前言
log4j2是apache在log4j的基础上，参考logback架构实现的一套新的日志系统（我感觉是apache害怕logback了）。
log4j2的官方文档上写着一些它的优点：
-
在拥有全部logback特性的情况下，还修复了一些隐藏问题
-
API 分离：现在log4j2也是门面模式使用日志，默认的日志实现是log4j2，当然你也可以用logback（应该没有人会这么做）
-
性能提升：log4j2包含下一代基于LMAX Disruptor library的异步logger，在多线程场景下，拥有18倍于log4j和logback的性能
-
多API支持：log4j2提供Log4j 1.2, SLF4J, Commons Logging and java.util.logging (JUL) 的API支持
-
避免锁定：使用Log4j2 API的应用程序始终可以选择使用任何符合SLF4J的库作为log4j-to-slf4j适配器的记录器实现
-
自动重新加载配置：与Logback一样，Log4j 2可以在修改时自动重新加载其配置。与Logback不同，它会在重新配置发生时不会丢失日志事件。
-
高级过滤： 与Logback一样，Log4j 2支持基于Log事件中的上下文数据，标记，正则表达式和其他组件进行过滤。
-
插件架构： Log4j使用插件模式配置组件。因此，您无需编写代码来创建和配置Appender，Layout，Pattern Converter等。Log4j自动识别插件并在配置引用它们时使用它们。
-
属性支持：您可以在配置中引用属性，Log4j将直接替换它们，或者Log4j将它们传递给将动态解析它们的底层组件。
-
Java 8 Lambda支持
-
自定义日志级别
-
产生垃圾少：在稳态日志记录期间，Log4j 2 在独立应用程序中是无垃圾的，在Web应用程序中是低垃圾。这减少了垃圾收集器的压力，并且可以提供更好的响应时间性能。
-
和应用server集成：版本2.10.0引入了一个模块log4j-appserver，以改进与Apache Tomcat和Eclipse Jetty的集成。
Log4j2类图：
这次从四个地方去探索源码：启动，配置，异步，插件化
源码探索
启动
log4j2的关键组件
-
LogManager
根据配置指定LogContexFactory，初始化对应的LoggerContext
-
LoggerContext
1、解析配置文件，解析为对应的java对象。
2、通过LoggerRegisty缓存Logger配置
3、Configuration配置信息
4、start方法解析配置文件，转化为对应的java对象
5、通过getLogger获取logger对象
-
Logger
LogManaer
该组件是Log4J启动的入口，后续的LoggerContext以及Logger都是通过调用LogManager的静态方法获得。我们可以使用下面的代码获取Logger
Logger logger = LogManager.getLogger();可以看出LogManager是十分关键的组件，因此在这个小节中我们详细分析LogManager的启动流程。
LogManager启动的入口是下面的static代码块：
/**
* Scans the classpath to find all logging implementation. Currently, only one will be used but this could be
* extended to allow multiple implementations to be used.
*/
static {
// Shortcut binding to force a specific logging implementation.
