/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.commons.logging.impl;
  
  import java.io.PrintWriter;
  import java.io.StringWriter;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.net.URL;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.Hashtable;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogConfigurationException;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * Concrete subclass of {@link LogFactory} that implements the
   * following algorithm to dynamically select a logging implementation
   * class to instantiate a wrapper for:
   * <ul>
   * <li>Use a factory configuration attribute named
   *     {@code org.apache.commons.logging.Log} to identify the
   *     requested implementation class.</li>
   * <li>Use the {@code org.apache.commons.logging.Log} system property
   *     to identify the requested implementation class.</li>
   * <li>If <em>Log4J</em> is available, return an instance of
   *     {@code org.apache.commons.logging.impl.Log4JLogger}.</li>
   * <li>If <em>JDK 1.4 or later</em> is available, return an instance of
   *     {@code org.apache.commons.logging.impl.Jdk14Logger}.</li>
   * <li>Otherwise, return an instance of
   *     {@code org.apache.commons.logging.impl.SimpleLog}.</li>
   * </ul>
   * <p>
   * If the selected {@link Log} implementation class has a
   * {@code setLogFactory()} method that accepts a {@link LogFactory}
   * parameter, this method will be called on each newly created instance
   * to identify the associated factory.  This makes factory configuration
   * attributes available to the Log instance, if it so desires.
   * </p>
   * <p>
   * This factory will remember previously created {@code Log} instances
   * for the same name, and will return them on repeated requests to the
   * {@code getInstance()} method.
   * </p>
   */
  public class LogFactoryImpl extends LogFactory {
  
      /** Log4JLogger class name */
      private static final String LOGGING_IMPL_LOG4J_LOGGER = "org.apache.commons.logging.impl.Log4JLogger";
  
      /** Jdk14Logger class name */
      private static final String LOGGING_IMPL_JDK14_LOGGER = "org.apache.commons.logging.impl.Jdk14Logger";
  
      /** Jdk13LumberjackLogger class name */
      private static final String LOGGING_IMPL_LUMBERJACK_LOGGER = "org.apache.commons.logging.impl.Jdk13LumberjackLogger";
  
      /** SimpleLog class name */
      private static final String LOGGING_IMPL_SIMPLE_LOGGER = "org.apache.commons.logging.impl.SimpleLog";
  
      private static final String PKG_IMPL="org.apache.commons.logging.impl.";
  
      private static final int PKG_LEN = PKG_IMPL.length();
  
      /**
       * An empty immutable {@code String} array.
       */
      private static final String[] EMPTY_STRING_ARRAY = {};
  
      /**
       * The name ({@code org.apache.commons.logging.Log}) of the system
       * property identifying our {@link Log} implementation class.
       */
      public static final String LOG_PROPERTY = "org.apache.commons.logging.Log";
  
      /**
       * The deprecated system property used for backwards compatibility with
       * old versions of JCL.
       */
      protected static final String LOG_PROPERTY_OLD = "org.apache.commons.logging.log";
  
      /**
      * The name ({@code org.apache.commons.logging.Log.allowFlawedContext})
      * of the system property which can be set true/false to
      * determine system behavior when a bad context class loader is encountered.
      * When set to false, a LogConfigurationException is thrown if
      * LogFactoryImpl is loaded via a child class loader of the TCCL (this
      * should never happen in sane systems).
      * <p>
      * Default behavior: true (tolerates bad context class loaders)
      * </p>
      * <p>
      * See also method setAttribute.
      * </p>
      */
     public static final String ALLOW_FLAWED_CONTEXT_PROPERTY =
         "org.apache.commons.logging.Log.allowFlawedContext";
 
     /**
      * The name ({@code org.apache.commons.logging.Log.allowFlawedDiscovery})
      * of the system property which can be set true/false to
      * determine system behavior when a bad logging adapter class is
      * encountered during logging discovery. When set to false, an
      * exception will be thrown and the app will fail to start. When set
      * to true, discovery will continue (though the user might end up
      * with a different logging implementation than they expected).
      * <p>
      * Default behavior: true (tolerates bad logging adapters)
      * </p>
      * <p>
      * See also method setAttribute.
      * </p>
      */
     public static final String ALLOW_FLAWED_DISCOVERY_PROPERTY =
         "org.apache.commons.logging.Log.allowFlawedDiscovery";
 
     /**
      * The name ({@code org.apache.commons.logging.Log.allowFlawedHierarchy})
      * of the system property which can be set true/false to
      * determine system behavior when a logging adapter class is
      * encountered which has bound to the wrong Log class implementation.
      * When set to false, an exception will be thrown and the app will fail
      * to start. When set to true, discovery will continue (though the user
      * might end up with a different logging implementation than they expected).
      * <p>
      * Default behavior: true (tolerates bad Log class hierarchy)
      * </p>
      * <p>
      * See also method setAttribute.
      * </p>
      */
     public static final String ALLOW_FLAWED_HIERARCHY_PROPERTY =
         "org.apache.commons.logging.Log.allowFlawedHierarchy";
 
     /**
      * The names of classes that will be tried (in order) as logging
      * adapters. Each class is expected to implement the Log interface,
      * and to throw NoClassDefFound or ExceptionInInitializerError when
      * loaded if the underlying logging library is not available. Any
      * other error indicates that the underlying logging library is available
      * but broken/unusable for some reason.
      */
     private static final String[] DISCOVER_CLASSES = {
             LOGGING_IMPL_JDK14_LOGGER,
             LOGGING_IMPL_SIMPLE_LOGGER
     };
 
