Category: Spring Batch

Spring Batch is an open source framework for batch processing. It is a lightweight, comprehensive solution designed to enable the development of robust batch applications, which are often found in modern enterprise systems. Spring Batch builds upon the POJO-based development approach of the Spring Framework.

How to Schedule Tasks with Spring Boot
06
Feb
2021

How to Schedule Tasks with Spring Boot

In this article, You’ll learn how to schedule tasks in Spring Boot using @Scheduled annotation. You’ll also learn how to use a custom thread pool for executing all the scheduled tasks.

The @Scheduled annotation is added to a method along with some information about when to execute it, and Spring Boot takes care of the rest.

Spring Boot internally uses the TaskScheduler interface for scheduling the annotated methods for execution.

The purpose of this article is to build a simple project demonstrating all the concepts related to task scheduling.

Create the Project

Let’s use Spring Boot CLI to create the Project. Fire up your terminal and type the following command to generate the project –

$ spring init --name=scheduler-demo scheduler-demo 

Alternatively, You can generate the project using Spring Initializer web app. Just go to http://start.spring.io/, enter the Artifact’s value as “scheduler-demo” and click Generate to generate and download the project.

Once the project is generated, import it in your favorite IDE. The project’s directory structure should like this –

Spring Boot Scheduled Annotation Example Directory Structure

Enable Scheduling

You can enable scheduling simply by adding the @EnableScheduling annotation to the main application class or one of the Configuration classes.

Open SchedulerDemoApplication.java and add @EnableScheduling annotation like so –

package com.example.schedulerdemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@SpringBootApplication
@EnableScheduling
public class SchedulerDemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(SchedulerDemoApplication.class, args);
	}
}

Scheduling Tasks

Scheduling a task with Spring Boot is as simple as annotating a method with @Scheduled annotation, and providing few parameters that will be used to decide the time at which the task will run.

Before adding tasks, Let’s first create the container for all the scheduled tasks. Create a new class called ScheduledTasks inside com.example.schedulerdemo package with the following contents –

package com.example.schedulerdemo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.TimeUnit;

@Component
public class ScheduledTasks {
    private static final Logger logger = LoggerFactory.getLogger(ScheduledTasks.class);
    private static final DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss");

    public void scheduleTaskWithFixedRate() {}

    public void scheduleTaskWithFixedDelay() {}

    public void scheduleTaskWithInitialDelay() {}

    public void scheduleTaskWithCronExpression() {}
}

The class contains four empty methods. We’ll look at the implementation of all the methods one by one.

All the scheduled methods should follow the following two criteria –

  • The method should have a void return type.
  • The method should not accept any arguments.

Cool! Let’s now jump into the implementation.

1. Scheduling a Task with Fixed Rate

You can schedule a method to be executed at a fixed interval by using fixedRate parameter in the @Scheduled annotation. In the following example, The annotated method will be executed every 2 seconds.

@Scheduled(fixedRate = 2000)
public void scheduleTaskWithFixedRate() {
    logger.info("Fixed Rate Task :: Execution Time - {}", dateTimeFormatter.format(LocalDateTime.now()) );
}
# Sample Output
Fixed Rate Task :: Execution Time - 10:26:58
Fixed Rate Task :: Execution Time - 10:27:00
Fixed Rate Task :: Execution Time - 10:27:02
....
....

The fixedRate task is invoked at the specified interval even if the previous invocation of the task is not finished.

2. Scheduling a Task with Fixed Delay

You can execute a task with a fixed delay between the completion of the last invocation and the start of the next, using fixedDelay parameter.

The fixedDelay parameter counts the delay after the completion of the last invocation.

Consider the following example –

@Scheduled(fixedDelay = 2000)
public void scheduleTaskWithFixedDelay() {
    logger.info("Fixed Delay Task :: Execution Time - {}", dateTimeFormatter.format(LocalDateTime.now()));
    try {
        TimeUnit.SECONDS.sleep(5);
    } catch (InterruptedException ex) {
        logger.error("Ran into an error {}", ex);
        throw new IllegalStateException(ex);
    }
}

Since the task itself takes 5 seconds to complete and we have specified a delay of 2 seconds between the completion of the last invocation and the start of the next, there will be a delay of 7 seconds between each invocation –

# Sample Output
Fixed Delay Task :: Execution Time - 10:30:01
Fixed Delay Task :: Execution Time - 10:30:08
Fixed Delay Task :: Execution Time - 10:30:15
....
....

3. Scheduling a Task With Fixed Rate and Initial Delay

You can use initialDelay parameter with fixedRate and fixedDelay to delay the first execution of the task with the specified number of milliseconds.

In the following example, the first execution of the task will be delayed by 5 seconds and then it will be executed normally at a fixed interval of 2 seconds –

@Scheduled(fixedRate = 2000, initialDelay = 5000)
public void scheduleTaskWithInitialDelay() {
    logger.info("Fixed Rate Task with Initial Delay :: Execution Time - {}", dateTimeFormatter.format(LocalDateTime.now()));
}
# Sample output (Server Started at 10:48:46)
Fixed Rate Task with Initial Delay :: Execution Time - 10:48:51
Fixed Rate Task with Initial Delay :: Execution Time - 10:48:53
Fixed Rate Task with Initial Delay :: Execution Time - 10:48:55
....
....

4. Scheduling a Task using Cron Expression

If the above simple parameters can not fulfill your needs, then you can use cron expressions to schedule the execution of your tasks.

In the following example, I have scheduled the task to be executed every minute –

@Scheduled(cron = "0 * * * * ?")
public void scheduleTaskWithCronExpression() {
    logger.info("Cron Task :: Execution Time - {}", dateTimeFormatter.format(LocalDateTime.now()));
}
# Sample Output
Cron Task :: Execution Time - 11:03:00
Cron Task :: Execution Time - 11:04:00
Cron Task :: Execution Time - 11:05:00

Running @Scheduled Tasks in a Custom Thread Pool

By default, all the @Scheduled tasks are executed in a default thread pool of size one created by Spring.

You can verify that by logging the name of the current thread in all the methods –

logger.info("Current Thread : {}", Thread.currentThread().getName());

All the methods will print the following –

Current Thread : pool-1-thread-1

But hey, You can create your own thread pool and configure Spring to use that thread pool for executing all the scheduled tasks.