final PropertiesUtil managerProps = PropertiesUtil.getProperties();
final String factoryClassName = managerProps.getStringProperty(FACTORY_PROPERTY_NAME);
if (factoryClassName != null) {
try {
factory = LoaderUtil.newCheckedInstanceOf(factoryClassName, LoggerContextFactory.class);
} catch (final ClassNotFoundException cnfe) {
LOGGER.error("Unable to locate configured LoggerContextFactory {}", factoryClassName);
} catch (final Exception ex) {
LOGGER.error("Unable to create configured LoggerContextFactory {}", factoryClassName, ex);
}
}
if (factory == null) {
final SortedMap<Integer, LoggerContextFactory> factories = new TreeMap<>();
// note that the following initial call to ProviderUtil may block until a Provider has been installed when
// running in an OSGi environment
if (ProviderUtil.hasProviders()) {
for (final Provider provider : ProviderUtil.getProviders()) {
final Class<? extends LoggerContextFactory> factoryClass = provider.loadLoggerContextFactory();
if (factoryClass != null) {
try {
factories.put(provider.getPriority(), factoryClass.newInstance());
} catch (final Exception e) {
LOGGER.error("Unable to create class {} specified in provider URL {}", factoryClass.getName(), provider
.getUrl(), e);
}
}
}
if (factories.isEmpty()) {
LOGGER.error("Log4j2 could not find a logging implementation. "
+ "Please add log4j-core to the classpath. Using SimpleLogger to log to the console...");
factory = new SimpleLoggerContextFactory();
} else if (factories.size() == 1) {
factory = factories.get(factories.lastKey());
} else {
final StringBuilder sb = new StringBuilder("Multiple logging implementations found: \n");
for (final Map.Entry<Integer, LoggerContextFactory> entry : factories.entrySet()) {
sb.append("Factory: ").append(entry.getValue().getClass().getName());
sb.append(", Weighting: ").append(entry.getKey()).append('\n');
}
factory = factories.get(factories.lastKey());
sb.append("Using factory: ").append(factory.getClass().getName());
LOGGER.warn(sb.toString());
}
} else {
LOGGER.error("Log4j2 could not find a logging implementation. "
+ "Please add log4j-core to the classpath. Using SimpleLogger to log to the console...");
factory = new SimpleLoggerContextFactory();
}
}
}这段静态代码段主要分为下面的几个步骤：
-
首先根据特定配置文件的配置信息获取loggerContextFactory
-
如果没有找到对应的Factory的实现类则通过ProviderUtil中的getProviders()方法载入providers，随后通过provider的loadLoggerContextFactory方法载入LoggerContextFactory的实现类
-
如果provider中没有获取到LoggerContextFactory的实现类或provider为空，则使用SimpleLoggerContextFactory作为LoggerContextFactory。
根据配置文件载入LoggerContextFactory
// Shortcut binding to force a specific logging implementation.
final PropertiesUtil managerProps = PropertiesUtil.getProperties();
final String factoryClassName = managerProps.getStringProperty(FACTORY_PROPERTY_NAME);
if (factoryClassName != null) {
try {
factory = LoaderUtil.newCheckedInstanceOf(factoryClassName, LoggerContextFactory.class);
} catch (final ClassNotFoundException cnfe) {
LOGGER.error("Unable to locate configured LoggerContextFactory {}", factoryClassName);
} catch (final Exception ex) {
LOGGER.error("Unable to create configured LoggerContextFactory {}", factoryClassName, ex);
}
}在这段逻辑中，LogManager优先通过配置文件”log4j2.component.properties”通过配置项”log4j2.loggerContextFactory”来获取LoggerContextFactory，如果用户做了对应的配置，通过newCheckedInstanceOf方法实例化LoggerContextFactory的对象，最终的实现方式为：
public static <T> T newInstanceOf(final Class<T> clazz)
throws InstantiationException, IllegalAccessException, InvocationTargetException {
try {
return clazz.getConstructor().newInstance();
} catch (final NoSuchMethodException ignored) {
