/* * Copyright 2001-2004 The Apache Software Foundation. *  * Licensed 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;/** * <p>A simple logging interface abstracting logging APIs.  In order to be * instantiated successfully by {@link LogFactory}, classes that implement * this interface must have a constructor that takes a single String * parameter representing the "name" of this Log.</p> * * <p> The six logging levels used by <code>Log</code> are (in order): * <ol> * <li>trace (the least serious)</li> * <li>debug</li> * <li>info</li> * <li>warn</li> * <li>error</li> * <li>fatal (the most serious)</li> * </ol> * The mapping of these log levels to the concepts used by the underlying * logging system is implementation dependent. * The implemention should ensure, though, that this ordering behaves * as expected.</p> * * <p>Performance is often a logging concern. * By examining the appropriate property, * a component can avoid expensive operations (producing information * to be logged).</p> * * <p> For example, * <code><pre> *    if (log.isDebugEnabled()) { *        ... do something expensive ... *        log.debug(theResult); *    } * </pre></code> * </p> * * <p>Configuration of the underlying logging system will generally be done * external to the Logging APIs, through whatever mechanism is supported by * that system.</p> * * @author <a href="mailto:sanders@apache.org">Scott Sanders</a> * @author Rod Waldhoff * @version $Id: Log.java,v 1.19 2004/06/06 21:16:04 rdonkin Exp $ */public interface Log {    // ----------------------------------------------------- Logging Properties    /**     * <p> Is debug logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than debug. </p>     */    public boolean isDebugEnabled();    /**     * <p> Is error logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than error. </p>     */    public boolean isErrorEnabled();    /**     * <p> Is fatal logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than fatal. </p>     */    public boolean isFatalEnabled();    /**     * <p> Is info logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than info. </p>     */    public boolean isInfoEnabled();    /**     * <p> Is trace logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than trace. </p>     */    public boolean isTraceEnabled();    /**     * <p> Is warn logging currently enabled? </p>     *     * <p> Call this method to prevent having to perform expensive operations     * (for example, <code>String</code> concatenation)     * when the log level is more than warn. </p>     */    public boolean isWarnEnabled();    // -------------------------------------------------------- Logging Methods    /**     * <p> Log a message with trace log level. </p>     *     * @param message log this message     */    public void trace(Object message);    /**     * <p> Log an error with trace log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void trace(Object message, Throwable t);    /**     * <p> Log a message with debug log level. </p>     *     * @param message log this message     */    public void debug(Object message);    /**     * <p> Log an error with debug log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void debug(Object message, Throwable t);    /**     * <p> Log a message with info log level. </p>     *     * @param message log this message     */    public void info(Object message);    /**     * <p> Log an error with info log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void info(Object message, Throwable t);    /**     * <p> Log a message with warn log level. </p>     *     * @param message log this message     */    public void warn(Object message);    /**     * <p> Log an error with warn log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void warn(Object message, Throwable t);    /**     * <p> Log a message with error log level. </p>     *     * @param message log this message     */    public void error(Object message);    /**     * <p> Log an error with error log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void error(Object message, Throwable t);    /**     * <p> Log a message with fatal log level. </p>     *     * @param message log this message     */    public void fatal(Object message);    /**     * <p> Log an error with fatal log level. </p>     *     * @param message log this message     * @param t log this cause     */    public void fatal(Object message, Throwable t);}