    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.logging.impl;
    019
    020import java.io.PrintWriter;
    021import java.io.StringWriter;
    022import java.lang.reflect.Constructor;
    023import java.lang.reflect.InvocationTargetException;
    024import java.lang.reflect.Method;
    025import java.net.URL;
    026import java.security.AccessController;
    027import java.security.PrivilegedAction;
    028import java.util.Hashtable;
    029
    030import org.apache.commons.logging.Log;
    031import org.apache.commons.logging.LogConfigurationException;
    032import org.apache.commons.logging.LogFactory;
    033
    034/**
    035 * Concrete subclass of {@link LogFactory} that implements the
    036 * following algorithm to dynamically select a logging implementation
    037 * class to instantiate a wrapper for:
    038 * <ul>
    039 * <li>Use a factory configuration attribute named
    040 *     {@code org.apache.commons.logging.Log} to identify the
    041 *     requested implementation class.</li>
    042 * <li>Use the {@code org.apache.commons.logging.Log} system property
    043 *     to identify the requested implementation class.</li>
    044 * <li>If <em>Log4J</em> is available, return an instance of
    045 *     {@code org.apache.commons.logging.impl.Log4JLogger}.</li>
    046 * <li>If <em>JDK 1.4 or later</em> is available, return an instance of
    047 *     {@code org.apache.commons.logging.impl.Jdk14Logger}.</li>
    048 * <li>Otherwise, return an instance of
    049 *     {@code org.apache.commons.logging.impl.SimpleLog}.</li>
    050 * </ul>
    051 * <p>
    052 * If the selected {@link Log} implementation class has a
    053 * {@code setLogFactory()} method that accepts a {@link LogFactory}
    054 * parameter, this method will be called on each newly created instance
    055 * to identify the associated factory.  This makes factory configuration
    056 * attributes available to the Log instance, if it so desires.
    057 * </p>
    058 * <p>
    059 * This factory will remember previously created {@code Log} instances
    060 * for the same name, and will return them on repeated requests to the
    061 * {@code getInstance()} method.
    062 * </p>
    063 */
    064public class LogFactoryImpl extends LogFactory {
    065
    066    /** Log4JLogger class name */
    067    private static final String LOGGING_IMPL_LOG4J_LOGGER = "org.apache.commons.logging.impl.Log4JLogger";
    068
    069    /** Jdk14Logger class name */
    070    private static final String LOGGING_IMPL_JDK14_LOGGER = "org.apache.commons.logging.impl.Jdk14Logger";
    071
    072    /** Jdk13LumberjackLogger class name */
    073    private static final String LOGGING_IMPL_LUMBERJACK_LOGGER = "org.apache.commons.logging.impl.Jdk13LumberjackLogger";
    074
    075    /** SimpleLog class name */
    076    private static final String LOGGING_IMPL_SIMPLE_LOGGER = "org.apache.commons.logging.impl.SimpleLog";
    077
    078    private static final String PKG_IMPL="org.apache.commons.logging.impl.";
    079
    080    private static final int PKG_LEN = PKG_IMPL.length();
    081
    082    /**
    083     * An empty immutable {@code String} array.
    084     */
    085    private static final String[] EMPTY_STRING_ARRAY = {};
    086
    087    /**
    088     * The name ({@code org.apache.commons.logging.Log}) of the system
    089     * property identifying our {@link Log} implementation class.
    090     */
    091    public static final String LOG_PROPERTY = "org.apache.commons.logging.Log";
    092
    093    /**
    094     * The deprecated system property used for backwards compatibility with
    095     * old versions of JCL.
    096     */
    097    protected static final String LOG_PROPERTY_OLD = "org.apache.commons.logging.log";
    098
    099    /**
    100     * The name ({@code org.apache.commons.logging.Log.allowFlawedContext})
    101     * of the system property which can be set true/false to
    102     * determine system behavior when a bad context class loader is encountered.
    103     * When set to false, a LogConfigurationException is thrown if
    104     * LogFactoryImpl is loaded via a child class loader of the TCCL (this
    105     * should never happen in sane systems).
    106     * <p>
    107     * Default behavior: true (tolerates bad context class loaders)
    108     * </p>
    109     * <p>
    110     * See also method setAttribute.
    111     * </p>
    112     */
    113    public static final String ALLOW_FLAWED_CONTEXT_PROPERTY =
    114        "org.apache.commons.logging.Log.allowFlawedContext";
    115
    116    /**
    117     * The name ({@code org.apache.commons.logging.Log.allowFlawedDiscovery})
    118     * of the system property which can be set true/false to
    119     * determine system behavior when a bad logging adapter class is
    120     * encountered during logging discovery. When set to false, an
    121     * exception will be thrown and the app will fail to start. When set
    122     * to true, discovery will continue (though the user might end up
    123     * with a different logging implementation than they expected).
    124     * <p>
    125     * Default behavior: true (tolerates bad logging adapters)
    126     * </p>
    127     * <p>
    128     * See also method setAttribute.
    129     * </p>
    130     */
    131    public static final String ALLOW_FLAWED_DISCOVERY_PROPERTY =
    132        "org.apache.commons.logging.Log.allowFlawedDiscovery";
    133
    134    /**
    135     * The name ({@code org.apache.commons.logging.Log.allowFlawedHierarchy})
    136     * of the system property which can be set true/false to
    137     * determine system behavior when a logging adapter class is
    138     * encountered which has bound to the wrong Log class implementation.
    139     * When set to false, an exception will be thrown and the app will fail
    140     * to start. When set to true, discovery will continue (though the user
    141     * might end up with a different logging implementation than they expected).
    142     * <p>
    143     * Default behavior: true (tolerates bad Log class hierarchy)
    144     * </p>
    145     * <p>
    146     * See also method setAttribute.
    147     * </p>
    148     */
    149    public static final String ALLOW_FLAWED_HIERARCHY_PROPERTY =
    150        "org.apache.commons.logging.Log.allowFlawedHierarchy";
    151
    152    /**
    153     * The names of classes that will be tried (in order) as logging
    154     * adapters. Each class is expected to implement the Log interface,
    155     * and to throw NoClassDefFound or ExceptionInInitializerError when
    156     * loaded if the underlying logging library is not available. Any
    157     * other error indicates that the underlying logging library is available
    158     * but broken/unusable for some reason.
    159     */
    160    private static final String[] DISCOVER_CLASSES = {
    161            LOGGING_IMPL_JDK14_LOGGER,
    162            LOGGING_IMPL_SIMPLE_LOGGER
    163    };
    164
    165    /**
    166     * Workaround for bug in Java1.2; in theory this method is not needed. {@link LogFactory#getClassLoader(Class)}.
