logger(三)log4j2简介及其实现原理

作者：恋之-风景- | 来源：互联网 | 2023-09-16 20:05

一、log4j2简介log4j2是log4j1.x和logback的改进版，据说采用了一些新技术（无锁异步、等等），使得日志

一、log4j2简介

log4j2是log4j 1.x和logback的改进版&＃xff0c;据说采用了一些新技术&＃xff08;无锁异步、等等&＃xff09;&＃xff0c;使得日志的吞吐量、性能比log4j 1.x提高10倍&＃xff0c;并解决了一些死锁的bug&＃xff0c;而且配置更加简单灵活

maven配置

<dependency><groupId>org.apache.logging.log4jgroupId><artifactId>log4j-apiartifactId><version>2.9.1version>
dependency>
<dependency><groupId>org.apache.logging.log4jgroupId><artifactId>log4j-coreartifactId><version>2.9.1version>
dependency>

<dependency><groupId>org.apache.logging.log4jgroupId><artifactId>log4j-webartifactId><version>2.9.1version>
dependency>

<dependency><groupId>org.apache.logging.log4jgroupId><artifactId>log4j-slf4j-implartifactId><version>2.9.1version>
dependency>

<dependency><groupId>org.slf4jgroupId><artifactId>slf4j-apiartifactId><version>1.7.25version>

也可以配置starter

<dependency><groupId>org.springframework.bootgroupId><artifactId>spring-boot-starter-log4j2artifactId>
dependency>

二、log4j2.xml配置

实现类在log4j2.xml配置文件中的标签名。

xml version&＃61;"1.0" encoding&＃61;"UTF-8"?>

<configuration status&＃61;"WARN" monitorInterval&＃61;"30"><properties><property name&＃61;"server.port">property>properties><appenders><console name&＃61;"Console" target&＃61;"SYSTEM_OUT"><PatternLayout pattern&＃61;"%d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %p %m%n"/>console><RollingFile name&＃61;"RollingFile" filePattern&＃61;"/data/log/tomcat${sys:server.port}/catalina.%d{yyyy-MM-dd}.log"><ThresholdFilter level&＃61;"info" onMatch&＃61;"ACCEPT" onMismatch&＃61;"DENY"/><PatternLayout pattern&＃61;"%d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %p %m%n"/><Policies><TimeBasedTriggeringPolicy interval&＃61;"1" modulate&＃61;"true"/>Policies><DirectWriteRolloverStrategy/>RollingFile>appenders><loggers><logger name&＃61;"org.springframework" level&＃61;"INFO">logger><logger name&＃61;"org.mybatis" level&＃61;"INFO">logger><root level&＃61;"INFO"><appender-ref ref&＃61;"Console"/><appender-ref ref&＃61;"RollingFile"/>root>loggers>
configuration>

简单说Appender就是一个管道&＃xff0c;定义了日志内容的去向(保存位置)。

配置一个或者多个Filter进行过滤

配置Layout来控制日志信息的输出格式。

配置Policies以控制日志何时(When)进行滚动。

配置Strategy以控制日志如何(How)进行滚动。

简单说了下配置项&＃xff0c;具体可参考博客&＃xff1a;https://www.imooc.com/article/78966

https://www.cnblogs.com/hafiz/p/6170702.html

三、log4j2其实现原理

首先介绍下log4j2中的几个重要的概念

LoggerContext

LoggerContext在Logging System中扮演了锚点的角色。根据情况的不同&＃xff0c;一个应用可能同时存在于多个有效的LoggerContext中。在同一LoggerContext下&＃xff0c;log system是互通的。如&＃xff1a;Standalone Application、Web Applications、Java EE Applications、”Shared” Web Applications 和REST Service Containers&＃xff0c;就是不同广度范围的log上下文环境。

