Blog 1: Adding Logging to Java Spring Boot

In this blog, we will truly understand logging in Java—what it is, how we can use it, and how to enable it. Unlike other blogs, as Senseyans, we prefer to approach blogging as a trial-and-error process, where you can follow our thought process as we search for answers and gain a deeper understanding of the problem.

So, rather than providing a short, straightforward blog that immediately presents the solution, I will take you through the learning journey, step by step.

Let’s start by looking at the current state of an example project without any logging, and the situation at hand:

As seen in the dependencies section of the pom.xml file, there is no logging library currently enabled in our project.


	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>io.netty</groupId>
				<artifactId>netty-bom</artifactId>
				<version>4.1.118.Final</version>
				<scope>import</scope>
				<type>pom</type>
			</dependency>
		</dependencies>
	</dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-security</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>io.micrometer</groupId>
			<artifactId>micrometer-registry-prometheus</artifactId>
		</dependency>
		<!-- <https://mvnrepository.com/artifact/com.azure/azure-storage-blob> -->
		<dependency>
    		<groupId>com.azure</groupId>
    		<artifactId>azure-storage-blob</artifactId>
    		<version>12.29.0</version>
		</dependency>
		<!-- <https://mvnrepository.com/artifact/com.github.librepdf/openpdf> -->
		<dependency>
			<groupId>com.github.librepdf</groupId>
			<artifactId>openpdf</artifactId>
			<version>2.0.3</version>
		</dependency>

		<dependency>
			<groupId>org.springdoc</groupId>
    		<artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
   			 <version>2.8.3</version>
		</dependency>
		<!-- <https://mvnrepository.com/artifact/io.swagger.core.v3/swagger-annotations> -->
		<dependency>
			<groupId>io.swagger.core.v3</groupId>
			<artifactId>swagger-annotations</artifactId>
			<version>2.2.27</version>
		</dependency>

		<dependency>
			<groupId>org.postgresql</groupId>
			<artifactId>postgresql</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.36</version>
            <scope>provided</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok-mapstruct-binding</artifactId>
            <version>0.2.0</version>
            <scope>provided</scope>
        </dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		  <!-- MapStruct Dependencies -->
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>1.5.5.Final</version>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-processor</artifactId>
            <version>1.5.5.Final</version>
            <scope>provided</scope>
        </dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-validation</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
			<scope>runtime</scope>
			<optional>true</optional>
		</dependency>
		<!-- OAuth2 Resource Server for JWT,
		Date:  Jan 23, 2025-->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
			 <version>3.4.2</version>
		</dependency>

	</dependencies>

	<build>
        <plugins>
            <!-- Spring Boot Plugin -->
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>

            <!-- Maven Compiler Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.13.0</version> <!-- Updated version to 3.13.0 -->
                <configuration>
                    <source>21</source> <!-- Updated Java version to 21 -->
                    <target>21</target> <!-- Updated Java version to 21 -->
                    <annotationProcessorPaths>
                        <annotationProcessorPath>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>1.18.36</version>
                        </annotationProcessorPath>
                        <annotationProcessorPath>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>1.5.5.Final</version>
                        </annotationProcessorPath>
                    </annotationProcessorPaths>
                </configuration>
            </plugin>
             <!-- Jacoco compatible with Java 21 -->
             <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.8.12</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>prepare-agent</goal>
                            <goal>report</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>

Part 1: The Logic

Why Would You Need a Logging Library, and Why Isn't System.out.println() Enough?

A major reason to use a logging library instead of System.out.println() is logging levels. With a proper logging system, you can categorize logs based on severity, such as:

INFO – General application flow (e.g., "Application started").
WARN – Something unexpected happened, but the application can still run.
ERROR – Critical failures that need immediate attention.
DEBUG/TRACE – Detailed information for developers, useful during debugging.

Part 2: The Theory Behind It

What Is a Logging Library?

A logging library is a pre-built Java framework designed to provide structured, efficient, and configurable logging. Instead of using System.out.println(), which lacks flexibility and performance, a logging library allows developers to:

Control log levels (INFO, ERROR, etc.)
Write logs to files, databases, or external monitoring systems
Format logs in a structured and readable way