当我们在用LoggerFactory.getLogger(xyz.class)时我们在干什么

我们在使用logback一类的logging system的时候

总是在代码的前面部分放上这段代码private final Logger log = LoggerFactory.getLogger(AdController.class

这段代码调用了org.slf4j.LoggerFactory line:280

public static Logger getLogger(Class clazz) { return getLogger(clazz.getName()); }

public static Logger getLogger(String name) { ILoggerFactory iLoggerFactory = getILoggerFactory(); return iLoggerFactory.getLogger(name); }

进入 ch.qos.logback.classic.LoggerContext  line:105

 

Logger childLogger = (Logger) loggerCache.get(name); loggerCache定义处

private Map<String, Logger> loggerCache; 初始化代码

public LoggerContext() { super(); this.loggerCache = new ConcurrentHashMap <String, Logger>(); this.loggerContextRemoteView = new LoggerContextVO(this); this.root = new Logger(Logger.ROOT_LOGGER_NAME, null, this); this.root.setLevel(Level.DEBUG); loggerCache.put(Logger.ROOT_LOGGER_NAME, root); initEvaluatorMap(); size = 1; this.frameworkPackages = new ArrayList <String>(); } 可以看到logger里通过name获取logger的实际上是访问了loggerCache这个支持高并发的hashmap.

以下50行代码 做了最重要的工作,请大家仔细阅读,就会明白了.其实很简单.

public final Logger getLogger(final String name) { if (name == null) { throw new IllegalArgumentException("name argument cannot be null"); } // if we are asking for the root logger, then let us return it without // wasting time if (Logger.ROOT_LOGGER_NAME.equalsIgnoreCase(name)) { return root; } int i = 0; Logger logger = root; // check if the desired logger exists, if it does, return it // without further ado. Logger childLogger = (Logger) loggerCache.get(name); // if we have the child, then let us return it without wasting time if (childLogger != null) { return childLogger; } // if the desired logger does not exist, them create all the loggers // in between as well (if they don't already exist) String childName; while (true) { int h = LoggerNameUtil.getSeparatorIndexOf(name, i); if (h == -1) { childName = name; } else { childName = name.substring(0, h); } // move i left of the last point i = h + 1; synchronized (logger) { childLogger = logger.getChildByName(childName); if (childLogger == null) { childLogger = logger.createChildByName(childName); loggerCache.put(childName, childLogger); incSize(); } } logger = childLogger; if (h == -1) { return childLogger; } } } 如果获取不了,就进入一个循环遍历

比如 我们给的name是com.colamachine.calendar.CalendarService

那么他会第一次会去找com 如果没有com就创建com的logger

再去寻找com.colamachine 同上创建

再去找并创建com.colamachine.calendar

再去找并创建com.colamachine.calendar.CalendarService.

好看完了代码,这只是我一厢情愿的猜测.现在来开始

果然如此 

这样的机制 在内存的开销上是否过大

对于只有6个模块的小系统,轻轻松松的mapsize达到了532个