Create a new package config inside com.example.schedulerdemo, and then create a new class called SchedulerConfig inside config package with the following contents –

package com.example.schedulerdemo.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.SchedulingConfigurer;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.scheduling.config.ScheduledTaskRegistrar;

@Configuration
public class SchedulerConfig implements SchedulingConfigurer {
    private final int POOL_SIZE = 10;

    @Override
    public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
        ThreadPoolTaskScheduler threadPoolTaskScheduler = new ThreadPoolTaskScheduler();

        threadPoolTaskScheduler.setPoolSize(POOL_SIZE);
        threadPoolTaskScheduler.setThreadNamePrefix("my-scheduled-task-pool-");
        threadPoolTaskScheduler.initialize();

        scheduledTaskRegistrar.setTaskScheduler(threadPoolTaskScheduler);
    }
}

That’s all you need to do for configuring Spring to use your own thread pool instead of the default one.

If you log the name of the current thread in the scheduled methods now, you’ll get the output like so –

Current Thread : my-scheduled-task-pool-1
Current Thread : my-scheduled-task-pool-2

# etc...

Conclusion

In this article, you learned how to schedule tasks in Spring Boot using @Scheduled annotation. You also learned how to use a custom thread pool for running these tasks.

The Scheduling abstraction provided by Spring Boot works pretty well for simple use-cases. But if you have more advanced use cases like Persistent JobsClusteringDynamically adding and triggering new jobs then check out the following article –

Spring Boot Quartz Scheduler Example: Building an Email Scheduling App

Thank you for reading. See you in the next Post!

Spring Boot Starter Maven Templates
30
Mar
2021

Spring Boot Starter Maven Templates

Not very long ago, with the exponential increase in number of libraries and their dependencies, dependency management was becoming very complex task which required good amount of technical expertise to do it correctly. With the introduction of String boot starter templates, you can get a lot of help in identifying the correct dependencies to use in project if you want to use any popular library into your project.

Spring Boot comes with over 50+ different starter modules, which provide ready-to-use integration libraries for many different frameworks, such as database connections that are both relational and NoSQL, web services, social network integration, monitoring libraries, logging, template rendering, and the list just keeps going on.

How starter template work?

Spring Boot starters are templates that contain a collection of all the relevant transitive dependencies that are needed to start a particular functionality. Each starter has a special file, which contains the list of all the provided dependencies Spring provides.

These files can be found inside pom.xml files in respective starter module. e.g.

The spring-boot-starter-data-jpa starter pom file can be found at github.

This tells us that by including spring-boot-starter-data-jpa in our build as a dependency, we will automatically get spring-ormhibernate-entity-manager and spring-data-jpa. These libraries will provide us all basic things to start writing JPA/DAO code .

So next time when you want to give your project any specific functionality, I will suggest to check for existing starter templates to see if you can use it directly. Ongoing community additions are always on, so this list is already growing and you can contribute to it as well.

Popular templates and their transitive dependencies

I am listing down some very frequently use spring starters and what dependencies they bring along, for information only.

STARTERDEPENDENCIES
spring-boot-starterspring-boot, spring-context, spring-beans
spring-boot-starter-jerseyjersey-container-servlet-core, jersey-container-servlet, jersey-server
spring-boot-starter-actuatorspring-boot-actuator, micrometer-core
spring-boot-starter-aopspring-aop, aspectjrt, aspectjweaver
spring-boot-starter-data-restspring-hateoas, spring-data-rest-webmvc
spring-boot-starter-hateoasspring-hateoas
spring-boot-starter-logginglogback-classic, jcl-over-slf4j, jul-to-slf4j
spring-boot-starter-log4j2log4j2, log4j-slf4j-impl
spring-boot-starter-securityspring-security-web, spring-security-config
spring-boot-starter-testspring-test, spring-boot,junit,mockito, hamcrest-library, assertj, jsonassert, json-path
spring-boot-starter-web-servicesspring-ws-core

Drop me your questions in comments section.

Happy Learning !!

References:

Spring boot starters
Using boot starters

Spring-boot-starter-parent Example
30
Mar
2021

Spring Boot Starter Parent Example

In this spring boot tutorial, we will learn about spring-boot-starter-parent dependency which is used internally by all spring boot dependencies. We will also learn what all configurations this dependency provides, and how to override them.

What is spring-boot-starter-parent dependency?

The spring-boot-starter-parent dependency is the parent POM providing dependency and plugin management for Spring Boot-based applications. It contains the default versions of Java to use, the default versions of dependencies that Spring Boot uses, and the default configuration of the Maven plugins.

Few important configurations provided by this file are as below. Please refer to this link to read the complete configuration.

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd;<modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-dependencies</artifactId><version>${revision}</version><relativePath>../../spring-boot-dependencies</relativePath></parent><artifactId>spring-boot-starter-parent</artifactId><packaging>pom</packaging><name>Spring Boot Starter Parent</name><description>Parent pom providing dependency and plugin management for applicationsbuilt with Maven</description><properties><java.version>1.8</java.version><resource.delimiter>@</resource.delimiter> <!-- delimiter that doesn't clash with Spring ${} placeholders --><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding><maven.compiler.source>${java.version}</maven.compiler.source><maven.compiler.target>${java.version}</maven.compiler.target></properties> ... <resource><directory>${basedir}/src/main/resources</directory><filtering>true</filtering><includes><include>**/application*.yml</include><include>**/application*.yaml</include><include>**/application*.properties</include></includes></resource> </project>

The spring-boot-starter-parent dependency further inherits from spring-boot-dependencies, which is defined at the top of above POM file at line number : 9.

This file is the actual file which contains the information of default version to use for all libraries. The following code shows the different versions of various dependencies that are configured in spring-boot-dependencies:

<properties><!-- Dependency versions --><activemq.version>5.15.3</activemq.version><antlr2.version>2.7.7</antlr2.version><appengine-sdk.version>1.9.63</appengine-sdk.version><artemis.version>2.4.0</artemis.version><aspectj.version>1.8.13</aspectj.version><assertj.version>3.9.1</assertj.version><atomikos.version>4.0.6</atomikos.version><bitronix.version>2.1.4</bitronix.version><byte-buddy.version>1.7.11</byte-buddy.version><caffeine.version>2.6.2</caffeine.version><cassandra-driver.version>3.4.0</cassandra-driver.version><classmate.version>1.3.4</classmate.version> ......</properties>

Above list is very long and you can read complete list in this link.

How to override default dependency version?

As you see, spring boot has default version to use for most of dependencies. You can override the version of your choice or project need, in properties tag in your project’s pom.xml file.

e.g. Spring boot used default version of google GSON library as 2.8.2.