     /**
      * Workaround for bug in Java1.2; in theory this method is not needed. {@link LogFactory#getClassLoader(Class)}.
      *
      * @param clazz See {@link LogFactory#getClassLoader(Class)}.
      * @return See {@link LogFactory#getClassLoader(Class)}.
      * @since 1.1
      */
     protected static ClassLoader getClassLoader(final Class<?> clazz) {
         return LogFactory.getClassLoader(clazz);
     }
 
     /**
      * Gets the context ClassLoader.
      * This method is a workaround for a Java 1.2 compiler bug.
      *
      * @return the context ClassLoader
      * @since 1.1
      */
     protected static ClassLoader getContextClassLoader() throws LogConfigurationException {
         return LogFactory.getContextClassLoader();
     }
 
     /**
      * Calls LogFactory.directGetContextClassLoader under the control of an
      * AccessController class. This means that Java code running under a
      * security manager that forbids access to ClassLoaders will still work
      * if this class is given appropriate privileges, even when the caller
      * doesn't have such privileges. Without using an AccessController, the
      * the entire call stack must have the privilege before the call is
      * allowed.
      *
      * @return the context class loader associated with the current thread,
      * or null if security doesn't allow it.
      *
      * @throws LogConfigurationException if there was some weird error while
      * attempting to get the context class loader.
      *
      * @throws SecurityException if the current Java security policy doesn't
      * allow this class to access the context class loader.
      */
     private static ClassLoader getContextClassLoaderInternal()
             throws LogConfigurationException {
         return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) LogFactory::directGetContextClassLoader);
     }
 
     /**
      * Reads the specified system property, using an AccessController so that
      * the property can be read if JCL has been granted the appropriate
      * security rights even if the calling code has not.
      * <p>
      * Take care not to expose the value returned by this method to the
      * calling application in any way; otherwise the calling app can use that
      * info to access data that should not be available to it.
      * </p>
      */
     private static String getSystemProperty(final String key, final String def)
             throws SecurityException {
         return AccessController.doPrivileged((PrivilegedAction<String>) () -> System.getProperty(key, def));
     }
 
     /**
      * Workaround for bug in Java1.2; in theory this method is not needed.
      *
      * @return Same as {@link LogFactory#isDiagnosticsEnabled()}.
      * @see LogFactory#isDiagnosticsEnabled()
      */
     protected static boolean isDiagnosticsEnabled() {
         return LogFactory.isDiagnosticsEnabled();
     }
 
     /** Utility method to safely trim a string. */
     private static String trim(final String src) {
         if (src == null) {
             return null;
         }
         return src.trim();
     }
 
     /**
      * Determines whether logging classes should be loaded using the thread-context
      * class loader, or via the class loader that loaded this LogFactoryImpl class.
      */
     private boolean useTCCL = true;
 
     /**
      * The string prefixed to every message output by the logDiagnostic method.
      */
     private String diagnosticPrefix;
 
     /**
      * Configuration attributes.
      */
     protected Hashtable<String, Object> attributes = new Hashtable<>();
 
     /**
      * The {@link org.apache.commons.logging.Log} instances that have
      * already been created, keyed by logger name.
      */
     protected Hashtable<String, Log> instances = new Hashtable<>();
 
     /**
      * Name of the class implementing the Log interface.
      */
     private String logClassName;
 
     /**
      * The one-argument constructor of the
      * {@link org.apache.commons.logging.Log}
      * implementation class that will be used to create new instances.
      * This value is initialized by {@code getLogConstructor()},
      * and then returned repeatedly.
      */
     protected Constructor<?> logConstructor;
 
     /**
      * The signature of the Constructor to be used.
      */
     protected Class<?>[] logConstructorSignature = { String.class };
 
     /**
      * The one-argument {@code setLogFactory} method of the selected
      * {@link org.apache.commons.logging.Log} method, if it exists.
      */
     protected Method logMethod;
 
     /**
      * The signature of the {@code setLogFactory} method to be used.
      */
     protected Class<?>[] logMethodSignature = { LogFactory.class };
 
     /**
      * See getBaseClassLoader and initConfiguration.
      */
     private boolean allowFlawedContext;
 
     /**
      * See handleFlawedDiscovery and initConfiguration.
      */
     private boolean allowFlawedDiscovery;
 
     /**
      * See handleFlawedHierarchy and initConfiguration.
      */
     private boolean allowFlawedHierarchy;
 
     /**
      * Public no-arguments constructor required by the lookup mechanism.
      */
     public LogFactoryImpl() {
         initDiagnostics();  // method on this object
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Instance created.");
         }
     }
 
