How to do it...

Let's have a look at the following steps:

1. Open the message-service project from Chapter 6, Security. The first change we'll make is to add the logback library to the build.gradle file:

group 'com.packtpub.microservices'
version '1.0-SNAPSHOT'

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'org.springframework.boot', name: 'spring-boot-gradle-plugin', version: '1.5.9.RELEASE'
    }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'org.springframework.boot', name: 'spring-boot-starter-web'
    compile group: 'io.github.resilience4j', name: 'resilience4j-circuitbreaker', version: '0.11.0'
    compile group: 'net.logstash.logback', name: 'logstash-logback-encoder', version: '4.7'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

2. Create a logback.xml configuration file. In the configuration file, we'll create a single logger, called jsonLogger, that references a single appender, called consoleAppender:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <appender name="consoleAppender" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="net.logstash.logback.encoder.LogstashEncoder"/>
    </appender>
    <logger name="jsonLogger" additivity="false" level="DEBUG">
        <appender-ref ref="consoleAppender"/>
    </logger>
    <root level="INFO">
        <appender-ref ref="consoleAppender"/>
    </root>
</configuration>

3. Add a single sample log message to Application.java to test our new logging configuration:

package com.packtpub.microservices.ch07.message;

import com.packtpub.microservices.ch07.message.clients.SocialGraphClient;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import java.util.concurrent.Executor;

@SpringBootApplication
@EnableAsync
public class Application {

    private Logger logger = LogManager.getLogger(Application.class);

    @Bean
    public MessageRepository messageRepository() {
        return new MessageRepository();
    }

    @Bean
    public SocialGraphClient socialGraphClient() {
        return new SocialGraphClient("http://localhost:4567");
    }

    public static void main(String[] args) {
        logger.info("Starting application");
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public Executor asyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(2);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(500);
        executor.setThreadNamePrefix("SocialServiceCall-");
        executor.initialize();
        return executor;
    }
}

4. Run the application and see that log messages are now emitted in JSON:

$ ./gradlew bootRun

> Task :bootRun
{"@timestamp":"2018-08-09T22:08:22.959-05:00","@version":1,"message":"Starting application","logger_name":"com.packtpub.microservices.ch07.message.Application","thread_name":"main","level":"INFO","level_value":20000}

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.9.RELEASE)

{"@timestamp":"2018-08-09T22:08:23.786-05:00","@version":1,"message":"Starting Application on fartlek.local with PID 82453 (/Users/posman/projects/microservices-cookbook/chapter07/message-service/build/classes/java/main started by posman in /Users/posman/projects/microservices-cookbook/chapter07/message-service)","logger_name":"com.packtpub.microservices.ch07.message.Application","thread_name":"main","level":"INFO","level_value":20000}