SpringBootLogging

Spring Boot uses Apache Commons logging for all internal logging.
Spring Boot’s default configurations provides a support for the use of Java Util Logging, Log4j2, and Logback.
Using these, we can configure the console logging as well as file logging.
If you are using Spring Boot Starters, Logback will provide a good support for logging.
Besides, Logback also provides a use of good support for Common Logging, Util Logging, Log4J, and SLF4J.

Log Format

This gives you information regarding the date and time of the log, Log level shows INFO, ERROR or WARN, Process ID, The --- which is a separator, Thread name is enclosed within the square brackets [], Logger Name that shows the Source class name, The Log message.

Console Log

The default log messages will print to the console window.
By default, “INFO”, “ERROR” and “WARN” log messages will print in the log file.
add the debug mode to your application.properties file as debug = true

File Log

By default, all logs will print on the console window and not in the files.
If you want to print the logs in a file, you need to set the property logging.file or logging.path in the application.properties file.
specify the log file path using the property as logging.path = /var/tmp/
specify the own log file name using the property as logging.file = /var/tmp/mylog.log Note − Logback does not support “FATAL” level log. It is mapped to the “ERROR” level log.

Configuring LogBack

Logback supports XML based configuration to handle Spring Boot Log configurations.
Logging configuration details are configured in logback.xml file.
The logback.xml file should be placed under the classpath.

configure the ROOT level log in Logback.xml file as

<?xml version = "1.0" encoding = "UTF-8"?>
<configuration>
   <root level = "INFO">
   </root>
</configuration>

configure the console appender in Logback.xml file as

<?xml version = "1.0" encoding = "UTF-8"?>
<configuration>
   <appender name = "STDOUT" class = "ch.qos.logback.core.ConsoleAppender"></appender>
   <root level = "INFO">
      <appender-ref ref = "STDOUT"/> 
   </root>
</configuration>

configure the file appender in Logback.xml file as

<?xml version = "1.0" encoding = "UTF-8"?>
<configuration>
   <appender name = "FILE" class = "ch.qos.logback.core.FileAppender">
      <File>...path</File>
   </appender>   
   <root level = "INFO">
      <appender-ref ref = "FILE"/>
   </root>
</configuration>

Define the Log pattern in logback.xml file as

<pattern>[%d{yyyy-MM-dd'T'HH:mm:ss.sss'Z'}] [%C] [%t] [%L] [%-5p] %m%n</pattern>

Complete logback.xml file with the rest of you logical code...

[refer in my application's Logbackxml file for more code]

use of .yml file

Using yml file, you can define log levels of Spring Boot loggers, application loggers, Hibernate loggers, Thymeleaf loggers, and more.
To set the logging level for any logger, add keys starting with logging.level.
Logging level can be one of one of TRACE , DEBUG , INFO , WARN , ERROR , FATAL , OFF

configure the application.yml file as

logging:
  level:
    org.springframework.web: ERROR
    com.application: DEBUG
  pattern:
    console: '%d{yyyy-MM-dd HH:mm:ss} - %msg%n'
    file: '%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n'
  file: C:\Users\Windows\spring-boot-logging\api.log

The last line in .yml configuration file is to mention the path in our system where the logged file has to e stored.

Adding SLF4J logger in applicaion

package com.application;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

    public static void main(String[] args) 
    {
        logger.info("......type some message here......");
        logger.warn("......type some message here......");
        logger.error("......type some message here......");
        SpringApplication.run(SpringBootLogging.class, args);
    }
}