java/org/apache/juli/logging/Log.java

/*
 * 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.juli.logging;

/**
 * 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>
 * 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>
 * <p>
 * The mapping of these log levels to the concepts used by the underlying logging system is implementation dependent.
 * The implementation should ensure, though, that this ordering behaves as expected.
 * <p>
 * Performance is often a logging concern. By examining the appropriate property, a component can avoid expensive
 * operations (producing information to be logged).
 * <p>
 * For example, <code>
 *    if (log.isDebugEnabled()) {
 *        ... do something expensive ...
 *        log.debug(theResult);
 *    }
 * </code>
 * <p>
 * Configuration of the underlying logging system will generally be done external to the Logging APIs, through whatever
 * mechanism is supported by that system.
 */
public interface Log {

    /**
     * <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>
     *
     * @return <code>true</code> if debug level logging is enabled, otherwise <code>false</code>
     */
    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>
     *
     * @return <code>true</code> if error level logging is enabled, otherwise <code>false</code>
     */
    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>
     *
     * @return <code>true</code> if fatal level logging is enabled, otherwise <code>false</code>
     */
    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>
     *
     * @return <code>true</code> if info level logging is enabled, otherwise <code>false</code>
     */
    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>
     *
     * @return <code>true</code> if trace level logging is enabled, otherwise <code>false</code>
     */
    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>
     *
     * @return <code>true</code> if warn level logging is enabled, otherwise <code>false</code>
     */
    boolean isWarnEnabled();


    // -------------------------------------------------------- Logging Methods


    /**
     * <p>
     * Log a message with trace log level.
     * </p>
     *
     * @param message log this message
     */
    void trace(Object message);


    /**
     * <p>
     * Log an error with trace log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void trace(Object message, Throwable t);


    /**
     * <p>
     * Log a message with debug log level.
     * </p>
     *
     * @param message log this message
     */
    void debug(Object message);


    /**
     * <p>
     * Log an error with debug log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void debug(Object message, Throwable t);


    /**
     * <p>
     * Log a message with info log level.
     * </p>
     *
     * @param message log this message
     */
    void info(Object message);


    /**
     * <p>
     * Log an error with info log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void info(Object message, Throwable t);


    /**
     * <p>
     * Log a message with warn log level.
     * </p>
     *
     * @param message log this message
     */
    void warn(Object message);


    /**
     * <p>
     * Log an error with warn log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void warn(Object message, Throwable t);


    /**
     * <p>
     * Log a message with error log level.
     * </p>
     *
     * @param message log this message
     */
    void error(Object message);


    /**
     * <p>
     * Log an error with error log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void error(Object message, Throwable t);


    /**
     * <p>
     * Log a message with fatal log level.
     * </p>
     *
     * @param message log this message
     */
    void fatal(Object message);


    /**
     * <p>
     * Log an error with fatal log level.
     * </p>
     *
     * @param message log this message
     * @param t       log this cause
     */
    void fatal(Object message, Throwable t);


}