java - log4j.properties 文件中的 log4j.rootLogger 属性有何意义？如果我不使用该属性会怎样？

Question

log4j.properties 文件中的 log4j.rootLogger 属性有何意义？如果我不使用此属性会发生什么？

示例:

# Set root logger level to DEBUG and its only appender to A1.
log4j.rootLogger=DEBUG, A1

# A1 is set to be a ConsoleAppender.
log4j.appender.A1=org.apache.log4j.ConsoleAppender

如果我将此属性设置为 ERROR 模式，会发生什么情况。

Answer 1

Samudra Gupta 在他的书中解释道¹:

The Logger object is the main object that an application developer uses to log any message. The Logger objects acting within a particular instance of an application follow a parent-child hierarchy.

如果您有以下配置:

log4j.rootLogger=WARN, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout
log4j.logger.com.me.proj2=INFO

这就是记录器层次结构最终的样子:²

Samudra Gupta 继续解释:

At the top of the hierarchy exists a root logger. The root logger exists outside the scope of any custom logger hierarchy that we may come up with. It always exists as the root logger for all possible logger hierarchies, and it has no namespace. All the other application-specific Logger objects are child objects to the root logger. The parent-child relationship of loggers signifies the dependency of the loggers acting within the same application. A child logger can inherit properties from its parent logger recursively up the tree. Typically, a child logger will inherit the following properties from its parent logger(s):

• Level: If the child logger has no explicit tree level specified, it will use the level of its closest parent or the first proper level it finds recursively up the hierarchy.
• Appender: If there is no appender attached to a logger, the child logger uses the appender of its closest parent logger or the first appender it finds recursively up the tree.
• ResourceBundle: ResourceBundles are key-value pattern properties files used for the localization of logging messages. A child logger inherits any ResourceBundle associated with its parent logger.

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注释

¹ Samudra Gupta，Pro Apache Log4j，第二版(加利福尼亚州伯克利:Apress，2005 年)，24-25，ISBN13:978-1-59059-499-5

² Dominic Mitchell，登录 Java，http://happygiraffe.net/blog/2008/09/03/logging-in-java/ ，检索于 2014 年 5 月 26 日。