Blog
Collection of curated blog posts from me.
Spring Boot Banner - Beyond ASCII art
If you’re working with Spring Boot you may see banner once your app is starting. The banner is not only decoration, but can serve as provider of helpful information. It can provide valuable information and even serve functional purposes. Let’s explore how to customize it beyond simple ASCII art. The basics: Text and image The simplest way of customization is to create banner.txt file. The banner.txt file should place in resource folder. Spring Boot picks this up and displays its content at startup. For graphic lovers, Spring Boot also Supports image - based banners. You need only add banner.jpg, or banner.png to your resource folder, and Spring Boot will convert it to ASCII art.
April 1, 2025
Maven plugin development from basic to advanced
Extensions Introduction Ever found yourself repeating the same mundane tasks during your build process? You might be checking for SNAPSHOT dependencies before a release. You could also check code formatting or do custom verifications that regular plugins don’t handle. We developers love automation. Maven plugins help us do that. They let you tweak and customize your build process to match your project’s need. In this article, I’ll guide you through creating your own Maven plugins, from simple to a sophisticated. After I missed SNAPSHOT dependencies during a release and caused production delay, I saw that a custom Maven plugin could fix this issue for good. Why manually check when you can automate?
March 27, 2025
Structured logging
Spring Boot 3.4 adds native support for structured logging. This makes it easier to create machine — readable logs that work well with log aggregation tools. In this quick guide, I’ll show you how to configure and use this powerful feature. What is structured logging? Traditional text — based logs are great for humans but challenging for machines to parse. Structured logging formats logs as JSON objects. These have defined fields, makint them easier to search, filter, and analyze. You can use tools like ELK Stack. Setting up structured logging
March 23, 2025
Understanding Java Memory Model and Thread Safety
In today’s world of multiple-core processors, it is vital to know how Java manages memory and threads. This understanding helps in creating strong, high - performance applications. We often overlook basic understanding threading mechanisms as developers. But when issues arise - and they will knowing the core concepts can save your hours of debugging. Java Memory Model: More than heap and stack The Java Memory Model (JMM) defines how threads interact through memory. It’s not just about how we organize memory. It’s also about the rules that control visibility, atomicity, and the order of memory operations. When Java code runs, each thread gets its own stack, storing local variables and method call information. But all threads share the heap, which contains all objects your program allocates. This shared nature is strong but risky. It lets threads communicate, but it can lead to race conditions. The JMM, introduced in Java 5 (JSR - 133), provides guarantees about when changes made by one thread become visible to other. Before we dive into the details, let’s understand why this matters. Consider this code that appears to be harmless:
March 20, 2025
Demystifying Java ClassLoaders - A deep dive into the JVM loading mechanism
Loading Have you ever wondered how your Java application finds all those imported classes? Or maybe you’ve faced the dreaded ClassNotFoundException and felt lost in classloader confusion? Perhaps you’ve dealt with dependency conflicts or library version issues in large applications. All these problems come from one key mechanism in Java: classloaders. In this article, I’ll take you into the exciting world of Java’s classloading. We will explore how class loaders operate. We’ll talk about their hierarchy. You’ll learn how to use them to solve real-world problems in your apps.
March 13, 2025
Spring AOP - Understanding proxy mechanics
Under hood When I first encountered Spring AOP (Aspect - Oriented Programming), it seemed like magic. My Java code began executing extra behavior without my explicit command. Log statements showed up, transaction handled themselves, and security check happened automatically. But as with any advanced technology, the magic has a clear explanation. In this article, we will pull back the curtain on Spring AOP and explore how it uses proxy patterns to weave behavior into your applications. We will look at both the theory and practical implementations so you can make the most of this powerful feature.
March 6, 2025
Understanding Spring Bean Lifecycle
Coffee beans, but today about different beans Introduction The Spring Framework is key for Java enterprise development. It manages “beans,” which are objects, using a smart lifecycle system. It’s important for developers to grasp this lifecycle in Spring applications. This knowledge gives them control over how resources are set up, how they behave, and how to clean them up properly.
