Log4j简单使用

1.环境

下载log4j架包，配置到项目lib中

配置log4j.xml，拷贝到classpath下

2.java代码

    static Logger log= Logger.getLogger("qqtt");
    public void log(){
       log.debug("Debug info.");
       log.info("Info info");
       log.warn("Warn info");
       log.error("Error info");
       log.fatal("Fatal info");
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Log4jTest l=new Log4jTest();
        l.log();
    }

3.log4j.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/'>
  <appender name="_rolling" class="org.apache.log4j.RollingFileAppender">
    <param name="Threshold" value="ERROR" />
    <param name="File" value="log4j_test.log" />
    <param name="Append" value="true" />
    <param name="MaxFileSize" value="3MB" />
    <!--default is 10KB, format=xxKB,xxMB,xxGB-->
    <param name="MaxBackupIndex" value="3" />
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm}] %-5p [%c]%n  %m%n" />
    </layout>
  </appender>
  <appender name="console" class="org.apache.log4j.ConsoleAppender">
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%d %-5p [%t] %C (%F:%L) - %m%n" />
    </layout>
  </appender>



  <root>
    <priority value="info" />  
    <appender-ref ref="_rolling" />
    <appender-ref ref="console" />
  </root>

</log4j:configuration>

4.说明

 root中指定了输出的地方：_rolling:文件 console：屏幕

priority指定了输出消息的最低层：info

threshold是消息的过滤器

5.其他