Spring Boot SLF4j Logback example

In this tutorial, we will show you how to use Logback in Spring Boot framework.

Technologies used :

• Spring Boot 2.1.2.RELEASE
• Spring 5.1.4.RELEASE
• Logback 1.2.3
• Maven 3
• Java 8

1. Project Directory

2. Maven

In Spring Boot, Logback is the default logging framework, just add spring-boot-starter-web, it will pull in the logback dependencies.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
		 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <artifactId>spring-boot-slf4j</artifactId>
    <packaging>jar</packaging>
    <name>Spring Boot SLF4j</name>
    <version>1.0</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.2.RELEASE</version>
    </parent>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <!-- Package as an executable jar/war -->
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.0</version>
            </plugin>
        </plugins>
    </build>
</project>

Display the project dependencies.

$ mvn dependency:tree
+- org.springframework.boot:spring-boot-starter-web:jar:2.1.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:2.1.2.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.1.2.RELEASE:compile
[INFO] |  |  |  +- ch.qos.logback:logback-classic:jar:1.2.3:compile
[INFO] |  |  |  |  \- ch.qos.logback:logback-core:jar:1.2.3:compile

$ mvn dependency:tree
org.springframework.boot:spring-boot-slf4j:jar:1.0
[INFO] +- org.springframework.boot:spring-boot-starter-web:jar:2.1.2.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:2.1.2.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.1.2.RELEASE:compile
[INFO] |  |  |  +- ch.qos.logback:logback-classic:jar:1.2.3:compile
[INFO] |  |  |  |  \- ch.qos.logback:logback-core:jar:1.2.3:compile
[INFO] |  |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.11.1:compile
[INFO] |  |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.11.1:compile
[INFO] |  |  |  \- org.slf4j:jul-to-slf4j:jar:1.7.25:compile
[INFO] |  |  +- javax.annotation:javax.annotation-api:jar:1.3.2:compile
[INFO] |  |  +- org.springframework:spring-core:jar:5.1.4.RELEASE:compile
[INFO] |  |  |  \- org.springframework:spring-jcl:jar:5.1.4.RELEASE:compile
[INFO] |  |  \- org.yaml:snakeyaml:jar:1.23:runtime
[INFO] |  +- org.springframework.boot:spring-boot-starter-json:jar:2.1.2.RELEASE:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.9.8:compile
[INFO] |  |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.9.0:compile
[INFO] |  |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.9.8:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.9.8:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.9.8:compile
[INFO] |  |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.9.8:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-tomcat:jar:2.1.2.RELEASE:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:9.0.14:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-el:jar:9.0.14:compile
[INFO] |  |  \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:9.0.14:compile
[INFO] |  +- org.hibernate.validator:hibernate-validator:jar:6.0.14.Final:compile
[INFO] |  |  +- javax.validation:validation-api:jar:2.0.1.Final:compile
[INFO] |  |  +- org.jboss.logging:jboss-logging:jar:3.3.2.Final:compile
[INFO] |  |  \- com.fasterxml:classmate:jar:1.4.0:compile
[INFO] |  +- org.springframework:spring-web:jar:5.1.4.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-beans:jar:5.1.4.RELEASE:compile
[INFO] |  \- org.springframework:spring-webmvc:jar:5.1.4.RELEASE:compile
[INFO] |     +- org.springframework:spring-aop:jar:5.1.4.RELEASE:compile
[INFO] |     +- org.springframework:spring-context:jar:5.1.4.RELEASE:compile
[INFO] |     \- org.springframework:spring-expression:jar:5.1.4.RELEASE:compile
[INFO] +- org.springframework.boot:spring-boot-starter-thymeleaf:jar:2.1.2.RELEASE:compile
[INFO] |  +- org.thymeleaf:thymeleaf-spring5:jar:3.0.11.RELEASE:compile
[INFO] |  |  +- org.thymeleaf:thymeleaf:jar:3.0.11.RELEASE:compile
[INFO] |  |  |  +- org.attoparser:attoparser:jar:2.0.5.RELEASE:compile
[INFO] |  |  |  \- org.unbescape:unbescape:jar:1.1.6.RELEASE:compile
[INFO] |  |  \- org.slf4j:slf4j-api:jar:1.7.25:compile
[INFO] |  \- org.thymeleaf.extras:thymeleaf-extras-java8time:jar:3.0.2.RELEASE:compile
[INFO] \- org.springframework.boot:spring-boot-devtools:jar:2.1.2.RELEASE:compile (optional)
[INFO]    +- org.springframework.boot:spring-boot:jar:2.1.2.RELEASE:compile
[INFO]    \- org.springframework.boot:spring-boot-autoconfigure:jar:2.1.2.RELEASE:compile

