[JAVA] Output log to external file with slf4j + logback with Maven

This is the first post. I think there are many points that cannot be reached, but thank you.

• Because the API was included in 20190303 spring-boot-starter I removed spring-boot-starter from maven and built the environment again.

I want to output the log to a file

I haven't introduced slf4j properly, so I took this opportunity to try it. goal --Output the log to the Eclipse console and log file. --The APIs used are slf4j and logback

Development environment

• java 1.8
• maven

Required API --slf4j-api: Output log when jar is executed --logback-classic: Output log to file --logback-core: Output log to file

Other necessary items

• logback.xml

definition of logback.xml

For the definition of logback.xml, I referred to the site that is summarized in quite detail. I hope you can refer to it. Logback usage memo

By the way, I defined it as follows.

logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE logback>
<configuration>
	<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
	    <encoder>
	        <pattern>%date{yyyy-MM-dd HH:mm:ss} [%thread] %level %logger{0} - %msg \(%file:%line\)%n</pattern>
	    </encoder>
	    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
	        <level>DEBUG</level>
	    </filter>
	</appender>

	<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
	    <file>logs/app.log</file>
	    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
	        <fileNamePattern>logs/app.%d{yyyy-MM-dd}.log.tar.gz</fileNamePattern>
	        <maxHistory>7</maxHistory>
	    </rollingPolicy>
	    <encoder>
	        <pattern>%d{yyyy-MM-dd'T'HH:mm:ss'Z'} - %m%n</pattern>
	    </encoder>
	</appender>

	<root level="DEBUG" additivity="false">
	    <appender-ref ref="STDOUT" />
	    <appender-ref ref="FILE" />
	</root>

</configuration>

definition of pom.xml

I tried to define the required API in maven dependency (this is wrong).

pom.xml

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.25</version>
</dependency>

<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.1.3</version>
</dependency>

<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-core</artifactId>
    <version>1.1.3</version>
</dependency>

So, write the following source and execute it.

main.java

public class App
{
    private static Logger log = LoggerFactory.getLogger("test");
    public static void main( String[] args )
    {
    	log.debug("Log output test");
    	log.info("Log output test");
    	log.warn("Log output test");
    	log.error("Log output test");
    }
}

Output to console log!

console.log

2019-03-03 14:56:28testtest [main] DEBUG test -Log output test(App.java:19)
2019-03-03 14:56:28testtest [main] INFO test -Log output test(App.java:20)
2019-03-03 14:56:28testtest [main] WARN test -Log output test(App.java:21)
2019-03-03 14:56:28testtest [main] ERROR test -Log output test(App.java:22)

Output to log file!

app.log

2019-03-03T14:56:28Z -Log output test
2019-03-03T14:56:28Z -Log output test
2019-03-03T14:56:28Z -Log output test
2019-03-03T14:56:28Z -Log output test

It was output safely.

By the way, if the following error occurs, the API may be booked.

SLF4J: No SLF4J providers were found.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#noProviders for further details.

It happened when I wrote this article, but initially I thought that logback-classic and logback-core were included in slf4j-api. However, what was actually included was spring-boot-starter, and logback-classic and logback-core were really required.

Reference site

Logback usage memo