     /**
      * Attempts to load the given class, find a suitable constructor,
      * and instantiate an instance of Log.
      *
      * @param logAdapterClassName class name of the Log implementation
      * @param logCategory  argument to pass to the Log implementation's constructor
      * @param affectState  {@code true} if this object's state should
      *  be affected by this method call, {@code false} otherwise.
      * @return  an instance of the given class, or null if the logging
      *  library associated with the specified adapter is not available.
      * @throws LogConfigurationException if there was a serious error with
      *  configuration and the handleFlawedDiscovery method decided this
      *  problem was fatal.
      */
     private Log createLogFromClass(final String logAdapterClassName, final String logCategory, final boolean affectState) throws LogConfigurationException {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Attempting to instantiate '" + logAdapterClassName + "'");
         }
         final Object[] params = { logCategory };
         Log logAdapter = null;
         Constructor<?> constructor = null;
         Class<?> logAdapterClass = null;
         ClassLoader currentCL = getBaseClassLoader();
         for (;;) {
             // Loop through the class loader hierarchy trying to find
             // a viable class loader.
             logDiagnostic("Trying to load '" + logAdapterClassName + "' from class loader " + objectId(currentCL));
             try {
                 if (isDiagnosticsEnabled()) {
                     // Show the location of the first occurrence of the .class file
                     // in the classpath. This is the location that ClassLoader.loadClass
                     // will load the class from -- unless the class loader is doing
                     // something weird.
                     URL url;
                     final String resourceName = logAdapterClassName.replace('.', '/') + ".class";
                     if (currentCL != null) {
                         url = currentCL.getResource(resourceName);
                     } else {
                         url = ClassLoader.getSystemResource(resourceName + ".class");
                     }
                     if (url == null) {
                         logDiagnostic("Class '" + logAdapterClassName + "' [" + resourceName + "] cannot be found.");
                     } else {
                         logDiagnostic("Class '" + logAdapterClassName + "' was found at '" + url + "'");
                     }
                 }
                 Class<?> clazz;
                 try {
                     clazz = Class.forName(logAdapterClassName, true, currentCL);
                 } catch (final ClassNotFoundException originalClassNotFoundException) {
                     // The current class loader was unable to find the log adapter
                     // in this or any ancestor class loader. There's no point in
                     // trying higher up in the hierarchy in this case.
                     String msg = originalClassNotFoundException.getMessage();
                     logDiagnostic("The log adapter '" + logAdapterClassName + "' is not available via class loader " + objectId(currentCL) + ": " + trim(msg));
                     try {
                         // Try the class class loader.
                         // This may work in cases where the TCCL
                         // does not contain the code executed or JCL.
                         // This behavior indicates that the application
                         // classloading strategy is not consistent with the
                         // Java 1.2 classloading guidelines but JCL can
                         // and so should handle this case.
                         clazz = Class.forName(logAdapterClassName);
                     } catch (final ClassNotFoundException secondaryClassNotFoundException) {
                         // no point continuing: this adapter isn't available
                         msg = secondaryClassNotFoundException.getMessage();
                         logDiagnostic("The log adapter '" + logAdapterClassName + "' is not available via the LogFactoryImpl class class loader: " + trim(msg));
                         break;
                     }
                 }
                 constructor = clazz.getConstructor(logConstructorSignature);
                 final Object o = constructor.newInstance(params);
                 // Note that we do this test after trying to create an instance
                 // [rather than testing Log.class.isAssignableFrom(c)] so that
                 // we don't complain about Log hierarchy problems when the
                 // adapter couldn't be instantiated anyway.
                 if (o instanceof Log) {
                     logAdapterClass = clazz;
                     logAdapter = (Log) o;
                     break;
                 }
                 // Oops, we have a potential problem here. An adapter class
                 // has been found and its underlying lib is present too, but
                 // there are multiple Log interface classes available making it
                 // impossible to cast to the type the caller wanted. We
                 // certainly can't use this logger, but we need to know whether
                 // to keep on discovering or terminate now.
                 //
                 // The handleFlawedHierarchy method will throw
                 // LogConfigurationException if it regards this problem as
                 // fatal, and just return if not.
                 handleFlawedHierarchy(currentCL, clazz);
             } catch (final NoClassDefFoundError e) {
                 // We were able to load the adapter but it had references to
                 // other classes that could not be found. This simply means that
                 // the underlying logger library is not present in this or any
                 // ancestor class loader. There's no point in trying higher up
                 // in the hierarchy in this case.
                 final String msg = e.getMessage();
                 logDiagnostic("The log adapter '" + logAdapterClassName + "' is missing dependencies when loaded via class loader " + objectId(currentCL) +
                         ": " + trim(msg));
                 break;
             } catch (final ExceptionInInitializerError e) {
                 // A static initializer block or the initializer code associated
                 // with a static variable on the log adapter class has thrown
                 // an exception.
                 //
                 // We treat this as meaning the adapter's underlying logging
                 // library could not be found.
                 final String msg = e.getMessage();
                 logDiagnostic("The log adapter '" + logAdapterClassName + "' is unable to initialize itself when loaded via class loader " +
                         objectId(currentCL) + ": " + trim(msg));
                 break;
             } catch (final LogConfigurationException e) {
                 // call to handleFlawedHierarchy above must have thrown
                 // a LogConfigurationException, so just throw it on
                 throw e;
             } catch (final Throwable t) {
                 handleThrowable(t); // may re-throw t
                 // handleFlawedDiscovery will determine whether this is a fatal
                 // problem or not. If it is fatal, then a LogConfigurationException
                 // will be thrown.
                 handleFlawedDiscovery(logAdapterClassName, t);
             }
             if (currentCL == null) {
                 break;
             }
             // try the parent class loader
             // currentCL = currentCL.getParent();
             currentCL = getParentClassLoader(currentCL);
         }
         if (logAdapterClass != null && affectState) {
             // We've succeeded, so set instance fields
             this.logClassName = logAdapterClassName;
             this.logConstructor = constructor;
             // Identify the {@code setLogFactory} method (if there is one)
             try {
                 this.logMethod = logAdapterClass.getMethod("setLogFactory", logMethodSignature);
                 logDiagnostic("Found method setLogFactory(LogFactory) in '" + logAdapterClassName + "'");
             } catch (final Throwable t) {
                 handleThrowable(t); // may re-throw t
                 this.logMethod = null;
                 logDiagnostic("[INFO] '" + logAdapterClassName + "' from class loader " + objectId(currentCL) + " does not declare optional method " +
                         "setLogFactory(LogFactory)");
             }
             logDiagnostic("Log adapter '" + logAdapterClassName + "' from class loader " + objectId(logAdapterClass.getClassLoader()) +
                     " has been selected for use.");
         }
         return logAdapter;
     }
 
         // Static Methods
     //
     // These methods only defined as workarounds for a java 1.2 bug;
     // theoretically none of these are needed.
 
