一、log4j2簡介
log4j2是log4j 1.x和logback的改進(jìn)版，據(jù)說采用了一些新技術(shù)（無鎖異步、等等），使得日志的吞吐量、性能比log4j 1.x提高10倍，并解決了一些死鎖的bug，而且配置更加簡單靈活
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項目需添加 -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-web</artifactId>
<version>2.9.1</version>
</dependency>
<!--用于與slf4j保持橋接-->
<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
實現(xiàn)類在log4j2.xml配置文件中的標(biāo)簽名。
<?xml version="1.0" encoding="UTF-8"?>
<!--日志級別以及優(yōu)先級排序: OFF > FATAL > ERROR > WARN > INFO > DEBUG > TRACE > ALL -->
<!--Configuration后面的status，這個用于設(shè)置log4j2自身內(nèi)部的信息輸出，可以不設(shè)置，當(dāng)設(shè)置成trace時，你會看到log4j2內(nèi)部各種詳細(xì)輸出-->
<!--monitorInterval：Log4j能夠自動檢測修改配置文件和重新配置本身，設(shè)置間隔秒數(shù)-->
<configuration status="WARN" monitorInterval="30">
<properties>
<property name="server.port"></property>
</properties>
<!--先定義所有的appender-->
<appenders>
<!--這個輸出控制臺的配置-->
<console name="Console" target="SYSTEM_OUT">
<!--輸出日志的格式-->
<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %p %m%n"/>
</console>
<!-- 這個會打印出所有的info及以下級別的信息 -->
<RollingFile name="RollingFile" filePattern="/data/log/tomcat${sys:server.port}/catalina.%d{yyyy-MM-dd}.log">
<!--控制臺只輸出level及以上級別的信息（onMatch），其他的直接拒絕（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>
<!--然后定義logger，只有定義了logger并引入的appender，appender才會生效-->
<loggers>
<!--過濾掉spring和mybatis的一些無用的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>
簡單說Appender就是一個管道，定義了日志內(nèi)容的去向(保存位置)。
配置一個或者多個Filter進(jìn)行過濾
配置Layout來控制日志信息的輸出格式。
配置Policies以控制日志何時(When)進(jìn)行滾動。
配置Strategy以控制日志如何(How)進(jìn)行滾動。
簡單說了下配置項，具體可參考博客：
https://www.imooc.com/article/78966
https://www.cnblogs.com/hafiz/p/6170702.html
三、log4j2其實現(xiàn)原理
首先介紹下log4j2中的幾個重要的概念
LoggerContext
LoggerContext在Logging System中扮演了錨點的角色。根據(jù)情況的不同，一個應(yīng)用可能同時存在于多個有效的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，就是不同廣度范圍的log上下文環(huán)境。
Configuration
每一個LoggerContext都有一個有效的Configuration。Configuration包含了所有的Appenders、上下文范圍內(nèi)的過濾器、LoggerConfigs以及StrSubstitutor.的引用。在重配置期間，新與舊的Configuration將同時存在。當(dāng)所有的Logger對象都被重定向到新的Configuration對象后，舊的Configuration對象將被停用和丟棄。
Logger
Loggers 是通過調(diào)用LogManager.getLogger方法獲得的。Logger對象本身并不實行任何實際的動作。它只是擁有一個name 以及與一個LoggerConfig相關(guān)聯(lián)。它繼承了AbstractLogger類并實現(xiàn)了所需的方法。當(dāng)Configuration改變時，Logger將會與另外的LoggerConfig相關(guān)聯(lián)，從而改變這個Logger的行為。
LoggerConfig
每個LoggerConfig和logger是對應(yīng)的，獲取到一個logger，寫日志時其實是通過LoggerConfig來記日志的
1、獲取LoggerFactory
和logback一樣，slf4j委托具體實現(xiàn)框架的StaticLoggerBinder來返回一個ILoggerFactory，從而對接到具體實現(xiàn)框架上，我們看下這個類(省略了部分代碼)
<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、通過getSingleton()獲取該類的單例
- 2、通過構(gòu)造函數(shù)新建了Log4jLoggerFactory實例，
- 3、通過getLoggerFactory()方法返回該實例
2、獲取logger
進(jìn)入Log4jLoggerFactory類中查看getLogger()方法，發(fā)現(xiàn)是在AbstractLoggerAdapter類中
@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、通過getContext()得到LoggerContext實例
2、在context中查找是否已經(jīng)有該logger，有就返回
3、如果沒有則調(diào)用newLogger(name, context)方法新建logger
Log4jLoggerFactory只有兩個方法，就是上面說的getContext()和newLogger(name, context)。下面分兩節(jié)分別講下這兩個方法
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()方法就是返回合適的loggerContext，進(jìn)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實在LoggerContext靜態(tài)代碼塊中初始化的，繼續(xù)進(jìn)入factory.getContext(FQCN, null, null, true)方法中，進(jìn)入實現(xiàn)類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是從selector.getContext(fqcn, loader, currentContext)中獲取的，此時判斷ctx.getState()是否等于LifeCycle.State.INITIALIZED，第一次調(diào)用getlogger()時，會進(jìn)入此方法，我們看下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);
}
進(jìn)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);
}
}
我們的配置文件log4j2.xml就是該函數(shù)中實現(xiàn)的，ConfigurationFactory.getInstance().getConfiguration(this, contextName, configURI, cl)得到了配置文件，并解析成Configuration。進(jìn)入setConfiguration(instance)方法，啟動當(dāng)前的configuration，并啟動該配置下的所有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);
}
進(jìn)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);
}
進(jìn)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;
}
可以看到首先從loggerConfigs也就是配置文件中配置的logger中獲取，如果獲取不到則循環(huán)遞歸name中"."之前的logger，如果還是獲取不到，則默認(rèn)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()方法中用來通過配置的filter來判斷是否符合，如果符合則進(jìn)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);
}
}
這時候終于到了appender的處理了，直接定位到RollingFileAppender類中
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();
}
}
這時候可以看到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);
}
}
最后寫日志。
四、通過代碼動態(tài)生成logger對象
public class LoggerHolder {
//加個前綴防止配置的name正好是我們某個類名，導(dǎo)致使用的日志路徑使用了類名的路徑
private static final String PREFIX = "logger_";
/**
* 支持生成寫大數(shù)據(jù)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();
//如果未加載過該logger,則新建一個
if (loggerFactory.getLoggersInContext(context).get(loggerName) == null) {
buildLogger(name);
}
//
return loggerFactory.getLogger(loggerName);
}
/**
* 包裝了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輸出格式
PatternLayout layout = PatternLayout.newBuilder()
.withCharset(UTF_8)
.withPattern("%msg%n")
.build();
//配置基于時間的滾動策略
TimeBasedTriggeringPolicy policy = TimeBasedTriggeringPolicy.newBuilder()
.withInterval(24)
.build();
//配置同類型日志策略
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();
//改變appender狀態(tài)
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();
}
}