// FIXME: looking at the code for Class.newInstance(), this seems to do the same thing as above
return clazz.newInstance();
}
}在默认情况下，不存在初始的默认配置文件log4j2.component.properties，因此需要从其他途径获取LoggerContextFactory。
通过Provider实例化LoggerContextFactory对象
代码：
if (factory == null) {
final SortedMap<Integer, LoggerContextFactory> factories = new TreeMap<>();
// note that the following initial call to ProviderUtil may block until a Provider has been installed when
// running in an OSGi environment
if (ProviderUtil.hasProviders()) {
for (final Provider provider : ProviderUtil.getProviders()) {
final Class<? extends LoggerContextFactory> factoryClass = provider.loadLoggerContextFactory();
if (factoryClass != null) {
try {
factories.put(provider.getPriority(), factoryClass.newInstance());
} catch (final Exception e) {
LOGGER.error("Unable to create class {} specified in provider URL {}", factoryClass.getName(), provider
.getUrl(), e);
}
}
}
if (factories.isEmpty()) {
LOGGER.error("Log4j2 could not find a logging implementation. "
+ "Please add log4j-core to the classpath. Using SimpleLogger to log to the console...");
factory = new SimpleLoggerContextFactory();
} else if (factories.size() == 1) {
factory = factories.get(factories.lastKey());
} else {
final StringBuilder sb = new StringBuilder("Multiple logging implementations found: \n");
for (final Map.Entry<Integer, LoggerContextFactory> entry : factories.entrySet()) {
sb.append("Factory: ").append(entry.getValue().getClass().getName());
sb.append(", Weighting: ").append(entry.getKey()).append('\n');
}
factory = factories.get(factories.lastKey());
sb.append("Using factory: ").append(factory.getClass().getName());
LOGGER.warn(sb.toString());
}
} else {
LOGGER.error("Log4j2 could not find a logging implementation. "
+ "Please add log4j-core to the classpath. Using SimpleLogger to log to the console...");
factory = new SimpleLoggerContextFactory();
}
}这里比较有意思的是hasProviders和getProviders都会通过线程安全的方式去懒加载ProviderUtil这个对象。跟进lazyInit方法：
protected static void lazyInit() {
//noinspection DoubleCheckedLocking
if (INSTANCE == null) {
try {
STARTUP_LOCK.lockInterruptibly();
if (INSTANCE == null) {
INSTANCE = new ProviderUtil();
}
} catch (final InterruptedException e) {
LOGGER.fatal("Interrupted before Log4j Providers could be loaded.", e);
Thread.currentThread().interrupt();
} finally {
STARTUP_LOCK.unlock();
}
}
}再看构造方法：
private ProviderUtil() {
for (final LoaderUtil.UrlResource resource : LoaderUtil.findUrlResources(PROVIDER_RESOURCE)) {
loadProvider(resource.getUrl(), resource.getClassLoader());
}
}这里的懒加载其实就是懒加载Provider对象。在创建新的providerUtil实例的过程中就会直接实例化provider对象，其过程是先通过getClassLoaders方法获取provider的类加载器，然后通过loadProviders(classLoader);加载类。在providerUtil实例化的最后，会统一查找”META-INF/log4j-provider.properties”文件中对应的provider的url，会考虑从远程加载provider。而loadProviders方法就是在ProviderUtil的PROVIDERS列表中添加对一个的provider。可以看到默认的provider是org.apache.logging.log4j.core.impl.Log4jContextFactory
LoggerContextFactory = org.apache.logging.log4j.core.impl.Log4jContextFactory
Log4jAPIVersion = 2.1.0
FactoryPriority= 10很有意思的是这里懒加载加上了锁，而且使用的是
lockInterruptibly这个方法。lockInterruptibly和lock的区别如下：
lock 与 lockInterruptibly比较区别在于：
lock 优先考虑获取锁，待获取锁成功后，才响应中断。
lockInterruptibly 优先考虑响应中断，而不是响应锁的普通获取或重入获取。
ReentrantLock.lockInterruptibly允许在等待时由其它线程调用等待线程的
Thread.interrupt 方法来中断等待线程的等待而直接返回，这时不用获取锁，而会抛出一个InterruptedException。 ReentrantLock.lock方法不允许Thread.interrupt中断,即使检测到Thread.isInterrupted,一样会继续尝试获取锁，失败则继续休眠。只是在最后获取锁成功后再把当前线程置为interrupted状态,然后再中断线程。
上面有一句注释值得注意：
/**
* Guards the ProviderUtil singleton instance from lazy initialization. This is primarily used for OSGi support.
