/*
    * 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
    *
    *      http://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;
  
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintStream;
  import java.lang.ref.WeakReference;
  import java.net.URL;
  import java.net.URLConnection;
  import java.nio.charset.StandardCharsets;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.Enumeration;
  import java.util.Hashtable;
  import java.util.Iterator;
  import java.util.Objects;
  import java.util.Properties;
  import java.util.ServiceConfigurationError;
  import java.util.ServiceLoader;
  import java.util.function.Supplier;
  
  /**
   * Factory for creating {@link Log} instances, with discovery and
   * configuration features similar to that employed by standard Java APIs
   * such as JAXP.
   * <p>
   * <strong>IMPLEMENTATION NOTE</strong> - This implementation is heavily
   * based on the SAXParserFactory and DocumentBuilderFactory implementations
   * (corresponding to the JAXP pluggability APIs) found in Apache Xerces.
   * </p>
   */
  public abstract class LogFactory {
      // Implementation note re AccessController usage
      //
      // It is important to keep code invoked via an AccessController to small
      // auditable blocks. Such code must carefully evaluate all user input
      // (parameters, system properties, configuration file contents, etc). As an
      // example, a Log implementation should not write to its log file
      // with an AccessController anywhere in the call stack, otherwise an
      // insecure application could configure the log implementation to write
      // to a protected file using the privileges granted to JCL rather than
      // to the calling application.
      //
      // Under no circumstance should a non-private method return data that is
      // retrieved via an AccessController. That would allow an insecure application
      // to invoke that method and obtain data that it is not permitted to have.
      //
      // Invoking user-supplied code with an AccessController set is not a major
      // issue (for example, invoking the constructor of the class specified by
      // HASHTABLE_IMPLEMENTATION_PROPERTY). That class will be in a different
      // trust domain, and therefore must have permissions to do whatever it
      // is trying to do regardless of the permissions granted to JCL. There is
      // a slight issue in that untrusted code may point that environment variable
      // to another trusted library, in which case the code runs if both that
      // library and JCL have the necessary permissions even when the untrusted
      // caller does not. That's a pretty hard route to exploit though.
  
      /**
       * The name ({@code priority}) of the key in the configuration file used to
       * specify the priority of that particular configuration file. The associated value
       * is a floating-point number; higher values take priority over lower values.
       */
      public static final String PRIORITY_KEY = "priority";
  
      /**
       * The name ({@code use_tccl}) of the key in the configuration file used
       * to specify whether logging classes should be loaded via the thread
       * context class loader (TCCL), or not. By default, the TCCL is used.
       */
      public static final String TCCL_KEY = "use_tccl";
  
      /**
       * The name ({@code org.apache.commons.logging.LogFactory}) of the property
       * used to identify the LogFactory implementation
       * class name. This can be used as a system property, or as an entry in a
       * configuration properties file.
       */
      public static final String FACTORY_PROPERTY = "org.apache.commons.logging.LogFactory";
  
      private static final String FACTORY_LOG4J_API = "org.apache.commons.logging.impl.Log4jApiLogFactory";
  
      private static final String LOG4J_TO_SLF4J_BRIDGE = "org.apache.logging.slf4j.SLF4JProvider";
 
     private static final String FACTORY_SLF4J = "org.apache.commons.logging.impl.Slf4jLogFactory";
 
     /**
      * The fully qualified class name of the fallback {@code LogFactory}
      * implementation class to use, if no other can be found.
      */
     public static final String FACTORY_DEFAULT = "org.apache.commons.logging.impl.LogFactoryImpl";
 
     /**
      * The name ({@code commons-logging.properties}) of the properties file to search for.
      */
     public static final String FACTORY_PROPERTIES = "commons-logging.properties";
 
     /**
      * JDK 1.3+ <a href="https://java.sun.com/j2se/1.3/docs/guide/jar/jar.html#Service%20Provider">
      * 'Service Provider' specification</a>.
      */
     protected static final String SERVICE_ID = "META-INF/services/org.apache.commons.logging.LogFactory";
 
     /**
      * The name ({@code org.apache.commons.logging.diagnostics.dest})
      * of the property used to enable internal commons-logging
      * diagnostic output, in order to get information on what logging
      * implementations are being discovered, what class loaders they
      * are loaded through, etc.
      * <p>
      * If a system property of this name is set then the value is
      * assumed to be the name of a file. The special strings
      * STDOUT or STDERR (case-sensitive) indicate output to
      * System.out and System.err respectively.
      * <p>
      * Diagnostic logging should be used only to debug problematic
      * configurations and should not be set in normal production use.
      */
     public static final String DIAGNOSTICS_DEST_PROPERTY = "org.apache.commons.logging.diagnostics.dest";
 
     /**
      * When null (the usual case), no diagnostic output will be
      * generated by LogFactory or LogFactoryImpl. When non-null,
      * interesting events will be written to the specified object.
      */
     private static final PrintStream DIAGNOSTICS_STREAM;
 
     /**
      * A string that gets prefixed to every message output by the
      * logDiagnostic method, so that users can clearly see which
      * LogFactory class is generating the output.
      */
     private static final String DIAGNOSTICS_PREFIX;
 
     /**
      * Setting this system property
      * ({@code org.apache.commons.logging.LogFactory.HashtableImpl})
      * value allows the {@code Hashtable} used to store
      * class loaders to be substituted by an alternative implementation.
      * <p>
      * <strong>Note:</strong> {@code LogFactory} will print:
      * </p>
      * <pre>
      * [ERROR] LogFactory: Load of custom hash table failed
      * </pre>
      * <p>
      * to system error and then continue using a standard Hashtable.
      * </p>
      * <p>
      * <strong>Usage:</strong> Set this property when Java is invoked
      * and {@code LogFactory} will attempt to load a new instance
      * of the given implementation class.
      * For example, running the following ant scriplet:
      * </p>
      * <pre>
      *  &lt;java classname="${test.runner}" fork="yes" failonerror="${test.failonerror}"&gt;
      *     ...
      *     &lt;sysproperty
      *        key="org.apache.commons.logging.LogFactory.HashtableImpl"
      *        value="org.apache.commons.logging.AltHashtable"/&gt;
      *  &lt;/java&gt;
      * </pre>
      * <p>
      * will mean that {@code LogFactory} will load an instance of
      * {@code org.apache.commons.logging.AltHashtable}.
      * </p>
      * <p>
      * A typical use case is to allow a custom
      * Hashtable implementation using weak references to be substituted.
      * This will allow class loaders to be garbage collected without
      * the need to release them (on 1.3+ JVMs only, of course ;).
      * </p>
      */
     public static final String HASHTABLE_IMPLEMENTATION_PROPERTY = "org.apache.commons.logging.LogFactory.HashtableImpl";
 
     /** Name used to load the weak hash table implementation by names. */
     private static final String WEAK_HASHTABLE_CLASSNAME = "org.apache.commons.logging.impl.WeakHashtable";
 
     /**
      * A reference to the class loader that loaded this class. This is the
      * same as LogFactory.class.getClassLoader(). However computing this
      * value isn't quite as simple as that, as we potentially need to use
      * AccessControllers etc. It's more efficient to compute it once and
      * cache it here.
      */
     private static final WeakReference<ClassLoader> thisClassLoaderRef;
 
     /**
      * Maximum number of {@link ServiceLoader} errors to ignore, while
      * looking for an implementation.
      */
     private static final int MAX_BROKEN_SERVICES = 3;
 
     /**
      * The previously constructed {@code LogFactory} instances, keyed by
      * the {@code ClassLoader} with which it was created.
      */
     protected static Hashtable<ClassLoader, LogFactory> factories;
 
