scr/src/main/java/org/apache/felix/scr/impl/logger/InternalLogger.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.felix.scr.impl.logger;

import java.text.MessageFormat;

import org.apache.felix.scr.impl.manager.ScrConfiguration;
import org.osgi.service.log.admin.LoggerAdmin;

/**
 * Base interface for the different SCR Loggers. Since this is not used outside
 * this package, it could be private. However, then Level should be standalone,
 * which would change most files. So minimize the code change, it is kept public.
 */
public interface InternalLogger {
	/**
	 * The level to log. This is aligned with the OSGi LogLevel
	 */
	public enum Level {
		AUDIT {
			boolean err() {
				return true;
			}
		},
		ERROR {
			boolean err() {
				return true;
			}
		},
		WARN, INFO, DEBUG, TRACE;

		/**
		 * Check if this log level is higher or the same of the other level.
		 * 
		 * @param other
		 *                  the other level
		 * @return true if the level other should be logged
		 */
		boolean implies(Level other) {
			return ordinal() >= other.ordinal();
		}

		boolean err() {
			return false;
		}

	}

	/**
	 * Logs the message to an appropriate OSGi logger. If not such logger can be
	 * found then it will log to stderr for ERROR & AUDIT messages and stdout
	 * for other messages
	 * 
	 * @param level
	 *                    only log when this level is implied by the current log
	 *                    level
	 * @param message
	 *                    the message to log
	 * @param ex
	 *                    a Throwable or null
	 */
	void log(Level level, String message, Throwable ex);

	/**
	 * Formats the message using the {@link MessageFormat} class, i.e. with {}
	 * place holders for the args. It then calls
	 * {@link #log(Level, String, Throwable)}.
	 * 
	 * @param level
	 *                    only log when this level is implied by the current log
	 *                    level
	 * @param message
	 *                    the message to log
	 * @param ex
	 *                    a Throwable or null
	 * @param args
	 *                    the arguments to the {@link MessageFormat} formatting
	 */
	void log(Level level, String message, Throwable ex, Object... args);

	/**
	 * Answer true if the current logging level is enabled for the given level.
	 * For stdout/stderr fallback the logging level is defined by the
	 * {@link ScrConfiguration#getLogLevel()}. If there is an OSGi logger
	 * available then the logger name will define the log level via
	 * {@link LoggerAdmin}.
	 *
	 * @param level
	 *                  the level to check
	 * @return true if the given log level is enabled
	 */
	boolean isLogEnabled(Level level);

}