JUL 执行原理和流程

https://www.bilibili.com/video/BV1iJ411H74S?p=10

日志原理解析

1. 初始化 LogManager
   1. Log Manager 加载 logging.properties 配置
   2. 添加 Logger 到 logManager
2. 从单例 LogManager 获取 Logger
3. 设置级别 Level，并指定日志记录 LogRecord
4. Filter 提供了日志级别之外更细粒度的控制
5. Handler 处理日志输出位置
6. Formatter 用来格式化 LogRecord

调试跟踪

class JULTest Logger logger = Logger.getLogger("io.github.jihch");
class java.util.logging.Logger @CallerSensitive public static Logger getLogger(String name) { return demandLogger(name, null, Reflection.getCallerClass()); }
class java.util.logging.Logger private static Logger demandLogger(String name, String resourceBundleName, Class<?> caller) { LogManager manager = LogManager.getLogManager(); SecurityManager sm = System.getSecurityManager(); if (sm != null && !SystemLoggerHelper.disableCallerCheck) { if (caller.getClassLoader() == null) { return manager.demandSystemLogger(name, resourceBundleName); } } return manager.demandLogger(name, resourceBundleName, caller); }
class java.util.logging.LogManager public static LogManager getLogManager() { if (manager != null) { manager.ensureLogManagerInitialized(); } return manager; }		class java.util.logging.LogManager
class java.util.logging.LogManager final void ensureLogManagerInitialized() { final LogManager owner = this; if (initializationDone || owner != manager) { return; } synchronized(this) { final boolean isRecursiveInitialization = (initializedCalled == true); assert initializedCalled || !initializationDone : "Initialization can't be done if initialized has not been called!"; if (isRecursiveInitialization || initializationDone) { return; } initializedCalled = true; try { AccessController.doPrivileged(new PrivilegedAction<Object>() { @Override public Object run() { assert rootLogger == null; assert initializedCalled && !initializationDone; // Read configuration. owner.readPrimordialConfiguration(); // Create and retain Logger for the root of the namespace. owner.rootLogger = owner.new RootLogger(); owner.addLogger(owner.rootLogger); if (!owner.rootLogger.isLevelInitialized()) { owner.rootLogger.setLevel(defaultLevel); } @SuppressWarnings("deprecation") final Logger global = Logger.global; owner.addLogger(global); return null; } }); } finally { initializationDone = true; } } }		manager.demandLogger(name, resourceBundleName, caller);
class java.util.logging.LogManager private void readPrimordialConfiguration() { if (!readPrimordialConfiguration) { synchronized (this) { if (!readPrimordialConfiguration) { if (System.out == null) { return; } readPrimordialConfiguration = true; try { AccessController.doPrivileged(new PrivilegedExceptionAction<Void>() { @Override public Void run() throws Exception { readConfiguration(); // Platform loggers begin to delegate to java.util.logging.Logger sun.util.logging.PlatformLogger.redirectPlatformLoggers(); return null; } }); } catch (Exception ex) { assert false : "Exception raised while reading logging configuration: " + ex; } } } } }