     /**
      * Previously constructed {@code LogFactory} instance as in the
      * {@code factories} map, but for the case where
      * {@code getClassLoader} returns {@code null}.
      * This can happen when:
      * <ul>
      * <li>using JDK1.1 and the calling code is loaded via the system
      *  class loader (very common)</li>
      * <li>using JDK1.2+ and the calling code is loaded via the boot
      *  class loader (only likely for embedded systems work).</li>
      * </ul>
      * Note that {@code factories} is a <em>Hashtable</em> (not a HashMap),
      * and hash tables don't allow null as a key.
      * @deprecated since 1.1.2
      */
     @Deprecated
     protected static volatile LogFactory nullClassLoaderFactory;
 
     static {
         // note: it's safe to call methods before initDiagnostics (though
         // diagnostic output gets discarded).
         final ClassLoader thisClassLoader = getClassLoader(LogFactory.class);
         thisClassLoaderRef = new WeakReference<>(thisClassLoader);
         // In order to avoid confusion where multiple instances of JCL are
         // being used via different class loaders within the same app, we
         // ensure each logged message has a prefix of form
         // [LogFactory from class loader OID]
         //
         // Note that this prefix should be kept consistent with that
         // in LogFactoryImpl. However here we don't need to output info
         // about the actual *instance* of LogFactory, as all methods that
         // output diagnostics from this class are static.
         String classLoaderName;
         try {
             classLoaderName = thisClassLoader != null ? objectId(thisClassLoader) : "BOOTLOADER"; 
         } catch (final SecurityException e) {
             classLoaderName = "UNKNOWN";
         }
         DIAGNOSTICS_PREFIX = "[LogFactory from " + classLoaderName + "] ";
         DIAGNOSTICS_STREAM = initDiagnostics();
         logClassLoaderEnvironment(LogFactory.class);
         factories = createFactoryStore();
         logDiagnostic("BOOTSTRAP COMPLETED");
     }
 
     /**
      * Remember this factory, so later calls to LogFactory.getCachedFactory
      * can return the previously created object (together with all its
      * cached Log objects).
      *
      * @param classLoader should be the current context class loader. Note that
      *  this can be null under some circumstances; this is ok.
      * @param factory should be the factory to cache. This should never be null.
      */
     private static void cacheFactory(final ClassLoader classLoader, final LogFactory factory) {
         // Ideally we would assert(factory != null) here. However reporting
         // errors from within a logging implementation is a little tricky!
         if (factory != null) {
             if (classLoader == null) {
                 nullClassLoaderFactory = factory;
             } else {
                 factories.put(classLoader, factory);
             }
         }
     }
 
     /**
      * Creates a LogFactory object or a LogConfigurationException object.
      *
      * @param factoryClassName Factory class.
      * @param classLoader      used to load the specified factory class. This is expected to be either the TCCL or the class loader which loaded this class.
      *                         Note that the class loader which loaded this class might be "null" (for example, the boot loader) for embedded systems.
      * @return either a LogFactory object or a LogConfigurationException object.
      * @since 1.1
      */
     protected static Object createFactory(final String factoryClassName, final ClassLoader classLoader) {
         // This will be used to diagnose bad configurations
         // and allow a useful message to be sent to the user
         Class<?> logFactoryClass = null;
         try {
             if (classLoader != null) {
                 try {
                     // First the given class loader param (thread class loader)
 
                     // Warning: must typecast here & allow exception
                     // to be generated/caught & recast properly.
                     logFactoryClass = classLoader.loadClass(factoryClassName);
                     if (LogFactory.class.isAssignableFrom(logFactoryClass)) {
                         if (isDiagnosticsEnabled()) {
                             logDiagnostic("Loaded class " + logFactoryClass.getName() + " from class loader " + objectId(classLoader));
                         }
                     } else //
                     // This indicates a problem with the ClassLoader tree.
                     // An incompatible ClassLoader was used to load the
                     // implementation.
                     // As the same classes
                     // must be available in multiple class loaders,
                     // it is very likely that multiple JCL jars are present.
                     // The most likely fix for this
                     // problem is to remove the extra JCL jars from the
                     // ClassLoader hierarchy.
                     //
                     if (isDiagnosticsEnabled()) {
                         logDiagnostic("Factory class " + logFactoryClass.getName() + " loaded from class loader " + objectId(logFactoryClass.getClassLoader())
                                 + " does not extend '" + LogFactory.class.getName() + "' as loaded by this class loader.");
                         logHierarchy("[BAD CL TREE] ", classLoader);
                     }
                     // Force a ClassCastException
                     return LogFactory.class.cast(logFactoryClass.getConstructor().newInstance());
 
                 } catch (final ClassNotFoundException ex) {
                     if (classLoader == thisClassLoaderRef.get()) {
                         // Nothing more to try, onwards.
                         if (isDiagnosticsEnabled()) {
                             logDiagnostic("Unable to locate any class called '" + factoryClassName + "' via class loader " + objectId(classLoader));
                         }
                         throw ex;
                     }
                     // ignore exception, continue
                 } catch (final NoClassDefFoundError e) {
                     if (classLoader == thisClassLoaderRef.get()) {
                         // Nothing more to try, onwards.
                         if (isDiagnosticsEnabled()) {
                             logDiagnostic("Class '" + factoryClassName + "' cannot be loaded" + " via class loader " + objectId(classLoader)
                                     + " - it depends on some other class that cannot be found.");
                         }
                         throw e;
                     }
                     // ignore exception, continue
                 } catch (final ClassCastException e) {
                     if (classLoader == thisClassLoaderRef.get()) {
                         // There's no point in falling through to the code below that
                         // tries again with thisClassLoaderRef, because we've just tried
                         // loading with that loader (not the TCCL). Just throw an
                         // appropriate exception here.
                         final boolean implementsLogFactory = implementsLogFactory(logFactoryClass);
                         //
                         // Construct a good message: users may not actual expect that a custom implementation
                         // has been specified. Several well known containers use this mechanism to adapt JCL
                         // to their native logging system.
                         //
                         final StringBuilder msg = new StringBuilder();
                         msg.append("The application has specified that a custom LogFactory implementation should be used but Class '");
                         msg.append(factoryClassName);
                         msg.append("' cannot be converted to '");
                         msg.append(LogFactory.class.getName());
                         msg.append("'. ");
                         if (implementsLogFactory) {
                             msg.append("The conflict is caused by the presence of multiple LogFactory classes in incompatible class loaders. Background can");
                             msg.append(" be found in https://commons.apache.org/logging/tech.html. If you have not explicitly specified a custom LogFactory");
                             msg.append(" then it is likely that the container has set one without your knowledge. In this case, consider using the ");
                             msg.append("commons-logging-adapters.jar file or specifying the standard LogFactory from the command line. ");
                         } else {
                             msg.append("Please check the custom implementation. ");
                         }
                         msg.append("Help can be found at https://commons.apache.org/logging/troubleshooting.html.");
                         logDiagnostic(msg.toString());
                         throw new ClassCastException(msg.toString());
                     }
                     // Ignore exception, continue. Presumably the class loader was the
                     // TCCL; the code below will try to load the class via thisClassLoaderRef.
                     // This will handle the case where the original calling class is in
                     // a shared classpath but the TCCL has a copy of LogFactory and the
                     // specified LogFactory implementation; we will fall back to using the
                     // LogFactory implementation from the same class loader as this class.
                     //
                     // Issue: this doesn't handle the reverse case, where this LogFactory
                     // is in the webapp, and the specified LogFactory implementation is
                     // in a shared classpath. In that case:
                     // (a) the class really does implement LogFactory (bad log msg above)
                     // (b) the fallback code will result in exactly the same problem.
                 }
             }
 
