配置log4j, 记录日志
１.在web-inf/lib下加入log4j.jar的包。
２.在classes下加上log4j.properties文件，文件内容如下：
log4j.rootLogger=ERROR, MVN_STRUTS2, CONSOLE
# Define all the appenders
log4j.appender.MVN_STRUTS2=org.apache.log4j.DailyRollingFileAppender
log4j.appender.MVN_STRUTS2.File=${catalina.base}/logs/mvn_struts2.txt
log4j.appender.MVN_STRUTS2.Append=true
log4j.appender.MVN_STRUTS2.Encoding=UTF-8
# Roll-over the log once per day
log4j.appender.MVN_STRUTS2.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.MVN_STRUTS2.layout = org.apache.log4j.PatternLayout
log4j.appender.MVN_STRUTS2.layout.ConversionPattern = %d [%t] %-5p %c- %m%n
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Encoding=UTF-8
log4j.appender.CONSOLE.layout = org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern = %d [%t] %-5p %c- %m%n
# Configure which loggers log to which appenders
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注：将错误信息打印到控制台和日志文件中。