    167     *
    168     * @param clazz See {@link LogFactory#getClassLoader(Class)}.
    169     * @return See {@link LogFactory#getClassLoader(Class)}.
    170     * @since 1.1
    171     */
    172    protected static ClassLoader getClassLoader(final Class<?> clazz) {
    173        return LogFactory.getClassLoader(clazz);
    174    }
    175
    176    /**
    177     * Gets the context ClassLoader.
    178     * This method is a workaround for a Java 1.2 compiler bug.
    179     *
    180     * @return the context ClassLoader
    181     * @since 1.1
    182     */
    183    protected static ClassLoader getContextClassLoader() throws LogConfigurationException {
    184        return LogFactory.getContextClassLoader();
    185    }
    186
    187    /**
    188     * Calls LogFactory.directGetContextClassLoader under the control of an
    189     * AccessController class. This means that Java code running under a
    190     * security manager that forbids access to ClassLoaders will still work
    191     * if this class is given appropriate privileges, even when the caller
    192     * doesn't have such privileges. Without using an AccessController, the
    193     * the entire call stack must have the privilege before the call is
    194     * allowed.
    195     *
    196     * @return the context class loader associated with the current thread,
    197     * or null if security doesn't allow it.
    198     *
    199     * @throws LogConfigurationException if there was some weird error while
    200     * attempting to get the context class loader.
    201     *
    202     * @throws SecurityException if the current Java security policy doesn't
    203     * allow this class to access the context class loader.
    204     */
    205    private static ClassLoader getContextClassLoaderInternal()
    206            throws LogConfigurationException {
    207        return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) LogFactory::directGetContextClassLoader);
    208    }
    209
    210    /**
    211     * Reads the specified system property, using an AccessController so that
    212     * the property can be read if JCL has been granted the appropriate
    213     * security rights even if the calling code has not.
    214     * <p>
    215     * Take care not to expose the value returned by this method to the
    216     * calling application in any way; otherwise the calling app can use that
    217     * info to access data that should not be available to it.
    218     * </p>
    219     */
    220    private static String getSystemProperty(final String key, final String def)
    221            throws SecurityException {
    222        return AccessController.doPrivileged((PrivilegedAction<String>) () -> System.getProperty(key, def));
    223    }
    224
    225    /**
    226     * Workaround for bug in Java1.2; in theory this method is not needed.
    227     *
    228     * @return Same as {@link LogFactory#isDiagnosticsEnabled()}.
    229     * @see LogFactory#isDiagnosticsEnabled()
    230     */
    231    protected static boolean isDiagnosticsEnabled() {
    232        return LogFactory.isDiagnosticsEnabled();
    233    }
    234
    235    /** Utility method to safely trim a string. */
    236    private static String trim(final String src) {
    237        if (src == null) {
    238            return null;
    239        }
    240        return src.trim();
    241    }
    242
    243    /**
    244     * Determines whether logging classes should be loaded using the thread-context
    245     * class loader, or via the class loader that loaded this LogFactoryImpl class.
    246     */
    247    private boolean useTCCL = true;
    248
    249    /**
    250     * The string prefixed to every message output by the logDiagnostic method.
    251     */
    252    private String diagnosticPrefix;
    253
    254    /**
    255     * Configuration attributes.
    256     */
    257    protected Hashtable<String, Object> attributes = new Hashtable<>();
    258
    259    /**
    260     * The {@link org.apache.commons.logging.Log} instances that have
    261     * already been created, keyed by logger name.
    262     */
    263    protected Hashtable<String, Log> instances = new Hashtable<>();
    264
    265    /**
    266     * Name of the class implementing the Log interface.
    267     */
    268    private String logClassName;
    269
    270    /**
    271     * The one-argument constructor of the
    272     * {@link org.apache.commons.logging.Log}
    273     * implementation class that will be used to create new instances.
    274     * This value is initialized by {@code getLogConstructor()},
    275     * and then returned repeatedly.
    276     */
    277    protected Constructor<?> logConstructor;
    278
    279    /**
    280     * The signature of the Constructor to be used.
    281     */
    282    protected Class<?>[] logConstructorSignature = { String.class };
    283
    284    /**
    285     * The one-argument {@code setLogFactory} method of the selected
    286     * {@link org.apache.commons.logging.Log} method, if it exists.
    287     */
    288    protected Method logMethod;
    289
    290    /**
    291     * The signature of the {@code setLogFactory} method to be used.
    292     */
    293    protected Class<?>[] logMethodSignature = { LogFactory.class };
    294
    295    /**
    296     * See getBaseClassLoader and initConfiguration.
    297     */
    298    private boolean allowFlawedContext;
    299
    300    /**
    301     * See handleFlawedDiscovery and initConfiguration.
    302     */
    303    private boolean allowFlawedDiscovery;
    304
    305    /**
    306     * See handleFlawedHierarchy and initConfiguration.
    307     */
    308    private boolean allowFlawedHierarchy;
    309
    310    /**
    311     * Public no-arguments constructor required by the lookup mechanism.
    312     */
    313    public LogFactoryImpl() {
    314        initDiagnostics();  // method on this object
    315        if (isDiagnosticsEnabled()) {
    316            logDiagnostic("Instance created.");
    317        }
    318    }
    319
    320    /**
    321     * Attempts to load the given class, find a suitable constructor,
    322     * and instantiate an instance of Log.
    323     *
    324     * @param logAdapterClassName class name of the Log implementation
    325     * @param logCategory  argument to pass to the Log implementation's constructor
    326     * @param affectState  {@code true} if this object's state should
    327     *  be affected by this method call, {@code false} otherwise.
    328     * @return  an instance of the given class, or null if the logging
    329     *  library associated with the specified adapter is not available.
    330     * @throws LogConfigurationException if there was a serious error with
    331     *  configuration and the handleFlawedDiscovery method decided this
    332     *  problem was fatal.
    333     */
    334    private Log createLogFromClass(final String logAdapterClassName, final String logCategory, final boolean affectState) throws LogConfigurationException {
    335        if (isDiagnosticsEnabled()) {
    336            logDiagnostic("Attempting to instantiate '" + logAdapterClassName + "'");
    337        }
    338        final Object[] params = { logCategory };
    339        Log logAdapter = null;
    340        Constructor<?> constructor = null;
    341        Class<?> logAdapterClass = null;
    342        ClassLoader currentCL = getBaseClassLoader();
    343        for (;;) {
    344            // Loop through the class loader hierarchy trying to find
    345            // a viable class loader.
