本文旨在解决使用log4j2使用包装器时,不能打印正确行号问题
slf4j+log4j2组合使用时,有时会使用包装器LoggerWrapper(装饰器LoggerDecorator)对原生的Logger能力进行增强,如修改日志的入参或对日志增加一些定位信息。如对日志的输入增加统一的前缀logPrefix
public class LoggerWrapper implements Logger {private final Logger logger;private final String logPrefix;public LoggerWrapper(String logPrefix, Logger logger) {this.logPrefix = logPrefix;this.logger = logger;}@Overridepublic void info(String message, Object arg) {this.logger.info(logPrefix + message, arg);}// ... 其他日志方法
}
在使用时通过统一的一个工厂内提供LoggerWrapper作为logger使用
public class MyLogger {public Logger logger(Class<?> clazz) {Logger logger = LoggerFactory.getLogger(clazz);// 未业务打印的日志都携带一个 “MyLogger”的标记,与其他包内的日志区分开来return new LoggerWrapper("MyLogger", logger);}
}
在其他业务类使用时可以按如下方式使用
public class MyBussiness {private static final Logger LOGGER = MyLogger.logger(MyBussiness.class);public void doSomething1() {LOGGER.info("MyBussiness doSomething1");}public void doSomething2() {LOGGER.info("MyBussiness doSomething2");}
}
期望日志为打印业务日志的类名与行号,使用log4j2的[%c %L]
配置,实际日志输出
[2023-11-01 16:00:00,000 +0800] [INFO ][main][MyBussiness 12] MyBussiness doSomething1
[2023-11-01 16:00:00,000 +0800] [INFO ][main][MyBussiness 12] MyBussiness doSomething2
发现log4j2打印的行号错误,都打印相同的行号,且是LoggerWrapper.info()
方法的行数,不是实际业务打印日志的行数。当使用包装器后如果只按上述配置可能会存在此问题。log4j2将自定义的logger也识别为业务代码。
解决此问题的方法是指定log4j2的FQCN。Log4j 会记住 Logger 的全限定类名(FQCN),并在打印位置时使用它在每个日志事件中堆栈进行遍历,打印全限定类名(FQCN)的上一个堆栈的行号。上述LoggerWrapper
没有指定FQCN,导致Log4j2认为FQCN是其内部的Logger,他的上一层日志事件是this.logger.info(logPrefix + message, arg);
,导致行号永远是LoggerWrapper的内部位置。
正确使用方式应该要实现LocationAwareLogger
public class LoggerWrapper implements LocationAwareLogger {private final LocationAwareLogger logger;private final String logPrefix;// 指定FQCNprivate final String FQCN = LoggerWrapper.class.getName();public LoggerWrapper(String logPrefix, LocationAwareLogger logger) {this.logPrefix = logPrefix;this.logger = logger;}private void writeLog(Marker marker, int level, Throwable exception, String format, Object... args) {String message = format;if (args != null && args.length > 0) {FormattingTuple formatted = MessageFormatter.arrayFormat(format, args);if (exception == null && formatted.getThrowable() != null) {exception = formatted.getThrowable();}message = formatted.getMessage();}// 将FQCN传入Log4j2的logger中logger.log(marker, FQCN, level, addPrefix(message), null, exception);}@Overridepublic void info(String message, Object arg) {writeLog(null, LocationAwareLogger.INFO_INT, null, message, arg);}// ... 其他日志方法
}
此时可以打印正常的日志行号
[2023-11-01 16:00:00,000 +0800] [INFO ][main][MyBussiness 5] MyBussiness doSomething1
[2023-11-01 16:00:00,000 +0800] [INFO ][main][MyBussiness 8] MyBussiness doSomething2
具体实现可以参考kafka-client
的LogContext
类如下所示:
/** 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.kafka.common.utils;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
import org.slf4j.helpers.FormattingTuple;
import org.slf4j.helpers.MessageFormatter;
import org.slf4j.spi.LocationAwareLogger;/*** This class provides a way to instrument loggers with a common context which can be used to* automatically enrich log messages. For example, in the KafkaConsumer, it is often useful to know* the groupId of the consumer, so this can be added to a context object which can then be passed to* all of the dependent components in order to build new loggers. This removes the need to manually* add the groupId to each message.*/
public class LogContext {private final String logPrefix;public LogContext(String logPrefix) {this.logPrefix = logPrefix == null ? "" : logPrefix;}public LogContext() {this("");}public Logger logger(Class<?> clazz) {Logger logger = LoggerFactory.getLogger(clazz);if (logger instanceof LocationAwareLogger) {return new LocationAwareKafkaLogger(logPrefix, (LocationAwareLogger) logger);} else {return new LocationIgnorantKafkaLogger(logPrefix, logger);}}public String logPrefix() {return logPrefix;}private static abstract class AbstractKafkaLogger implements Logger {private final String prefix;protected AbstractKafkaLogger(final String prefix) {this.prefix = prefix;}protected String addPrefix(final String message) {return prefix + message;}}private static class LocationAwareKafkaLogger extends AbstractKafkaLogger {private final LocationAwareLogger logger;private final String fqcn;LocationAwareKafkaLogger(String logPrefix, LocationAwareLogger logger) {super(logPrefix);this.logger = logger;this.fqcn = LocationAwareKafkaLogger.class.getName();}@Overridepublic String getName() {return logger.getName();}@Overridepublic void info(String msg) {writeLog(null, LocationAwareLogger.INFO_INT, msg, null, null);}private void writeLog(Marker marker, int level, String format, Object[] args, Throwable exception) {String message = format;if (args != null && args.length > 0) {FormattingTuple formatted = MessageFormatter.arrayFormat(format, args);if (exception == null && formatted.getThrowable() != null) {exception = formatted.getThrowable();}message = formatted.getMessage();}logger.log(marker, fqcn, level, addPrefix(message), null, exception);}}private static class LocationIgnorantKafkaLogger extends AbstractKafkaLogger {private final Logger logger;LocationIgnorantKafkaLogger(String logPrefix, Logger logger) {super(logPrefix);this.logger = logger;}@Overridepublic String getName() {return logger.getName();}@Overridepublic void info(String message) {logger.info(addPrefix(message));}}}