<groovy.version>2.4.14</groovy.version><gson.version>2.8.2</gson.version><h2.version>1.4.197</h2.version>

I want to use 2.7 of gson dependency. So I will give this information in properties tag like this.

<properties><java.version>1.8</java.version><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><gson.version>2.7</gson.version></properties>

Now in your eclipse editor, you can see the message as : The managed version is 2.7 The artifact is managed in org.springframework.boot:spring-boot-dependencies:2.0.0.RELEASE.

GSON resolved dependency
GSON resolved dependency

Drop me your questions in comments section.

Happy Learning !!

Spring Boot Quartz Scheduler Example Building an Email Scheduling App
06
Feb
2021

Spring Boot Quartz Scheduler Example Building an Email Scheduling App

Quartz is an open source Java library for scheduling Jobs. It has a very rich set of features including but not limited to persistent Jobs, transactions, and clustering.

You can schedule Jobs to be executed at a certain time of day, or periodically at a certain interval, and much more. Quartz provides a fluent API for creating jobs and scheduling them.

Quartz Jobs can be persisted into a database, or a cache, or in-memory.

In this article, you’ll learn how to schedule Jobs in spring boot using Quartz Scheduler by building a simple Email Scheduling application. The application will have a Rest API that allows clients to schedule Emails at a later time.

We’ll use MySQL to persist all the jobs and other job-related data.

Creating the Application

Let’s bootstrap the application using Spring Boot CLI. Open your terminal and type the following command –

spring init -d=web,jpa,mysql,quartz,mail -n=quartz-demo quartz-demo

The above command will generate the project with all the specified dependencies in a folder named quartz-demo.

Note that, you can also use Spring Initializr web tool to bootstrap the project by following the instructions below –

  • Open http://start.spring.io
  • Enter quartz-demo in the Artifact field.
  • Add WebJPAMySQLQuartz, and Mail in the dependencies section.
  • Click Generate to generate and download the project.

That’s it! You may now import the project into your favorite IDE and start working.

Directory Structure

Following is the directory structure of the complete application for your reference. We’ll create all the required folders and classes one-by-one in this article –

Spring Boot Quartz Scheduler Email Scheduling App directory structure

Configuring MySQL database, Quartz Scheduler, and Mail Sender

Let’s configure Quartz Scheduler, MySQL database, and Spring Mail. MySQL database will be used for storing Quartz Jobs, and Spring Mail will be used to send emails.

Open src/main/resources/application.properties file and add the following properties –

## Spring DATASOURCE (DataSourceAutoConfiguration & DataSourceProperties)
spring.datasource.url = jdbc:mysql://localhost:3306/quartz_demo?useSSL=false
spring.datasource.username = root
spring.datasource.password = password

## QuartzProperties
spring.quartz.job-store-type = jdbc
spring.quartz.properties.org.quartz.threadPool.threadCount = 5

## MailProperties
spring.mail.host=smtp.gmail.com
spring.mail.port=587
spring.mail.username=testme@gmail.com
spring.mail.password=

spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

You’ll need to create a MySQL database named quartz_demo. Also, don’t forget to change the spring.datasource.username and spring.datasource.password properties as per your MySQL installation.

We’ll be using Gmail’s SMTP server for sending emails. Please add your password in the spring.mail.password property. You may also pass this property at runtime as command line argument or set it in the environment variable.

Note that, Gmail’s SMTP access is disabled by default. To allow this app to send emails using your Gmail account –

All the quartz specific properties are prefixed with spring.quartz. You can refer to the complete set of configurations supported by Quartz in its official documentation. To directly set configurations for Quartz scheduler, you can use the format spring.quartz.properties.<quartz_configuration_name>=<value>.

Creating Quartz Tables

Since we have configured Quartz to store Jobs in the database, we’ll need to create the tables that Quartz uses to store Jobs and other job-related meta-data.

Please download the following SQL script and run it in your MySQL database to create all the Quartz specific tables.

After downloading the above SQL script, login to MySQL and run the script like this –

mysql> source <PATH_TO_QUARTZ_TABLES.sql> 

Overview of Quartz Scheduler’s APIs and Terminologies

1. Scheduler

The Primary API for scheduling, unscheduling, adding, and removing Jobs.

2. Job

The interface to be implemented by classes that represent a ‘job’ in Quartz. It has a single method called execute() where you write the work that needs to be performed by the Job.

3. JobDetail

A JobDetail represents an instance of a Job. It also contains additional data in the form of a JobDataMap that is passed to the Job when it is executed.

Every JobDetail is identified by a JobKey that consists of a name and a group. The name must be unique within a group.

4. Trigger

A Trigger, as the name suggests, defines the schedule at which a given Job will be executed. A Job can have many Triggers, but a Trigger can only be associated with one Job.

Every Trigger is identified by a TriggerKey that comprises of a name and a group. The name must be unique within a group.

Just like JobDetails, Triggers can also send parameters/data to the Job.

5. JobBuilder

JobBuilder is a fluent builder-style API to construct JobDetail instances.

6. TriggerBuilder

TriggerBuilder is used to instantiate Triggers.

Creating a REST API to schedule Email Jobs dynamically in Quartz

All right! Let’s now create a REST API to schedule email Jobs in Quartz dynamically. All the Jobs will be persisted in the database and executed at the specified schedule.

Before writing the API, Let’s create the DTO classes that will be used as request and response payloads for the scheduleEmail API –

ScheduleEmailRequest

package com.example.quartzdemo.payload;

import javax.validation.constraints.Email;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;
import java.time.LocalDateTime;
import java.time.ZoneId;

public class ScheduleEmailRequest {
    @Email
    @NotEmpty
    private String email;

    @NotEmpty
    private String subject;

    @NotEmpty
    private String body;

    @NotNull
    private LocalDateTime dateTime;

    @NotNull
    private ZoneId timeZone;
	
	// Getters and Setters (Omitted for brevity)
}

ScheduleEmailResponse

package com.example.quartzdemo.payload;

import com.fasterxml.jackson.annotation.JsonInclude;

@JsonInclude(JsonInclude.Include.NON_NULL)
public class ScheduleEmailResponse {
    private boolean success;
    private String jobId;
    private String jobGroup;
    private String message;

    public ScheduleEmailResponse(boolean success, String message) {
        this.success = success;
        this.message = message;
    }

    public ScheduleEmailResponse(boolean success, String jobId, String jobGroup, String message) {
        this.success = success;
        this.jobId = jobId;
        this.jobGroup = jobGroup;
        this.message = message;
    }

