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