Spring Boot - Logging

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Lets look at the Logging options for Spring Boot.

If you use starters(spring-boot-starter artifact in pom.xml), Logback is used for logging by default. This is because spring-boot-starter contains spring-boot-starter-logging.

Logging level

The logging levels are ERROR, WARN, INFO, DEBUG, or TRACE. Default is INFO so DEBUG and TRACE logs are not visible.

Controller to test Logging level

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@RestController
public class LoggingController {
    private static final Logger LOG = LoggerFactory.getLogger(LoggingController.class);
    
    // http://localhost:8080/log
    @RequestMapping("/log")
    public String log() {
        LOG.error("This is an error message.");
        LOG.warn("This is a warning message.");
        LOG.info("This is an info message.");
        LOG.debug("This is a debug message.");
        LOG.trace("This is a trace message.");
        return "foo";
    }
}

You can set logging level in application.properties file or using program arguments.

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logging.level.root=info

or

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logging.level.root=INFO

we can also pass log level via command line arguments

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java -jar target/app.jar --logging.level.root=error

Spring Boot also allows you to set the logging level for a specific package in application.properties file.

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logging.level.org.hibernate=DEBUG

Logback

You can configure logback by adding one of the following files to classpath

  • logback-spring.xml
  • logback.xml

Sample logback.xml

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<?xml version="1.0" encoding="UTF-8"?>
<configuration>
	<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
		<encoder>
			<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
		</encoder>
	</appender>

	<!-- set default log level to be INFO -->
	<!-- Log Level: ALL < DEBUG < INFO < WARN < ERROR < FATAL -->
	<root level="INFO">
		<appender-ref ref="STDOUT" />
	</root>
</configuration>

Log4j

To use Log4j, we need to exclude spring-boot-starter-logging for all dependencies that uses spring-boot-starter-logging. Then add log4j2 dependency

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<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter</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-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>

Then add one of the log4j2 files

  • log4j2-spring.xml
  • log4j2.xml

Reference

source code: https://github.com/xinghua24/SpringBootExamples/tree/master/logging