*
* @since 2.1
*/
protected static final Lock STARTUP_LOCK = new ReentrantLock();
// STARTUP_LOCK guards INSTANCE for lazy initialization; this allows the OSGi Activator to pause the startup and
// wait for a Provider to be installed. See LOG4J2-373
private static volatile ProviderUtil INSTANCE;原来这里是为了让osgi可以阻止启动。
再回到logManager：
可以看到在加载完Provider之后，会做factory的绑定：
if (factories.isEmpty()) {
LOGGER.error("Log4j2 could not find a logging implementation. "
+ "Please add log4j-core to the classpath. Using SimpleLogger to log to the console...");
factory = new SimpleLoggerContextFactory();
} else if (factories.size() == 1) {
factory = factories.get(factories.lastKey());
} else {
final StringBuilder sb = new StringBuilder("Multiple logging implementations found: \n");
for (final Map.Entry<Integer, LoggerContextFactory> entry : factories.entrySet()) {
sb.append("Factory: ").append(entry.getValue().getClass().getName());
sb.append(", Weighting: ").append(entry.getKey()).append('\n');
}
factory = factories.get(factories.lastKey());
sb.append("Using factory: ").append(factory.getClass().getName());
LOGGER.warn(sb.toString());
}到这里，logmanager的启动流程就结束了。
配置
在不使用slf4j的情况下，我们获取logger的方式是这样的：
Logger logger = logManager.getLogger(xx.class)跟进getLogger方法：
public static Logger getLogger(final Class<?> clazz) {
final Class<?> cls = callerClass(clazz);
return getContext(cls.getClassLoader(), false).getLogger(toLoggerName(cls));
}这里有一个getContext方法，跟进，
public static LoggerContext getContext(final ClassLoader loader, final boolean currentContext) {
try {
return factory.getContext(FQCN, loader, null, currentContext);
} catch (final IllegalStateException ex) {
LOGGER.warn(ex.getMessage() + " Using SimpleLogger");
return new SimpleLoggerContextFactory().getContext(FQCN, loader, null, currentContext);
}
}上文提到factory的具体实现是Log4jContextFactory，跟进getContext
方法：
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;
}直接看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);
}发现其中的核心方法是reconfigure方法，继续跟进：
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);
}
}可以看到每一个configuration都是从ConfigurationFactory拿出来的，我们先看看这个类的getInstance看看：
public static ConfigurationFactory getInstance() {
// volatile works in Java 1.6+, so double-checked locking also works properly
//noinspection DoubleCheckedLocking
if (factories == null) {
LOCK.lock();
try {
if (factories == null) {
final List<ConfigurationFactory> list = new ArrayList<ConfigurationFactory>();
final String factoryClass = PropertiesUtil.getProperties().getStringProperty(CONFIGURATION_FACTORY_PROPERTY);
if (factoryClass != null) {
addFactory(list, factoryClass);
}
final PluginManager manager = new PluginManager(CATEGORY);
manager.collectPlugins();
final Map<String, PluginType<?>> plugins = manager.getPlugins();
final List<Class<? extends ConfigurationFactory>> ordered =
new ArrayList<Class<? extends ConfigurationFactory>>(plugins.size());
for (final PluginType<?> type : plugins.values()) {
try {
ordered.add(type.getPluginClass().asSubclass(ConfigurationFactory.class));
} catch (final Exception ex) {
LOGGER.warn("Unable to add class {}", type.getPluginClass(), ex);
}
}
Collections.sort(ordered, OrderComparator.getInstance());
for (final Class<? extends ConfigurationFactory> clazz : ordered) {
addFactory(list, clazz);
}
// see above comments about double-checked locking
//noinspection NonThreadSafeLazyInitialization
factories = Collections.unmodifiableList(list);
}
} finally {
LOCK.unlock();
}
}
LOGGER.debug("Using configurationFactory {}", configFactory);
return configFactory;
}这里可以看到ConfigurationFactory中利用了PluginManager来进行初始化，PluginManager会将ConfigurationFactory的子类加载进来，默认使用的XmlConfigurationFactory，JsonConfigurationFactory，YamlConfigurationFactory这三个子类，这里插件化加载暂时按下不表。
回到reconfigure这个方法，我们看到获取ConfigurationFactory实例之后会去调用getConfiguration方法：
public Configuration getConfiguration(final String name, final URI configLocation, final ClassLoader loader) {
if (!isActive()) {
return null;
}
if (loader == null) {
return getConfiguration(name, configLocation);
}
if (isClassLoaderUri(configLocation)) {
final String path = extractClassLoaderUriPath(configLocation);
final ConfigurationSource source = getInputFromResource(path, loader);
if (source != null) {
final Configuration configuration = getConfiguration(source);
if (configuration != null) {
return configuration;
}
}
}
return getConfiguration(name, configLocation);
}跟进getConfiguration，这里值得注意的是有很多个getConfiguration，注意甄别，如果不确定的话可以通过debug的方式来确定。
public Configuration getConfiguration(final String name, final URI configLocation) {
if (configLocation == null) {
final String config = this.substitutor.replace(
PropertiesUtil.getProperties().getStringProperty(CONFIGURATION_FILE_PROPERTY));
if (config != null) {
ConfigurationSource source = null;
try {
source = getInputFromUri(FileUtils.getCorrectedFilePathUri(config));
} catch (final Exception ex) {
// Ignore the error and try as a String.
