logger(三)log4j2简介及其实现原理
一、log4j2简介
log4j2是log4j 1.x和logback的改进版,据说采用了一些新技术(无锁异步、等等),使得日志的吞吐量、性能比log4j 1.x提高10倍,并解决了一些死锁的bug,而且配置更加简单灵活
maven配置
- <!--log4j2核心包-->
- <dependency>
- <groupId>org.apache.logging.log4j</groupId>
- <artifactId>log4j-api</artifactId>
- <version>2.9.1</version>
- </dependency>
- <dependency>
- <groupId>org.apache.logging.log4j</groupId>
- <artifactId>log4j-core</artifactId>
- <version>2.9.1</version>
- </dependency>
- <!-- Web项目需添加 -->
- <dependency>
- <groupId>org.apache.logging.log4j</groupId>
- <artifactId>log4j-web</artifactId>
- <version>2.9.1</version>
- </dependency>
- <!--用于与slf4j保持桥接-->
- <dependency>
- <groupId>org.apache.logging.log4j</groupId>
- <artifactId>log4j-slf4j-impl</artifactId>
- <version>2.9.1</version>
- </dependency>
- <!-- slf4j核心包-->
- <dependency>
- <groupId>org.slf4j</groupId>
- <artifactId>slf4j-api</artifactId>
- <version>1.7.25</version>
也可以配置starter
- <dependency>
- <groupId>org.springframework.boot</groupId>
- <artifactId>spring-boot-starter-log4j2</artifactId>
- </dependency>
二、log4j2.xml配置
实现类在log4j2.xml
配置文件中的标签名。
- <?xml version="1.0" encoding="UTF-8"?>
- <!--日志级别以及优先级排序: OFF > FATAL > ERROR > WARN > INFO > DEBUG > TRACE > ALL -->
- <!--Configuration后面的status,这个用于设置log4j2自身内部的信息输出,可以不设置,当设置成trace时,你会看到log4j2内部各种详细输出-->
- <!--monitorInterval:Log4j能够自动检测修改配置文件和重新配置本身,设置间隔秒数-->
- <configuration status="WARN" monitorInterval="30">
- <properties>
- <property name="server.port"></property>
- </properties>
- <!--先定义所有的appender-->
- <appenders>
- <!--这个输出控制台的配置-->
- <console name="Console" target="SYSTEM_OUT">
- <!--输出日志的格式-->
- <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %p %m%n"/>
- </console>
- <!-- 这个会打印出所有的info及以下级别的信息 -->
- <RollingFile name="RollingFile" filePattern="/data/log/tomcat${sys:server.port}/catalina.%d{yyyy-MM-dd}.log">
- <!--控制台只输出level及以上级别的信息(onMatch),其他的直接拒绝(onMismatch)-->
- <ThresholdFilter level="info" onMatch="ACCEPT" onMismatch="DENY"/>
- <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %p %m%n"/>
- <Policies>
- <TimeBasedTriggeringPolicy interval="1" modulate="true"/>
- </Policies>
- <DirectWriteRolloverStrategy/>
- </RollingFile>
- </appenders>
- <!--然后定义logger,只有定义了logger并引入的appender,appender才会生效-->
- <loggers>
- <!--过滤掉spring和mybatis的一些无用的DEBUG信息-->
- <logger name="org.springframework" level="INFO"></logger>
- <logger name="org.mybatis" level="INFO"></logger>
- <root level="INFO">
- <appender-ref ref="Console"/>
- <appender-ref ref="RollingFile"/>
- </root>
- </loggers>
- </configuration>
简单说Appender就是一个管道,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,具体可参考博客: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,一个应用可能同时存在于多个有效的LoggerContext中。在同一LoggerContext下,log system是互通的。如:Standalone Application、Web Applications、Java EE Applications、”Shared” Web Applications 和REST Service Containers,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,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,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,Logger将会与另外的LoggerConfig相关联,从而改变这个Logger的行为。
LoggerConfig
每个LoggerConfig和logger是对应的,获取到一个logger,写日志时其实是通过LoggerConfig来记日志的
1、获取LoggerFactory
和logback一样,slf4j委托具体实现框架的StaticLoggerBinder来返回一个ILoggerFactory,从而对接到具体实现框架上,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 = new StaticLoggerBinder();
- private final ILoggerFactory loggerFactory;
- /**
- * Private constructor to prevent instantiation
- */
- private StaticLoggerBinder() {
- loggerFactory = new Log4jLoggerFactory();
- }
- /**
- * Returns the singleton of this class.
- *
- * @return the StaticLoggerBinder singleton
- */
- public static StaticLoggerBinder getSingleton() {
- return SINGLETON;
- }
- /**
- * Returns the factory.
- * @return the factor.