    // Getters and Setters (Omitted for brevity)
}

ScheduleEmail Rest API

The following controller defines the /scheduleEmail REST API that schedules email Jobs in Quartz –

package com.example.quartzdemo.controller;

import com.example.quartzdemo.job.EmailJob;
import com.example.quartzdemo.payload.ScheduleEmailRequest;
import com.example.quartzdemo.payload.ScheduleEmailResponse;
import org.quartz.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import javax.validation.Valid;
import java.time.ZonedDateTime;
import java.util.Date;
import java.util.UUID;

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

    @Autowired
    private Scheduler scheduler;

    @PostMapping("/scheduleEmail")
    public ResponseEntity<ScheduleEmailResponse> scheduleEmail(@Valid @RequestBody ScheduleEmailRequest scheduleEmailRequest) {
        try {
            ZonedDateTime dateTime = ZonedDateTime.of(scheduleEmailRequest.getDateTime(), scheduleEmailRequest.getTimeZone());
            if(dateTime.isBefore(ZonedDateTime.now())) {
                ScheduleEmailResponse scheduleEmailResponse = new ScheduleEmailResponse(false,
                        "dateTime must be after current time");
                return ResponseEntity.badRequest().body(scheduleEmailResponse);
            }

            JobDetail jobDetail = buildJobDetail(scheduleEmailRequest);
            Trigger trigger = buildJobTrigger(jobDetail, dateTime);
            scheduler.scheduleJob(jobDetail, trigger);

            ScheduleEmailResponse scheduleEmailResponse = new ScheduleEmailResponse(true,
                    jobDetail.getKey().getName(), jobDetail.getKey().getGroup(), "Email Scheduled Successfully!");
            return ResponseEntity.ok(scheduleEmailResponse);
        } catch (SchedulerException ex) {
            logger.error("Error scheduling email", ex);

            ScheduleEmailResponse scheduleEmailResponse = new ScheduleEmailResponse(false,
                    "Error scheduling email. Please try later!");
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(scheduleEmailResponse);
        }
    }

    private JobDetail buildJobDetail(ScheduleEmailRequest scheduleEmailRequest) {
        JobDataMap jobDataMap = new JobDataMap();

        jobDataMap.put("email", scheduleEmailRequest.getEmail());
        jobDataMap.put("subject", scheduleEmailRequest.getSubject());
        jobDataMap.put("body", scheduleEmailRequest.getBody());

        return JobBuilder.newJob(EmailJob.class)
                .withIdentity(UUID.randomUUID().toString(), "email-jobs")
                .withDescription("Send Email Job")
                .usingJobData(jobDataMap)
                .storeDurably()
                .build();
    }

    private Trigger buildJobTrigger(JobDetail jobDetail, ZonedDateTime startAt) {
        return TriggerBuilder.newTrigger()
                .forJob(jobDetail)
                .withIdentity(jobDetail.getKey().getName(), "email-triggers")
                .withDescription("Send Email Trigger")
                .startAt(Date.from(startAt.toInstant()))
                .withSchedule(SimpleScheduleBuilder.simpleSchedule().withMisfireHandlingInstructionFireNow())
                .build();
    }
}

Spring Boot has built-in support for Quartz. It automatically creates a Quartz Scheduler bean with the configuration that we supplied in the application.properties file. That’s why we could directly inject the Scheduler in the controller.

In the /scheduleEmail API,

  • We first validate the request body
  • Then, Build a JobDetail instance with a JobDataMap that contains the recipient email, subject, and body. The JobDetail that we create is of type EmailJob. We’ll define EmailJob in the next section.
  • Next, we Build a Trigger instance that defines when the Job should be executed.
  • Finally, we schedule the Job using scheduler.scheduleJob() API.

Creating the Quartz Job to sends emails

Let’s now define the Job that sends the actual emails. Spring Boot provides a wrapper around Quartz Scheduler’s Job interface called QuartzJobBean. This allows you to create Quartz Jobs as Spring beans where you can autowire other beans.

Let’s create our EmailJob by extending QuartzJobBean –

package com.example.quartzdemo.job;

import org.quartz.JobDataMap;
import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.mail.MailProperties;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.scheduling.quartz.QuartzJobBean;
import org.springframework.stereotype.Component;

import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
import java.nio.charset.StandardCharsets;

@Component
public class EmailJob extends QuartzJobBean {
    private static final Logger logger = LoggerFactory.getLogger(EmailJob.class);

    @Autowired
    private JavaMailSender mailSender;

    @Autowired
    private MailProperties mailProperties;
    
    @Override
    protected void executeInternal(JobExecutionContext jobExecutionContext) throws JobExecutionException {
        logger.info("Executing Job with key {}", jobExecutionContext.getJobDetail().getKey());

        JobDataMap jobDataMap = jobExecutionContext.getMergedJobDataMap();
        String subject = jobDataMap.getString("subject");
        String body = jobDataMap.getString("body");
        String recipientEmail = jobDataMap.getString("email");

        sendMail(mailProperties.getUsername(), recipientEmail, subject, body);
    }

    private void sendMail(String fromEmail, String toEmail, String subject, String body) {
        try {
            logger.info("Sending Email to {}", toEmail);
            MimeMessage message = mailSender.createMimeMessage();

            MimeMessageHelper messageHelper = new MimeMessageHelper(message, StandardCharsets.UTF_8.toString());
            messageHelper.setSubject(subject);
            messageHelper.setText(body, true);
            messageHelper.setFrom(fromEmail);
            messageHelper.setTo(toEmail);

            mailSender.send(message);
        } catch (MessagingException ex) {
            logger.error("Failed to send email to {}", toEmail);
        }
    }
}

Running the Application and Testing the API

It’s time to run the application and watch the live action. Open your terminal, go to the root directory of the project and type the following command to run it –

mvn spring-boot:run -Dspring.mail.password=<YOUR_SMTP_PASSWORD>

You don’t need to pass the spring.mail.password command line argument if you have already set the password in the application.properties file.

The application will start on port 8080 by default. Let’s now schedule an email using the /scheduleEmail API –

Spring Boot Quartz Scheduler Email Job Scheduler API

And, Here I get the email at the specified time 🙂

Spring Boot Quartz Scheduler Dynamic Email Job Scheduler API Example

Conclusion

That’s all folks! I hope you enjoyed the article. You can find the complete source code of the project in the Github Repository. Consider giving the project a star on Github if you find it useful.

