Log4j.xml和Log4j2.xml的简单认识 - log4j2/log4j的区别

问题描述：

有时在项目中导入log4j的jar包，并配置log4j.xml或者是log4j2.xml后，在代码中引入log4j的API，并不能成功的将log写入控制台或者文件中。

原因有很多很多种，下面将介绍经过我测试log写入成功的事例。

在开始前，需要谨记log4j的几种级别：trace<debug<info<warn<error<fatal， 级别之间是包含的关系，意思是如果你设置日志级别是trace，则大于等于这个级别的日志都会输出。

成功例子1 log4j.xml：

1. 导入log4j2的jar包，主需要导入log4j2的core包即可。如：log4j-core.2.1.jar,引入改jar包会自动引入

log4j-api.2.1.jar.

<dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-core</artifactId>
      <version>2.1</version>
</dependency>

2.在classpath中配置log4j.xml，注意不是log4j2.xml,其内容如下

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="false">

<!-- Set INFO to WARN for warning-level logging, or DEBUG for debug-level logging. -->

	<!-- Output to terminal by default. -->
	<appender name="terminal" class="org.apache.log4j.ConsoleAppender">
		<param name="Threshold" value="INFO" />
		<param name="Target" value="System.out" />
		<layout class="org.apache.log4j.PatternLayout">
<!-- param name="ConversionPattern" value="%d{ABSOLUTE} [%t] %-5p [%c{1}] %m%n"/ -->
		<param name="ConversionPattern" value="%-d [%t] %-5p %c:%L - %m%n" />
		</layout>
	</appender>

	<!-- Optional: asynchronous file output (set <appender-ref ref="asynch-file"/> in root below). -->
	<appender name="asynch-file" class="org.apache.log4j.AsyncAppender">
		<param name="locationInfo" value="false" />
		<appender-ref ref="out-file" />
	</appender>

	<!-- Optional: asynchronous file location (set <appender-ref ref="asynch-file"/> in root below). -->
	<appender name="out-file" class="org.apache.log4j.RollingFileAppender">
		<param name="Threshold" value="INFO" />
		<!-- <param name="file" value="${app.logfile}"/> -->
		<param name="file" value="log/automation.log" />
		<param name="MaxFileSize" value="50MB" />
		<param name="MaxBackupIndex" value="50" />
		<layout class="org.apache.log4j.PatternLayout">
       <param name="ConversionPattern" value="%-d [%t] %-5p %c %X{processID}-%X{queryIndex} -  %m  %n" />
		</layout>
	</appender>

	<logger name="com.wsheng.uiautomation.test">
		<level value="INFO" />
	</logger>

	<logger name="com.wsheng.uiautomation.sitestatus">
		<level value="INFO" />
	</logger>

	<root>
		<level value="INFO" />
		<appender-ref ref="terminal" />
		<appender-ref ref="out-file" />
	</root>
</log4j:configuration>

3. 在项目中写log的代码：

import org.apache.log4j.Logger;

protected static Logger logger = Logger.getLogger(BaseTestPlan.class);

 需要注意的是此处导入的是org.apache.log4j.Logger;如果使用下面的代码，则不能写入log

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

protected static Logger logger = LogManager.getLogger(BaseTestPlan.class);

即便是将上面的log4j.xml改为log4j2.xml也不能写入log。

这是因为log4j2.xml和log4j.xml在配置上有区别。

成功例子2: log4j2.xml

1. 和log4j.xml一样，也导入log4j2的jar包，主需要导入log4j2的core包即可。如：log4j-core.2.1.jar,引入改jar包会自动引入log4j-api.2.1.jar.

 <dependency>
     <groupId>org.apache.logging.log4j</groupId>
     <artifactId>log4j-core</artifactId>
     <version>2.1</version>
</dependency>

2.在classpath中配置log4j2.xml，注意不是log4j.xml,其内容如下

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">

	<properties>
		<property name="logPath">log</property>
	</properties>
	
	<Appenders>
		<Console name="Console" target="SYSTEM_OUT">
			<PatternLayout pattern="%d{YYYY-MM-dd HH:mm:ss} [%t] %-5p %c{1}:%L - %msg%n" />
			<!-- <PatternLayout pattern="%d{HH:mm:ss} [%t] %-5level %logger{36} - %msg%n" /> -->
			<!-- <PatternLayout pattern="%-d [%t] %-5p %c{1}:%L - %m%n" /> -->
		</Console>
		
	<!-- <File name="LogFile" filename="${sys:catalina.home}/logs/automation.log">
	<PatternLayout pattern="%d{YYYY-MM-dd HH:mm:ss} [%t] %-5p %c{1}:%L - %msg%n" />
		</File> -->
		
		<RollingFile name="RollingFile" filename="${logPath}/automation.log"
			filepattern="${logPath}/%d{YYYYMMddHHmmss}-automation.log">
	<PatternLayout pattern="%d{YYYY-MM-dd HH:mm:ss} [%t] %-5p %c{1}:%L - %msg%n" />
			<Policies>
				<SizeBasedTriggeringPolicy size="100 MB"/>
			</Policies>	
			 <DefaultRolloverStrategy max="20"/>
		</RollingFile>
		
	</Appenders>
	<Loggers>
		<Root level="info">
			<AppenderRef ref="Console" />
			<!-- <AppenderRef ref="LogFile" /> -->
			<AppenderRef ref="RollingFile" />
		</Root>
	</Loggers>
</Configuration>

3. 在项目中写log的代码：

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

protected static Logger logger = LogManager.getLogger(BaseTestPlan.class);

 如果使用 org.apache.log4j.Logger,得到的结果是能写入控制台，但不能写入对应的文件。

import org.apache.log4j.Logger;

protected static Logger logger = Logger.getLogger(BaseTestPlan.class);

 Note: 如果启动的时候报类似下面的异常：

2015-04-30 15:10:07,962 WARN Could not instantiate SimpleDateFormat with pattern YYYYMMddHHmmss java.lang.IllegalArgumentException: Illegal pattern character 'Y'

可将YYYY改成小写的yyyy试一试。