Configuration

每一个LoggerContext都有一个有效的Configuration。Configuration包含了所有的Appenders、上下文范围内的过滤器、LoggerConfigs以及StrSubstitutor.的引用。在重配置期间&＃xff0c;新与旧的Configuration将同时存在。当所有的Logger对象都被重定向到新的Configuration对象后&＃xff0c;旧的Configuration对象将被停用和丢弃。

Logger

Loggers 是通过调用LogManager.getLogger方法获得的。Logger对象本身并不实行任何实际的动作。它只是拥有一个name 以及与一个LoggerConfig相关联。它继承了AbstractLogger类并实现了所需的方法。当Configuration改变时&＃xff0c;Logger将会与另外的LoggerConfig相关联&＃xff0c;从而改变这个Logger的行为。

LoggerConfig

每个LoggerConfig和logger是对应的&＃xff0c;获取到一个logger&＃xff0c;写日志时其实是通过LoggerConfig来记日志的

1、获取LoggerFactory

和logback一样&＃xff0c;slf4j委托具体实现框架的StaticLoggerBinder来返回一个ILoggerFactory&＃xff0c;从而对接到具体实现框架上&＃xff0c;我们看下这个类(省略了部分代码)

public final class StaticLoggerBinder implements LoggerFactoryBinder {private static final StaticLoggerBinder SINGLETON &＃61; new StaticLoggerBinder();private final ILoggerFactory loggerFactory;/*** Private constructor to prevent instantiation*/private StaticLoggerBinder() {loggerFactory &＃61; new Log4jLoggerFactory();}/*** Returns the singleton of this class.** &＃64;return the StaticLoggerBinder singleton*/public static StaticLoggerBinder getSingleton() {return SINGLETON;}/*** Returns the factory.* &＃64;return the factor.*/&＃64;Overridepublic ILoggerFactory getLoggerFactory() {return loggerFactory;}
}

可以看到

1、通过getSingleton()获取该类的单例
2、通过构造函数新建了Log4jLoggerFactory实例&＃xff0c;
3、通过getLoggerFactory()方法返回该实例

2、获取logger

进入Log4jLoggerFactory类中查看getLogger()方法&＃xff0c;发现是在AbstractLoggerAdapter类中

&＃64;Overridepublic L getLogger(final String name) {final LoggerContext context &＃61; getContext();final ConcurrentMap loggers &＃61; getLoggersInContext(context);final L logger &＃61; loggers.get(name);if (logger !&＃61; null) {return logger;}loggers.putIfAbsent(name, newLogger(name, context));return loggers.get(name);}

1、通过getContext()得到LoggerContext实例

2、在context中查找是否已经有该logger&＃xff0c;有就返回

3、如果没有则调用newLogger(name, context)方法新建logger

Log4jLoggerFactory只有两个方法&＃xff0c;就是上面说的getContext()和newLogger(name, context)。下面分两节分别讲下这两个方法

public class Log4jLoggerFactory extends AbstractLoggerAdapter implements ILoggerFactory {private static final String FQCN &＃61; Log4jLoggerFactory.class.getName();private static final String PACKAGE &＃61; "org.slf4j";&＃64;Overrideprotected Logger newLogger(final String name, final LoggerContext context) {final String key &＃61; Logger.ROOT_LOGGER_NAME.equals(name) ? LogManager.ROOT_LOGGER_NAME : name;return new Log4jLogger(context.getLogger(key), name);}&＃64;Overrideprotected LoggerContext getContext() {final Class anchor &＃61; StackLocatorUtil.getCallerClass(FQCN, PACKAGE);return anchor &＃61;&＃61; null ? LogManager.getContext() : getContext(StackLocatorUtil.getCallerClass(anchor));}}