References

Sounds interesting? Let’s start…

Intro to Spring Boot Starters
26
Mar
2021

Intro to Spring Boot Starters

1. Overview

Dependency management is a critical aspects of any complex project. And doing this manually is less than ideal; the more time you spent on it the less time you have on the other important aspects of the project.

Spring Boot starters were built to address exactly this problem. Starter POMs are a set of convenient dependency descriptors that you can include in your application. You get a one-stop-shop for all the Spring and related technology that you need, without having to hunt through sample code and copy-paste loads of dependency descriptors.

We have more than 30 Boot starters available – let’s see some of them in the following section

2. The Web Starter

First, let’s look at developing the REST service; we can use libraries like Spring MVC, Tomcat and Jackson – a lot of dependencies for a single application.

Spring Boot starters can help to reduce the number of manually added dependencies just by adding one dependency. So instead of manually specifying the dependencies just add one starter as in the following example:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Now we can create a REST controller. For the sake of simplicity we won’t use the database and focus on the REST controller:

@RestController
public class GenericEntityController {
    private List<GenericEntity> entityList = new ArrayList<>();

    @RequestMapping("/entity/all")
    public List<GenericEntity> findAll() {
        return entityList;
    }

    @RequestMapping(value = "/entity", method = RequestMethod.POST)
    public GenericEntity addEntity(GenericEntity entity) {
        entityList.add(entity);
        return entity;
    }

    @RequestMapping("/entity/findby/{id}")
    public GenericEntity findById(@PathVariable Long id) {
        return entityList.stream().
                 filter(entity -> entity.getId().equals(id)).
                   findFirst().get();
    }
}

The GenericEntity is a simple bean with id of type Long and value of type String.

That’s it – with the application running, you can access http://localhost:8080/entity/all and check the controller is working.

We have created a REST application with quite a minimal configuration.

3. The Test Starter

For testing we usually use the following set of libraries: Spring Test, JUnit, Hamcrest, and Mockito. We can include all of these libraries manually, but Spring Boot starter can be used to automatically include these libraries in the following way:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

Notice that you don’t need to specify the version number of an artifact. Spring Boot will figure out what version to use – all you need to specify is the version of spring-boot-starter-parent artifact. If later on you need to upgrade the Boot library and dependencies, just upgrade the Boot version in one place and it will take care of the rest.

Let’s actually test the controller we created in the previous example.

There are two ways to test the controller:

  • Using the mock environment
  • Using the embedded Servlet container (like Tomcat or Jetty)

In this example we’ll use a mock environment:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
@WebAppConfiguration
public class SpringBootApplicationIntegrationTest {
    @Autowired
    private WebApplicationContext webApplicationContext;
    private MockMvc mockMvc;

    @Before
    public void setupMockMvc() {
        mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
    }

    @Test
    public void givenRequestHasBeenMade_whenMeetsAllOfGivenConditions_thenCorrect()
      throws Exception { 
        MediaType contentType = new MediaType(MediaType.APPLICATION_JSON.getType(),
        MediaType.APPLICATION_JSON.getSubtype(), Charset.forName("utf8"));
        mockMvc.perform(MockMvcRequestBuilders.get("/entity/all")).
        andExpect(MockMvcResultMatchers.status().isOk()).
        andExpect(MockMvcResultMatchers.content().contentType(contentType)).
        andExpect(jsonPath("$", hasSize(4))); 
    } 
}

The above test calls the /entity/all endpoint and verifies that the JSON response contains 4 elements. For this test to pass, we also have to initialize our list in the controller class:

public class GenericEntityController {
    private List<GenericEntity> entityList = new ArrayList<>();

    {
        entityList.add(new GenericEntity(1l, "entity_1"));
        entityList.add(new GenericEntity(2l, "entity_2"));
        entityList.add(new GenericEntity(3l, "entity_3"));
        entityList.add(new GenericEntity(4l, "entity_4"));
    }
    //...
}

What is important here is that @WebAppConfiguration annotation and MockMVC are part of the spring-test module, hasSize is a Hamcrest matcher, and @Before is a JUnit annotation. These are all available by importing one this one starter dependency.

4. The Data JPA Starter

Most web applications have some sort of persistence – and that’s quite often JPA.

Instead of defining all of the associated dependencies manually – let’s go with the starter instead:

<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>

Notice that out of the box we have automatic support for at least the following databases: H2, Derby and Hsqldb. In our example, we’ll use H2.

Now let’s create the repository for our entity:

public interface GenericEntityRepository extends JpaRepository<GenericEntity, Long> {}

Time to test the code. Here is the JUnit test:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
public class SpringBootJPATest {
    
    @Autowired
    private GenericEntityRepository genericEntityRepository;

    @Test
    public void givenGenericEntityRepository_whenSaveAndRetreiveEntity_thenOK() {
        GenericEntity genericEntity = 
          genericEntityRepository.save(new GenericEntity("test"));
        GenericEntity foundedEntity = 
          genericEntityRepository.findOne(genericEntity.getId());
        
        assertNotNull(foundedEntity);
        assertEquals(genericEntity.getValue(), foundedEntity.getValue());
    }
}

We didn’t spend time on specifying the database vendor, URL connection, and credentials. No extra configuration is necessary as we’re benefiting from the solid Boot defaults; but of course all of these details can still be configured if necessary.

5. The Mail Starter

A very common task in enterprise development is sending email, and dealing directly with Java Mail API usually can be difficult.

Spring Boot starter hides this complexity – mail dependencies can be specified in the following way:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-mail</artifactId>
</dependency>

Now we can directly use the JavaMailSender, so let’s write some tests.

For the testing purpose, we need a simple SMTP server. In this example, we’ll use Wiser. This is how we can include it in our POM:

<dependency>
    <groupId>org.subethamail</groupId>
    <artifactId>subethasmtp</artifactId>
    <version>3.1.7</version>
    <scope>test</scope>
</dependency>

Here is the source code for the test:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
public class SpringBootMailTest {
    @Autowired
    private JavaMailSender javaMailSender;

    private Wiser wiser;

    private String userTo = "user2@localhost";
    private String userFrom = "user1@localhost";
    private String subject = "Test subject";
    private String textMail = "Text subject mail";

    @Before
    public void setUp() throws Exception {
        final int TEST_PORT = 25;
        wiser = new Wiser(TEST_PORT);
        wiser.start();
    }

