Apache Log4j 2 is an upgrade to Log4j 1.x that provides significant improvements over its predecessor such as performance improvement, automatic reloading of modified configuration files, java 8 lambda support and custom log levels.
Log4j 2.4 and greater requires Java 7, versions 2.0-alpha1 to 2.3 required Java 6.
To include Log4j2 in your project, include below dependency in your project.
<dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>2.6.1</version> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>2.6.1</version> </dependency>
log4j2.xml for logging into Console
You can use below log4j2.xml file logging output into console. Please note that if no configuration file could be located then DefaultConfiguration will be used. This also causes logging output to go to the console.
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
<Appenders>
<Console name="console" target="SYSTEM_OUT">
<PatternLayout
pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
</Console>
</Appenders>
<Loggers>
<Root level="debug" additivity="false">
<AppenderRef ref="console" />
</Root>
</Loggers>
</Configuration>
log4j2.xml for logging into rolling files
You can use below log4j2.xml file logging output into date based rolling files – along with console.
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn">
<Properties>
<Property name="basePath">C:\\logs</Property>
</Properties>
<Appenders>
<RollingFile name="fileLogger" fileName="${basePath}/app-info.log" filePattern="${basePath}/app-info-%d{yyyy-MM-dd}.log">
<PatternLayout>
<pattern>[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n</pattern>
</PatternLayout>
<Policies>
<TimeBasedTriggeringPolicy interval="1" modulate="true" />
</Policies>
</RollingFile>
<Console name="console" target="SYSTEM_OUT">
<PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
</Console>
</Appenders>
<Loggers>
<Logger name="com.howtodoinjava" level="debug" additivity="true">
<appender-ref ref="fileLogger" level="debug" />
</Logger>
<Root level="debug" additivity="false">
<appender-ref ref="console" />
</Root>
</Loggers>
</Configuration>
log4j2.xml file location
You should put log4j2.xml anywhere in application’s classpath. Log4j will scan all classpath locations to find out this file and then load it.
log4j2.xml example
Let’s write a java class and write few log statements to verify that logs are appreaing in console and log file as well. It logs different log levels to different logs
package com.howtodoinjava.log4j2.examples;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class Log4j2HelloWorldExample
{
private static final Logger LOGGER = LogManager.getLogger(Log4j2HelloWorldExample.class.getName());
public static void main(String[] args)
{
LOGGER.debug("Debug Message Logged !!!");
LOGGER.info("Info Message Logged !!!");
LOGGER.error("Error Message Logged !!!", new NullPointerException("NullError"));
}
}
Now when you run the above program, you will get below logs in console.
[DEBUG] 2016-06-16 12:17:42.972 [main] Log4j2HelloWorldExample - Debug Message Logged !!! [INFO ] 2016-06-16 12:17:42.996 [main] Log4j2HelloWorldExample - Info Message Logged !!! [ERROR] 2016-06-16 12:17:42.997 [main] Log4j2HelloWorldExample - Error Message Logged !!! java.lang.NullPointerException: NullError at com.howtodoinjava.log4j2.examples.Log4j2HelloWorldExample.main(Log4j2HelloWorldExample.java:14) [classes/:?]
If you change the system date and run the application again, you will find two log files in configured location i.e. app-info.log and app-info-2016-06-15.log – where second file is rolled over file.
Simple log4j2.xml with multile file appenders
Use this simple log4j2.xml for quick reference to log statements in multiple log files. It logs different level of logs (debug, info etc.) to different files, using LevelRangeFilter, so that your logs are clean and seperated for easy analysis.
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="30">
<!-- Logging Properties -->
<Properties>
<Property name="LOG_PATTERN">%d{yyyy-MM-dd'T'HH:mm:ss.SSSZ} %p %m%n</Property>
<Property name="APP_LOG_ROOT">c:/temp</Property>
</Properties>
<Appenders>
<!-- Console Appender -->
<Console name="Console" target="SYSTEM_OUT" follow="true">
<PatternLayout pattern="${LOG_PATTERN}"/>
</Console>
<!-- File Appenders on need basis -->
<RollingFile name="frameworkLog" fileName="${APP_LOG_ROOT}/app-framework.log"
filePattern="${APP_LOG_ROOT}/app-framework-%d{yyyy-MM-dd}-%i.log">
<LevelRangeFilter minLevel="ERROR" maxLevel="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="10"/>
</RollingFile>
<RollingFile name="debugLog" fileName="${APP_LOG_ROOT}/app-debug.log"
filePattern="${APP_LOG_ROOT}/app-debug-%d{yyyy-MM-dd}-%i.log">
<LevelRangeFilter minLevel="DEBUG" maxLevel="DEBUG" onMatch="ACCEPT" onMismatch="DENY"/>
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="10"/>
</RollingFile>
<RollingFile name="infoLog" fileName="${APP_LOG_ROOT}/app-info.log"
filePattern="${APP_LOG_ROOT}/app-info-%d{yyyy-MM-dd}-%i.log" >
<LevelRangeFilter minLevel="INFO" maxLevel="INFO" onMatch="ACCEPT" onMismatch="DENY"/>
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="10"/>
</RollingFile>
<RollingFile name="errorLog" fileName="${APP_LOG_ROOT}/app-error.log"
filePattern="${APP_LOG_ROOT}/app-error-%d{yyyy-MM-dd}-%i.log" >
<LevelRangeFilter minLevel="ERROR" maxLevel="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="10"/>
</RollingFile>
<RollingFile name="perfLog" fileName="${APP_LOG_ROOT}/app-perf.log"
filePattern="${APP_LOG_ROOT}/app-perf-%d{yyyy-MM-dd}-%i.log" >
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="1"/>
</RollingFile>
<RollingFile name="traceLog" fileName="${APP_LOG_ROOT}/app-trace.log"
filePattern="${APP_LOG_ROOT}/app-trace-%d{yyyy-MM-dd}-%i.log" >
<PatternLayout pattern="${LOG_PATTERN}"/>
<Policies>
<SizeBasedTriggeringPolicy size="19500KB" />
</Policies>
<DefaultRolloverStrategy max="1"/>
</RollingFile>
</Appenders>
<Loggers>
<Logger name="com.howtodoinjava.app.somePackage" additivity="false" level="trace">
<AppenderRef ref="traceLog" />
<AppenderRef ref="Console" />
</Logger>
<Logger name="com.howtodoinjava.app" additivity="false" level="debug">
<AppenderRef ref="debugLog" />
<AppenderRef ref="infoLog" />
<AppenderRef ref="errorLog" />
<AppenderRef ref="Console" />
</Logger>
<Logger name="org.framework.package" additivity="false" level="info">
<AppenderRef ref="perfLog" />
<AppenderRef ref="Console"/>
</Logger>
<Root level="warn">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>
Happy Learning !!
Ravi
How to read the configuration file from a directory(C:\config)?
Hien Khuu
how to log into console with json format?
Tal
Hello Lokesh,
I copied exactly the xml file and the java code and run the project on Eclipse using Run-Debug.
I could see the log lines on the Eclipse console but the file was empty.
Thank you, Tal
brahim
<Logger name="com.howtodoinjava"
In the logger name, replace "com.howtodoinjava" by the package of your class.