2.1 getContext()

getContext()方法就是返回合适的loggerContext&＃xff0c;进入LogManager.getContext()方法

public static LoggerContext getContext() {try {return factory.getContext(FQCN, null, null, true);} catch (final IllegalStateException ex) {LOGGER.warn(ex.getMessage() &＃43; " Using SimpleLogger");return new SimpleLoggerContextFactory().getContext(FQCN, null, null, true);}}

factory实在LoggerContext静态代码块中初始化的&＃xff0c;继续进入factory.getContext(FQCN, null, null, true)方法中&＃xff0c;进入实现类Log4jContextFactory中

&＃64;Overridepublic LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,final boolean currentContext) {final LoggerContext ctx &＃61; selector.getContext(fqcn, loader, currentContext);if (externalContext !&＃61; null && ctx.getExternalContext() &＃61;&＃61; null) {ctx.setExternalContext(externalContext);}if (ctx.getState() &＃61;&＃61; LifeCycle.State.INITIALIZED) {ctx.start();}return ctx;}

LoggerContext是从selector.getContext(fqcn, loader, currentContext)中获取的&＃xff0c;此时判断ctx.getState()是否等于LifeCycle.State.INITIALIZED&＃xff0c;第一次调用getlogger()时&＃xff0c;会进入此方法&＃xff0c;我们看下ctx.start();

public void start() {LOGGER.debug("Starting LoggerContext[name&＃61;{}, {}]...", getName(), this);if (PropertiesUtil.getProperties().getBooleanProperty("log4j.LoggerContext.stacktrace.on.start", false)) {LOGGER.debug("Stack trace to locate invoker",new Exception("Not a real error, showing stack trace to locate invoker"));}if (configLock.tryLock()) {try {if (this.isInitialized() || this.isStopped()) {this.setStarting();reconfigure();if (this.configuration.isShutdownHookEnabled()) {setUpShutdownHook();}this.setStarted();}} finally {configLock.unlock();}}LOGGER.debug("LoggerContext[name&＃61;{}, {}] started OK.", getName(), this);}

进入reconfigure()方法

private void reconfigure(final URI configURI) {final ClassLoader cl &＃61; ClassLoader.class.isInstance(externalContext) ? (ClassLoader) externalContext : null;LOGGER.debug("Reconfiguration started for context[name&＃61;{}] at URI {} ({}) with optional ClassLoader: {}",contextName, configURI, this, cl);final Configuration instance &＃61; ConfigurationFactory.getInstance().getConfiguration(this, contextName, configURI, cl);if (instance &＃61;&＃61; null) {LOGGER.error("Reconfiguration failed: No configuration found for &＃39;{}&＃39; at &＃39;{}&＃39; in &＃39;{}&＃39;", contextName, configURI, cl);} else {setConfiguration(instance);/** instance.start(); Configuration old &＃61; setConfiguration(instance); updateLoggers(); if (old !&＃61; null) {* old.stop(); }*/final String location &＃61; configuration &＃61;&＃61; null ? "?" : String.valueOf(configuration.getConfigurationSource());LOGGER.debug("Reconfiguration complete for context[name&＃61;{}] at URI {} ({}) with optional ClassLoader: {}",contextName, location, this, cl);}}

我们的配置文件log4j2.xml就是该函数中实现的&＃xff0c;ConfigurationFactory.getInstance().getConfiguration(this, contextName, configURI, cl)得到了配置文件&＃xff0c;并解析成Configuration。进入setConfiguration(instance)方法&＃xff0c;启动当前的configuration&＃xff0c;并启动该配置下的所有appender&＃xff0c;logger和root。