    346            logDiagnostic("Trying to load '" + logAdapterClassName + "' from class loader " + objectId(currentCL));
    347            try {
    348                if (isDiagnosticsEnabled()) {
    349                    // Show the location of the first occurrence of the .class file
    350                    // in the classpath. This is the location that ClassLoader.loadClass
    351                    // will load the class from -- unless the class loader is doing
    352                    // something weird.
    353                    URL url;
    354                    final String resourceName = logAdapterClassName.replace('.', '/') + ".class";
    355                    if (currentCL != null) {
    356                        url = currentCL.getResource(resourceName);
    357                    } else {
    358                        url = ClassLoader.getSystemResource(resourceName + ".class");
    359                    }
    360                    if (url == null) {
    361                        logDiagnostic("Class '" + logAdapterClassName + "' [" + resourceName + "] cannot be found.");
    362                    } else {
    363                        logDiagnostic("Class '" + logAdapterClassName + "' was found at '" + url + "'");
    364                    }
    365                }
    366                Class<?> clazz;
    367                try {
    368                    clazz = Class.forName(logAdapterClassName, true, currentCL);
    369                } catch (final ClassNotFoundException originalClassNotFoundException) {
    370                    // The current class loader was unable to find the log adapter
    371                    // in this or any ancestor class loader. There's no point in
    372                    // trying higher up in the hierarchy in this case.
    373                    String msg = originalClassNotFoundException.getMessage();
    374                    logDiagnostic("The log adapter '" + logAdapterClassName + "' is not available via class loader " + objectId(currentCL) + ": " + trim(msg));
    375                    try {
    376                        // Try the class class loader.
    377                        // This may work in cases where the TCCL
    378                        // does not contain the code executed or JCL.
    379                        // This behavior indicates that the application
    380                        // classloading strategy is not consistent with the
    381                        // Java 1.2 classloading guidelines but JCL can
    382                        // and so should handle this case.
    383                        clazz = Class.forName(logAdapterClassName);
    384                    } catch (final ClassNotFoundException secondaryClassNotFoundException) {
    385                        // no point continuing: this adapter isn't available
    386                        msg = secondaryClassNotFoundException.getMessage();
    387                        logDiagnostic("The log adapter '" + logAdapterClassName + "' is not available via the LogFactoryImpl class class loader: " + trim(msg));
    388                        break;
    389                    }
    390                }
    391                constructor = clazz.getConstructor(logConstructorSignature);
    392                final Object o = constructor.newInstance(params);
    393                // Note that we do this test after trying to create an instance
    394                // [rather than testing Log.class.isAssignableFrom(c)] so that
    395                // we don't complain about Log hierarchy problems when the
    396                // adapter couldn't be instantiated anyway.
    397                if (o instanceof Log) {
    398                    logAdapterClass = clazz;
    399                    logAdapter = (Log) o;
    400                    break;
    401                }
    402                // Oops, we have a potential problem here. An adapter class
    403                // has been found and its underlying lib is present too, but
    404                // there are multiple Log interface classes available making it
    405                // impossible to cast to the type the caller wanted. We
    406                // certainly can't use this logger, but we need to know whether
    407                // to keep on discovering or terminate now.
    408                //
    409                // The handleFlawedHierarchy method will throw
    410                // LogConfigurationException if it regards this problem as
    411                // fatal, and just return if not.
    412                handleFlawedHierarchy(currentCL, clazz);
    413            } catch (final NoClassDefFoundError e) {
    414                // We were able to load the adapter but it had references to
    415                // other classes that could not be found. This simply means that
    416                // the underlying logger library is not present in this or any
    417                // ancestor class loader. There's no point in trying higher up
    418                // in the hierarchy in this case.
    419                final String msg = e.getMessage();
    420                logDiagnostic("The log adapter '" + logAdapterClassName + "' is missing dependencies when loaded via class loader " + objectId(currentCL) +
    421                        ": " + trim(msg));
    422                break;
    423            } catch (final ExceptionInInitializerError e) {
    424                // A static initializer block or the initializer code associated
    425                // with a static variable on the log adapter class has thrown
    426                // an exception.
    427                //
    428                // We treat this as meaning the adapter's underlying logging
    429                // library could not be found.
    430                final String msg = e.getMessage();
    431                logDiagnostic("The log adapter '" + logAdapterClassName + "' is unable to initialize itself when loaded via class loader " +
    432                        objectId(currentCL) + ": " + trim(msg));
    433                break;
    434            } catch (final LogConfigurationException e) {
    435                // call to handleFlawedHierarchy above must have thrown
    436                // a LogConfigurationException, so just throw it on
    437                throw e;
    438            } catch (final Throwable t) {
    439                handleThrowable(t); // may re-throw t
    440                // handleFlawedDiscovery will determine whether this is a fatal
    441                // problem or not. If it is fatal, then a LogConfigurationException
    442                // will be thrown.
    443                handleFlawedDiscovery(logAdapterClassName, t);
    444            }
    445            if (currentCL == null) {
    446                break;
    447            }
    448            // try the parent class loader
    449            // currentCL = currentCL.getParent();
    450            currentCL = getParentClassLoader(currentCL);
    451        }
    452        if (logAdapterClass != null && affectState) {
    453            // We've succeeded, so set instance fields
    454            this.logClassName = logAdapterClassName;
    455            this.logConstructor = constructor;
    456            // Identify the {@code setLogFactory} method (if there is one)
    457            try {
    458                this.logMethod = logAdapterClass.getMethod("setLogFactory", logMethodSignature);
    459                logDiagnostic("Found method setLogFactory(LogFactory) in '" + logAdapterClassName + "'");
    460            } catch (final Throwable t) {
    461                handleThrowable(t); // may re-throw t
    462                this.logMethod = null;
    463                logDiagnostic("[INFO] '" + logAdapterClassName + "' from class loader " + objectId(currentCL) + " does not declare optional method " +
    464                        "setLogFactory(LogFactory)");
    465            }
    466            logDiagnostic("Log adapter '" + logAdapterClassName + "' from class loader " + objectId(logAdapterClass.getClassLoader()) +
    467                    " has been selected for use.");
    468        }
    469        return logAdapter;
    470    }
    471
    472        // Static Methods
    473    //
    474    // These methods only defined as workarounds for a java 1.2 bug;
    475    // theoretically none of these are needed.
    476
    477    /**
    478     * Attempts to create a Log instance for the given category name.
    479     * Follows the discovery process described in the class Javadoc.