    @After
    public void tearDown() throws Exception {
        wiser.stop();
    }

    @Test
    public void givenMail_whenSendAndReceived_thenCorrect() throws Exception {
        SimpleMailMessage message = composeEmailMessage();
        javaMailSender.send(message);
        List<WiserMessage> messages = wiser.getMessages();

        assertThat(messages, hasSize(1));
        WiserMessage wiserMessage = messages.get(0);
        assertEquals(userFrom, wiserMessage.getEnvelopeSender());
        assertEquals(userTo, wiserMessage.getEnvelopeReceiver());
        assertEquals(subject, getSubject(wiserMessage));
        assertEquals(textMail, getMessage(wiserMessage));
    }

    private String getMessage(WiserMessage wiserMessage)
      throws MessagingException, IOException {
        return wiserMessage.getMimeMessage().getContent().toString().trim();
    }

    private String getSubject(WiserMessage wiserMessage) throws MessagingException {
        return wiserMessage.getMimeMessage().getSubject();
    }

    private SimpleMailMessage composeEmailMessage() {
        SimpleMailMessage mailMessage = new SimpleMailMessage();
        mailMessage.setTo(userTo);
        mailMessage.setReplyTo(userFrom);
        mailMessage.setFrom(userFrom);
        mailMessage.setSubject(subject);
        mailMessage.setText(textMail);
        return mailMessage;
    }
}

In the test, the @Before and @After methods are in charge of starting and stopping the mail server.

Notice that we’re wiring in the JavaMailSender bean – the bean was automatically created by Spring Boot.

Just like any other defaults in Boot, the email settings for the JavaMailSender can be customized in application.properties:

spring.mail.host=localhost
spring.mail.port=25
spring.mail.properties.mail.smtp.auth=false

So we configured the mail server on localhost:25 and we didn’t require authentication.

6. Conclusion

In this article we have given an overview of Starters, explained why we need them and provided examples on how to use them in your projects.

Let’s recap the benefits of using Spring Boot starters:

  • increase pom manageability
  • production-ready, tested & supported dependency configurations
  • decrease the overall configuration time for the project
How to Change the Default Port in Spring Boot
26
Mar
2021

How to Change the Default Port in Spring Boot

Spring Boot provides sensible defaults for many configuration properties. But we sometimes need to customize these with our case-specific values.

And a common use case is changing the default port for the embedded server.

In this quick tutorial, we’ll cover several ways to achieve this.

2. Using Property Files

The fastest and easiest way to customize Spring Boot is by overriding the values of the default properties.

For the server port, the property we want to change is server.port.

By default, the embedded server starts on port 8080.

So, let’s see how to provide a different value in an application.properties file:

server.port=8081

Now the server will start on port 8081.

And we can do the same if we’re using an application.yml file:

server:
  port : 8081

Both files are loaded automatically by Spring Boot if placed in the src/main/resources directory of a Maven application.

2.1. Environment-Specific Ports

If we have an application deployed in different environments, we may want it to run on different ports on each system.

We can easily achieve this by combining the property files approach with Spring profiles. Specifically, we can create a property file for each environment.

For example, we’ll have an application-dev.properties file with this content:

server.port=8081

Then we’ll add another application-qa.properties file with a different port:

server.port=8082

Now, the property files configuration should be sufficient for most cases. However, there are other options for this goal, so let’s explore them as well.

3. Programmatic Configuration

We can configure the port programmatically either by setting the specific property when starting the application or by customizing the embedded server configuration.

First, let’s see how to set the property in the main @SpringBootApplication class:

@SpringBootApplication
public class CustomApplication {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(CustomApplication.class);
        app.setDefaultProperties(Collections
          .singletonMap("server.port", "8083"));
        app.run(args);
    }
}

Next, to customize the server configuration, we have to implement the WebServerFactoryCustomizer interface:

@Component
public class ServerPortCustomizer 
  implements WebServerFactoryCustomizer<ConfigurableWebServerFactory> {
 
    @Override
    public void customize(ConfigurableWebServerFactory factory) {
        factory.setPort(8086);
    }
}

Note that this applies to the Spring Boot 2.x version.

For Spring Boot 1.x, we can similarly implement the EmbeddedServletContainerCustomizer interface.

4. Using Command-Line Arguments

When packaging and running our application as a jar, we can set the server.port argument with the java command:

java -jar spring-5.jar --server.port=8083

or by using the equivalent syntax:

java -jar -Dserver.port=8083 spring-5.jar

5. Order of Evaluation

As a final note, let’s look at the order in which these approaches are evaluated by Spring Boot.

Basically, the configurations priority is

  • embedded server configuration
  • command-line arguments
  • property files
  • main @SpringBootApplication configuration

6. Conclusion

In this article, we saw how to configure the server port in a Spring Boot application.

Spring Boot Logging Best Practices Guide
05
May
2021

Spring Boot Logging Best Practices Guide

Logging in Spring Boot can be confusing, and the wide range of tools and frameworks make it a challenge to even know where to start. This guide talks through the most common best practices for Spring Boot logging and gives five key suggestions to add to your logging tool kit.

What’s in the Spring Boot Box?

The Spring Boot Starters all depend on spring-boot-starter-logging. This is where the majority of the logging dependencies for your application come from. The dependencies involve a facade (SLF4J) and frameworks (Logback). It’s important to know what these are and how they fit together.

SLF4J is a simple front-facing facade supported by several logging frameworks. It’s main advantage is that you can easily switch from one logging framework to another. In our case, we can easily switch our logging from Logback to Log4j, Log4j2 or JUL.

The dependencies we use will also write logs. For example, Hibernate uses SLF4J, which fits perfectly as we have that available. However, the AWS SDK for Java uses Apache Commons Logging (JCL). Spring-boot-starter-logging includes the necessary bridges to ensure those logs are delegated to our logging framework out of the box.

SLF4J usage:

At a high level, all the application code has to worry about is:

  1. Getting an instance of an SLF4J logger (Regardless of the underlying framework):
    private static final Logger LOG = LoggerFactory.getLogger(MyClass.class);Copy
  2. Writing some logs:
    LOG.info(“My message set at info level”);Copy

Logback or Log4j2?

Spring Boot’s default logging framework is Logback. Your application code should interface only with the SLF4J facade so that it’s easy to switch to an alternative framework if necessary.

Log4j2 is newer and claims to improve on the performance of Logback. Log4j2 also supports a wide range of appenders so it can log to files, HTTP, databases, Cassandra, Kafka, as well as supporting asynchronous loggers. If logging performance is of high importance, switching to log4j2 may improve your metrics. Otherwise, for simplicity, you may want to stick with the default Logback implementation.

This guide will provide configuration examples for both frameworks.