public Configuration setConfiguration(final Configuration config) {if (config &＃61;&＃61; null) {LOGGER.error("No configuration found for context &＃39;{}&＃39;.", contextName);// No change, return the current configuration.return this.configuration;}configLock.lock();try {final Configuration prev &＃61; this.configuration;config.addListener(this);final ConcurrentMap map &＃61; config.getComponent(Configuration.CONTEXT_PROPERTIES);try { // LOG4J2-719 network access may throw android.os.NetworkOnMainThreadExceptionmap.putIfAbsent("hostName", NetUtils.getLocalHostname());} catch (final Exception ex) {LOGGER.debug("Ignoring {}, setting hostName to &＃39;unknown&＃39;", ex.toString());map.putIfAbsent("hostName", "unknown");}map.putIfAbsent("contextName", contextName);config.start();this.configuration &＃61; config;updateLoggers();if (prev !&＃61; null) {prev.removeListener(this);prev.stop();}firePropertyChangeEvent(new PropertyChangeEvent(this, PROPERTY_CONFIG, prev, config));try {Server.reregisterMBeansAfterReconfigure();} catch (final LinkageError | Exception e) {// LOG4J2-716: Android has no java.lang.managementLOGGER.error("Could not reconfigure JMX", e);}// AsyncLoggers update their nanoClock when the configuration changes
Log4jLogEvent.setNanoClock(configuration.getNanoClock());return prev;} finally {configLock.unlock();}}

2.2 newLogger(name, context)

protected Logger newLogger(final String name, final LoggerContext context) {final String key &＃61; Logger.ROOT_LOGGER_NAME.equals(name) ? LogManager.ROOT_LOGGER_NAME : name;return new Log4jLogger(context.getLogger(key), name);}

进入context.getLogger(key)方法

&＃64;Overridepublic Logger getLogger(final String name) {return getLogger(name, null);}
&＃64;Override
public Logger getLogger(final String name, final MessageFactory messageFactory) {// Note: This is the only method where we add entries to the &＃39;loggerRegistry&＃39; ivar.Logger logger &＃61; loggerRegistry.getLogger(name, messageFactory);if (logger !&＃61; null) {AbstractLogger.checkMessageFactory(logger, messageFactory);return logger;}logger &＃61; newInstance(this, name, messageFactory);loggerRegistry.putIfAbsent(name, messageFactory, logger);return loggerRegistry.getLogger(name, messageFactory);}

进入newInstance(this, name, messageFactory)方法

protected Logger newInstance(final LoggerContext ctx, final String name, final MessageFactory messageFactory) {return new Logger(ctx, name, messageFactory);}

protected Logger(final LoggerContext context, final String name, final MessageFactory messageFactory) {super(name, messageFactory);this.context &＃61; context;privateConfig &＃61; new PrivateConfig(context.getConfiguration(), this);}

public PrivateConfig(final Configuration config, final Logger logger) {this.config &＃61; config;this.loggerConfig &＃61; config.getLoggerConfig(getName());this.loggerConfigLevel &＃61; this.loggerConfig.getLevel();this.intLevel &＃61; this.loggerConfigLevel.intLevel();this.logger &＃61; logger;}

public LoggerConfig getLoggerConfig(final String loggerName) {LoggerConfig loggerConfig &＃61; loggerConfigs.get(loggerName);if (loggerConfig !&＃61; null) {return loggerConfig;}String substr &＃61; loggerName;while ((substr &＃61; NameUtil.getSubName(substr)) !&＃61; null) {loggerConfig &＃61; loggerConfigs.get(substr);if (loggerConfig !&＃61; null) {return loggerConfig;}}return root;}

可以看到首先从loggerConfigs也就是配置文件中配置的logger中获取&＃xff0c;如果获取不到则循环递归name中"."之前的logger&＃xff0c;如果还是获取不到&＃xff0c;则默认使用root的配置。

3、logger.info()

Log4jLogger.class

public void info(final String format) {logger.logIfEnabled(FQCN, Level.INFO, null, format);}

&＃64;Overridepublic void logIfEnabled(final String fqcn, final Level level, final Marker marker, final String message) {if (isEnabled(level, marker, message)) {logMessage(fqcn, level, marker, message);}}public boolean isEnabled(final Level level, final Marker marker, final String message) {return privateConfig.filter(level, marker, message);}protected void logMessage(final String fqcn, final Level level, final Marker marker, final String message) {final Message msg &＃61; messageFactory.newMessage(message);logMessageSafely(fqcn, level, marker, msg, msg.getThrowable());}

