1.log4j有三種主要組件：logger、appender and layout2.Log4j提供的appender有以下幾種：org.apache.log4j.ConsoleAppender（控制台)org.apache.log4j.FileAppender（文件)org.apache.log4j.DailyRollingFileAppender（每天產生一個日志文件）org.apache.log4j.RollingFileAppender（文件大小到達指定尺寸的時候產生一個新的文件）org.apache.log4j.WriterAppender（將日志信息以流格式發送到任意指定的地方）3.Log4j提供的layout有以下幾種：org.apache.log4j.HTMLLayout（以Html表格形式布局)org.apache.log4j.PatternLayout（可以靈活地指定布局模式）org.apache.log4j.SimpleLayout（包含日志信息的級別和信息字符串）org.apache.log4j.TTCCLayout（包含日志產生的時間、線程、類別等等信息）4.Log4j提供的幾種輸出格式：％M：Used to output the method name where the logging request was issued.％m：Used to output the application supplied message associated with the logging event.％l：Used to output location information of the caller which generated the logging event％L：Used to output the line number from where the logging request was issued.％p：Used to output the priority of the logging event.％n：Outputs the platform dependent line separator character or characters. ％r：Used to output the number of milliseconds elapsed since the start of the application until the creation of the logging event.％F：Used to output the file name where the logging request was issued.％d：Used to output the date of the logging event. ％c：Used to output the category of the logging event％C：Used to output the fully qualifIEd class name of the caller issuing the logging request5.如果是對於效率要求比較高的話，要在log.debug()之前加上log.isDebugEnabled()進行判斷，這樣能夠大大減少執行時間6.對於各個appenders,共有的屬性是layout（一般設置為org.apache.log4j.PatternLayout）,Threshold(Log的級別)(1)ConsoleAppender:Target(System.out和System.err)(2)FileAppender:File(定義輸出的文件名），Append（定義是否為追加）(3）DailyRollingFileAppender（除FileAppender屬性外）:MaxFileSize（最大文件大小），MaxBackupIndex（）
必要的時候可以參考一下：http://dev.csdn.Net/develop/article/62/62201.shtm