             /*
              * At this point, either classLoader == null, OR classLoader was unable to load factoryClass.
              *
              * In either case, we call Class.forName, which is equivalent to LogFactory.class.getClassLoader().load(name), that is, we ignore the class loader
              * parameter the caller passed, and fall back to trying the class loader associated with this class. See the Javadoc for the newFactory method for
              * more info on the consequences of this.
              *
              * Notes: * LogFactory.class.getClassLoader() may return 'null' if LogFactory is loaded by the bootstrap class loader.
              */
             // Warning: must typecast here & allow exception
             // to be generated/caught & recast properly.
             if (isDiagnosticsEnabled()) {
                 logDiagnostic(
                         "Unable to load factory class via class loader " + objectId(classLoader) + " - trying the class loader associated with this LogFactory.");
             }
             logFactoryClass = Class.forName(factoryClassName);
             // Force a ClassCastException
             return LogFactory.class.cast(logFactoryClass.getConstructor().newInstance());
         } catch (final Exception e) {
             // Check to see if we've got a bad configuration
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Unable to create LogFactory instance.");
             }
             if (logFactoryClass != null && !LogFactory.class.isAssignableFrom(logFactoryClass)) {
                 return new LogConfigurationException("The chosen LogFactory implementation does not extend LogFactory. Please check your configuration.", e);
             }
             return new LogConfigurationException(e);
         }
     }
 
     /**
      * Creates the hash table which will be used to store a map of
      * (context class loader -> logfactory-object). Version 1.2+ of Java
      * supports "weak references", allowing a custom Hashtable class
      * to be used which uses only weak references to its keys. Using weak
      * references can fix memory leaks on webapp unload in some cases (though
      * not all). Version 1.1 of Java does not support weak references, so we
      * must dynamically determine which we are using. And just for fun, this
      * code also supports the ability for a system property to specify an
      * arbitrary Hashtable implementation name.
      * <p>
      * Note that the correct way to ensure no memory leaks occur is to ensure
      * that LogFactory.release(contextClassLoader) is called whenever a
      * webapp is undeployed.
      * </p>
      */
     private static Hashtable<ClassLoader, LogFactory> createFactoryStore() {
         Hashtable<ClassLoader, LogFactory> result = null;
         String storeImplementationClass;
         try {
             storeImplementationClass = getSystemProperty(HASHTABLE_IMPLEMENTATION_PROPERTY, null);
         } catch (final SecurityException ex) {
             // Permissions don't allow this to be accessed. Default to the "modern"
             // weak hash table implementation if it is available.
             storeImplementationClass = null;
         }
         if (storeImplementationClass == null) {
             storeImplementationClass = WEAK_HASHTABLE_CLASSNAME;
         }
         try {
             final Class<Hashtable<ClassLoader, LogFactory>> implementationClass = (Class<Hashtable<ClassLoader, LogFactory>>) Class
                     .forName(storeImplementationClass);
             result = implementationClass.getConstructor().newInstance();
         } catch (final Throwable t) {
             handleThrowable(t); // may re-throw t
             // ignore
             if (!WEAK_HASHTABLE_CLASSNAME.equals(storeImplementationClass)) {
                 // if the user's trying to set up a custom implementation, give a clue
                 if (isDiagnosticsEnabled()) {
                     // use internal logging to issue the warning
                     logDiagnostic("[ERROR] LogFactory: Load of custom Hashtable failed");
                 } else {
                     // we *really* want this output, even if diagnostics weren't
                     // explicitly enabled by the user.
                     System.err.println("[ERROR] LogFactory: Load of custom Hashtable failed");
                 }
             }
         }
         if (result == null) {
             result = new Hashtable<>();
         }
         return result;
     }
 
     /**
      * Gets the thread context class loader if available; otherwise return null.
      * <p>
      * Most/all code should call getContextClassLoaderInternal rather than
      * calling this method directly.
      * </p>
      * <p>
      * The thread context class loader is available for JDK 1.2
      * or later, if certain security conditions are met.
      * </p>
      * <p>
      * Note that no internal logging is done within this method because
      * this method is called every time LogFactory.getLogger() is called,
      * and we don't want too much output generated here.
      * </p>
      *
      * @throws LogConfigurationException if a suitable class loader
      *  cannot be identified.
      * @return the thread's context class loader or {@code null} if the Java security
      *  policy forbids access to the context class loader from one of the classes
      *  in the current call stack.
      * @since 1.1
      */
     protected static ClassLoader directGetContextClassLoader() throws LogConfigurationException {
         ClassLoader classLoader = null;
         try {
             classLoader = Thread.currentThread().getContextClassLoader();
         } catch (final SecurityException ignore) {
             // getContextClassLoader() throws SecurityException when
             // the context class loader isn't an ancestor of the
             // calling class's class loader, or if security
             // permissions are restricted.
             //
             // We ignore this exception to be consistent with the previous
             // behavior (e.g. 1.1.3 and earlier).
         }
         // Return the selected class loader
         return classLoader;
     }
 
     /**
      * Gets a cached log factory (keyed by contextClassLoader)
      *
      * @param contextClassLoader is the context class loader associated
      * with the current thread. This allows separate LogFactory objects
      * per component within a container, provided each component has
      * a distinct context class loader set. This parameter may be null
      * in JDK1.1, and in embedded systems where jcl-using code is
      * placed in the bootclasspath.
      *
      * @return the factory associated with the specified class loader if
      *  one has previously been created, or null if this is the first time
      *  we have seen this particular class loader.
      */
     private static LogFactory getCachedFactory(final ClassLoader contextClassLoader) {
         if (contextClassLoader == null) {
             // We have to handle this specially, as factories is a Hashtable
             // and those don't accept null as a key value.
             //
             // nb: nullClassLoaderFactory might be null. That's ok.
             return nullClassLoaderFactory;
         }
         return factories.get(contextClassLoader);
     }
 
     /**
      * Safely get access to the class loader for the specified class.
      * <p>
      * Theoretically, calling getClassLoader can throw a security exception,
      * and so should be done under an AccessController in order to provide
      * maximum flexibility. However in practice people don't appear to use
      * security policies that forbid getClassLoader calls. So for the moment
      * all code is written to call this method rather than Class.getClassLoader,
      * so that we could put AccessController stuff in this method without any
      * disruption later if we need to.
      * </p>
      * <p>
      * Even when using an AccessController, however, this method can still
      * throw SecurityException. Commons Logging basically relies on the
      * ability to access class loaders. A policy that forbids all
      * class loader access will also prevent commons-logging from working:
      * currently this method will throw an exception preventing the entire app
      * from starting up. Maybe it would be good to detect this situation and
      * just disable all commons-logging? Not high priority though - as stated
      * above, security policies that prevent class loader access aren't common.
      * </p>
      * <p>
      * Note that returning an object fetched via an AccessController would
      * technically be a security flaw anyway; untrusted code that has access
      * to a trusted JCL library could use it to fetch the class loader for
      * a class even when forbidden to do so directly.
      * </p>
      *
      * @param clazz Class.
      * @return a ClassLoader.
      *
      * @since 1.1
      */
     protected static ClassLoader getClassLoader(final Class<?> clazz) {
         try {
             return clazz.getClassLoader();
         } catch (final SecurityException ex) {
             logDiagnostic(() -> "Unable to get class loader for class '" + clazz + "' due to security restrictions - " + ex.getMessage());
             throw ex;
         }
     }
 
