Spring Boot 2 Logging

1. Default Zero Configuration Logging

Spring boot active enabled logging is determined by spring-boot-starter-logging artifact and it’s auto-configuration which enables anyone of supported logging providers (Java Util Logging, Log4J2, and Logback) based on configuration provided.

2. Logback Logging

logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <property name="LOG_LOCATION" value="c:/temp" />
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} - %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    <appender name="FILE" class="ch.qos.logback.core.FileAppender">
        <File>{LOG_LOCATION}/mylog.log</File>
        <encoder>
             <pattern>%d{yyyy-MM-dd HH:mm:ss} - %logger{36} - %msg%n</pattern>
        </encoder>
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <fileNamePattern>${LOG_LOCATION}/archived/mylog-%d{yyyy-MM-dd}.%i.log
            </fileNamePattern>
            <timeBasedFileNamingAndTriggeringPolicy
                class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
                <maxFileSize>10MB</maxFileSize>
            </timeBasedFileNamingAndTriggeringPolicy>
        </rollingPolicy>
    </appender>
    <root level="INFO">
        <appender-ref ref="CONSOLE"/>
        <appender-ref ref="FILE"/>
    </root>
    <!-- Application logs at trace level -->
    <logger name="com.howtodoinjava" level="trace" additivity="false">
        <appender-ref ref="RollingFile" />
        <appender-ref ref="Console" />
    </logger>
</configuration>

3. Log4j2 Logging

Step 1: Exclude logback and include log4j2

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>

Step 2: Add log4j2 configuration file

log4j2.xml or (log4j2.properties)

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="30">
	<Properties>
		<Property name="LOG_PATTERN">%d{yyyy-MM-dd'T'HH:mm:ss.SSSZ} %p %m%n</Property>
		<Property name="APP_LOG_ROOT">spring-boot/spring-boot2/logs</Property>
	</Properties>
	<Appenders>
		<Console name="Console" target="SYSTEM_OUT" follow="true">
			<PatternLayout pattern="${LOG_PATTERN}"/>
		</Console>
		<RollingFile name="appLog"
					 fileName="${APP_LOG_ROOT}/boot2application.log"
					 filePattern="${APP_LOG_ROOT}/boot2application-%d{yyyy-MM-dd}-%i.log">
			<PatternLayout pattern="${LOG_PATTERN}"/>
			<Policies>
				<SizeBasedTriggeringPolicy size="19500KB"/>
			</Policies>
			<DefaultRolloverStrategy max="1"/>
		</RollingFile>
	</Appenders>
	<Loggers>
		<Logger name="t5750.springboot2" additivity="false">
			<AppenderRef ref="appLog"/>
			<AppenderRef ref="Console"/>
		</Logger>
		<Root level="info">
			<AppenderRef ref="Console"/>
		</Root>
	</Loggers>
</Configuration>

Step 3: With or without Slf4j

By default, if you are using SLF4J logger classes i.e. org.slf4j.Logger and org.slf4j.LoggerFactory, nothing needs to be changed in application code and all log statement will continue printing in target appenders.

If you are targeting to use log4j2 specific classes only, use org.apache.logging.log4j.Logger and org.apache.logging.log4j.LogManager.

I will recommend to use SLF4J logger classes.

SLF4J logger classes

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@SpringBootApplication
public class Application {
    private static final Logger LOGGER = LoggerFactory.getLogger(Application.class);

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
        LOGGER.info("Simple log statement with inputs {}, {} and {}", 1,2,3);
    }
}

LOG4J2 logger classes

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

@SpringBootApplication
public class Application {
    private static Logger LOGGER = LogManager.getLogger(Application.class);

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
        LOGGER.info("Simple log statement with inputs 1, 2 and 3");
    }
}