     /**
      * Attempts to create a Log instance for the given category name.
      * Follows the discovery process described in the class Javadoc.
      *
      * @param logCategory the name of the log category
      * @throws LogConfigurationException if an error in discovery occurs,
      * or if no adapter at all can be instantiated
      */
     private Log discoverLogImplementation(final String logCategory)
             throws LogConfigurationException {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Discovering a Log implementation...");
         }
         initConfiguration();
         Log result = null;
         // See if the user specified the Log implementation to use
         final String specifiedLogClassName = findUserSpecifiedLogClassName();
         if (specifiedLogClassName != null) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Attempting to load user-specified log class '" + specifiedLogClassName + "'...");
             }
             result = createLogFromClass(specifiedLogClassName, logCategory, true);
             if (result == null) {
                 final StringBuilder messageBuffer = new StringBuilder("User-specified log class '");
                 messageBuffer.append(specifiedLogClassName);
                 messageBuffer.append("' cannot be found or is not useable.");
                 // Mistyping or misspelling names is a common fault.
                 // Construct a good error message, if we can
                 informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LOG4J_LOGGER);
                 informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_JDK14_LOGGER);
                 informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LUMBERJACK_LOGGER);
                 informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_SIMPLE_LOGGER);
                 throw new LogConfigurationException(messageBuffer.toString());
             }
             return result;
         }
         // No user specified log; try to discover what's on the classpath
         //
         // Note that we deliberately loop here over classesToDiscover and
         // expect method createLogFromClass to loop over the possible source
         // class loaders. The effect is:
         // for each discoverable log adapter
         // for each possible class loader
         // see if it works
         //
         // It appears reasonable at first glance to do the opposite:
         // for each possible class loader
         // for each discoverable log adapter
         // see if it works
         //
         // The latter certainly has advantages for user-installable logging
         // libraries such as Log4j; in a webapp for example this code should
         // first check whether the user has provided any of the possible
         // logging libraries before looking in the parent class loader.
         // Unfortunately, however, Jdk14Logger will always work in jvm>=1.4,
         // and SimpleLog will always work in any JVM. So the loop would never
         // ever look for logging libraries in the parent classpath. Yet many
         // users would expect that putting Log4j there would cause it to be
         // detected (and this is the historical JCL behavior). So we go with
         // the first approach. A user that has bundled a specific logging lib
         // in a webapp should use a commons-logging.properties file or a
         // service file in META-INF to force use of that logging lib anyway,
         // rather than relying on discovery.
         if (isDiagnosticsEnabled()) {
             logDiagnostic("No user-specified Log implementation; performing discovery using the standard supported logging implementations...");
         }
         for (int i = 0; i < DISCOVER_CLASSES.length && result == null; ++i) {
             result = createLogFromClass(DISCOVER_CLASSES[i], logCategory, true);
         }
         if (result == null) {
             throw new LogConfigurationException("No suitable Log implementation");
         }
         return result;
     }
 
     /**
      * Checks system properties and the attribute map for
      * a Log implementation specified by the user under the
      * property names {@link #LOG_PROPERTY} or {@link #LOG_PROPERTY_OLD}.
      *
      * @return class name specified by the user, or {@code null}
      */
     private String findUserSpecifiedLogClassName() {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Trying to get log class from attribute '" + LOG_PROPERTY + "'");
         }
         String specifiedClass = (String) getAttribute(LOG_PROPERTY);
         if (specifiedClass == null) { // @deprecated
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Trying to get log class from attribute '" + LOG_PROPERTY_OLD + "'");
             }
             specifiedClass = (String) getAttribute(LOG_PROPERTY_OLD);
         }
         if (specifiedClass == null) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Trying to get log class from system property '" + LOG_PROPERTY + "'");
             }
             try {
                 specifiedClass = getSystemProperty(LOG_PROPERTY, null);
             } catch (final SecurityException e) {
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic("No access allowed to system property '" + LOG_PROPERTY + "' - " + e.getMessage());
                 }
             }
         }
         if (specifiedClass == null) { // @deprecated
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Trying to get log class from system property '" + LOG_PROPERTY_OLD + "'");
             }
             try {
                 specifiedClass = getSystemProperty(LOG_PROPERTY_OLD, null);
             } catch (final SecurityException e) {
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic("No access allowed to system property '" + LOG_PROPERTY_OLD + "' - " + e.getMessage());
                 }
             }
         }
         // Remove any whitespace; it's never valid in a class name so its
         // presence just means a user mistake. As we know what they meant,
         // we may as well strip the spaces.
         if (specifiedClass != null) {
             specifiedClass = specifiedClass.trim();
         }
         return specifiedClass;
     }
 
     /**
      * Gets the configuration attribute with the specified name (if any),
      * or {@code null} if there is no such attribute.
      *
      * @param name Name of the attribute to return
      */
     @Override
     public Object getAttribute(final String name) {
         return attributes.get(name);
     }
 
     /**
      * Gets an array containing the names of all currently defined
      * configuration attributes.  If there are no such attributes, a zero
      * length array is returned.
      */
     @Override
     public String[] getAttributeNames() {
         return attributes.keySet().toArray(EMPTY_STRING_ARRAY);
     }
 