3. application.properties

3.1 Configure the logging in application.properties

# logging level
logging.level.org.springframework=ERROR
logging.level.com.mkyong=DEBUG
# output to a file
logging.file=app.log
# temp folder example
#logging.file=${java.io.tmpdir}/app.log
logging.pattern.file=%d %p %c{1.} [%t] %m%n
logging.pattern.console=%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n
## if no active profile, default is 'default'
##spring.profiles.active=prod
# root level
#logging.level.=INFO

3.2 This is the equivalent in YAML format.

logging:
  level:
    org.springframework: ERROR
    com.mkyong: DEBUG
  pattern:
    console: "%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"
    file: "%d %p %c{1.} [%t] %m%n"
  file: app.log

4. logback.xml

The above logging configuration is sufficient for development. For production, we need more logging features like file rolling or SMTP. In Spring Boot, we still allow to configure logback via the standard logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <property name="HOME_LOG" value="logs/app.log"/>
    <appender name="FILE-ROLLING" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>${HOME_LOG}</file>
        <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
            <fileNamePattern>logs/archived/app.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
            <!-- each archived file, size max 10MB -->
            <maxFileSize>10MB</maxFileSize>
            <!-- total size of all archive files, if total size > 20GB, 
				it will delete old archived file -->
            <totalSizeCap>20GB</totalSizeCap>
            <!-- 60 days to keep -->
            <maxHistory>60</maxHistory>
        </rollingPolicy>
        <encoder>
            <pattern>%d %p %c{1.} [%t] %m%n</pattern>
        </encoder>
    </appender>
    <logger name="com.mkyong" level="debug" additivity="false">
        <appender-ref ref="FILE-ROLLING"/>
    </logger>
    <root level="error">
        <appender-ref ref="FILE-ROLLING"/>
    </root>
</configuration>

5. Spring Boot logging by Profile

To take advantage of the templating features provided by Spring Boot, we can create a logback-spring.xml in the root of the classpath.

In below configuration :

• If no active profile (default), logs to console.
• If the profile is prod, logs to a rolling file.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/defaults.xml" />
    <springProfile name="default">
        <include resource="org/springframework/boot/logging/logback/console-appender.xml"/>
        <root level="INFO">
            <appender-ref ref="CONSOLE"/>
        </root>
    </springProfile>
    <springProfile name="prod">
        <appender name="FILE-ROLLING" class="ch.qos.logback.core.rolling.RollingFileAppender">
            <file>app.log</file>
            <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
                <fileNamePattern>logs/archived/app.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
                <!-- each archived file, size max 10MB -->
                <maxFileSize>10MB</maxFileSize>
                <!-- total size of all archive files, if total size > 20GB, it will delete old archived file -->
                <totalSizeCap>20GB</totalSizeCap>
                <!-- 60 days to keep -->
                <maxHistory>60</maxHistory>
            </rollingPolicy>
            <encoder>
                <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </encoder>
        </appender>
        <logger name="org.springframework" level="INFO"/>
        <logger name="com.mkyong" level="DEBUG"/>
        <root level="ERROR">
            <appender-ref ref="FILE-ROLLING"/>
        </root>
    </springProfile>
</configuration>

Define a spring.profiles.active property to set the current active profile.

## if no active profile, default is 'default'
spring.profiles.active=prod

6. Hello Logback

6.1 A simple Spring MVC web application, logs something.

package com.mkyong;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import java.util.Arrays;
import java.util.List;
@Controller
public class HelloController {
    private static final Logger logger = LoggerFactory.getLogger(HelloController.class);
    @GetMapping("/")
    public String hello(Model model) {
        List<Integer> data = Arrays.asList(1, 2, 3, 4, 5);
        logger.debug("Hello from Logback {}", data);
        model.addAttribute("num", data);
        return "index"; // index.html

6.2 Template

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Spring Boot SLF4j Logback</title>
    <link rel="stylesheet" th:href="@{/css/main.css}" href="../../css/main.css"/>
</head>
<body>
<h1>Spring Boot + SLF4j Logback example</h1>
<ul>
    <li th:each="n : ${num}" th:text="${n}"></li>
</ul>
</body>
</html>

6.3 CSS

h1{
	color:#0000FF;

7. Demo

7.1 Start Spring Boot

package com.mkyong;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class StartWebApplication {
	public static void main(String[] args) {
		SpringApplication.run(StartWebApplication.class, args);

http://localhost:8080

15:15:11.588 [http-nio-8080-exec-1] DEBUG com.mkyong.HelloController - Hello from Logback [1, 2, 3, 4, 5]