Want to use log4j2? You’ll need to exclude spring-boot-starter-logging and include spring-boot-starter-logging-log4j2.

spring boot logging frameworks

5 Tips for Getting the Most Out of Your Spring Boot Logging

With your initial set up out of the way, here are 5 top tips for spring boot logging.

1. Configuring Your Log Format

Spring Boot Logging provides default configurations for logback and log4j2. These specify the logging level, the appenders (where to log) and the format of the log messages.

For all but a few specific packages, the default log level is set to INFO, and by default, the only appender used is the Console Appender, so logs will be directed only to the console.

The default format for the logs using logback looks like this:

logback default logging format

Let’s take a look at that last line of log, which was a statement created from within a controller with the message “My message set at info level”.

It looks simple, yet the default log pattern for logback seems “off” at first glance. As much as it looks like it could be, it’s not regex, it doesn’t parse email addresses, and actually, when we break it down it’s not so bad.

%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint}
%clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint}
%clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint}
%m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}Copy

Understanding the Default Logback Pattern

The variables that are available for the log format allow you to create meaningful logs, so let’s look a bit deeper at the ones in the default log pattern example.Show 102550100 entriesSearch:

Pattern PartWhat it Means
%clr%clr specifies a colour. By default, it is based on log levels, e.g, INFO is green. If you want to specify specific colours, you can do that too.

The format is:
%clr(Your message){your colour}

So for example, if we wanted to add “Demo” to the start of every log message, in green, we would write:
%clr(Demo){green}
%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}%d is the current date, and the part in curly braces is the format. ${VARIABLE}:-default is a way of specifying that we should use the $VARIABLE environment variable for the format, if it is available, and if not, fall back to default. This is handy if you want to override these values in your properties files, by providing arguments, or by setting environment variables.

In this example, the default format is yyyy-MM-dd HH:mm:ss.SSS unless we specify a variable named LOG_DATEFORMAT_PATTERN. In the logs above, we can see 2020-10-19 10:09:58.152 matches the default pattern, meaning we did not specify a custom LOG_DATEFORMAT_PATTERN.
${LOG_LEVEL_PATTERN:-%5p}Uses the LOG_LEVEL_PATTERN if it is defined, else will print the log level with right padding up to 5 characters (E.g “INFO” becomes “INFO “ but “TRACE” will not have the trailing space). This keeps the rest of the log aligned as it’ll always be 5 characters.
${PID:- }The environment variable $PID, if it exists. If not, space.
tThe name of the thread triggering the log message.
loggerThe name of the logger (up to 39 characters), in our case this is the class name.
%mThe log message.
%nThe platform-specific line separator.
%wExIf one exists, wEx is the stack trace of any exception, formatted using Spring Boot’s ExtendedWhitespaceThrowableProxyConverter.

Showing 1 to 9 of 9 entriesPreviousNext

Customising the log format

You can customise the ${} variables that are found in the logback-spring.xml by passing in properties or environment variables. For example, you may set logging.pattern.console to override the whole of the console log pattern. 

However, for more control, including adding additional appenders, it is recommended to create your logback-spring.xml and place it inside your resources folder. You can do the same with log4j2 by adding log4j2-spring.xml to your resources folder.

Armed with the ability to customise your logs, you should consider adding:

  • Application name.
  • A request ID.
  • The endpoint being requested (E.g /health).

There are a few items in the default log that I would remove unless you have a specific use case for them:

  • The ‘—’ separator.
  • The thread name.
  • The process ID.

With the ability to customise these through the use of the logback-spring.xml or log4j2-spring.xml, the format of your logs is fully within your control.

2. Configuring the Destination for Your Logs (Appenders and Loggers)

An appender is just a fancy name for the part of the logging framework that sends your logs to a particular target. Both frameworks can output to console, over HTTP, to databases, or over a TCP socket, as well as to many other targets. The way we configure the destination for the logs is by adding, removing and configuring these appenders. 

You have more control over which appenders you use, and the configuration of them, if you create your own custom .xml configuration. However, the default logging configuration does make use of environment properties that allow you to override some parts of it, for example, the date format.

Preset configuration for logging to files are available within Spring Boot Logging. You can use the logback configuration with a file appender or the log4j2 configuration with a file appender if you specify logging.file or logging.path in your application properties.

The official docs for logback appenders and log4j2 appenders detail the parameters required for each of the appenders available, and how to configure them in your XML file. One tip for choosing the destination for your logs is to have a plan for rotating them. Writing logs to a file always feels like a great idea, until the storage used for that file runs out and brings down the whole service. 

Log4j and logback both have a RollingFileAppender which handles rotating these log files based on file size, or time, and it’s exactly that which Spring Boot Logging uses if you set the logging.file property. 

3. Logging as a Cross-Cutting Concern to Keep Your Code Clean (Using Filters and Aspects)

You might want to log every HTTP request your API receives. That’s a fairly normal requirement, but putting a log statement into every controller is unnecessary duplication. It’s easy to forget and make mistakes. A requirement that you want to log every method within your packages that your application calls would be even more cumbersome. 

I’ve seen developers use this style of logging at trace level so that they can turn it on to see exactly what is happening in a production environment. Adding log statements to the start and end of every method is messy, and there is a better way. This is where filters and aspects save the day and avoid the code duplication.

When to Use a Filter Vs When to Use Aspect-Oriented Programming

If you are looking to create log statements related to specific requests, you should opt for using filters, as they are part of the handling chain that your application already goes through for each request. They are easier to write, easier to test and usually more performant than using aspects. If you are considering more cross-cutting concerns, for example, audit logging, or logging every method that causes an exception to be thrown, use AOP. 

Using a Filter to Log Every Request

Filters can be registered with your web container by creating a class implementing javax.servlet.Filter and annotating it with @Component, or adding it as an @Bean in one of your configuration classes. When your spring-boot-starter application starts up, it will create the Filter and register it with the container.

You can choose to create your own Filter, or to use an existing one. To make use of the existing Filter, you need to supply a CommonsRequestLoggingFilter bean and set your logging level to debug. You’ll get something that looks like:

2020-10-27 18:50:50.427 DEBUG 24168 --- [nio-8080-exec-2] o.a.coyote.http11.Http11InputBuffer      : Received [GET /health HTTP/1.1
tracking-header: my-tracking
User-Agent: PostmanRuntime/7.26.5
Accept: */*
Postman-Token: 04a661b7-209c-43c3-83ea-e09466cf3d92
Host: localhost:8080
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
]Copy

If you use the existing one, you have little control over the message that gets logged. 

