, ExceptionHandler.class, AsyncLoggerDefaultExceptionHandler::new);
         } catch (final ReflectiveOperationException e) {
             LOGGER.debug("Invalid AsyncLogger.ExceptionHandler value: {}", e.getMessage(), e);
+            return new AsyncLoggerDefaultExceptionHandler();
         }
-        if (handler != null) {
-            return handler;
-        }
-        return new AsyncLoggerDefaultExceptionHandler();
     }
 
     static ExceptionHandler<AsyncLoggerConfigDisruptor.Log4jEventWrapper> getAsyncLoggerConfigExceptionHandler() {
-        ExceptionHandler<AsyncLoggerConfigDisruptor.Log4jEventWrapper> handler = null;
         try {
-            handler = LoaderUtil.newCheckedInstanceOfProperty(
-                    LOGGER_CONFIG_EXCEPTION_HANDLER_PROPERTY, ExceptionHandler.class);
+            return LoaderUtil.newCheckedInstanceOfProperty(
+                    LOGGER_CONFIG_EXCEPTION_HANDLER_PROPERTY,
+                    ExceptionHandler.class,
+                    AsyncLoggerConfigDefaultExceptionHandler::new);
         } catch (final ReflectiveOperationException e) {
             LOGGER.debug("Invalid AsyncLogger.ExceptionHandler value: {}", e.getMessage(), e);
+            return new AsyncLoggerConfigDefaultExceptionHandler();
         }
-        if (handler != null) {
-            return handler;
-        }
-        return new AsyncLoggerConfigDefaultExceptionHandler();
     }
 
     /**

log4j-core/src/main/java/org/apache/logging/log4j/core/config/LoggerConfig.java

@@ -82,15 +82,18 @@ public class LoggerConfig extends AbstractFilterable implements LocationAware {
 
     static {
         try {
-            LOG_EVENT_FACTORY =
-                    LoaderUtil.newCheckedInstanceOfProperty(Constants.LOG4J_LOG_EVENT_FACTORY, LogEventFactory.class);
+            LOG_EVENT_FACTORY = LoaderUtil.newCheckedInstanceOfProperty(
+                    Constants.LOG4J_LOG_EVENT_FACTORY,
+                    LogEventFactory.class,
+                    LoggerConfig::createDefaultLogEventFactory);
         } catch (final Exception ex) {
             LOGGER.error("Unable to create LogEventFactory: {}", ex.getMessage(), ex);
+            LOG_EVENT_FACTORY = createDefaultLogEventFactory();
         }
-        if (LOG_EVENT_FACTORY == null) {
-            LOG_EVENT_FACTORY =
-                    Constants.ENABLE_THREADLOCALS ? new ReusableLogEventFactory() : new DefaultLogEventFactory();
-        }
+    }
+
+    private static LogEventFactory createDefaultLogEventFactory() {
+        return Constants.ENABLE_THREADLOCALS ? new ReusableLogEventFactory() : new DefaultLogEventFactory();
     }
 
     @PluginBuilderFactory

log4j-core/src/main/java/org/apache/logging/log4j/core/impl/ContextDataInjectorFactory.java

@@ -67,17 +67,15 @@ public class ContextDataInjectorFactory {
      * @see ContextDataInjector
      */
     public static ContextDataInjector createInjector() {
-        ContextDataInjector injector = null;
         try {
-            injector =
-                    LoaderUtil.newCheckedInstanceOfProperty(CONTEXT_DATA_INJECTOR_PROPERTY, ContextDataInjector.class);
+            return LoaderUtil.newCheckedInstanceOfProperty(
+                    CONTEXT_DATA_INJECTOR_PROPERTY,
+                    ContextDataInjector.class,
+                    ContextDataInjectorFactory::createDefaultInjector);
         } catch (final ReflectiveOperationException e) {
             StatusLogger.getLogger().warn("Could not create ContextDataInjector: {}", e.getMessage(), e);
+            return createDefaultInjector();
         }
-        if (injector != null) {
-            return injector;
-        }
-        return createDefaultInjector();
     }
 
     private static ContextDataInjector createDefaultInjector() {