- */
- @Override
- public 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,
- 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,发现是在AbstractLoggerAdapter类中
- @Override
- public L getLogger(final String name) {
- final LoggerContext context = getContext();
- final ConcurrentMap<String, L> loggers = getLoggersInContext(context);
- final L logger = loggers.get(name);
- if (logger != 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,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,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<Logger> implements ILoggerFactory {
- private static final String FQCN = Log4jLoggerFactory.class.getName();
- private static final String PACKAGE = "org.slf4j";
- @Override
- protected Logger newLogger(final String name, final LoggerContext context) {
- final String key = Logger.ROOT_LOGGER_NAME.equals(name) ? LogManager.ROOT_LOGGER_NAME : name;
- return new Log4jLogger(context.getLogger(key), name);
- }
- @Override
- protected LoggerContext getContext() {
- final Class<?> anchor = StackLocatorUtil.getCallerClass(FQCN, PACKAGE);
- return anchor == null ? LogManager.getContext() : getContext(StackLocatorUtil.getCallerClass(anchor));
- }
- }
2.1 getContext()
getContext()方法就是返回合适的loggerContext,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() + " Using SimpleLogger");
- return new SimpleLoggerContextFactory().getContext(FQCN, null, null, true);
- }
- }
factory实在LoggerContext静态代码块中初始化的,继续进入factory.getContext(FQCN, null, null, true)方法中,进入实现类Log4jContextFactory中
- @Override
- public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
- final boolean currentContext) {
- final LoggerContext ctx = selector.getContext(fqcn, loader, currentContext);
- if (externalContext != null && ctx.getExternalContext() == null) {
- ctx.setExternalContext(externalContext);
- }
- if (ctx.getState() == LifeCycle.State.INITIALIZED) {
- ctx.start();
- }
- return ctx;
- }
LoggerContext是从selector.getContext(fqcn, loader, currentContext)中获取的,此时判断ctx.getState()是否等于LifeCycle.State.INITIALIZED,第一次调用getlogger()时,会进入此方法,我们看下ctx.start();
- public void start() {
- LOGGER.debug("Starting LoggerContext[name={}, {}]...", 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={}, {}] started OK.", getName(), this);
- }
进入reconfigure()方法
- private void reconfigure(final URI configURI) {
- final ClassLoader cl = ClassLoader.class.isInstance(externalContext) ? (ClassLoader) externalContext : null;
- LOGGER.debug("Reconfiguration started for context[name={}] at URI {} ({}) with optional ClassLoader: {}",
- contextName, configURI, this, cl);
- final Configuration instance = ConfigurationFactory.getInstance().getConfiguration(this, contextName, configURI, cl);
- if (instance == null) {
- LOGGER.error("Reconfiguration failed: No configuration found for '{}' at '{}' in '{}'", contextName, configURI, cl);
- } else {
- setConfiguration(instance);
- /*
- * instance.start(); Configuration old = setConfiguration(instance); updateLoggers(); if (old != null) {
- * old.stop(); }
- */
- final String location = configuration == null ? "?" : String.valueOf(configuration.getConfigurationSource());
- LOGGER.debug("Reconfiguration complete for context[name={}] 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,ConfigurationFactory.getInstance().getConfiguration(this, contextName, configURI, cl)得到了配置文件,并解析成Configuration。进入setConfiguration(instance)方法,启动当前的configuration,并启动该配置下的所有appender,logger和root。
- public Configuration setConfiguration(final Configuration config) {
- if (config == null) {
- LOGGER.error("No configuration found for context '{}'.", contextName);
- // No change, return the current configuration.
- return this.configuration;
- }
- configLock.lock();
- try {
- final Configuration prev = this.configuration;
- config.addListener(this);
- final ConcurrentMap<String, String> map = config.getComponent(Configuration.CONTEXT_PROPERTIES);
- try { // LOG4J2-719 network access may throw android.os.NetworkOnMainThreadException
- map.putIfAbsent("hostName", NetUtils.getLocalHostname());
- } catch (final Exception ex) {
- LOGGER.debug("Ignoring {}, setting hostName to 'unknown'", ex.toString());
- map.putIfAbsent("hostName", "unknown");
- }
- map.putIfAbsent("contextName", contextName);
- config.start();
- this.configuration = config;
- updateLoggers();
- if (prev != 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.management
- LOGGER.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 = 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
- @Override
- public Logger getLogger(final String name) {
- return getLogger(name, null);
- }
- @Override
- public Logger getLogger(final String name, final MessageFactory messageFactory) {
- // Note: This is the only method where we add entries to the 'loggerRegistry' ivar.