LOGGER.catching(Level.DEBUG, ex);
}
if (source == null) {
final ClassLoader loader = LoaderUtil.getThreadContextClassLoader();
source = getInputFromString(config, loader);
}
if (source != null) {
for (final ConfigurationFactory factory : factories) {
final String[] types = factory.getSupportedTypes();
if (types != null) {
for (final String type : types) {
if (type.equals("*") || config.endsWith(type)) {
final Configuration c = factory.getConfiguration(source);
if (c != null) {
return c;
}
}
}
}
}
}
}
} else {
for (final ConfigurationFactory factory : factories) {
final String[] types = factory.getSupportedTypes();
if (types != null) {
for (final String type : types) {
if (type.equals("*") || configLocation.toString().endsWith(type)) {
final Configuration config = factory.getConfiguration(name, configLocation);
if (config != null) {
return config;
}
}
}
}
}
}
Configuration config = getConfiguration(true, name);
if (config == null) {
config = getConfiguration(true, null);
if (config == null) {
config = getConfiguration(false, name);
if (config == null) {
config = getConfiguration(false, null);
}
}
}
if (config != null) {
return config;
}
LOGGER.error("No log4j2 configuration file found. Using default configuration: logging only errors to the console.");
return new DefaultConfiguration();
}这里就会根据之前加载进来的factory进行配置的获取，具体的不再解析。
回到reconfigure，之后的步骤就是setConfiguration，入参就是刚才获取的config
private synchronized Configuration setConfiguration(final Configuration config) {
Assert.requireNonNull(config, "No Configuration was provided");
final Configuration prev = this.config;
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", name);
config.start();
this.config = config;
updateLoggers();
if (prev != null) {
prev.removeListener(this);
prev.stop();
}
firePropertyChangeEvent(new PropertyChangeEvent(this, PROPERTY_CONFIG, prev, config));
try {
Server.reregisterMBeansAfterReconfigure();
} catch (final Throwable t) {
// LOG4J2-716: Android has no java.lang.management
LOGGER.error("Could not reconfigure JMX", t);
}
return prev;
}这个方法最重要的步骤就是config.start,这才是真正做配置解析的
public void start() {
LOGGER.debug("Starting configuration {}", this);
this.setStarting();
pluginManager.collectPlugins(pluginPackages);
final PluginManager levelPlugins = new PluginManager(Level.CATEGORY);
levelPlugins.collectPlugins(pluginPackages);
final Map<String, PluginType<?>> plugins = levelPlugins.getPlugins();
if (plugins != null) {
for (final PluginType<?> type : plugins.values()) {
try {
// Cause the class to be initialized if it isn't already.
Loader.initializeClass(type.getPluginClass().getName(), type.getPluginClass().getClassLoader());
} catch (final Exception e) {
LOGGER.error("Unable to initialize {} due to {}", type.getPluginClass().getName(), e.getClass()
.getSimpleName(), e);
}
}
}
setup();
setupAdvertisement();
doConfigure();
final Set<LoggerConfig> alreadyStarted = new HashSet<LoggerConfig>();
for (final LoggerConfig logger : loggers.values()) {
logger.start();
alreadyStarted.add(logger);
}
for (final Appender appender : appenders.values()) {
appender.start();
}
if (!alreadyStarted.contains(root)) { // LOG4J2-392
root.start(); // LOG4J2-336
}
super.start();
LOGGER.debug("Started configuration {} OK.", this);
}这里面有如下步骤：
-
获取日志等级的插件
-
初始化
-
初始化Advertiser
-
配置
先看一下初始化，也就是setup这个方法，setup是一个需要被复写的方法，我们以XMLConfiguration作为例子，
@Override
public void setup() {
if (rootElement == null) {
LOGGER.error("No logging configuration");
return;
}
constructHierarchy(rootNode, rootElement);
if (status.size() > 0) {
for (final Status s : status) {
LOGGER.error("Error processing element {}: {}", s.name, s.errorType);
}
return;
}
rootElement = null;
}发现这里面有一个比较重要的方法constructHierarchy，跟进：
private void constructHierarchy(final Node node, final Element element) {