     /**
      * Gets a user-provided configuration file.
      * <p>
      * The classpath of the specified classLoader (usually the context class loader)
      * is searched for properties files of the specified name. If none is found,
      * null is returned. If more than one is found, then the file with the greatest
      * value for its PRIORITY property is returned. If multiple files have the
      * same PRIORITY value then the first in the classpath is returned.
      * </p>
      * <p>
      * This differs from the 1.0.x releases; those always use the first one found.
      * However as the priority is a new field, this change is backwards compatible.
      * </p>
      * <p>
      * The purpose of the priority field is to allow a webserver administrator to
      * override logging settings in all webapps by placing a commons-logging.properties
      * file in a shared classpath location with a priority > 0; this overrides any
      * commons-logging.properties files without priorities which are in the
      * webapps. Webapps can also use explicit priorities to override a configuration
      * file in the shared classpath if needed.
      * </p>
      */
     private static Properties getConfigurationFile(final ClassLoader classLoader, final String fileName) {
         Properties props = null;
         double priority = 0.0;
         URL propsUrl = null;
         try {
             final Enumeration<URL> urls = getResources(classLoader, fileName);
             if (urls == null) {
                 return null;
             }
             while (urls.hasMoreElements()) {
                 final URL url = urls.nextElement();
                 final Properties newProps = getProperties(url);
                 if (newProps != null) {
                     if (props == null) {
                         propsUrl = url;
                         props = newProps;
                         final String priorityStr = props.getProperty(PRIORITY_KEY);
                         priority = 0.0;
                         if (priorityStr != null) {
                             priority = Double.parseDouble(priorityStr);
                         }
                         if (isDiagnosticsEnabled()) {
                             logDiagnostic("[LOOKUP] Properties file found at '" + url + "'" + " with priority " + priority);
                         }
                     } else {
                         final String newPriorityStr = newProps.getProperty(PRIORITY_KEY);
                         double newPriority = 0.0;
                         if (newPriorityStr != null) {
                             newPriority = Double.parseDouble(newPriorityStr);
                         }
                         if (newPriority > priority) {
                             if (isDiagnosticsEnabled()) {
                                 logDiagnostic("[LOOKUP] Properties file at '" + url + "'" + " with priority " + newPriority + " overrides file at '" + propsUrl
                                         + "'" + " with priority " + priority);
                             }
                             propsUrl = url;
                             props = newProps;
                             priority = newPriority;
                         } else if (isDiagnosticsEnabled()) {
                             logDiagnostic("[LOOKUP] Properties file at '" + url + "'" + " with priority " + newPriority + " does not override file at '"
                                     + propsUrl + "'" + " with priority " + priority);
                         }
                     }
 
                 }
             }
         } catch (final SecurityException e) {
             logDiagnostic("SecurityException thrown while trying to find/read config files.");
         }
         if (isDiagnosticsEnabled()) {
             if (props == null) {
                 logDiagnostic("[LOOKUP] No properties file of name '" + fileName + "' found.");
             } else {
                 logDiagnostic("[LOOKUP] Properties file of name '" + fileName + "' found at '" + propsUrl + '"');
             }
         }
         return props;
     }
 
     /**
      * Gets the current context class loader.
      * <p>
      * In versions prior to 1.1, this method did not use an AccessController.
      * In version 1.1, an AccessController wrapper was incorrectly added to
      * this method, causing a minor security flaw.
      * </p>
      * <p>
      * In version 1.1.1 this change was reverted; this method no longer uses
      * an AccessController. User code wishing to obtain the context class loader
      * must invoke this method via AccessController.doPrivileged if it needs
      * support for that.
      * </p>
      *
      * @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.
      */
     protected static ClassLoader getContextClassLoader() throws LogConfigurationException {
         return directGetContextClassLoader();
     }
 
     /**
      * Calls {@link 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.
      */
     private static ClassLoader getContextClassLoaderInternal() throws LogConfigurationException {
         return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) LogFactory::directGetContextClassLoader);
     }
 
     /**
      * Constructs (if necessary) and return a {@code LogFactory} instance, using the following ordered lookup procedure to determine the name of the
      * implementation class to be loaded.
      * <ul>
      * <li>The {@code org.apache.commons.logging.LogFactory} system property.</li>
      * <li>The JDK 1.3 Service Discovery mechanism</li>
      * <li>Use the properties file {@code commons-logging.properties} file, if found in the class path of this class. The configuration file is in standard
      * {@link java.util.Properties} format and contains the fully qualified name of the implementation class with the key being the system property defined
      * above.</li>
      * <li>Fall back to a default implementation class ({@code org.apache.commons.logging.impl.LogFactoryImpl}).</li>
      * </ul>
      * <p>
      * <em>NOTE</em> - If the properties file method of identifying the {@code LogFactory} implementation class is utilized, all of the properties defined in
      * this file will be set as configuration attributes on the corresponding {@code LogFactory} instance.
      * </p>
      * <p>
      * <em>NOTE</em> - In a multi-threaded environment it is possible that two different instances will be returned for the same class loader environment.
      * </p>
      *
      * @return a {@code LogFactory}.
      * @throws LogConfigurationException if the implementation class is not available or cannot be instantiated.
      */
     public static LogFactory getFactory() throws LogConfigurationException {
         // Identify the class loader we will be using
         final ClassLoader contextClassLoader = getContextClassLoaderInternal();
 
         // This is an odd enough situation to report about. This
         // output will be a nuisance on JDK1.1, as the system
         // class loader is null in that environment.
         if (contextClassLoader == null) {
             logDiagnostic("Context class loader is null.");
         }
 
         // Return any previously registered factory for this class loader
         LogFactory factory = getCachedFactory(contextClassLoader);
         if (factory != null) {
             return factory;
         }
 
         if (isDiagnosticsEnabled()) {
             logDiagnostic(
                     "[LOOKUP] LogFactory implementation requested for the first time for context class loader " +
                     objectId(contextClassLoader));
             logHierarchy("[LOOKUP] ", contextClassLoader);
         }
 
         // Load properties file.
         //
         // If the properties file exists, then its contents are used as
         // "attributes" on the LogFactory implementation class. One particular
         // property may also control which LogFactory concrete subclass is
         // used, but only if other discovery mechanisms fail..
         //
         // As the properties file (if it exists) will be used one way or
         // another in the end we may as well look for it first.
 
         final Properties props = getConfigurationFile(contextClassLoader, FACTORY_PROPERTIES);
 
         // Determine whether we will be using the thread context class loader to
         // load logging classes or not by checking the loaded properties file (if any).
         boolean useTccl = contextClassLoader != null;
         if (props != null) {
             final String useTCCLStr = props.getProperty(TCCL_KEY);
             useTccl &= useTCCLStr == null || Boolean.parseBoolean(useTCCLStr);
         }
         // If TCCL is still enabled at this point, we check if it resolves this class
         if (useTccl) {
             try {
                 if (!LogFactory.class.equals(Class.forName(LogFactory.class.getName(), false, contextClassLoader))) {
                     logDiagnostic(() -> "The class " + LogFactory.class.getName() + " loaded by the context class loader " + objectId(contextClassLoader)
                             + " and this class differ. Disabling the usage of the context class loader."
                             + "Background can be found in https://commons.apache.org/logging/tech.html. ");
                     logHierarchy("[BAD CL TREE] ", contextClassLoader);
                     useTccl = false;
                 }
             } catch (final ClassNotFoundException ignored) {
                 logDiagnostic(() -> "The class " + LogFactory.class.getName() + " is not present in the the context class loader "
                         + objectId(contextClassLoader) + ". Disabling the usage of the context class loader."
                         + "Background can be found in https://commons.apache.org/logging/tech.html. ");
                 logHierarchy("[BAD CL TREE] ", contextClassLoader);
                 useTccl = false;
             }
         }
         final ClassLoader baseClassLoader = useTccl ? contextClassLoader : thisClassLoaderRef.get();
 
