Log4j

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For log4j configuration, please refer to http://logging.apache.org/log4j/2.x/manual/configuration.html

1. 首先去官方下载apache-log4j-2.1-bin.tar.gz，解压后导入jar包，基本上你只需要导入下面两个jar包就可以了(xx是版本号)：log4j-core-xx.jar和 log4j-api-xx.jar。

2. 将log4j-api-2.1.jar 和 log4j-core-2.1.jar 导入到project中。

3. 为log4j增加配置文件， 2.0版本中的配置只能为Xml和Json，而且要注意配置文件命名是log4j2.xml或者log4j2.json。

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Console"/>
    </Root>
  </Loggers>
</Configuration>

Once the file above is placed into the classpath as log4j2.xml you will get results identical to those listed above.

4. package com.logging;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.LogManager;

public class LogExample {

private static final Logger logger = LogManager.getLogger(LogExample.class);

public static void main(final String... args) {

logger.trace("Entering application.");

logger.error("Didn't do it.");

logger.trace("Exiting application.");

}
}

Comments: the result is like below:14:37:23.065 [main] ERROR com.logging.LogExample - Didn't do it.。

一直在寻找如何将log输出到一个特定的文件的xml配置，找了半天，在官网上找到了。http://logging.apache.org/log4j/2.x/manual/appenders.html#FileAppender

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <File name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </File>
    <Async name="Async">
      <AppenderRef ref="MyFile"/>
    </Async>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Async"/>
    </Root>
  </Loggers>
</Configuration>

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