    480     *
    481     * @param logCategory the name of the log category
    482     * @throws LogConfigurationException if an error in discovery occurs,
    483     * or if no adapter at all can be instantiated
    484     */
    485    private Log discoverLogImplementation(final String logCategory)
    486            throws LogConfigurationException {
    487        if (isDiagnosticsEnabled()) {
    488            logDiagnostic("Discovering a Log implementation...");
    489        }
    490        initConfiguration();
    491        Log result = null;
    492        // See if the user specified the Log implementation to use
    493        final String specifiedLogClassName = findUserSpecifiedLogClassName();
    494        if (specifiedLogClassName != null) {
    495            if (isDiagnosticsEnabled()) {
    496                logDiagnostic("Attempting to load user-specified log class '" + specifiedLogClassName + "'...");
    497            }
    498            result = createLogFromClass(specifiedLogClassName, logCategory, true);
    499            if (result == null) {
    500                final StringBuilder messageBuffer = new StringBuilder("User-specified log class '");
    501                messageBuffer.append(specifiedLogClassName);
    502                messageBuffer.append("' cannot be found or is not useable.");
    503                // Mistyping or misspelling names is a common fault.
    504                // Construct a good error message, if we can
    505                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LOG4J_LOGGER);
    506                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_JDK14_LOGGER);
    507                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LUMBERJACK_LOGGER);
    508                informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_SIMPLE_LOGGER);
    509                throw new LogConfigurationException(messageBuffer.toString());
    510            }
    511            return result;
    512        }
    513        // No user specified log; try to discover what's on the classpath
    514        //
    515        // Note that we deliberately loop here over classesToDiscover and
    516        // expect method createLogFromClass to loop over the possible source
    517        // class loaders. The effect is:
    518        // for each discoverable log adapter
    519        // for each possible class loader
    520        // see if it works
    521        //
    522        // It appears reasonable at first glance to do the opposite:
    523        // for each possible class loader
    524        // for each discoverable log adapter
    525        // see if it works
    526        //
    527        // The latter certainly has advantages for user-installable logging
    528        // libraries such as Log4j; in a webapp for example this code should
    529        // first check whether the user has provided any of the possible
    530        // logging libraries before looking in the parent class loader.
    531        // Unfortunately, however, Jdk14Logger will always work in jvm>=1.4,
    532        // and SimpleLog will always work in any JVM. So the loop would never
    533        // ever look for logging libraries in the parent classpath. Yet many
    534        // users would expect that putting Log4j there would cause it to be
    535        // detected (and this is the historical JCL behavior). So we go with
    536        // the first approach. A user that has bundled a specific logging lib
    537        // in a webapp should use a commons-logging.properties file or a
    538        // service file in META-INF to force use of that logging lib anyway,
    539        // rather than relying on discovery.
    540        if (isDiagnosticsEnabled()) {
    541            logDiagnostic("No user-specified Log implementation; performing discovery using the standard supported logging implementations...");
    542        }
    543        for (int i = 0; i < DISCOVER_CLASSES.length && result == null; ++i) {
    544            result = createLogFromClass(DISCOVER_CLASSES[i], logCategory, true);
    545        }
    546        if (result == null) {
    547            throw new LogConfigurationException("No suitable Log implementation");
    548        }
    549        return result;
    550    }
    551
    552    /**
    553     * Checks system properties and the attribute map for
    554     * a Log implementation specified by the user under the
    555     * property names {@link #LOG_PROPERTY} or {@link #LOG_PROPERTY_OLD}.
    556     *
    557     * @return class name specified by the user, or {@code null}
    558     */
    559    private String findUserSpecifiedLogClassName() {
    560        if (isDiagnosticsEnabled()) {
    561            logDiagnostic("Trying to get log class from attribute '" + LOG_PROPERTY + "'");
    562        }
    563        String specifiedClass = (String) getAttribute(LOG_PROPERTY);
    564        if (specifiedClass == null) { // @deprecated
    565            if (isDiagnosticsEnabled()) {
    566                logDiagnostic("Trying to get log class from attribute '" + LOG_PROPERTY_OLD + "'");
    567            }
    568            specifiedClass = (String) getAttribute(LOG_PROPERTY_OLD);
    569        }
    570        if (specifiedClass == null) {
    571            if (isDiagnosticsEnabled()) {
    572                logDiagnostic("Trying to get log class from system property '" + LOG_PROPERTY + "'");
    573            }
    574            try {
    575                specifiedClass = getSystemProperty(LOG_PROPERTY, null);
    576            } catch (final SecurityException e) {
    577                if (isDiagnosticsEnabled()) {
    578                    logDiagnostic("No access allowed to system property '" + LOG_PROPERTY + "' - " + e.getMessage());
    579                }
    580            }
    581        }
    582        if (specifiedClass == null) { // @deprecated
    583            if (isDiagnosticsEnabled()) {
    584                logDiagnostic("Trying to get log class from system property '" + LOG_PROPERTY_OLD + "'");
    585            }
    586            try {
    587                specifiedClass = getSystemProperty(LOG_PROPERTY_OLD, null);
    588            } catch (final SecurityException e) {
    589                if (isDiagnosticsEnabled()) {
    590                    logDiagnostic("No access allowed to system property '" + LOG_PROPERTY_OLD + "' - " + e.getMessage());
    591                }
    592            }
    593        }
    594        // Remove any whitespace; it's never valid in a class name so its
    595        // presence just means a user mistake. As we know what they meant,
    596        // we may as well strip the spaces.
    597        if (specifiedClass != null) {
    598            specifiedClass = specifiedClass.trim();
    599        }
    600        return specifiedClass;
    601    }
    602
    603    /**
    604     * Gets the configuration attribute with the specified name (if any),
    605     * or {@code null} if there is no such attribute.
    606     *
    607     * @param name Name of the attribute to return
    608     */
    609    @Override
    610    public Object getAttribute(final String name) {
    611        return attributes.get(name);
    612    }
    613
    614    /**
    615     * Gets an array containing the names of all currently defined
    616     * configuration attributes.  If there are no such attributes, a zero
    617     * length array is returned.
    618     */
    619    @Override
    620    public String[] getAttributeNames() {
    621        return attributes.keySet().toArray(EMPTY_STRING_ARRAY);
    622    }
    623
    624    /**
    625     * Gets the class loader from which we should try to load the logging
    626     * adapter classes.
    627     * <p>
    628     * This method usually returns the context class loader. However if it
    629     * is discovered that the class loader which loaded this class is a child
    630     * of the context class loader <em>and</em> the allowFlawedContext option
    631     * has been set then the class loader which loaded this class is returned
    632     * instead.
    633     * </p>
    634     * <p>
    635     * The only time when the class loader which loaded this class is a
    636     * descendant (rather than the same as or an ancestor of the context
    637     * class loader) is when an app has created custom class loaders but
    638     * failed to correctly set the context class loader. This is a bug in
    639     * the calling application; however we provide the option for JCL to
    640     * simply generate a warning rather than fail outright.