     /**
      * Gets the class loader from which we should try to load the logging
      * adapter classes.
      * <p>
      * This method usually returns the context class loader. However if it
      * is discovered that the class loader which loaded this class is a child
      * of the context class loader <em>and</em> the allowFlawedContext option
      * has been set then the class loader which loaded this class is returned
      * instead.
      * </p>
      * <p>
      * The only time when the class loader which loaded this class is a
      * descendant (rather than the same as or an ancestor of the context
      * class loader) is when an app has created custom class loaders but
      * failed to correctly set the context class loader. This is a bug in
      * the calling application; however we provide the option for JCL to
      * simply generate a warning rather than fail outright.
      * </p>
      */
     private ClassLoader getBaseClassLoader() throws LogConfigurationException {
         final ClassLoader thisClassLoader = getClassLoader(LogFactoryImpl.class);
         if (!useTCCL) {
             return thisClassLoader;
         }
         final ClassLoader contextClassLoader = getContextClassLoaderInternal();
         final ClassLoader baseClassLoader = getLowestClassLoader(contextClassLoader, thisClassLoader);
         if (baseClassLoader == null) {
             // The two class loaders are not part of a parent child relationship.
             // In some classloading setups (e.g. JBoss with its
             // UnifiedLoaderRepository) this can still work, so if user hasn't
             // forbidden it, just return the contextClassLoader.
             if (!allowFlawedContext) {
                 throw new LogConfigurationException(
                         "Bad class loader hierarchy; LogFactoryImpl was loaded via a class loader that is not related to the current context class loader.");
             }
             if (isDiagnosticsEnabled()) {
                 logDiagnostic(
                         "[WARNING] the context class loader is not part of a parent-child relationship with the class loader that loaded LogFactoryImpl.");
             }
             // If contextClassLoader were null, getLowestClassLoader() would
             // have returned thisClassLoader. The fact we are here means
             // contextClassLoader is not null, so we can just return it.
             return contextClassLoader;
         }
         if (baseClassLoader != contextClassLoader) {
             // We really should just use the contextClassLoader as the starting
             // point for scanning for log adapter classes. However it is expected
             // that there are a number of broken systems out there which create
             // custom class loaders but fail to set the context class loader so
             // we handle those flawed systems anyway.
             if (!allowFlawedContext) {
                 throw new LogConfigurationException(
                         "Bad class loader hierarchy; LogFactoryImpl was loaded via a class loader that is not related to the current context class loader.");
             }
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Warning: the context class loader is an ancestor of the class loader that loaded LogFactoryImpl; it should be" +
                         " the same or a descendant. The application using commons-logging should ensure the context class loader is used correctly.");
             }
         }
         return baseClassLoader;
     }
 
     /**
      * Gets the setting for the user-configurable behavior specified by key.
      * If nothing has explicitly been set, then return dflt.
      */
     private boolean getBooleanConfiguration(final String key, final boolean dflt) {
         final String val = getConfigurationValue(key);
         if (val == null) {
             return dflt;
         }
         return Boolean.parseBoolean(val);
     }
 
     /**
      * Attempt to find an attribute (see method setAttribute) or a
      * system property with the provided name and return its value.
      * <p>
      * The attributes associated with this object are checked before
      * system properties in case someone has explicitly called setAttribute,
      * or a configuration property has been set in a commons-logging.properties
      * file.
      * </p>
      *
      * @return the value associated with the property, or null.
      */
     private String getConfigurationValue(final String property) {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("[ENV] Trying to get configuration for item " + property);
         }
         final Object valueObj = getAttribute(property);
         if (valueObj != null) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("[ENV] Found LogFactory attribute [" + valueObj + "] for " + property);
             }
             return valueObj.toString();
         }
         if (isDiagnosticsEnabled()) {
             logDiagnostic("[ENV] No LogFactory attribute found for " + property);
         }
         try {
             // warning: minor security hole here, in that we potentially read a system
             // property that the caller cannot, then output it in readable form as a
             // diagnostic message. However it's only ever JCL-specific properties
             // involved here, so the harm is truly trivial.
             final String value = getSystemProperty(property, null);
             if (value != null) {
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic("[ENV] Found system property [" + value + "] for " + property);
                 }
                 return value;
             }
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("[ENV] No system property found for property " + property);
             }
         } catch (final SecurityException e) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("[ENV] Security prevented reading system property " + property);
             }
         }
         if (isDiagnosticsEnabled()) {
             logDiagnostic("[ENV] No configuration defined for item " + property);
         }
         return null;
     }
 
     /**
      * Convenience method to derive a name from the specified class and
      * call {@code getInstance(String)} with it.
      *
      * @param clazz Class for which a suitable Log name will be derived
      * @throws LogConfigurationException if a suitable {@code Log}
      *  instance cannot be returned
      */
     @Override
     public Log getInstance(final Class<?> clazz) throws LogConfigurationException {
         return getInstance(clazz.getName());
     }
 
     /**
      * Construct (if necessary) and return a {@code Log} instance,
      * using the factory's current set of configuration attributes.
      *
      * <p><strong>NOTE</strong> - Depending upon the implementation of
      * the {@code LogFactory} you are using, the {@code Log}
      * instance you are returned may or may not be local to the current
      * application, and may or may not be returned again on a subsequent
      * call with the same name argument.</p>
      *
      * @param name Logical name of the {@code Log} instance to be
      *  returned (the meaning of this name is only known to the underlying
      *  logging implementation that is being wrapped)
      *
      * @throws LogConfigurationException if a suitable {@code Log}
      *  instance cannot be returned
      */
     @Override
     public Log getInstance(final String name) throws LogConfigurationException {
         return instances.computeIfAbsent(name, this::newInstance);
     }
 
     /**
      * Gets the fully qualified Java class name of the {@link Log} implementation we will be using.
      *
      * @return the fully qualified Java class name of the {@link Log} implementation we will be using.
      * @deprecated Never invoked by this class; subclasses should not assume it will be.
      */
     @Deprecated
     protected String getLogClassName() {
         if (logClassName == null) {
             discoverLogImplementation(getClass().getName());
         }
         return logClassName;
     }
 
