    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 *     http://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.configuration2.io;
    019
    020import org.apache.commons.logging.Log;
    021import org.apache.commons.logging.LogFactory;
    022import org.apache.commons.logging.impl.NoOpLog;
    023
    024/**
    025 * <p>
    026 * A class providing basic logging capabilities.
    027 * </p>
    028 * <p>
    029 * When reading configuration files in complex scenarios having log output is
    030 * useful for diagnostic purposes. Therefore, <em>Commons Configuration</em>
    031 * produces some logging output. As concrete projects have different
    032 * requirements on the amount and detail of logging, there is a way of
    033 * configuring logging: All classes derived from
    034 * {@link org.apache.commons.configuration2.AbstractConfiguration}
    035 * can be assigned a logger which is then used for all log statements generated.
    036 * </p>
    037 * <p>
    038 * Allowing a logger object to be passed to a configuration creates a direct
    039 * dependency to a concrete logging framework in the configuration API. This
    040 * would make it impossible to switch to an alternative logging framework
    041 * without breaking backwards compatibility. To avoid this, the
    042 * {@code ConfigurationLogger} class is introduced. It is a minimum abstraction
    043 * over a logging framework offering only very basic logging capabilities. The
    044 * methods defined in this class are used by configuration implementations to
    045 * produce their logging statements. Client applications can create specialized
    046 * instances and pass them to configuration objects without having to deal with
    047 * a concrete logging framework. It is even possible to create a subclass that
    048 * uses a completely different logging framework.
    049 * </p>
    050 *
    051 * @since 2.0
    052 */
    053public class ConfigurationLogger
    054{
    055    /** The internal logger. */
    056    private final Log log;
    057
    058    /**
    059     * Creates a new instance of {@code ConfigurationLogger} that uses the
    060     * specified logger name.
    061     *
    062     * @param loggerName the logger name (must not be <b>null</b>)
    063     * @throws IllegalArgumentException if the logger name is <b>null</b>
    064     */
    065    public ConfigurationLogger(final String loggerName)
    066    {
    067        this(createLoggerForName(loggerName));
    068    }
    069
    070    /**
    071     * Creates a new instance of {@code ConfigurationLogger} that uses a logger
    072     * whose name is derived from the provided class.
    073     *
    074     * @param logCls the class whose name is to be used for logging (must not be
    075     *        <b>null</b>)
    076     * @throws IllegalArgumentException if the logger class is <b>null</b>
    077     */
    078    public ConfigurationLogger(final Class<?> logCls)
    079    {
    080        this(createLoggerForClass(logCls));
    081    }
    082
    083    /**
    084     * Creates a new, uninitialized instance of {@code ConfigurationLogger}.
    085     * This constructor can be used by derived classes that implement their own
    086     * specific logging mechanism. Such classes must override all methods
    087     * because the default implementations do not work in this uninitialized
    088     * state.
    089     */
    090    protected ConfigurationLogger()
    091    {
    092        this((Log) null);
    093    }
    094
    095    /**
    096     * Creates a new instance of {@code ConfigurationLogger} which wraps the
    097     * specified logger.
    098     *
    099     * @param wrapped the logger to be wrapped
    100     */
    101    ConfigurationLogger(final Log wrapped)
    102    {
    103        log = wrapped;
    104    }
    105
    106    /**
    107     * Creates a new dummy logger which produces no output. If such a logger is
    108     * passed to a configuration object, logging is effectively disabled.
    109     *
    110     * @return the new dummy logger
    111     */
    112    public static ConfigurationLogger newDummyLogger()
    113    {
    114        return new ConfigurationLogger(new NoOpLog());
    115    }
    116
    117    /**
    118     * Returns a flag whether logging on debug level is enabled.
    119     *
    120     * @return <b>true</b> if debug logging is enabled, <b>false</b> otherwise
    121     */
    122    public boolean isDebugEnabled()
    123    {
    124        return getLog().isDebugEnabled();
    125    }
    126
    127    /**
    128     * Logs the specified message on debug level.
    129     *
    130     * @param msg the message to be logged
    131     */
    132    public void debug(final String msg)
    133    {
    134        getLog().debug(msg);
    135    }
    136
    137    /**
    138     * Returns a flag whether logging on info level is enabled.
    139     *
    140     * @return <b>true</b> if debug logging is enabled, <b>false</b> otherwise
    141     */
    142    public boolean isInfoEnabled()
    143    {
    144        return getLog().isInfoEnabled();
    145    }
    146
    147    /**
    148     * Logs the specified message on info level.
    149     *
    150     * @param msg the message to be logged
    151     */
    152    public void info(final String msg)
    153    {
    154        getLog().info(msg);
    155    }
    156
    157    /**
    158     * Logs the specified message on warn level.
    159     *
    160     * @param msg the message to be logged
    161     */
    162    public void warn(final String msg)
    163    {
    164        getLog().warn(msg);
    165    }
    166
    167    /**
    168     * Logs the specified exception on warn level.
    169     *
    170     * @param msg the message to be logged
    171     * @param ex the exception to be logged
    172     */
    173    public void warn(final String msg, final Throwable ex)
    174    {
    175        getLog().warn(msg, ex);
    176    }
    177
    178    /**
    179     * Logs the specified message on error level.
    180     *
    181     * @param msg the message to be logged
    182     */
    183    public void error(final String msg)
    184    {
    185        getLog().error(msg);
    186    }
    187
    188    /**
    189     * Logs the specified exception on error level.
    190     *
    191     * @param msg the message to be logged
    192     * @param ex the exception to be logged
    193     */
    194    public void error(final String msg, final Throwable ex)
    195    {
    196        getLog().error(msg, ex);
    197    }
    198
    199    /**
    200     * Returns the internal logger.
    201     *
    202     * @return the internal logger
    203     */
    204    Log getLog()
    205    {
    206        return log;
    207    }
    208
    209    /**
    210     * Creates an internal logger for the given name. Throws an exception if the
    211     * name is undefined.
    212     *
    213     * @param name the name of the logger
    214     * @return the logger object
    215     * @throws IllegalArgumentException if the logger name is undefined
    216     */
    217    private static Log createLoggerForName(final String name)
    218    {
    219        if (name == null)
    220        {
    221            throw new IllegalArgumentException("Logger name must not be null!");
    222        }
    223        return LogFactory.getLog(name);
    224    }
    225
    226    /**
    227     * Creates an internal logger for the given class. Throws an exception if
    228     * the class is undefined.
    229     *
    230     * @param cls the logger class
    231     * @return the logger object
    232     * @throws IllegalArgumentException if the logger class is undefined
    233     */
    234    private static Log createLoggerForClass(final Class<?> cls)
    235    {
    236        if (cls == null)
    237        {
    238            throw new IllegalArgumentException(
    239                    "Logger class must not be null!");
    240        }
    241        return LogFactory.getLog(cls);
    242    }
    243}