         // Determine which concrete LogFactory subclass to use.
         // First, try a global system property
         logDiagnostic(() -> "[LOOKUP] Looking for system property [" + FACTORY_PROPERTY +
                       "] to define the LogFactory subclass to use...");
 
         try {
             final String factoryClass = getSystemProperty(FACTORY_PROPERTY, null);
             if (factoryClass != null) {
                 logDiagnostic(() -> "[LOOKUP] Creating an instance of LogFactory class '" + factoryClass +
                               "' as specified by system property " + FACTORY_PROPERTY);
                 factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
             } else {
                 logDiagnostic(() -> "[LOOKUP] No system property [" + FACTORY_PROPERTY + "] defined.");
             }
         } catch (final SecurityException e) {
             logDiagnostic(() -> "[LOOKUP] A security exception occurred while trying to create an instance of the custom factory class" + ": ["
                     + trim(e.getMessage()) + "]. Trying alternative implementations...");
             // ignore
         } catch (final RuntimeException e) {
             // This is not consistent with the behavior when a bad LogFactory class is
             // specified in a services file.
             //
             // One possible exception that can occur here is a ClassCastException when
             // the specified class wasn't castable to this LogFactory type.
             logDiagnostic(() -> "[LOOKUP] An exception occurred while trying to create an instance of the custom factory class: [" + trim(e.getMessage())
                     + "] as specified by a system property.");
             throw e;
         }
         //
         // Second, try to find a service by using the JDK 1.3 class
         // discovery mechanism, which involves putting a file with the name
         // of an interface class in the META-INF/services directory, where the
         // contents of the file is a single line specifying a concrete class
         // that implements the desired interface.
         if (factory == null) {
             logDiagnostic("[LOOKUP] Using ServiceLoader  to define the LogFactory subclass to use...");
             try {
                 final ServiceLoader<LogFactory> serviceLoader = ServiceLoader.load(LogFactory.class, baseClassLoader);
                 final Iterator<LogFactory> iterator = serviceLoader.iterator();
 
                 int i = MAX_BROKEN_SERVICES;
                 while (factory == null && i-- > 0) {
                     try {
                         if (iterator.hasNext()) {
                             factory = iterator.next();
                         }
                     } catch (final ServiceConfigurationError | LinkageError ex) {
                         logDiagnostic(() -> "[LOOKUP] An exception occurred while trying to find an instance of LogFactory: [" + trim(ex.getMessage())
                                 + "]. Trying alternative implementations...");
                     }
                 }
             } catch (final Exception ex) {
                 // note: if the specified LogFactory class wasn't compatible with LogFactory
                 // for some reason, a ClassCastException will be caught here, and attempts will
                 // continue to find a compatible class.
                 logDiagnostic(() -> "[LOOKUP] A security exception occurred while trying to create an instance of the custom factory class: ["
                         + trim(ex.getMessage()) + "]. Trying alternative implementations...");
                 // ignore
             }
         }
         //
         // Third try looking into the properties file read earlier (if found)
         if (factory == null) {
             if (props != null) {
                 logDiagnostic(() -> 
                     "[LOOKUP] Looking in properties file for entry with key '" + FACTORY_PROPERTY +
                     "' to define the LogFactory subclass to use...");
                 final String factoryClass = props.getProperty(FACTORY_PROPERTY);
                 if (factoryClass != null) {
                     logDiagnostic(() -> 
                         "[LOOKUP] Properties file specifies LogFactory subclass '" + factoryClass + "'");
                     factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
                     // TODO: think about whether we need to handle exceptions from newFactory
                 } else {
                     logDiagnostic("[LOOKUP] Properties file has no entry specifying LogFactory subclass.");
                 }
             } else {
                 logDiagnostic("[LOOKUP] No properties file available to determine LogFactory subclass from..");
             }
         }
         //
         // Fourth, try one of the three provided factories first from the specified classloader
         // and then from the current one.
         if (factory == null) {
             factory = newStandardFactory(baseClassLoader);
         }
         if (factory == null && baseClassLoader != thisClassLoaderRef.get()) {
             factory = newStandardFactory(thisClassLoaderRef.get());
         }
         if (factory != null) {
             if (isDiagnosticsEnabled()) {
                 logDiagnostic("Created object " + objectId(factory) + " to manage class loader " + objectId(contextClassLoader));
             }
         } else {
             logDiagnostic(() -> 
                 "[LOOKUP] Loading the default LogFactory implementation '" + FACTORY_DEFAULT +
                 "' via the same class loader that loaded this LogFactory class (ie not looking in the context class loader).");
             // Note: unlike the above code which can try to load custom LogFactory
             // implementations via the TCCL, we don't try to load the default LogFactory
             // implementation via the context class loader because:
             // * that can cause problems (see comments in newFactory method)
             // * no-one should be customising the code of the default class
             // Yes, we do give up the ability for the child to ship a newer
             // version of the LogFactoryImpl class and have it used dynamically
             // by an old LogFactory class in the parent, but that isn't
             // necessarily a good idea anyway.
             factory = newFactory(FACTORY_DEFAULT, thisClassLoaderRef.get(), contextClassLoader);
         }
         if (factory != null) {
             /**
              * Always cache using context class loader.
              */
             cacheFactory(contextClassLoader, factory);
             if (props != null) {
                 final Enumeration<?> names = props.propertyNames();
                 while (names.hasMoreElements()) {
                     final String name = Objects.toString(names.nextElement(), null);
                     final String value = props.getProperty(name);
                     factory.setAttribute(name, value);
                 }
             }
         }
         return factory;
     }
 
     /**
      * Gets a named logger, without the application having to care about factories.
      *
      * @param clazz Class from which a log name will be derived
      * @return a named logger.
      * @throws LogConfigurationException if a suitable {@code Log} instance cannot be returned
      */
     public static Log getLog(final Class<?> clazz) throws LogConfigurationException {
         return getFactory().getInstance(clazz);
     }
 
     /**
      * Gets a named logger, without the application having to care about factories.
      *
      * @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)
      * @return a named logger.
      * @throws LogConfigurationException if a suitable {@code Log} instance cannot be returned
      */
     public static Log getLog(final String name) throws LogConfigurationException {
         return getFactory().getInstance(name);
     }
 
