Logger对象是否会重复创建呢? (以Log4j为例)
不久前有人问及 重复调用Logger.getLogger之类的语句,是否会拿到不同的Logger对象呢? 起初我并未在意,但现在觉得是应该探究一下.
故,先是设计这样的代码:
import org.apache.log4j.Logger;
public class LogTest {
public static void main(String[] args) {
Logger log = Logger.getLogger(LogTest.class);
Logger log2 = Logger.getLogger(LogTest.class);
System.out.println(log == log2);
}
}
log4j.properties文件的内容:
log4j.rootLogger=DEBUG,Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=log4j: %d [%t] %-5p %c - %m%n
打印的结果是true,即同一个Log对象
恩,为什么呢?? 好,下载源码.
经过简单探寻,找到关键代码,位于org.apache.log4j.Hierarchy类:
public
Logger getLogger(String name, LoggerFactory factory) {
//System.out.println("getInstance("+name+") called.");
CategoryKey key = new CategoryKey(name);
// Synchronize to prevent write conflicts. Read conflicts (in
// getChainedLevel method) are possible only if variable
// assignments are non-atomic.
Logger logger;
synchronized(ht) {
Object o = ht.get(key);
if(o == null) {
logger = factory.makeNewLoggerInstance(name);
logger.setHierarchy(this);
ht.put(key, logger);
updateParents(logger);
return logger;
} else if(o instanceof Logger) {
return (Logger) o;
} else if (o instanceof ProvisionNode) {
//System.out.println("("+name+") ht.get(this) returned ProvisionNode");
logger = factory.makeNewLoggerInstance(name);
logger.setHierarchy(this);
ht.put(key, logger);
updateChildren((ProvisionNode) o, logger);
updateParents(logger);
return logger;
}
else {
// It should be impossible to arrive here
return null; // but let's keep the compiler happy.
}
}
}
以上代码简单含义为,构建一个查询的key,然后获取特定的Logger对象,如果没有就创建它
问题又来啦,按照上述代码,获取Logger对象的过程,是一个同步过程,因为写着synchronized(ht) 呢!
另外说一句,按照当前的Nutz.Log实现,每次调用getLog都是返回新的Logger封装对象哦,不过这个对象只有一个变量,就是实际的logger,故,内存消耗依旧很小的.
blog comments powered by Disqus