     /**
      * Gets the {@code Constructor} that can be called to instantiate new {@link org.apache.commons.logging.Log} instances.
      * <p>
      * <strong>IMPLEMENTATION NOTE</strong> - Race conditions caused by calling this method from more than one thread are ignored, because the same
      * {@code Constructor} instance will ultimately be derived in all circumstances.
      * </p>
      *
      * @return the {@code Constructor} that can be called to instantiate new {@link org.apache.commons.logging.Log} instances.
      * @throws LogConfigurationException if a suitable constructor cannot be returned
      * @deprecated Never invoked by this class; subclasses should not assume it will be.
      */
     @Deprecated
     protected Constructor<?> getLogConstructor() throws LogConfigurationException {
         // Return the previously identified Constructor (if any)
         if (logConstructor == null) {
             discoverLogImplementation(getClass().getName());
         }
         return logConstructor;
     }
     //  ------------------------------------------------------ Private Methods
 
     /**
      * Given two related class loaders, return the one which is a child of
      * the other.
      *
      * @param c1 is a class loader (including the null class loader)
      * @param c2 is a class loader (including the null class loader)
      * @return c1 if it has c2 as an ancestor, c2 if it has c1 as an ancestor,
      * and null if neither is an ancestor of the other.
      */
     private ClassLoader getLowestClassLoader(final ClassLoader c1, final ClassLoader c2) {
         // TODO: use AccessController when dealing with class loaders here
         if (c1 == null) {
             return c2;
         }
         if (c2 == null) {
             return c1;
         }
         ClassLoader current;
         // scan c1's ancestors to find c2
         current = c1;
         while (current != null) {
             if (current == c2) {
                 return c1;
             }
             // current = current.getParent();
             current = getParentClassLoader(current);
         }
         // scan c2's ancestors to find c1
         current = c2;
         while (current != null) {
             if (current == c1) {
                 return c2;
             }
             // current = current.getParent();
             current = getParentClassLoader(current);
         }
         return null;
     }
 
     /**
      * Fetch the parent class loader of a specified class loader.
      * <p>
      * If a SecurityException occurs, null is returned.
      * </p>
      * <p>
      * Note that this method is non-static merely so logDiagnostic is available.
      * </p>
      */
     private ClassLoader getParentClassLoader(final ClassLoader cl) {
         try {
             return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) () -> cl.getParent());
         } catch (final SecurityException ex) {
             logDiagnostic("[SECURITY] Unable to obtain parent class loader");
             return null;
         }
     }
 
     /**
      * Generates an internal diagnostic logging of the discovery failure and
      * then throws a {@code LogConfigurationException} that wraps
      * the passed {@code Throwable}.
      *
      * @param logAdapterClassName is the class name of the Log implementation
      * that could not be instantiated. Cannot be {@code null}.
      * @param discoveryFlaw is the Throwable created by the class loader
      * @throws LogConfigurationException    ALWAYS
      */
     private void handleFlawedDiscovery(final String logAdapterClassName, final Throwable discoveryFlaw) {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Could not instantiate Log '" + logAdapterClassName + "' -- " + discoveryFlaw.getClass().getName() + ": " +
                     discoveryFlaw.getLocalizedMessage());
             if (discoveryFlaw instanceof InvocationTargetException) {
                 // Ok, the lib is there but while trying to create a real underlying
                 // logger something failed in the underlying lib; display info about
                 // that if possible.
                 final InvocationTargetException ite = (InvocationTargetException) discoveryFlaw;
                 final Throwable cause = ite.getTargetException();
                 if (cause != null) {
                     logDiagnostic("... InvocationTargetException: " + cause.getClass().getName() + ": " + cause.getLocalizedMessage());
                     if (cause instanceof ExceptionInInitializerError) {
                         final ExceptionInInitializerError eiie = (ExceptionInInitializerError) cause;
                         final Throwable cause2 = eiie.getCause();
                         if (cause2 != null) {
                             final StringWriter sw = new StringWriter();
                             cause2.printStackTrace(new PrintWriter(sw, true));
                             logDiagnostic("... ExceptionInInitializerError: " + sw.toString());
                         }
                     }
                 }
             }
         }
         if (!allowFlawedDiscovery) {
             throw new LogConfigurationException(discoveryFlaw);
         }
     }
 