processAttributes(node, element);
final StringBuilder buffer = new StringBuilder();
final NodeList list = element.getChildNodes();
final List<Node> children = node.getChildren();
for (int i = 0; i < list.getLength(); i++) {
final org.w3c.dom.Node w3cNode = list.item(i);
if (w3cNode instanceof Element) {
final Element child = (Element) w3cNode;
final String name = getType(child);
final PluginType<?> type = pluginManager.getPluginType(name);
final Node childNode = new Node(node, name, type);
constructHierarchy(childNode, child);
if (type == null) {
final String value = childNode.getValue();
if (!childNode.hasChildren() && value != null) {
node.getAttributes().put(name, value);
} else {
status.add(new Status(name, element, ErrorType.CLASS_NOT_FOUND));
}
} else {
children.add(childNode);
}
} else if (w3cNode instanceof Text) {
final Text data = (Text) w3cNode;
buffer.append(data.getData());
}
}
final String text = buffer.toString().trim();
if (text.length() > 0 || (!node.hasChildren() && !node.isRoot())) {
node.setValue(text);
}
}发现这个就是一个树遍历的过程。诚然，配置文件是以xml的形式给出的，xml的结构就是一个树形结构。回到start方法，跟进doConfiguration：
protected void doConfigure() {
if (rootNode.hasChildren() && rootNode.getChildren().get(0).getName().equalsIgnoreCase("Properties")) {
final Node first = rootNode.getChildren().get(0);
createConfiguration(first, null);
if (first.getObject() != null) {
subst.setVariableResolver((StrLookup) first.getObject());
}
} else {
final Map<String, String> map = this.getComponent(CONTEXT_PROPERTIES);
final StrLookup lookup = map == null ? null : new MapLookup(map);
subst.setVariableResolver(new Interpolator(lookup, pluginPackages));
}
boolean setLoggers = false;
boolean setRoot = false;
for (final Node child : rootNode.getChildren()) {
if (child.getName().equalsIgnoreCase("Properties")) {
if (tempLookup == subst.getVariableResolver()) {
LOGGER.error("Properties declaration must be the first element in the configuration");
}
continue;
}
createConfiguration(child, null);
if (child.getObject() == null) {
continue;
}
if (child.getName().equalsIgnoreCase("Appenders")) {
appenders = child.getObject();
} else if (child.isInstanceOf(Filter.class)) {
addFilter(child.getObject(Filter.class));
} else if (child.getName().equalsIgnoreCase("Loggers")) {
final Loggers l = child.getObject();
loggers = l.getMap();
setLoggers = true;
if (l.getRoot() != null) {
root = l.getRoot();
setRoot = true;
}
} else if (child.getName().equalsIgnoreCase("CustomLevels")) {
customLevels = child.getObject(CustomLevels.class).getCustomLevels();
} else if (child.isInstanceOf(CustomLevelConfig.class)) {
final List<CustomLevelConfig> copy = new ArrayList<CustomLevelConfig>(customLevels);
copy.add(child.getObject(CustomLevelConfig.class));
customLevels = copy;
} else {
LOGGER.error("Unknown object \"{}\" of type {} is ignored.", child.getName(),
child.getObject().getClass().getName());
}
}
if (!setLoggers) {
LOGGER.warn("No Loggers were configured, using default. Is the Loggers element missing?");
setToDefault();
return;
} else if (!setRoot) {
LOGGER.warn("No Root logger was configured, creating default ERROR-level Root logger with Console appender");
setToDefault();
// return; // LOG4J2-219: creating default root=ok, but don't exclude configured Loggers
}
for (final Map.Entry<String, LoggerConfig> entry : loggers.entrySet()) {
final LoggerConfig l = entry.getValue();
for (final AppenderRef ref : l.getAppenderRefs()) {
final Appender app = appenders.get(ref.getRef());
if (app != null) {
l.addAppender(app, ref.getLevel(), ref.getFilter());
} else {
LOGGER.error("Unable to locate appender {} for logger {}", ref.getRef(), l.getName());
}
}
}
setParents();
}发现就是对刚刚获取的configuration进行解析，然后塞进正确的地方。回到start方法，可以看到昨晚配置之后就是开启logger和appender了。