     /**
      * Given a URL that refers to a .properties file, load that file.
      * This is done under an AccessController so that this method will
      * succeed when this jarfile is privileged but the caller is not.
      * This method must therefore remain private to avoid security issues.
      * <p>
      * {@code Null} is returned if the URL cannot be opened.
      * </p>
      */
     private static Properties getProperties(final URL url) {
         return AccessController.doPrivileged((PrivilegedAction<Properties>) () -> {
             // We must ensure that useCaches is set to false, as the
             // default behavior of java is to cache file handles, and
             // this "locks" files, preventing hot-redeploy on windows.
             try {
                 final URLConnection connection = url.openConnection();
                 connection.setUseCaches(false);
                 try (InputStream stream = connection.getInputStream()) {
                     if (stream != null) {
                         final Properties props = new Properties();
                         props.load(stream);
                         return props;
                     }
                 } catch (final IOException e) {
                     logDiagnostic(() -> "Unable to close stream for URL " + url);
                 }
             } catch (final IOException e) {
                 logDiagnostic(() -> "Unable to read URL " + url);
             }
 
             return null;
         });
     }
 
     /**
      * Given a file name, return an enumeration of URLs pointing to
      * all the occurrences of that file name in the classpath.
      * <p>
      * This is just like ClassLoader.getResources except that the
      * operation is done under an AccessController so that this method will
      * succeed when this jarfile is privileged but the caller is not.
      * This method must therefore remain private to avoid security issues.
      * </p>
      * <p>
      * If no instances are found, an Enumeration is returned whose
      * hasMoreElements method returns false (ie an "empty" enumeration).
      * If resources could not be listed for some reason, null is returned.
      * </p>
      */
     private static Enumeration<URL> getResources(final ClassLoader loader, final String name) {
         return AccessController.doPrivileged((PrivilegedAction<Enumeration<URL>>) () -> {
             try {
                 if (loader != null) {
                     return loader.getResources(name);
                 }
                 return ClassLoader.getSystemResources(name);
             } catch (final IOException e) {
                 logDiagnostic(() -> "Exception while trying to find configuration file " + name + ":" + e.getMessage());
                 return null;
             } catch (final NoSuchMethodError e) {
                 // we must be running on a 1.1 JVM which doesn't support
                 // ClassLoader.getSystemResources; just return null in
                 // this case.
                 return null;
             }
         });
     }
 
     /**
      * Read 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));
     }
 
     /**
      * Checks whether the supplied Throwable is one that needs to be
      * re-thrown and ignores all others.
      *
      * The following errors are re-thrown:
      * <ul>
      *   <li>ThreadDeath</li>
      *   <li>VirtualMachineError</li>
      * </ul>
      *
      * @param t the Throwable to check
      */
     protected static void handleThrowable(final Throwable t) {
         if (t instanceof ThreadDeath) {
             throw (ThreadDeath) t;
         }
         if (t instanceof VirtualMachineError) {
             throw (VirtualMachineError) t;
         }
         // All other instances of Throwable will be silently ignored
     }
 
     /**
      * Determines whether the given class actually implements {@code LogFactory}.
      * Diagnostic information is also logged.
      * <p>
      * <strong>Usage:</strong> to diagnose whether a class loader conflict is the cause
      * of incompatibility. The test used is whether the class is assignable from
      * the {@code LogFactory} class loaded by the class's class loader.
      * @param logFactoryClass {@code Class} which may implement {@code LogFactory}
      * @return true if the {@code logFactoryClass} does extend
      * {@code LogFactory} when that class is loaded via the same
      * class loader that loaded the {@code logFactoryClass}.
      * </p>
      */
     private static boolean implementsLogFactory(final Class<?> logFactoryClass) {
         boolean implementsLogFactory = false;
         if (logFactoryClass != null) {
             try {
                 final ClassLoader logFactoryClassLoader = logFactoryClass.getClassLoader();
                 if (logFactoryClassLoader == null) {
                     logDiagnostic("[CUSTOM LOG FACTORY] was loaded by the boot class loader");
                 } else {
                     logHierarchy("[CUSTOM LOG FACTORY] ", logFactoryClassLoader);
                     final Class<?> factoryFromCustomLoader = Class.forName("org.apache.commons.logging.LogFactory", false, logFactoryClassLoader);
                     implementsLogFactory = factoryFromCustomLoader.isAssignableFrom(logFactoryClass);
                     final String logFactoryClassName = logFactoryClass.getName();
                     if (implementsLogFactory) {
                         logDiagnostic(() -> "[CUSTOM LOG FACTORY] " + logFactoryClassName + " implements LogFactory but was loaded by an incompatible class loader.");
                     } else {
                         logDiagnostic(() -> "[CUSTOM LOG FACTORY] " + logFactoryClassName + " does not implement LogFactory.");
                     }
                 }
             } catch (final SecurityException e) {
                 //
                 // The application is running within a hostile security environment.
                 // This will make it very hard to diagnose issues with JCL.
                 // Consider running less securely whilst debugging this issue.
                 //
                 logDiagnostic(
                         () -> "[CUSTOM LOG FACTORY] SecurityException caught trying to determine whether the compatibility was caused by a class loader conflict: "
                                 + e.getMessage());
             } catch (final LinkageError e) {
                 //
                 // This should be an unusual circumstance.
                 // LinkageError's usually indicate that a dependent class has incompatibly changed.
                 // Another possibility may be an exception thrown by an initializer.
                 // Time for a clean rebuild?
                 //
                 logDiagnostic(
                         () -> "[CUSTOM LOG FACTORY] LinkageError caught trying to determine whether the compatibility was caused by a class loader conflict: "
                                 + e.getMessage());
             } catch (final ClassNotFoundException e) {
                 //
                 // LogFactory cannot be loaded by the class loader which loaded the custom factory implementation.
                 // The custom implementation is not viable until this is corrected.
                 // Ensure that the JCL jar and the custom class are available from the same class loader.
                 // Running with diagnostics on should give information about the class loaders used
                 // to load the custom factory.
                 //
                 logDiagnostic(() -> "[CUSTOM LOG FACTORY] LogFactory class cannot be loaded by the class loader which loaded "
                         + "the custom LogFactory implementation. Is the custom factory in the right class loader?");
             }
         }
         return implementsLogFactory;
     }
 
     /**
      * Tests whether the user wants internal diagnostic output. If so,
      * returns an appropriate writer object. Users can enable diagnostic
      * output by setting the system property named {@link #DIAGNOSTICS_DEST_PROPERTY} to
      * a file name, or the special values STDOUT or STDERR.
      */
     private static PrintStream initDiagnostics() {
         String dest;
         try {
             dest = getSystemProperty(DIAGNOSTICS_DEST_PROPERTY, null);
             if (dest == null) {
                 return null;
             }
         } catch (final SecurityException ex) {
             // We must be running in some very secure environment.
             // We just have to assume output is not wanted..
             return null;
         }
 
         if (dest.equals("STDOUT")) {
             return System.out;
         }
         if (dest.equals("STDERR")) {
             return System.err;
         }
         try {
             // open the file in append mode
             final FileOutputStream fos = new FileOutputStream(dest, true);
             return new PrintStream(fos, false, StandardCharsets.UTF_8.name());
         } catch (final IOException ex) {
             // We should report this to the user - but how?
             return null;
         }
     }
 
     private static boolean isClassAvailable(final String className, final ClassLoader classLoader) {
         logDiagnostic(() -> "Checking if class '" + className + "' is available in class loader " + objectId(classLoader));
         try {
             Class.forName(className, true, classLoader);
             return true;
         } catch (final ClassNotFoundException | LinkageError e) {
             logDiagnostic(() -> "Failed to load class '" + className + "' from class loader " + objectId(classLoader) + ": " + e.getMessage());
         }
         return false;
     }
 
     /**
      * Tests whether the user enabled internal logging.
      * <p>
      * By the way, sorry for the incorrect grammar, but calling this method
      * areDiagnosticsEnabled just isn't Java beans style.
      * </p>
      *
      * @return true if calls to logDiagnostic will have any effect.
      * @since 1.1
      */
     protected static boolean isDiagnosticsEnabled() {
         return DIAGNOSTICS_STREAM != null;
     }
 