可以看到isEnabled()方法中用来通过配置的filter来判断是否符合&＃xff0c;如果符合则进入logMessage()方法

protected void logMessage(final String fqcn, final Level level, final Marker marker, final String message) {final Message msg &＃61; messageFactory.newMessage(message);logMessageSafely(fqcn, level, marker, msg, msg.getThrowable());}private void logMessageSafely(final String fqcn, final Level level, final Marker marker, final Message msg,final Throwable throwable) {try {logMessageTrackRecursion(fqcn, level, marker, msg, throwable);} finally {// LOG4J2-1583 prevent scrambled logs when logging calls are nested (logging in toString())
ReusableMessageFactory.release(msg);}}private void logMessageTrackRecursion(final String fqcn,final Level level,final Marker marker,final Message msg,final Throwable throwable) {try {incrementRecursionDepth(); // LOG4J2-1518, LOG4J2-2031
tryLogMessage(fqcn, level, marker, msg, throwable);} finally {decrementRecursionDepth();}}

private void tryLogMessage(final String fqcn,final Level level,final Marker marker,final Message msg,final Throwable throwable) {try {logMessage(fqcn, level, marker, msg, throwable);} catch (final Exception e) {// LOG4J2-1990 Log4j2 suppresses all exceptions that occur once application called the logger
handleLogMessageException(e, fqcn, msg);}}

public void logMessage(final String fqcn, final Level level, final Marker marker, final Message message,final Throwable t) {final Message msg &＃61; message &＃61;&＃61; null ? new SimpleMessage(Strings.EMPTY) : message;final ReliabilityStrategy strategy &＃61; privateConfig.loggerConfig.getReliabilityStrategy();strategy.log(this, getName(), fqcn, marker, level, msg, t);}

public void log(final Supplier reconfigured, final String loggerName, final String fqcn, final Marker marker, final Level level,final Message data, final Throwable t) {loggerConfig.log(loggerName, fqcn, marker, level, data, t);}

public void log(final String loggerName, final String fqcn, final Marker marker, final Level level,final Message data, final Throwable t) {List props &＃61; null;if (!propertiesRequireLookup) {props &＃61; properties;} else {if (properties !&＃61; null) {props &＃61; new ArrayList<>(properties.size());final LogEvent event &＃61; Log4jLogEvent.newBuilder().setMessage(data).setMarker(marker).setLevel(level).setLoggerName(loggerName).setLoggerFqcn(fqcn).setThrown(t).build();for (int i &＃61; 0; i ) {final Property prop &＃61; properties.get(i);final String value &＃61; prop.isValueNeedsLookup() // since LOG4J2-1575? config.getStrSubstitutor().replace(event, prop.getValue()) //
: prop.getValue();props.add(Property.createProperty(prop.getName(), value));}}}final LogEvent logEvent &＃61; logEventFactory.createEvent(loggerName, marker, fqcn, level, data, props, t);try {log(logEvent, LoggerConfigPredicate.ALL);} finally {// LOG4J2-1583 prevent scrambled logs when logging calls are nested (logging in toString())
ReusableLogEventFactory.release(logEvent);}}

protected void log(final LogEvent event, final LoggerConfigPredicate predicate) {if (!isFiltered(event)) { processLogEvent(event, predicate);}}

private void processLogEvent(final LogEvent event, final LoggerConfigPredicate predicate) {event.setIncludeLocation(isIncludeLocation());if (predicate.allow(this)) {callAppenders(event);}logParent(event, predicate);}protected void callAppenders(final LogEvent event) {final AppenderControl[] controls &＃61; appenders.get();//noinspection ForLoopReplaceableByForEachfor (int i &＃61; 0; i ) {controls[i].callAppender(event);}}