     /**
      * Report a problem loading the log adapter, then either return
      * (if the situation is considered recoverable) or throw a
      * LogConfigurationException.
      * <p>
      * There are two possible reasons why we successfully loaded the
      * specified log adapter class then failed to cast it to a Log object:
      * </p>
      * <ol>
      * <li>the specific class just doesn't implement the Log interface
      *     (user screwed up), or</li>
      * <li> the specified class has bound to a Log class loaded by some other
      *      class loader; Log@ClassLoaderX cannot be cast to Log@ClassLoaderY.</li>
      * </ol>
      * <p>
      * Here we try to figure out which case has occurred so we can give the
      * user some reasonable feedback.
      * </p>
      *
      * @param badClassLoader is the class loader we loaded the problem class from,
      * ie it is equivalent to badClass.getClassLoader().
      *
      * @param badClass is a Class object with the desired name, but which
      * does not implement Log correctly.
      *
      * @throws LogConfigurationException when the situation
      * should not be recovered from.
      */
     private void handleFlawedHierarchy(final ClassLoader badClassLoader, final Class<?> badClass) throws LogConfigurationException {
         boolean implementsLog = false;
         final String logInterfaceName = Log.class.getName();
         final Class<?>[] interfaces = badClass.getInterfaces();
         for (final Class<?> element : interfaces) {
             if (logInterfaceName.equals(element.getName())) {
                 implementsLog = true;
                 break;
             }
         }
         if (implementsLog) {
             // the class does implement an interface called Log, but
             // it is in the wrong class loader
             if (isDiagnosticsEnabled()) {
                 try {
                     final ClassLoader logInterfaceClassLoader = getClassLoader(Log.class);
                     logDiagnostic("Class '" + badClass.getName() + "' was found in class loader " + objectId(badClassLoader) +
                             ". It is bound to a Log interface which is not the one loaded from class loader " + objectId(logInterfaceClassLoader));
                 } catch (final Throwable t) {
                     handleThrowable(t); // may re-throw t
                     logDiagnostic("Error while trying to output diagnostics about bad class '" + badClass + "'");
                 }
             }
             if (!allowFlawedHierarchy) {
                 final StringBuilder msg = new StringBuilder();
                 msg.append("Terminating logging for this context ");
                 msg.append("due to bad log hierarchy. ");
                 msg.append("You have more than one version of '");
                 msg.append(Log.class.getName());
                 msg.append("' visible.");
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic(msg.toString());
                 }
                 throw new LogConfigurationException(msg.toString());
             }
             if (isDiagnosticsEnabled()) {
                 final StringBuilder msg = new StringBuilder();
                 msg.append("Warning: bad log hierarchy. ");
                 msg.append("You have more than one version of '");
                 msg.append(Log.class.getName());
                 msg.append("' visible.");
                 logDiagnostic(msg.toString());
             }
         } else {
             // this is just a bad adapter class
             if (!allowFlawedDiscovery) {
                 final StringBuilder msg = new StringBuilder();
                 msg.append("Terminating logging for this context. ");
                 msg.append("Log class '");
                 msg.append(badClass.getName());
                 msg.append("' does not implement the Log interface.");
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic(msg.toString());
                 }
                 throw new LogConfigurationException(msg.toString());
             }
             if (isDiagnosticsEnabled()) {
                 final StringBuilder msg = new StringBuilder();
                 msg.append("[WARNING] Log class '");
                 msg.append(badClass.getName());
                 msg.append("' does not implement the Log interface.");
                 logDiagnostic(msg.toString());
             }
         }
     }
 
     /**
      * Appends message if the given name is similar to the candidate.
      *
      * @param messageBuffer {@code StringBuffer} the message should be appended to,
      * not null
      * @param name the (trimmed) name to be test against the candidate, not null
      * @param candidate the candidate name (not null)
      */
     private void informUponSimilarName(final StringBuilder messageBuffer, final String name, final String candidate) {
         if (name.equals(candidate)) {
             // Don't suggest a name that is exactly the same as the one the
             // user tried...
             return;
         }
         // If the user provides a name that is in the right package, and gets
         // the first 5 characters of the adapter class right (ignoring case),
         // then suggest the candidate adapter class name.
         if (name.regionMatches(true, 0, candidate, 0, PKG_LEN + 5)) {
             messageBuffer.append(" Did you mean '");
             messageBuffer.append(candidate);
             messageBuffer.append("'?");
         }
     }
 
     /**
      * Initializes a number of variables that control the behavior of this
      * class and that can be tweaked by the user. This is done when the first
      * logger is created, not in the constructor of this class, because we
      * need to give the user a chance to call method setAttribute in order to
      * configure this object.
      */
     private void initConfiguration() {
         allowFlawedContext = getBooleanConfiguration(ALLOW_FLAWED_CONTEXT_PROPERTY, true);
         allowFlawedDiscovery = getBooleanConfiguration(ALLOW_FLAWED_DISCOVERY_PROPERTY, true);
         allowFlawedHierarchy = getBooleanConfiguration(ALLOW_FLAWED_HIERARCHY_PROPERTY, true);
     }
 
     /**
      * Initializes a string that uniquely identifies this instance,
      * including which class loader the object was loaded from.
      * <p>
      * This string will later be prefixed to each "internal logging" message
      * emitted, so that users can clearly see any unexpected behavior.
      * <p>
      * Note that this method does not detect whether internal logging is
      * enabled or not, nor where to output stuff if it is; that is all
      * handled by the parent LogFactory class. This method just computes
      * its own unique prefix for log messages.
      */
     private void initDiagnostics() {
         // It would be nice to include an identifier of the context class loader
         // that this LogFactoryImpl object is responsible for. However that
         // isn't possible as that information isn't available. It is possible
         // to figure this out by looking at the logging from LogFactory to
         // see the context & impl ids from when this object was instantiated,
         // in order to link the impl id output as this object's prefix back to
         // the context it is intended to manage.
         // Note that this prefix should be kept consistent with that
         // in LogFactory.
         @SuppressWarnings("unchecked")
         final Class<LogFactoryImpl> clazz = (Class<LogFactoryImpl>) this.getClass();
         final ClassLoader classLoader = getClassLoader(clazz);
         String classLoaderName;
         try {
             if (classLoader == null) {
                 classLoaderName = "BOOTLOADER";
             } else {
                 classLoaderName = objectId(classLoader);
             }
         } catch (final SecurityException e) {
             classLoaderName = "UNKNOWN";
         }
         diagnosticPrefix = "[LogFactoryImpl@" + System.identityHashCode(this) + " from " + classLoaderName + "] ";
     }
 