    641     * </p>
    642     */
    643    private ClassLoader getBaseClassLoader() throws LogConfigurationException {
    644        final ClassLoader thisClassLoader = getClassLoader(LogFactoryImpl.class);
    645        if (!useTCCL) {
    646            return thisClassLoader;
    647        }
    648        final ClassLoader contextClassLoader = getContextClassLoaderInternal();
    649        final ClassLoader baseClassLoader = getLowestClassLoader(contextClassLoader, thisClassLoader);
    650        if (baseClassLoader == null) {
    651            // The two class loaders are not part of a parent child relationship.
    652            // In some classloading setups (e.g. JBoss with its
    653            // UnifiedLoaderRepository) this can still work, so if user hasn't
    654            // forbidden it, just return the contextClassLoader.
    655            if (!allowFlawedContext) {
    656                throw new LogConfigurationException(
    657                        "Bad class loader hierarchy; LogFactoryImpl was loaded via a class loader that is not related to the current context class loader.");
    658            }
    659            if (isDiagnosticsEnabled()) {
    660                logDiagnostic(
    661                        "[WARNING] the context class loader is not part of a parent-child relationship with the class loader that loaded LogFactoryImpl.");
    662            }
    663            // If contextClassLoader were null, getLowestClassLoader() would
    664            // have returned thisClassLoader. The fact we are here means
    665            // contextClassLoader is not null, so we can just return it.
    666            return contextClassLoader;
    667        }
    668        if (baseClassLoader != contextClassLoader) {
    669            // We really should just use the contextClassLoader as the starting
    670            // point for scanning for log adapter classes. However it is expected
    671            // that there are a number of broken systems out there which create
    672            // custom class loaders but fail to set the context class loader so
    673            // we handle those flawed systems anyway.
    674            if (!allowFlawedContext) {
    675                throw new LogConfigurationException(
    676                        "Bad class loader hierarchy; LogFactoryImpl was loaded via a class loader that is not related to the current context class loader.");
    677            }
    678            if (isDiagnosticsEnabled()) {
    679                logDiagnostic("Warning: the context class loader is an ancestor of the class loader that loaded LogFactoryImpl; it should be" +
    680                        " the same or a descendant. The application using commons-logging should ensure the context class loader is used correctly.");
    681            }
    682        }
    683        return baseClassLoader;
    684    }
    685
    686    /**
    687     * Gets the setting for the user-configurable behavior specified by key.
    688     * If nothing has explicitly been set, then return dflt.
    689     */
    690    private boolean getBooleanConfiguration(final String key, final boolean dflt) {
    691        final String val = getConfigurationValue(key);
    692        if (val == null) {
    693            return dflt;
    694        }
    695        return Boolean.parseBoolean(val);
    696    }
    697
    698    /**
    699     * Attempt to find an attribute (see method setAttribute) or a
    700     * system property with the provided name and return its value.
    701     * <p>
    702     * The attributes associated with this object are checked before
    703     * system properties in case someone has explicitly called setAttribute,
    704     * or a configuration property has been set in a commons-logging.properties
    705     * file.
    706     * </p>
    707     *
    708     * @return the value associated with the property, or null.
    709     */
    710    private String getConfigurationValue(final String property) {
    711        if (isDiagnosticsEnabled()) {
    712            logDiagnostic("[ENV] Trying to get configuration for item " + property);
    713        }
    714        final Object valueObj = getAttribute(property);
    715        if (valueObj != null) {
    716            if (isDiagnosticsEnabled()) {
    717                logDiagnostic("[ENV] Found LogFactory attribute [" + valueObj + "] for " + property);
    718            }
    719            return valueObj.toString();
    720        }
    721        if (isDiagnosticsEnabled()) {
    722            logDiagnostic("[ENV] No LogFactory attribute found for " + property);
    723        }
    724        try {
    725            // warning: minor security hole here, in that we potentially read a system
    726            // property that the caller cannot, then output it in readable form as a
    727            // diagnostic message. However it's only ever JCL-specific properties
    728            // involved here, so the harm is truly trivial.
    729            final String value = getSystemProperty(property, null);
    730            if (value != null) {
    731                if (isDiagnosticsEnabled()) {
    732                    logDiagnostic("[ENV] Found system property [" + value + "] for " + property);
    733                }
    734                return value;
    735            }
    736            if (isDiagnosticsEnabled()) {
    737                logDiagnostic("[ENV] No system property found for property " + property);
    738            }
    739        } catch (final SecurityException e) {
    740            if (isDiagnosticsEnabled()) {
    741                logDiagnostic("[ENV] Security prevented reading system property " + property);
    742            }
    743        }
    744        if (isDiagnosticsEnabled()) {
    745            logDiagnostic("[ENV] No configuration defined for item " + property);
    746        }
    747        return null;
    748    }
    749
    750    /**
    751     * Convenience method to derive a name from the specified class and
    752     * call {@code getInstance(String)} with it.
    753     *
    754     * @param clazz Class for which a suitable Log name will be derived
    755     * @throws LogConfigurationException if a suitable {@code Log}
    756     *  instance cannot be returned
    757     */
    758    @Override
    759    public Log getInstance(final Class<?> clazz) throws LogConfigurationException {
    760        return getInstance(clazz.getName());
    761    }
    762
    763    /**
    764     * Construct (if necessary) and return a {@code Log} instance,
    765     * using the factory's current set of configuration attributes.
    766     *
    767     * <p><strong>NOTE</strong> - Depending upon the implementation of
    768     * the {@code LogFactory} you are using, the {@code Log}
    769     * instance you are returned may or may not be local to the current
    770     * application, and may or may not be returned again on a subsequent
    771     * call with the same name argument.</p>
    772     *
    773     * @param name Logical name of the {@code Log} instance to be
    774     *  returned (the meaning of this name is only known to the underlying
    775     *  logging implementation that is being wrapped)
    776     *
    777     * @throws LogConfigurationException if a suitable {@code Log}
    778     *  instance cannot be returned
    779     */
    780    @Override
    781    public Log getInstance(final String name) throws LogConfigurationException {
    782        return instances.computeIfAbsent(name, this::newInstance);
    783    }
    784
    785    /**
    786     * Gets the fully qualified Java class name of the {@link Log} implementation we will be using.
    787     *
    788     * @return the fully qualified Java class name of the {@link Log} implementation we will be using.
    789     * @deprecated Never invoked by this class; subclasses should not assume it will be.