- Logger logger = loggerRegistry.getLogger(name, messageFactory);
- if (logger != null) {
- AbstractLogger.checkMessageFactory(logger, messageFactory);
- return logger;
- }
- logger = 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 = context;
- privateConfig = new PrivateConfig(context.getConfiguration(), this);
- }
- public PrivateConfig(final Configuration config, final Logger logger) {
- this.config = config;
- this.loggerConfig = config.getLoggerConfig(getName());
- this.loggerConfigLevel = this.loggerConfig.getLevel();
- this.intLevel = this.loggerConfigLevel.intLevel();
- this.logger = logger;
- }
- public LoggerConfig getLoggerConfig(final String loggerName) {
- LoggerConfig loggerConfig = loggerConfigs.get(loggerName);
- if (loggerConfig != null) {
- return loggerConfig;
- }
- String substr = loggerName;
- while ((substr = NameUtil.getSubName(substr)) != null) {
- loggerConfig = loggerConfigs.get(substr);
- if (loggerConfig != 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,如果获取不到则循环递归name中"."之前的logger,如果还是获取不到,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);
- }
- @Override
- public 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 = 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,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 = 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 = message == null ? new SimpleMessage(Strings.EMPTY) : message;
- final ReliabilityStrategy strategy = privateConfig.loggerConfig.getReliabilityStrategy();
- strategy.log(this, getName(), fqcn, marker, level, msg, t);
- }
- public void log(final Supplier<LoggerConfig> 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<Property> props = null;
- if (!propertiesRequireLookup) {
- props = properties;
- } else {
- if (properties != null) {
- props = new ArrayList<>(properties.size());
- final LogEvent event = Log4jLogEvent.newBuilder()
- .setMessage(data)
- .setMarker(marker)
- .setLevel(level)
- .setLoggerName(loggerName)
- .setLoggerFqcn(fqcn)
- .setThrown(t)
- .build();
- for (int i = 0; i < properties.size(); i++) {
- final Property prop = properties.get(i);
- final String value = prop.isValueNeedsLookup() // since LOG4J2-1575
- ? config.getStrSubstitutor().replace(event, prop.getValue()) //
- : prop.getValue();
- props.add(Property.createProperty(prop.getName(), value));
- }
- }
- }
- final LogEvent logEvent = 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 = appenders.get();
- //noinspection ForLoopReplaceableByForEach
- for (int i = 0; i < controls.length; i++) {
- controls[i].callAppender(event);
- }
- }
这时候终于到了appender的处理了,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 = getThreadLocalState();
- final CharsetEncoder charsetEncoder = (CharsetEncoder) threadLocalState[0];
- final CharBuffer charBuffer = (CharBuffer) threadLocalState[1];
- final ByteBuffer byteBuffer = (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,导致使用的日志路径使用了类名的路径
- private static final String PREFIX = "logger_";
- /**
- * 支持生成写大数据文件的logger
- *
- * @param name logger name
- * @return Logger
- */
- public static Logger getLogger(String name) {
- String loggerName = PREFIX + name;
- Log4jLoggerFactory loggerFactory = (Log4jLoggerFactory) LoggerFactory.getILoggerFactory();
- LoggerContext context = (LoggerContext) LogManager.getContext();
- //如果未加载过该logger,则新建一个
- if (loggerFactory.getLoggersInContext(context).get(loggerName) == null) {
- buildLogger(name);
- }
- //
- return loggerFactory.getLogger(loggerName);
- }
- /**
- * 包装了Loggerfactory,和LoggerFactory.getLogger(T.class)功能一致
- *
- * @param clazz
- * @return
- */
- public static Logger getLogger(Class<?> clazz) {
- Log4jLoggerFactory loggerFactory = (Log4jLoggerFactory) LoggerFactory.getILoggerFactory();
- return loggerFactory.getLogger(clazz.getName());
- }
- /**
- * @param name logger name
- */
- private static void buildLogger(String name) {
- String loggerName = PREFIX + name;
- LoggerContext context = (LoggerContext) LogManager.getContext();
- Configuration configuration = context.getConfiguration();
- //配置PatternLayout输出格式
- PatternLayout layout = PatternLayout.newBuilder()
- .withCharset(UTF_8)
- .withPattern("%msg%n")
- .build();
- //配置基于时间的滚动策略
- TimeBasedTriggeringPolicy policy = TimeBasedTriggeringPolicy.newBuilder()
- .withInterval(24)
- .build();
- //配置同类型日志策略
- DirectWriteRolloverStrategy strategy = DirectWriteRolloverStrategy.newBuilder()
- .withConfig(configuration)
- .build();
- //配置appender
- RollingFileAppender appender = RollingFileAppender.newBuilder()
- .setName(loggerName)
- .withFilePattern("/data/bigdata/" + name + "/" + name + ".%d{yyyyMMdd}.log")
- .setLayout(layout)
- .withPolicy(policy)
- .withStrategy(strategy)
- .withAppend(true)
- .build();
- //改变appender状态
- appender.start();
- //新建logger
- LoggerConfig loggerConfig = new LoggerConfig(loggerName, Level.INFO, false);
- loggerConfig.addAppender(appender, Level.INFO, null);
- configuration.addLogger(loggerName, loggerConfig);
- context.updateLoggers();
- }
- }
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