     /**
      * Generates useful diagnostics regarding the class loader tree for
      * the specified class.
      * <p>
      * As an example, if the specified class was loaded via a webapp's
      * class loader, then you may get the following output:
      * </p>
      * <pre>
      * Class com.acme.Foo was loaded via class loader 11111
      * ClassLoader tree: 11111 -> 22222 (SYSTEM) -> 33333 -> BOOT
      * </pre>
      * <p>
      * This method returns immediately if isDiagnosticsEnabled()
      * returns false.
      * </p>
      *
      * @param clazz is the class whose class loader + tree are to be
      * output.
      */
     private static void logClassLoaderEnvironment(final Class<?> clazz) {
         if (!isDiagnosticsEnabled()) {
             return;
         }
         try {
             // Deliberately use System.getProperty here instead of getSystemProperty; if
             // the overall security policy for the calling application forbids access to
             // these variables then we do not want to output them to the diagnostic stream.
             logDiagnostic("[ENV] Extension directories (java.ext.dir): " + System.getProperty("java.ext.dir"));
             logDiagnostic("[ENV] Application classpath (java.class.path): " + System.getProperty("java.class.path"));
         } catch (final SecurityException ex) {
             logDiagnostic("[ENV] Security setting prevent interrogation of system classpaths.");
         }
         final String className = clazz.getName();
         ClassLoader classLoader;
         try {
             classLoader = getClassLoader(clazz);
         } catch (final SecurityException ex) {
             // not much useful diagnostics we can print here!
             logDiagnostic("[ENV] Security forbids determining the class loader for " + className);
             return;
         }
         logDiagnostic("[ENV] Class " + className + " was loaded via class loader " + objectId(classLoader));
         logHierarchy("[ENV] Ancestry of class loader which loaded " + className + " is ", classLoader);
     }
 
     /**
      * Writes the specified message to the internal logging destination.
      * <p>
      * Note that this method is private; concrete subclasses of this class
      * should not call it because the diagnosticPrefix string this
      * method puts in front of all its messages is LogFactory@....,
      * while subclasses should put SomeSubClass@...
      * </p>
      * <p>
      * Subclasses should instead compute their own prefix, then call
      * logRawDiagnostic. Note that calling isDiagnosticsEnabled is
      * fine for subclasses.
      * </p>
      * <p>
      * Note that it is safe to call this method before initDiagnostics
      * is called; any output will just be ignored (as isDiagnosticsEnabled
      * will return false).
      * </p>
      *
      * @param msg is the diagnostic message to be output.
      */
     private static void logDiagnostic(final String msg) {
         if (DIAGNOSTICS_STREAM != null) {
             logDiagnosticDirect(msg);
         }
     }
 
     /**
      * Writes the specified message to the internal logging destination.
      * <p>
      * Note that this method is private; concrete subclasses of this class
      * should not call it because the diagnosticPrefix string this
      * method puts in front of all its messages is LogFactory@....,
      * while subclasses should put SomeSubClass@...
      * </p>
      * <p>
      * Subclasses should instead compute their own prefix, then call
      * logRawDiagnostic. Note that calling isDiagnosticsEnabled is
      * fine for subclasses.
      * </p>
      * <p>
      * Note that it is safe to call this method before initDiagnostics
      * is called; any output will just be ignored (as isDiagnosticsEnabled
      * will return false).
      * </p>
      *
      * @param msg is the diagnostic message to be output.
      */
     private static void logDiagnostic(final Supplier<String> msg) {
         if (DIAGNOSTICS_STREAM != null) {
             logDiagnosticDirect(msg.get());
         }
     }
 
     private static void logDiagnosticDirect(final String msg) {
         DIAGNOSTICS_STREAM.print(DIAGNOSTICS_PREFIX);
         DIAGNOSTICS_STREAM.println(msg);
         DIAGNOSTICS_STREAM.flush();
     }
 
     /**
      * Logs diagnostic messages about the given class loader
      * and it's hierarchy. The prefix is prepended to the message
      * and is intended to make it easier to understand the logs.
      * @param prefix
      * @param classLoader
      */
     private static void logHierarchy(final String prefix, ClassLoader classLoader) {
         if (!isDiagnosticsEnabled()) {
             return;
         }
         ClassLoader systemClassLoader;
         if (classLoader != null) {
             logDiagnostic(prefix + objectId(classLoader) + " == '" + classLoader.toString() + "'");
         }
         try {
             systemClassLoader = ClassLoader.getSystemClassLoader();
         } catch (final SecurityException ex) {
             logDiagnostic(prefix + "Security forbids determining the system class loader.");
             return;
         }
         if (classLoader != null) {
             final StringBuilder buf = new StringBuilder(prefix + "ClassLoader tree:");
             for(;;) {
                 buf.append(objectId(classLoader));
                 if (classLoader == systemClassLoader) {
                     buf.append(" (SYSTEM) ");
                 }
                 try {
                     classLoader = classLoader.getParent();
                 } catch (final SecurityException ex) {
                     buf.append(" --> SECRET");
                     break;
                 }
                 buf.append(" --> ");
                 if (classLoader == null) {
                     buf.append("BOOT");
                     break;
                 }
             }
             logDiagnostic(buf.toString());
         }
     }
 
     /**
      * Writes the specified message to the internal logging destination.
      *
      * @param msg is the diagnostic message to be output.
      * @since 1.1
      */
     protected static final void logRawDiagnostic(final String msg) {
         if (DIAGNOSTICS_STREAM != null) {
             DIAGNOSTICS_STREAM.println(msg);
             DIAGNOSTICS_STREAM.flush();
         }
     }
 
     /**
      * Method provided for backwards compatibility; see newFactory version that
      * takes 3 parameters.
      * <p>
      * This method would only ever be called in some rather odd situation.
      * Note that this method is static, so overriding in a subclass doesn't
      * have any effect unless this method is called from a method in that
      * subclass. However this method only makes sense to use from the
      * getFactory method, and as that is almost always invoked via
      * LogFactory.getFactory, any custom definition in a subclass would be
      * pointless. Only a class with a custom getFactory method, then invoked
      * directly via CustomFactoryImpl.getFactory or similar would ever call
      * this. Anyway, it's here just in case, though the "managed class loader"
      * value output to the diagnostics will not report the correct value.
      * </p>
      *
      * @param factoryClass factory class.
      * @param classLoader class loader.
      * @return a LogFactory.
      */
     protected static LogFactory newFactory(final String factoryClass,
                                            final ClassLoader classLoader) {
         return newFactory(factoryClass, classLoader, null);
     }
 