    790     */
    791    @Deprecated
    792    protected String getLogClassName() {
    793        if (logClassName == null) {
    794            discoverLogImplementation(getClass().getName());
    795        }
    796        return logClassName;
    797    }
    798
    799    /**
    800     * Gets the {@code Constructor} that can be called to instantiate new {@link org.apache.commons.logging.Log} instances.
    801     * <p>
    802     * <strong>IMPLEMENTATION NOTE</strong> - Race conditions caused by calling this method from more than one thread are ignored, because the same
    803     * {@code Constructor} instance will ultimately be derived in all circumstances.
    804     * </p>
    805     *
    806     * @return the {@code Constructor} that can be called to instantiate new {@link org.apache.commons.logging.Log} instances.
    807     * @throws LogConfigurationException if a suitable constructor cannot be returned
    808     * @deprecated Never invoked by this class; subclasses should not assume it will be.
    809     */
    810    @Deprecated
    811    protected Constructor<?> getLogConstructor() throws LogConfigurationException {
    812        // Return the previously identified Constructor (if any)
    813        if (logConstructor == null) {
    814            discoverLogImplementation(getClass().getName());
    815        }
    816        return logConstructor;
    817    }
    818    //  ------------------------------------------------------ Private Methods
    819
    820    /**
    821     * Given two related class loaders, return the one which is a child of
    822     * the other.
    823     *
    824     * @param c1 is a class loader (including the null class loader)
    825     * @param c2 is a class loader (including the null class loader)
    826     * @return c1 if it has c2 as an ancestor, c2 if it has c1 as an ancestor,
    827     * and null if neither is an ancestor of the other.
    828     */
    829    private ClassLoader getLowestClassLoader(final ClassLoader c1, final ClassLoader c2) {
    830        // TODO: use AccessController when dealing with class loaders here
    831        if (c1 == null) {
    832            return c2;
    833        }
    834        if (c2 == null) {
    835            return c1;
    836        }
    837        ClassLoader current;
    838        // scan c1's ancestors to find c2
    839        current = c1;
    840        while (current != null) {
    841            if (current == c2) {
    842                return c1;
    843            }
    844            // current = current.getParent();
    845            current = getParentClassLoader(current);
    846        }
    847        // scan c2's ancestors to find c1
    848        current = c2;
    849        while (current != null) {
    850            if (current == c1) {
    851                return c2;
    852            }
    853            // current = current.getParent();
    854            current = getParentClassLoader(current);
    855        }
    856        return null;
    857    }
    858
    859    /**
    860     * Fetch the parent class loader of a specified class loader.
    861     * <p>
    862     * If a SecurityException occurs, null is returned.
    863     * </p>
    864     * <p>
    865     * Note that this method is non-static merely so logDiagnostic is available.
    866     * </p>
    867     */
    868    private ClassLoader getParentClassLoader(final ClassLoader cl) {
    869        try {
    870            return AccessController.doPrivileged((PrivilegedAction<ClassLoader>) () -> cl.getParent());
    871        } catch (final SecurityException ex) {
    872            logDiagnostic("[SECURITY] Unable to obtain parent class loader");
    873            return null;
    874        }
    875    }
    876
    877    /**
    878     * Generates an internal diagnostic logging of the discovery failure and
    879     * then throws a {@code LogConfigurationException} that wraps
    880     * the passed {@code Throwable}.
    881     *
    882     * @param logAdapterClassName is the class name of the Log implementation
    883     * that could not be instantiated. Cannot be {@code null}.
    884     * @param discoveryFlaw is the Throwable created by the class loader
    885     * @throws LogConfigurationException    ALWAYS
    886     */
    887    private void handleFlawedDiscovery(final String logAdapterClassName, final Throwable discoveryFlaw) {
    888        if (isDiagnosticsEnabled()) {
    889            logDiagnostic("Could not instantiate Log '" + logAdapterClassName + "' -- " + discoveryFlaw.getClass().getName() + ": " +
    890                    discoveryFlaw.getLocalizedMessage());
    891            if (discoveryFlaw instanceof InvocationTargetException) {
    892                // Ok, the lib is there but while trying to create a real underlying
    893                // logger something failed in the underlying lib; display info about
    894                // that if possible.
    895                final InvocationTargetException ite = (InvocationTargetException) discoveryFlaw;
    896                final Throwable cause = ite.getTargetException();
    897                if (cause != null) {
    898                    logDiagnostic("... InvocationTargetException: " + cause.getClass().getName() + ": " + cause.getLocalizedMessage());
    899                    if (cause instanceof ExceptionInInitializerError) {
    900                        final ExceptionInInitializerError eiie = (ExceptionInInitializerError) cause;
    901                        final Throwable cause2 = eiie.getCause();
    902                        if (cause2 != null) {
    903                            final StringWriter sw = new StringWriter();
    904                            cause2.printStackTrace(new PrintWriter(sw, true));
    905                            logDiagnostic("... ExceptionInInitializerError: " + sw.toString());
    906                        }
    907                    }
    908                }
    909            }
    910        }
    911        if (!allowFlawedDiscovery) {
    912            throw new LogConfigurationException(discoveryFlaw);
    913        }
    914    }
    915
    916    /**
    917     * Report a problem loading the log adapter, then either return
    918     * (if the situation is considered recoverable) or throw a
    919     * LogConfigurationException.
    920     * <p>
    921     * There are two possible reasons why we successfully loaded the
    922     * specified log adapter class then failed to cast it to a Log object:
    923     * </p>
    924     * <ol>
    925     * <li>the specific class just doesn't implement the Log interface
    926     *     (user screwed up), or</li>
    927     * <li> the specified class has bound to a Log class loaded by some other
    928     *      class loader; Log@ClassLoaderX cannot be cast to Log@ClassLoaderY.</li>
    929     * </ol>
    930     * <p>
    931     * Here we try to figure out which case has occurred so we can give the
    932     * user some reasonable feedback.
    933     * </p>
    934     *
    935     * @param badClassLoader is the class loader we loaded the problem class from,
    936     * ie it is equivalent to badClass.getClassLoader().
    937     *
    938     * @param badClass is a Class object with the desired name, but which
    939     * does not implement Log correctly.
    940     *
    941     * @throws LogConfigurationException when the situation
    942     * should not be recovered from.
