log4j日志配置文件：
log4j.rootLogger=ERROR,R
log4j.appender.R=org.apache.log4j.DailyRollingFileAppender
log4j.appender.R.File=app.log
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} [%t] [%c] [%p] - %m%n