     /**
      * Tests whether <em>JDK 1.3 with Lumberjack</em> logging available.
      *
      * @return whether <em>JDK 1.3 with Lumberjack</em> logging available.
      * @deprecated Never invoked by this class; subclasses should not assume it will be.
      */
     @Deprecated
     protected boolean isJdk13LumberjackAvailable() {
         return isLogLibraryAvailable("Jdk13Lumberjack", "org.apache.commons.logging.impl.Jdk13LumberjackLogger");
     }
 
     /**
      * Tests {@code true} whether <em>JDK 1.4 or later</em> logging is available. Also checks that the {@code Throwable} class supports {@code getStackTrace()},
      * which is required by Jdk14Logger.
      *
      * @return Whether <em>JDK 1.4 or later</em> logging is available.
      * @deprecated Never invoked by this class; subclasses should not assume it will be.
      */
     @Deprecated
     protected boolean isJdk14Available() {
         return isLogLibraryAvailable("Jdk14", "org.apache.commons.logging.impl.Jdk14Logger");
     }
 
     /**
      * Tests whether a <em>Log4J</em> implementation available.
      *
      * @return whether a <em>Log4J</em> implementation available.
      * @deprecated Never invoked by this class; subclasses should not assume it will be.
      */
     @Deprecated
     protected boolean isLog4JAvailable() {
         return isLogLibraryAvailable("Log4J", LOGGING_IMPL_LOG4J_LOGGER);
     }
 
     /**
      * Tests whether a particular logging library is present and available for use. Note that this does <em>not</em> affect the future behavior of this class.
      */
     private boolean isLogLibraryAvailable(final String name, final String className) {
         if (isDiagnosticsEnabled()) {
             logDiagnostic("Checking for '" + name + "'.");
         }
         try {
             final Log log = createLogFromClass(className, this.getClass().getName(), // dummy category
                     false);
             if (log == null) {
                 if (isDiagnosticsEnabled()) {
                     logDiagnostic("Did not find '" + name + "'.");
                 }
                 return false;
             }
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Found '" + name + "'.");
             }
             return true;
         } catch (final LogConfigurationException e) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Logging system '" + name + "' is available but not useable.");
             }
             return false;
         }
     }
 
     /**
      * Output a diagnostic message to a user-specified destination (if the
      * user has enabled diagnostic logging).
      *
      * @param msg diagnostic message
      * @since 1.1
      */
     protected void logDiagnostic(final String msg) {
         if (isDiagnosticsEnabled()) {
             logRawDiagnostic(diagnosticPrefix + msg);
         }
     }
 
     /**
      * Create and return a new {@link org.apache.commons.logging.Log} instance for the specified name.
      *
      * @param name Name of the new logger
      * @return a new {@link org.apache.commons.logging.Log}
      * @throws LogConfigurationException if a new instance cannot be created
      */
     protected Log newInstance(final String name) throws LogConfigurationException {
         Log instance;
         try {
             if (logConstructor == null) {
                 instance = discoverLogImplementation(name);
             } else {
                 final Object[] params = { name };
                 instance = (Log) logConstructor.newInstance(params);
             }
             if (logMethod != null) {
                 final Object[] params = { this };
                 logMethod.invoke(instance, params);
             }
             return instance;
         } catch (final LogConfigurationException lce) {
             // this type of exception means there was a problem in discovery
             // and we've already output diagnostics about the issue, etc.;
             // just pass it on
             throw lce;
         } catch (final InvocationTargetException e) {
             // A problem occurred invoking the Constructor or Method
             // previously discovered
             final Throwable c = e.getTargetException();
             throw new LogConfigurationException(c == null ? e : c);
         } catch (final Throwable t) {
             handleThrowable(t); // may re-throw t
             // A problem occurred invoking the Constructor or Method
             // previously discovered
             throw new LogConfigurationException(t);
         }
     }
 
     /**
      * Releases any internal references to previously created
      * {@link org.apache.commons.logging.Log}
      * instances returned by this factory.  This is useful in environments
      * like servlet containers, which implement application reloading by
      * throwing away a ClassLoader.  Dangling references to objects in that
      * class loader would prevent garbage collection.
      */
     @Override
     public void release() {
         logDiagnostic("Releasing all known loggers");
         instances.clear();
     }
 
     /**
      * Remove any configuration attribute associated with the specified name.
      * If there is no such attribute, no action is taken.
      *
      * @param name Name of the attribute to remove
      */
     @Override
     public void removeAttribute(final String name) {
         attributes.remove(name);
     }
 
     /**
      * Sets the configuration attribute with the specified name.  Calling
      * this with a {@code null} value is equivalent to calling
      * {@code removeAttribute(name)}.
      * <p>
      * This method can be used to set logging configuration programmatically
      * rather than via system properties. It can also be used in code running
      * within a container (such as a webapp) to configure behavior on a
      * per-component level instead of globally as system properties would do.
      * To use this method instead of a system property, call
      * </p>
      * <pre>
      * LogFactory.getFactory().setAttribute(...)
      * </pre>
      * <p>
      * This must be done before the first Log object is created; configuration
      * changes after that point will be ignored.
      * </p>
      * <p>
      * This method is also called automatically if LogFactory detects a
      * commons-logging.properties file; every entry in that file is set
      * automatically as an attribute here.
      * </p>
      *
      * @param name Name of the attribute to set
      * @param value Value of the attribute to set, or {@code null}
      *  to remove any setting for this attribute
      */
     @Override
     public void setAttribute(final String name, final Object value) {
         if (logConstructor != null) {
             logDiagnostic("setAttribute: call too late; configuration already performed.");
         }
         if (value == null) {
             attributes.remove(name);
         } else {
             attributes.put(name, value);
         }
         if (name.equals(TCCL_KEY)) {
             useTCCL = value != null && Boolean.parseBoolean(value.toString());
         }
     }
 }