怎么让java项目打印日志

将这三个jar包导入项目

1、log4j-1.2.x.jar

2、slf4j-api-1.x.x.jar

3、slf4j-log4j12-1.x.x.jar 

在你的src目录下：放入log4j.properties文件

文件内容如下：

### set log levels ###
log4j.rootLogger = DEBUG,stdout,D,E

log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.Threshold = INFO
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss} %l%m%n

log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = C://log.txt
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =C://error.txt
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

在项目的web.xml文件中添加log4j配置

<!-- log4j配置文件位置 -->
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath:log4j.properties</param-value>
</context-param>

<!-- 利用spring来使用log4j -->
<listener>
<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>

写得不如这篇博客，http://blog.csdn.net/xiao_mengxi/article/details/54910450