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></pre>
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></pre>
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)
<pre style="margin: 0px; padding: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">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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