apache-comnons系列之commons-logging1.2 学习笔记

概述

• 参考
  
  • http://blog.csdn.net/linshuhe1/article/details/53761571

Log

• A simple logging interface abstracting logging APIs. In order to be instantiated successfully by {@link LogFactory}, classes that implement
• this interface must have a constructor that takes a single String parameter representing the “name” of this Log
• trace/debug/info/warn/error/fatal

LogFactory

• Factory for creating {@link Log} instances, with discovery and configuration features similar to that employed by standard Java APIs such as JAXP.
• org.apache.commons.logging.LogFactory.getFactory
  
  • The org.apache.commons.logging.LogFactory system property.
  • The JDK 1.3 Service Discovery mechanism
  • Use the properties file commons-logging.properties
  • Fall back to a default implementation class (org.apache.commons.logging.impl.LogFactoryImpl)

LogFactoryImpl

• instances = new Hashtable();—->拥有存放创建的Log
• attributes = new Hashtable();—->用于存放加载的属性
• classesToDiscover—->存放相关Log实现类数组(Log4JLogger/Jdk14Logger/Jdk13LumberjackLogger/SimpleLog)
• org.apache.commons.logging.impl.LogFactoryImpl.getInstance(java.lang.String)
  
  • org.apache.commons.logging.impl.LogFactoryImpl#discoverLogImplementation—->查找Log的实现
    
    • Attempts to create a Log instance for the given category name.Follows the discovery process described in the class javadoc.
    • org.apache.commons.logging.impl.LogFactoryImpl#findUserSpecifiedLogClassName(查找是否有设定org.apache.commons.logging.Log属性)
    • Checks system properties and the attribute map for a Log implementation specified by the user under the property names {@link #LOG_PROPERTY} or {@link #LOG_PROPERTY_OLD}
    • createLogFromClass—->通过类路径查找相关实现类
    • 从classesToDiscover数组中查找相关实现类,第一个为Log4JLogger,相关加载过程如下

Log4JLogger

• Implementation of {@link Log} that maps directly to a Logger for log4J version 1.2.
• org.apache.log4j.Logger logger—->Log to this logger
• String name—->Logger name
• org.apache.commons.logging.impl.Log4JLogger.getLogger
  
  • LogManager.getLogger
  • org.apache.log4j.LogManager
    
    • Use the LogManager class to retreive {@link Logger} instances or to operate on the current {@link LoggerRepository}
    • static{}—->静态初始化块,进行RootLogger、以及log4j配置文件的加载
    • OptionConverter.selectAndConfigure—->Configure log4j given a URL
    • org.apache.log4j.PropertyConfigurator.doConfigure(java.net.URL, org.apache.log4j.spi.LoggerRepository)
      
      • configureRootCategory(properties, hierarchy);
      • configureLoggerFactory(properties);
      • parseCatsAndRenderers(properties, hierarchy);

Jdk14Logger

• Implementation of the org.apache.commons.logging.Log interface that wraps the standard JDK logging mechanisms that were introduced in the Merlin release

测试

• org.apache.commons.logging.LogTestCase
  
  • LogFactory.getLog(this.getClass().getName())—->加载过程
    
    • getFactory().getInstance(name)—->加载LogFactory与配置文件comomns.properties/log4j.properties文件如上所述
    • 看下如何创建我们传入的Logger对象
    • instance = (Log) logConstructor.newInstance(params);
      
      • 反转调用public Log4JLogger(String name)
      • org.apache.commons.logging.impl.Log4JLogger.getLogger
      • org.apache.log4j.Hierarchy.getLogger(java.lang.String, org.apache.log4j.spi.LoggerFactory)
        
        • logger = factory.makeNewLoggerInstance(name);—->利用工厂创建Logger
        • logger.setHierarchy(this);—->创建Logger层次
        • ht.put(key, logger);—->存放缓存的Logger
        • updateParents(logger);—->更新创建的Logger的父类