Reactive programming frameworks, such as Spring WebFlux, provide a powerful and efficient way to develop responsive and resource-efficient applications. However, when working with reactive applications, it’s essential to have proper logging in place for monitoring and debugging purposes.

In this tutorial, we’ll explore how to use Log4j, a popular logging framework, with reactive programming frameworks like Spring WebFlux.

Step 1: Add Log4j Dependency

First, you need to add the Log4j dependency to your project. If you are using Maven, you can add the following dependency to your pom.xml:

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-spring-cloud-starter</artifactId>
    <version>2.14.1</version>
</dependency>

If you are using Gradle, add the following dependency to your build.gradle:

implementation 'org.apache.logging.log4j:log4j-spring-cloud-starter:2.14.1'

Step 2: Configure Log4j

Once the Log4j dependency is added, you need to configure it to use the appropriate logging levels, appenders, and patterns. Create a log4j2.xml or log4j2.properties file and place it in your classpath (e.g., src/main/resources).

Here’s an example configuration using the XML format (log4j2.xml):

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d %-5p [%t] %C{2.} (%F:%L) - %m%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

In this example, we configure Log4j to log messages to the console, using a pattern layout that includes the date, log level, thread name, class name (abbreviated), file name, line number, and log message.

You can customize the configuration based on your requirements, such as adding file-based appenders or configuring different logging levels for specific packages or classes.

Step 3: Use Log4j in Reactive Applications

Now that Log4j is configured, you can start using it in your reactive applications. Log4j provides logging APIs for different levels, including debug, info, warn, error, etc. You can use these APIs to log messages throughout your application code.

Here’s an example of using Log4j in a Spring WebFlux controller:

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    private static final Logger LOGGER = LogManager.getLogger(MyController.class);

    @GetMapping("/my-endpoint")
    public Mono<String> myEndpoint() {
        LOGGER.info("Processing request in myEndpoint");
        // Perform some business logic and return a response
    }
}

In this example, we import the Logger class from Log4j and create a logger instance for the MyController class. We then use the logger to log an informational message within the myEndpoint method.

Conclusion

By using Log4j with reactive programming frameworks like Spring WebFlux, you can effectively log messages and monitor your application’s behavior. Configuring Log4j and using its logging APIs will provide you with valuable insights and help in troubleshooting issues when working with reactive applications.

#log4j #reactiveprogramming #springwebflux