    943     */
    944    private void handleFlawedHierarchy(final ClassLoader badClassLoader, final Class<?> badClass) throws LogConfigurationException {
    945        boolean implementsLog = false;
    946        final String logInterfaceName = Log.class.getName();
    947        final Class<?>[] interfaces = badClass.getInterfaces();
    948        for (final Class<?> element : interfaces) {
    949            if (logInterfaceName.equals(element.getName())) {
    950                implementsLog = true;
    951                break;
    952            }
    953        }
    954        if (implementsLog) {
    955            // the class does implement an interface called Log, but
    956            // it is in the wrong class loader
    957            if (isDiagnosticsEnabled()) {
    958                try {
    959                    final ClassLoader logInterfaceClassLoader = getClassLoader(Log.class);
    960                    logDiagnostic("Class '" + badClass.getName() + "' was found in class loader " + objectId(badClassLoader) +
    961                            ". It is bound to a Log interface which is not the one loaded from class loader " + objectId(logInterfaceClassLoader));
    962                } catch (final Throwable t) {
    963                    handleThrowable(t); // may re-throw t
    964                    logDiagnostic("Error while trying to output diagnostics about bad class '" + badClass + "'");
    965                }
    966            }
    967            if (!allowFlawedHierarchy) {
    968                final StringBuilder msg = new StringBuilder();
    969                msg.append("Terminating logging for this context ");
    970                msg.append("due to bad log hierarchy. ");
    971                msg.append("You have more than one version of '");
    972                msg.append(Log.class.getName());
    973                msg.append("' visible.");
    974                if (isDiagnosticsEnabled()) {
    975                    logDiagnostic(msg.toString());
    976                }
    977                throw new LogConfigurationException(msg.toString());
    978            }
    979            if (isDiagnosticsEnabled()) {
    980                final StringBuilder msg = new StringBuilder();
    981                msg.append("Warning: bad log hierarchy. ");
    982                msg.append("You have more than one version of '");
    983                msg.append(Log.class.getName());
    984                msg.append("' visible.");
    985                logDiagnostic(msg.toString());
    986            }
    987        } else {
    988            // this is just a bad adapter class
    989            if (!allowFlawedDiscovery) {
    990                final StringBuilder msg = new StringBuilder();
    991                msg.append("Terminating logging for this context. ");
    992                msg.append("Log class '");
    993                msg.append(badClass.getName());
    994                msg.append("' does not implement the Log interface.");
    995                if (isDiagnosticsEnabled()) {
    996                    logDiagnostic(msg.toString());
    997                }
    998                throw new LogConfigurationException(msg.toString());
    999            }
    1000            if (isDiagnosticsEnabled()) {
    1001                final StringBuilder msg = new StringBuilder();
    1002                msg.append("[WARNING] Log class '");
    1003                msg.append(badClass.getName());
    1004                msg.append("' does not implement the Log interface.");
    1005                logDiagnostic(msg.toString());
    1006            }
    1007        }
    1008    }
    1009
    1010    /**
    1011     * Appends message if the given name is similar to the candidate.
    1012     *
    1013     * @param messageBuffer {@code StringBuffer} the message should be appended to,
    1014     * not null
    1015     * @param name the (trimmed) name to be test against the candidate, not null
    1016     * @param candidate the candidate name (not null)
    1017     */
    1018    private void informUponSimilarName(final StringBuilder messageBuffer, final String name, final String candidate) {
    1019        if (name.equals(candidate)) {
    1020            // Don't suggest a name that is exactly the same as the one the
    1021            // user tried...
    1022            return;
    1023        }
    1024        // If the user provides a name that is in the right package, and gets
    1025        // the first 5 characters of the adapter class right (ignoring case),
    1026        // then suggest the candidate adapter class name.
    1027        if (name.regionMatches(true, 0, candidate, 0, PKG_LEN + 5)) {
    1028            messageBuffer.append(" Did you mean '");
    1029            messageBuffer.append(candidate);
    1030            messageBuffer.append("'?");
    1031        }
    1032    }
    1033
    1034    /**
    1035     * Initializes a number of variables that control the behavior of this
    1036     * class and that can be tweaked by the user. This is done when the first
    1037     * logger is created, not in the constructor of this class, because we
    1038     * need to give the user a chance to call method setAttribute in order to
    1039     * configure this object.
    1040     */
    1041    private void initConfiguration() {
    1042        allowFlawedContext = getBooleanConfiguration(ALLOW_FLAWED_CONTEXT_PROPERTY, true);
    1043        allowFlawedDiscovery = getBooleanConfiguration(ALLOW_FLAWED_DISCOVERY_PROPERTY, true);
    1044        allowFlawedHierarchy = getBooleanConfiguration(ALLOW_FLAWED_HIERARCHY_PROPERTY, true);
    1045    }
    1046
    1047    /**
    1048     * Initializes a string that uniquely identifies this instance,
    1049     * including which class loader the object was loaded from.
    1050     * <p>
    1051     * This string will later be prefixed to each "internal logging" message
    1052     * emitted, so that users can clearly see any unexpected behavior.
    1053     * <p>
    1054     * Note that this method does not detect whether internal logging is
    1055     * enabled or not, nor where to output stuff if it is; that is all
    1056     * handled by the parent LogFactory class. This method just computes
    1057     * its own unique prefix for log messages.
    1058     */
    1059    private void initDiagnostics() {
    1060        // It would be nice to include an identifier of the context class loader
    1061        // that this LogFactoryImpl object is responsible for. However that
    1062        // isn't possible as that information isn't available. It is possible
    1063        // to figure this out by looking at the logging from LogFactory to
    1064        // see the context & impl ids from when this object was instantiated,
    1065        // in order to link the impl id output as this object's prefix back to
    1066        // the context it is intended to manage.
    1067        // Note that this prefix should be kept consistent with that
    1068        // in LogFactory.
    1069        @SuppressWarnings("unchecked")
    1070        final Class<LogFactoryImpl> clazz = (Class<LogFactoryImpl>) this.getClass();
    1071        final ClassLoader classLoader = getClassLoader(clazz);
    1072        String classLoaderName;
    1073        try {
    1074            if (classLoader == null) {
    1075                classLoaderName = "BOOTLOADER";
    1076            } else {
    1077                classLoaderName = objectId(classLoader);
    1078            }
    1079        } catch (final SecurityException e) {
    1080            classLoaderName = "UNKNOWN";
    1081        }
    1082        diagnosticPrefix = "[LogFactoryImpl@" + System.identityHashCode(this) + " from " + classLoaderName + "] ";
    1083    }
    1084
    1085    /**
    1086     * Tests whether <em>JDK 1.3 with Lumberjack</em> logging available.
    1087     *
    1088     * @return whether <em>JDK 1.3 with Lumberjack</em> logging available.
    1089     * @deprecated Never invoked by this class; subclasses should not assume it will be.
    1090     */
    1091    @Deprecated
    1092    protected boolean isJdk13LumberjackAvailable() {
    1093        return isLogLibraryAvailable("Jdk13Lumberjack", "org.apache.commons.logging.impl.Jdk13LumberjackLogger");
    1094    }
    1095
    1096    /**
    1097     * Tests {@code true} whether <em>JDK 1.4 or later</em> logging is available. Also checks that the {@code Throwable} class supports {@code getStackTrace()},
    1098     * which is required by Jdk14Logger.