这时候终于到了appender的处理了&＃xff0c;直接定位到RollingFileAppender类中

public void append(final LogEvent event) {getManager().checkRollover(event);super.append(event);}

private void tryAppend(final LogEvent event) {if (Constants.ENABLE_DIRECT_ENCODERS) {directEncodeEvent(event);} else {writeByteArrayToManager(event);}}
protected void directEncodeEvent(final LogEvent event) {getLayout().encode(event, manager);if (this.immediateFlush || event.isEndOfBatch()) {manager.flush();}}

这时候可以看到layout和encode的使用了

public void encode(final StringBuilder source, final ByteBufferDestination destination) {try {final Object[] threadLocalState &＃61; getThreadLocalState();final CharsetEncoder charsetEncoder &＃61; (CharsetEncoder) threadLocalState[0];final CharBuffer charBuffer &＃61; (CharBuffer) threadLocalState[1];final ByteBuffer byteBuffer &＃61; (ByteBuffer) threadLocalState[2];TextEncoderHelper.encodeText(charsetEncoder, charBuffer, byteBuffer, source, destination);} catch (final Exception ex) {logEncodeTextException(ex, source, destination);TextEncoderHelper.encodeTextFallBack(charset, source, destination);}}

最后写日志。

四、通过代码动态生成logger对象

public class LoggerHolder {//加个前缀防止配置的name正好是我们某个类名&＃xff0c;导致使用的日志路径使用了类名的路径private static final String PREFIX &＃61; "logger_";/*** 支持生成写大数据文件的logger** &＃64;param name logger name* &＃64;return Logger*/public static Logger getLogger(String name) {String loggerName &＃61; PREFIX &＃43; name;Log4jLoggerFactory loggerFactory &＃61; (Log4jLoggerFactory) LoggerFactory.getILoggerFactory();LoggerContext context &＃61; (LoggerContext) LogManager.getContext();//如果未加载过该logger,则新建一个if (loggerFactory.getLoggersInContext(context).get(loggerName) &＃61;&＃61; null) {buildLogger(name);}//
return loggerFactory.getLogger(loggerName);}/*** 包装了Loggerfactory&＃xff0c;和LoggerFactory.getLogger(T.class)功能一致** &＃64;param clazz* &＃64;return*/public static Logger getLogger(Class clazz) {Log4jLoggerFactory loggerFactory &＃61; (Log4jLoggerFactory) LoggerFactory.getILoggerFactory();return loggerFactory.getLogger(clazz.getName());}/*** &＃64;param name logger name*/private static void buildLogger(String name) {String loggerName &＃61; PREFIX &＃43; name;LoggerContext context &＃61; (LoggerContext) LogManager.getContext();Configuration configuration &＃61; context.getConfiguration();//配置PatternLayout输出格式PatternLayout layout &＃61; PatternLayout.newBuilder().withCharset(UTF_8).withPattern("%msg%n").build();//配置基于时间的滚动策略TimeBasedTriggeringPolicy policy &＃61; TimeBasedTriggeringPolicy.newBuilder().withInterval(24).build();//配置同类型日志策略DirectWriteRolloverStrategy strategy &＃61; DirectWriteRolloverStrategy.newBuilder().withConfig(configuration).build();//配置appenderRollingFileAppender appender &＃61; RollingFileAppender.newBuilder().setName(loggerName).withFilePattern("/data/bigdata/" &＃43; name &＃43; "/" &＃43; name &＃43; ".%d{yyyyMMdd}.log").setLayout(layout).withPolicy(policy).withStrategy(strategy).withAppend(true).build();//改变appender状态
appender.start();//新建loggerLoggerConfig loggerConfig &＃61; new LoggerConfig(loggerName, Level.INFO, false);loggerConfig.addAppender(appender, Level.INFO, null);configuration.addLogger(loggerName, loggerConfig);
context.updateLoggers();}
}