logback.md

Overview

1. How to setup logback for slf4j
2. See alternaive: log4j2 doc doc

Concept

1. API: slf4j
2. Implementation: logback
   1. Appender

Example logback.xml config

1. Official docs
2. Store app log config at src/main/resources/logback.xml
   1. Store Test log configuration at src/test/resources/logback-test.xml

<configuration>

    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{HH:mm:ss.SSS} [%thread] [%-5level] %logger{24} - %msg%n</pattern>
        </encoder>
    </appender>

    <logger name="com.mystuff" level="DEBUG"/>

    <logger name="ch.qos.logback" level="WARN"/>
    <logger name="io.netty" level="INFO"/>
    <logger name="io.netty.buffer" level="WARN"/>
    <logger name="io.netty.channel" level="WARN"/>

    <root level="debug">
        <appender-ref ref="STDOUT"/>
    </root>

</configuration>

• For layouts: see pattern, ...
• JSON layout requires extra (abandonware) dependencies (like ch.qos.logback.contrib:logback-json-classic, ch.qos.logback.contrib:logback-jackson, ...)
  • last updated in 2016 (abandonware)

build.gradle.kts snippet

dependencies {
    // -- For the API
    implementation("org.slf4j:slf4j-api:2.0.16") // or latest
    
    // -- For the implementation
    implementation("ch.qos.logback:logback-classic:1.5.16")  // or latest
    implementation("ch.qos.logback:logback-core:1.5.16")     // or latest
    implementation("ch.qos.logback:logback-access:1.5.16")   // or latest

    // -- To forward other log statements (logging bridge)
    // -- See https://logging.apache.org/log4j/2.x/faq.html#missing_core
    // -- See https://www.slf4j.org/legacy.html
    implementation("org.apache.logging.log4j:log4j-to-slf4j:2.19.0") // log4j2 api to slf4j api
    implementation("org.slf4j:jcl-over-slf4j:2.0.5")                 // apache commons logging to slf4j
    implementation("org.slf4j:jul-to-slf4j:2.0.5")                   // java.util.logging to slf4j
    implementation("org.slf4j:log4j-over-slf4j:2.0.5")               // legacy log4j to slf4j

    ...
}

configurations.all {

    // -- Exclude conflicting/redundant jars
    exclude(group = "commons-logging", module = "commons-logging")              // legacy
    exclude(group = "jboss-logging", module = "org.jboss.logging")              // legacy
    exclude(group = "log4j", module = "log4j")                                  // legacy
    exclude(group = "org.apache.logging.log4j", module = "log4j-core")          // log4j2 impl
    exclude(group = "org.apache.logging.log4j", module = "log4j-jcl")           // apache commons logging to log4j2 impl 
    exclude(group = "org.apache.logging.log4j", module = "log4j-jul")           // java.util.logging to log4j2 impl
    exclude(group = "org.apache.logging.log4j", module = "log4j-slf4j-impl")    // slf4j to log4j2 impl
    exclude(group = "org.slf4j", module = "slf4j-jcl")                          // slf4j to apache commons logging
    exclude(group = "org.slf4j", module = "slf4j-jdk14")                        // slf4j to java.util.logging
    exclude(group = "org.slf4j", module = "slf4j-log4j12")                      // slf4j to old 1.x log4j api
    exclude(group = "org.slf4j", module = "slf4j-nop")                          // slf4j to nowhere
    exclude(group = "org.slf4j", module = "slf4j-reload4j")                     // slf4j to reload4j's impl of legacy log4j
    exclude(group = "org.slf4j", module = "slf4j-simple")                       // slf4j to stderr
    exclude(group = "org.springframework.boot", module = "spring-boot-starter-log4j2")

    ...
}

Example usage

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

/**
 * <brief description of purpose>
 */
public final class SomeClass {

    private static final Logger LOG = LoggerFactory.getLogger(SomeClass.class);
    ...
}

• Lombok's @Slf4j annotation does the same
  • tradeoff: less code, slower builds

With spring boot

• See 1. See https://docs.spring.io/spring-boot/docs/3.0.0/reference/html/features.html#features.logging
• See https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-logging

Other Resources

1. https://docs.spring.io/spring-boot/docs/3.0.0/reference/html/features.html#features.logging
2. https://www.slf4j.org/images/concrete-bindings.png