Spring Boot log4j2

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
	<Properties>
		<Property name="PID">????</Property>
		<Property name="LOG_EXCEPTION_CONVERSION_WORD">%xwEx</Property>
		<Property name="LOG_LEVEL_PATTERN">%5p</Property>
		<Property name="LOG_DATEFORMAT_PATTERN">yyyy-MM-dd HH:mm:ss.SSS</Property>
		<Property name="CONSOLE_LOG_PATTERN">%clr{%d{${LOG_DATEFORMAT_PATTERN}}}{faint} %clr{${LOG_LEVEL_PATTERN}} %clr{${sys:PID}}{magenta} %clr{---}{faint} %clr{[%15.15t]}{faint} %clr{%-40.40c{1.}}{cyan} %clr{:}{faint} %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
		<Property name="FILE_LOG_PATTERN">%d{${LOG_DATEFORMAT_PATTERN}} ${LOG_LEVEL_PATTERN} ${sys:PID} --- [%t] %-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
	</Properties>
	<Appenders>
		<Console name="Console" target="SYSTEM_OUT" follow="true">
			<PatternLayout pattern="${sys:CONSOLE_LOG_PATTERN}" />
		</Console>
	</Appenders>
	<Loggers>
		<Logger name="org.apache.catalina.startup.DigesterFactory" level="error" />
		<Logger name="org.apache.catalina.util.LifecycleBase" level="error" />
		<Logger name="org.apache.coyote.http11.Http11NioProtocol" level="warn" />
		<logger name="org.apache.sshd.common.util.SecurityUtils" level="warn"/>
		<Logger name="org.apache.tomcat.util.net.NioSelectorPool" level="warn" />
		<Logger name="org.eclipse.jetty.util.component.AbstractLifeCycle" level="error" />
		<Logger name="org.hibernate.validator.internal.util.Version" level="warn" />
		<logger name="org.springframework.boot.actuate.endpoint.jmx" level="warn"/>
		<Root level="info">
			<AppenderRef ref="Console" />
		</Root>
	</Loggers>
</Configuration>

log4j2-file.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
	<Properties>
		<Property name="PID">????</Property>
		<Property name="LOG_EXCEPTION_CONVERSION_WORD">%xwEx</Property>
		<Property name="LOG_LEVEL_PATTERN">%5p</Property>
		<Property name="LOG_DATEFORMAT_PATTERN">yyyy-MM-dd HH:mm:ss.SSS</Property>
		<Property name="CONSOLE_LOG_PATTERN">%clr{%d{${LOG_DATEFORMAT_PATTERN}}}{faint} %clr{${LOG_LEVEL_PATTERN}} %clr{${sys:PID}}{magenta} %clr{---}{faint} %clr{[%15.15t]}{faint} %clr{%-40.40c{1.}}{cyan} %clr{:}{faint} %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
		<Property name="FILE_LOG_PATTERN">%d{${LOG_DATEFORMAT_PATTERN}} ${LOG_LEVEL_PATTERN} ${sys:PID} --- [%t] %-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
	</Properties>
	<Appenders>
		<Console name="Console" target="SYSTEM_OUT" follow="true">
			<PatternLayout pattern="${sys:CONSOLE_LOG_PATTERN}" />
		</Console>
		<RollingFile name="File" fileName="${sys:LOG_FILE}" filePattern="${sys:LOG_PATH}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
			<PatternLayout>
				<Pattern>${sys:FILE_LOG_PATTERN}</Pattern>
			</PatternLayout>
			<Policies>
				<SizeBasedTriggeringPolicy size="10 MB" />
			</Policies>
		</RollingFile>
	</Appenders>
	<Loggers>
		<Logger name="org.apache.catalina.startup.DigesterFactory" level="error" />
		<Logger name="org.apache.catalina.util.LifecycleBase" level="error" />
		<Logger name="org.apache.coyote.http11.Http11NioProtocol" level="warn" />
		<logger name="org.apache.sshd.common.util.SecurityUtils" level="warn"/>
		<Logger name="org.apache.tomcat.util.net.NioSelectorPool" level="warn" />
		<Logger name="org.eclipse.jetty.util.component.AbstractLifeCycle" level="error" />
		<Logger name="org.hibernate.validator.internal.util.Version" level="warn" />
		<logger name="org.springframework.boot.actuate.endpoint.jmx" level="warn"/>
		<Root level="info">
			<AppenderRef ref="Console" />
			<AppenderRef ref="File" />
		</Root>
	</Loggers>
</Configuration>