    1099     *
    1100     * @return Whether <em>JDK 1.4 or later</em> logging is available.
    1101     * @deprecated Never invoked by this class; subclasses should not assume it will be.
    1102     */
    1103    @Deprecated
    1104    protected boolean isJdk14Available() {
    1105        return isLogLibraryAvailable("Jdk14", "org.apache.commons.logging.impl.Jdk14Logger");
    1106    }
    1107
    1108    /**
    1109     * Tests whether a <em>Log4J</em> implementation available.
    1110     *
    1111     * @return whether a <em>Log4J</em> implementation available.
    1112     * @deprecated Never invoked by this class; subclasses should not assume it will be.
    1113     */
    1114    @Deprecated
    1115    protected boolean isLog4JAvailable() {
    1116        return isLogLibraryAvailable("Log4J", LOGGING_IMPL_LOG4J_LOGGER);
    1117    }
    1118
    1119    /**
    1120     * 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.
    1121     */
    1122    private boolean isLogLibraryAvailable(final String name, final String className) {
    1123        if (isDiagnosticsEnabled()) {
    1124            logDiagnostic("Checking for '" + name + "'.");
    1125        }
    1126        try {
    1127            final Log log = createLogFromClass(className, this.getClass().getName(), // dummy category
    1128                    false);
    1129            if (log == null) {
    1130                if (isDiagnosticsEnabled()) {
    1131                    logDiagnostic("Did not find '" + name + "'.");
    1132                }
    1133                return false;
    1134            }
    1135            if (isDiagnosticsEnabled()) {
    1136                logDiagnostic("Found '" + name + "'.");
    1137            }
    1138            return true;
    1139        } catch (final LogConfigurationException e) {
    1140            if (isDiagnosticsEnabled()) {
    1141                logDiagnostic("Logging system '" + name + "' is available but not useable.");
    1142            }
    1143            return false;
    1144        }
    1145    }
    1146
    1147    /**
    1148     * Output a diagnostic message to a user-specified destination (if the
    1149     * user has enabled diagnostic logging).
    1150     *
    1151     * @param msg diagnostic message
    1152     * @since 1.1
    1153     */
    1154    protected void logDiagnostic(final String msg) {
    1155        if (isDiagnosticsEnabled()) {
    1156            logRawDiagnostic(diagnosticPrefix + msg);
    1157        }
    1158    }
    1159
    1160    /**
    1161     * Create and return a new {@link org.apache.commons.logging.Log} instance for the specified name.
    1162     *
    1163     * @param name Name of the new logger
    1164     * @return a new {@link org.apache.commons.logging.Log}
    1165     * @throws LogConfigurationException if a new instance cannot be created
    1166     */
    1167    protected Log newInstance(final String name) throws LogConfigurationException {
    1168        Log instance;
    1169        try {
    1170            if (logConstructor == null) {
    1171                instance = discoverLogImplementation(name);
    1172            } else {
    1173                final Object[] params = { name };
    1174                instance = (Log) logConstructor.newInstance(params);
    1175            }
    1176            if (logMethod != null) {
    1177                final Object[] params = { this };
    1178                logMethod.invoke(instance, params);
    1179            }
    1180            return instance;
    1181        } catch (final LogConfigurationException lce) {
    1182            // this type of exception means there was a problem in discovery
    1183            // and we've already output diagnostics about the issue, etc.;
    1184            // just pass it on
    1185            throw lce;
    1186        } catch (final InvocationTargetException e) {
    1187            // A problem occurred invoking the Constructor or Method
    1188            // previously discovered
    1189            final Throwable c = e.getTargetException();
    1190            throw new LogConfigurationException(c == null ? e : c);
    1191        } catch (final Throwable t) {
    1192            handleThrowable(t); // may re-throw t
    1193            // A problem occurred invoking the Constructor or Method
    1194            // previously discovered
    1195            throw new LogConfigurationException(t);
    1196        }
    1197    }
    1198
    1199    /**
    1200     * Releases any internal references to previously created
    1201     * {@link org.apache.commons.logging.Log}
    1202     * instances returned by this factory.  This is useful in environments
    1203     * like servlet containers, which implement application reloading by
    1204     * throwing away a ClassLoader.  Dangling references to objects in that
    1205     * class loader would prevent garbage collection.
    1206     */
    1207    @Override
    1208    public void release() {
    1209        logDiagnostic("Releasing all known loggers");
    1210        instances.clear();
    1211    }
    1212
    1213    /**
    1214     * Remove any configuration attribute associated with the specified name.
    1215     * If there is no such attribute, no action is taken.
    1216     *
    1217     * @param name Name of the attribute to remove
    1218     */
    1219    @Override
    1220    public void removeAttribute(final String name) {
    1221        attributes.remove(name);
    1222    }
    1223
    1224    /**
    1225     * Sets the configuration attribute with the specified name.  Calling
    1226     * this with a {@code null} value is equivalent to calling
    1227     * {@code removeAttribute(name)}.
    1228     * <p>
    1229     * This method can be used to set logging configuration programmatically
    1230     * rather than via system properties. It can also be used in code running
    1231     * within a container (such as a webapp) to configure behavior on a
    1232     * per-component level instead of globally as system properties would do.
    1233     * To use this method instead of a system property, call
    1234     * </p>
    1235     * <pre>
    1236     * LogFactory.getFactory().setAttribute(...)
    1237     * </pre>
    1238     * <p>
    1239     * This must be done before the first Log object is created; configuration
    1240     * changes after that point will be ignored.
    1241     * </p>
    1242     * <p>
    1243     * This method is also called automatically if LogFactory detects a
    1244     * commons-logging.properties file; every entry in that file is set
    1245     * automatically as an attribute here.
    1246     * </p>
    1247     *
    1248     * @param name Name of the attribute to set
    1249     * @param value Value of the attribute to set, or {@code null}
    1250     *  to remove any setting for this attribute
    1251     */
    1252    @Override
    1253    public void setAttribute(final String name, final Object value) {
    1254        if (logConstructor != null) {
    1255            logDiagnostic("setAttribute: call too late; configuration already performed.");
    1256        }
    1257        if (value == null) {
    1258            attributes.remove(name);
    1259        } else {
    1260            attributes.put(name, value);
    1261        }
    1262        if (name.equals(TCCL_KEY)) {
    1263            useTCCL = value != null && Boolean.parseBoolean(value.toString());
    1264        }
    1265    }
    1266}