     /**
      * Gets a new instance of the specified {@code LogFactory} implementation class, loaded by the specified class loader. If that fails, try the class loader
      * used to load this (abstract) LogFactory.
      * <p>
      * <b>ClassLoader conflicts</b>
      * </p>
      * <p>
      * Note that there can be problems if the specified ClassLoader is not the same as the class loader that loaded this class, that is, when loading a concrete
      * LogFactory subclass via a context class loader.
      * </p>
      * <p>
      * The problem is the same one that can occur when loading a concrete Log subclass via a context class loader.
      * </p>
      * <p>
      * The problem occurs when code running in the context class loader calls class X which was loaded via a parent class loader, and class X then calls
      * LogFactory.getFactory (either directly or via LogFactory.getLog). Because class X was loaded via the parent, it binds to LogFactory loaded via the
      * parent. When the code in this method finds some LogFactoryYYYY class in the child (context) class loader, and there also happens to be a LogFactory class
      * defined in the child class loader, then LogFactoryYYYY will be bound to LogFactory@childloader. It cannot be cast to LogFactory@parentloader, that is,
      * this method cannot return the object as the desired type. Note that it doesn't matter if the LogFactory class in the child class loader is identical to
      * the LogFactory class in the parent class loader, they are not compatible.
      * </p>
      * <p>
      * The solution taken here is to simply print out an error message when this occurs then throw an exception. The deployer of the application must ensure
      * they remove all occurrences of the LogFactory class from the child class loader in order to resolve the issue. Note that they do not have to move the
      * custom LogFactory subclass; that is ok as long as the only LogFactory class it can find to bind to is in the parent class loader.
      * </p>
      *
      * @param factoryClass       Fully qualified name of the {@code LogFactory} implementation class
      * @param classLoader        ClassLoader from which to load this class
      * @param contextClassLoader is the context that this new factory will manage logging for.
      * @return a new instance of the specified {@code LogFactory}.
      * @throws LogConfigurationException if a suitable instance cannot be created
      * @since 1.1
      */
     protected static LogFactory newFactory(final String factoryClass,
                                            final ClassLoader classLoader,
                                            final ClassLoader contextClassLoader)
             throws LogConfigurationException {
         // Note that any unchecked exceptions thrown by the createFactory
         // method will propagate out of this method; in particular a
         // ClassCastException can be thrown.
         final Object result = AccessController.doPrivileged((PrivilegedAction<?>) () -> createFactory(factoryClass, classLoader));
         if (result instanceof LogConfigurationException) {
             final LogConfigurationException ex = (LogConfigurationException) result;
             logDiagnostic(() -> "An error occurred while loading the factory class:" + ex.getMessage());
             throw ex;
         }
         logDiagnostic(() -> "Created object " + objectId(result) + " to manage class loader " + objectId(contextClassLoader));
         return (LogFactory) result;
     }
 
     /**
      * Tries to load one of the standard three implementations from the given classloader.
      * <p>
      *     We assume that {@code classLoader} can load this class.
      * </p>
      * @param classLoader The classloader to use.
      * @return An implementation of this class.
      */
     private static LogFactory newStandardFactory(final ClassLoader classLoader) {
         if (isClassAvailable(LOG4J_TO_SLF4J_BRIDGE, classLoader)) {
             try {
                 return (LogFactory) Class.forName(FACTORY_SLF4J, true, classLoader).getConstructor().newInstance();
             } catch (final LinkageError | ReflectiveOperationException ignored) {
             } finally {
                 logDiagnostic(() ->
                         "[LOOKUP] Log4j API to SLF4J redirection detected. Loading the SLF4J LogFactory implementation '" + FACTORY_SLF4J + "'.");
             }
         }
         try {
             return (LogFactory) Class.forName(FACTORY_LOG4J_API, true, classLoader).getConstructor().newInstance();
         } catch (final LinkageError | ReflectiveOperationException ignored) {
         } finally {
             logDiagnostic(() -> "[LOOKUP] Loading the Log4j API LogFactory implementation '" + FACTORY_LOG4J_API + "'.");
         }
         try {
             return (LogFactory) Class.forName(FACTORY_SLF4J, true, classLoader).getConstructor().newInstance();
         } catch (final LinkageError | ReflectiveOperationException ignored) {
         } finally {
             logDiagnostic(() -> "[LOOKUP] Loading the SLF4J LogFactory implementation '" + FACTORY_SLF4J + "'.");
         }
         try {
             return (LogFactory) Class.forName(FACTORY_DEFAULT, true, classLoader).getConstructor().newInstance();
         } catch (final LinkageError | ReflectiveOperationException ignored) {
         } finally {
             logDiagnostic(() -> "[LOOKUP] Loading the legacy LogFactory implementation '" + FACTORY_DEFAULT + "'.");
         }
         return null;
     }
 
     /**
      * Returns a string that uniquely identifies the specified object, including
      * its class.
      * <p>
      * The returned string is of form {@code "className@hashCode"}, that is, is the same as
      * the return value of the {@link Object#toString()} method, but works even when
      * the specified object's class has overridden the toString method.
      * </p>
      *
      * @param obj may be null.
      * @return a string of form {@code className@hashCode}, or "null" if obj is null.
      * @since 1.1
      */
     public static String objectId(final Object obj) {
         if (obj == null) {
             return "null";
         }
         return obj.getClass().getName() + "@" + System.identityHashCode(obj);
     }
 
     /**
      * Releases any internal references to previously created {@link LogFactory}
      * instances that have been associated with the specified class loader
      * (if any), after calling the instance method {@code release()} on
      * each of them.
      *
      * @param classLoader ClassLoader for which to release the LogFactory
      */
     public static void release(final ClassLoader classLoader) {
         logDiagnostic(() -> "Releasing factory for class loader " + objectId(classLoader));
         // factories is not final and could be replaced in this block.
         final Hashtable<ClassLoader, LogFactory> factories = LogFactory.factories;
         synchronized (factories) {
             if (classLoader == null) {
                 if (nullClassLoaderFactory != null) {
                     nullClassLoaderFactory.release();
                     nullClassLoaderFactory = null;
                 }
             } else {
                 final LogFactory factory = factories.get(classLoader);
                 if (factory != null) {
                     factory.release();
                     factories.remove(classLoader);
                 }
             }
         }
     }
 
     /**
      * Release any internal references to previously created {@link LogFactory}
      * instances, after calling the instance method {@code release()} on
      * each of them.  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.
      */
     public static void releaseAll() {
         logDiagnostic("Releasing factory for all class loaders.");
         // factories is not final and could be replaced in this block.
         final Hashtable<ClassLoader, LogFactory> factories = LogFactory.factories;
         synchronized (factories) {
             factories.values().forEach(LogFactory::release);
             factories.clear();
             if (nullClassLoaderFactory != null) {
                 nullClassLoaderFactory.release();
                 nullClassLoaderFactory = null;
             }
         }
     }
 
     /** Trims the given string in a null-safe manner. */
     private static String trim(final String src) {
         return src != null ? src.trim() : null;
     }
 
     /**
      * Constructs a new instance.
      */
     protected LogFactory() {
     }
 
     /**
      * 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
      * @return the configuration attribute with the specified name.
      */
     public abstract Object getAttribute(String 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.
      *
      * @return an array containing the names of all currently defined configuration attributes
      */
     public abstract String[] getAttributeNames();
 
     /**
      * Gets a Log for the given class.
      *
      * @param clazz Class for which a suitable Log name will be derived
      * @return a name from the specified class.
      * @throws LogConfigurationException if a suitable {@code Log} instance cannot be returned
      */
     public abstract Log getInstance(Class<?> clazz) throws LogConfigurationException;
 
     /**
      * Gets a (possibly new) {@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)
      * @return a {@code Log} instance.
      * @throws LogConfigurationException if a suitable {@code Log} instance cannot be returned
      */
     public abstract Log getInstance(String name)
         throws LogConfigurationException;
 
     /**
      * Releases any internal references to previously created {@link 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.
      */
     public abstract void release();
 
     /**
      * Removes 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
      */
     public abstract void removeAttribute(String name);
 
     //
     // We can't do this in the class constructor, as there are many
     // static methods on this class that can be called before any
     // LogFactory instances are created, and they depend upon this
     // stuff having been set up.
     //
     // Note that this block must come after any variable declarations used
     // by any methods called from this block, as we want any static initializer
     // associated with the variable to run first. If static initializers for
     // variables run after this code, then (a) their value might be needed
     // by methods called from here, and (b) they might *override* any value
     // computed here!
     //
     // So the wisest thing to do is just to place this code at the very end
     // of the class file.
 
     /**
      * Sets the configuration attribute with the specified name.  Calling
      * this with a {@code null} value is equivalent to calling
      * {@code removeAttribute(name)}.
      *
      * @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
      */
     public abstract void setAttribute(String name, Object value);
 
 }