If you want more control, create your own Filter using this example, and you then have full control over the content of the log message.

Using Aspects for Cross-Cutting Concerns

Aspect-oriented programming enables you to fulfill cross-cutting concerns, like logging for example, in one place. You can do this without your logging code needing to sprawl across every class.

This approach is great for use cases such as:

  • Logging any exceptions thrown from any method within your packages (See @AfterThrowing)
  • Logging performance metrics by timing before/after each method is run (See @Around)
  • Audit logging. You can log calls to methods that have your a custom annotation on, such as adding @Audit. You only need to create a pointcut matching calls to methods with that annotation

Let’s start with a simple example – we want to log the name of every public method that we call within our package, com.example.demo. There are only a few steps to writing an Aspect that will run before every public method in a package that you specify.

  1. Include spring-boot-starter-aop in your pom.xml or build.gradle.
  2. Add @EnableAspectJAutoProxy to one of your configuration classes. This line tells spring-boot that you want to enable AspectJ support.
  3. Add your pointcut, which defines a pattern that is matched against method signatures as they run. You can find more about how to construct your matching pattern in the spring boot documentation for AOP. In our example, we match any method inside the com.example.demo package.
  4. Add your Aspect. This defines when you want to run your code in relation to the pointcut (E.g, before, after or around the methods that it matches). In this example, the @Before annotation causes the method to be executed before any methods that match the pointcut. 

That’s all there is to logging every method call. The logs will appear as:

2020-10-27 19:26:33.269  INFO 2052 --- [nio-8080-exec-2]
com.example.demo.MyAspect                : Called checkHealthCopy

By making changes to your pointcut, you can write logs for every method annotated with a specific annotation. For example, consider what you can do with:

@annotation(com.example.demo.Audit)Copy

4. Applying Context to Your Logs Using MDC

(This would run for every method annotated with a custom annotation, @Audit).

MDC (Mapped Diagnostic Context) is a complex-sounding name for a map of key-value pairs, associated with a single thread. Each thread has its own map. You can add keys/values to the map at runtime, and then reference the keys from that map in your logging pattern. 

The approach comes with a warning that threads may be reused, and so you’ll need to make sure to clear your MDC after each request to avoid your context leaking from one request to the next.

MDC is accessible through SLF4J and supported by both Logback and Log4j2, so we don’t need to worry about the specifics of the underlying implementation. 

The MDC section in the SLF4J documentation gives the simplest examples.

Tracking Requests Through Your Application Using Filters and MDC

Want to be able to group logs for a specific request? The Mapped Diagnostic Context (MDC) will help. 

The steps are:

  1. Add a header to each request going to your API, for example, ‘tracking-id’. You can generate this on the fly (I suggest using a UUID) if your client cannot provide one.
  2. Create a filter that runs once per request and stores that value in the MDC.
  3. Update your logging pattern to reference the key in the MDC to retrieve the value.

Using a Filter, this is how you can read values from the request and set them on the MDC. Make sure to clear up after the request by calling MDC.clear(), preferably in a finally block so that it always runs. 

After setting the value on your MDC, just add %X{tracking}  to your logging pattern (Replacing the word “tracking” with the key you have put in MDC) and your logs will contain the value in every log message for that request. 

If a client reports a problem, as long as you can get a unique tracking-id from your client, then you’ll be able to search your logs and pull up every log statement generated from that specific request.

Other use cases that you may want to put into your MDC and include on every log message include:

  • The application version.
  • Details of the request, for example, the path.
  • Details of the logged-in user, for example, the username.

5. Unit Testing Your Log Statements

Why Test Your Logs?

You can unit test your logging code. Too often this is overlooked because the log statements return void. For example, logger.info(“foo”);  does not return a value that you can assert against. 

It’s easy to make mistakes. Log statements usually involve parameters or formatted strings, and it’s easy to put log statements in the wrong place. Unit testing reassures you that your logs do what you expect and that you’re covered when refactoring to avoid any accidental modifications to your logging behaviour.

The Approach to Testing Your Logs

The Problem

SLF4J’s LoggerFactory.getLogger is static, making it difficult to mock. Searching through any outputted log files in our unit tests is error-prone (E.g we need to consider resetting the log files between each unit test). How do we assert against the logs?

The Solution

The trick is to add your own test appender to the logging framework (e.g Logback or Log4j2) that captures the logs from your application in memory, allowing us to assert against the output later. The steps are:

  1. Before each test case, add an appender to your logger.
  2. Within the test, call your application code that logs some output.
  3. The logger will delegate to your test appender.
  4. Assert that your expected logs have been received by your test appender.

Each logging framework has suitable appenders, but referencing those concrete appenders in our tests means we need to depend on the specific framework rather than SLF4J. That’s not ideal, but the alternatives of searching through logged output in files, or implementing our own SLF4J implementation is overkill, making this the pragmatic choice.

Here are a couple of tricks for unit testing using JUnit 4 rules or JUnit 5 extensions that will keep your test classes clean, and reduce the coupling with the logging framework.

Testing Log Statements Using Junit 5 Extensions in Two Steps

JUnit 5 extensions help to avoid code duplicates between your tests. Here’s how to set up your logging tests in two steps:

Step 1: Create your JUnit extension

Create your extension for Logback

Create your extension for Log4j2

Step 2: Use that rule to assert against your log statement with logback or log4j2

Testing Log Statements Using Junit 4 Rules in Two Steps

JUnit 4 rules help to avoid code duplication by extracting the common test code away from the test classes. In our example, we don’t want to duplicate the code for adding a test appender to our logger in every test class.

Step 1: Create your JUnit rule. 

Create your rule for Logback

Create your rule for Log4j2

Step 2: Use that rule to assert against your log statements using logback or log4j2.

With these approaches, you can assert that your log statements have been called with a message and level that you expect. 

Conclusion

The Spring Boot Logging Starter provides everything you need to quickly get started, whilst allowing full control when you need it. We’ve looked at how most logging concerns (formatting, destinations, cross-cutting logging, context and unit tests) can be abstracted away from your core application code.

Any global changes to your logging can be done in one place, and the classes for the rest of your application don’t need to change. At the same time, unit tests for your log statements provide you with reassurance that your log statements are being fired after making any alterations to your business logic.

These are my top 5 tips for configuring Spring Boot Logging. However, when your logging configuration is set up, remember that your logs are only ever as good as the content you put in them. Be mindful of the content you are logging, and make sure you are using the right logging levels.