Demonstration of using SLF4J with various logging frameworks

In this project, I want to show you different usages of the popular logging wrapper, SLF4J, in the same context to help you gain basic knowledge about this logging tool.

Introduction

As of writing this document, there have been two most widely used logging wrappers that are SLF4J and JCL (Apache Java Commons Logging). We can view these wrappers as an abstraction or interface to logging process. A specific logging framework will be detected at runtime by these wrappers if it is defined in the class paths. In other words, we have to declare appropriate dependencies to allow SFL4J to be coordinated with either of log4j (version 1.x and 2.x), logback, simplelogger, or java util logging (JUL). The steps of testing are detailed below.

How to test logging implementations

This is a Maven-based project where the dependencies are defined in the pom.xml file. To test each logging framework and avoid unexpected side effects, I recommend you to uncomment the required dependencies and comment the others.

For example: the snippet below shows three different sections of defining logging frameworks. The current version is enabling the Java Logging API while the others are disabled.

<dependencies>
    <!-- logging -->

    <!-- SimpleLogger framework -->
    <!--<dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-simple</artifactId>
        <version>1.7.32</version>
    </dependency>-->

    <!-- Logback framework -->
    <!--<dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>${logback.version}</version>
    </dependency>-->

    <!-- Java util logging (JUL) (aka. Java Logging API) framework -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.32</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-jdk14</artifactId>
        <version>1.7.32</version>
        <scope>runtime</scope>
    </dependency>
</dependencies>

Always check the pom.xml file to update all required dependencies when we want to use any of those implementations.

Notes:

• don't uncomment two different frameworks to prevent unexpected conflicts.
• Regarding log4j framework, we have to define the configuration file under the resources folder.

Analysis

MainEntry class

In the main method, we directly use the logging levels from an instance of the object java.util.logging.Logger. It won't be affected when changing dependencies. The Logger class has severe level which is equivalent to error in the other logging frameworks. We are going to see this change in the next section.

CircleApp class

In the main method, we have tried three common different levels. Switching between frameworks, we don't have to change levels such as serve to error. The facade will perform the exchangeability for us. The output format looks different, see the screenshots below.

Output generated by logback

Output generated by java logging api

Output generated by log4j 2.x