February 28, 2025
Building a custom Spring Boot Starter - From theory to practice
Introduction Spring Boot starters are key feature of the Spring Boot ecosystem. They simplify dependency management and auto — configuration. A starter mix of dependencies and auto — configuration.It provides specific features with little setup needed. Spring Boot offers many official starters. However, you may need to create a custom starter for reusable functionality across different projects. In this guide, we’ll look at the theory and practice fo building a custom Spring Boot starter. We’ll learn how to start working under the hood and create a real — world example that you can use as template for you own custom starter.
February 26, 2025
Building Streaming API with gRPC
In this article, I’ll guide you through implementing streaming APIs using gRPC in Java. We’ll look at various types of streaming. Then, we’ll create a practical example to show real-time flow. Introduction Many developers know about traditional request-response APIs. Yet, modern apps often need real-time data streaming. gRPC provides powerful streaming capabilities that can transform how your services communicate. Whether you’re making chat apps, real-time analytics, or IoT systems, knowing gRPC streaming is key. Let’s create a weather monitoring service. It will stream temperature updates to clients.
February 21, 2025
Redis Caching Pattern in Java Applications - From Theory to Practice
Introduction Picture this: your Java application is handling thousands of requests per second, but your database is struggling to keep up. Response times are climbing, and your team is debating whether to throw more hardware at the problem. Sounds familiar? This is where Redis shines. Redis started as a tool for real-time analytics at Twitter (now X). Now, it’s a versatile caching solution. It manages everything from basic key-value storage to advanced message brokering.
February 13, 2025
Spring Boot & Resilience4j - Mastering circuit breakers with Prometheus and Grafana
A comprehensive guide to implementing resilient microservices: from basic circuit breaker patterns to advanced monitoring with Prometheus and Grafana Electrical chain Introduction Imagine you’re building a microservice—based application where many services depend on each other. What happens when one service strt failing? Without proper error handling, failures can cascade through your system. They could bring down the entire application. This is where circuit breaker pattern comes in.
February 3, 2025
Essential code review practices that actually save time
Code reviews are crucial for software quality, but without proper best practices, they can become a bottleneck. Here are three (of course, it can be more) reviews efficient yet high - quality. I’ll include real examples where they help 1. Review in small batches Don’t wait to review 500+ lines of code at once. Encourage small, focused pull request of 200–300 lines at a maximum. Real situation: Last month, our team had to review a massive pull request that touched our entire authentication system.
January 30, 2025
Property-Based Testing with jqwik - A Practical Guide
Introduction As software grows more complex, traditional example-based testing often fails. It can’t find edge cases and unexpected behaviors. Property-based testing (PBT) is a powerful alternative. It generates test cases based on properties that your code should meet without any manual input. This article will explore property-based testing using jqwik. It’s a modern property-based testing library for Java. What is property-based testing? Property-based testing is a method. Instead of writing specific test cases, you define properties. Your code must meet them in all cases. The testing framework then generates many test cases to verify these properties.
January 23, 2025
Building Event-Driven Microservices with Spring Cloud Stream and Kafka
Modern applications face increasingly complex challenges in handling data and interactions between services. As our systems grow, traditional request-response patterns often become bottlenecks. This leads to seek more flexible, scalable solutions. This is where event-driven architecture (EDA) comes in. It offers a powerful way to build resilient microservices. Why event-driven architecture? Think of event architecture like a city’s postal system. Instead of calling each other, services send messages (events) through a central messaging system. This approach enables services to operate without relying on one another. It’s like how different postal offices operate without knowing each other’s internal workings. When one service has something important to share, it publishes an event, and any interested services can react to it in their own time.
December 19, 2024
Spring Boot with Temporal - Building Resillient Workflow Applications
A guide to building resilient, distributed apps with Spring Boot and Temporal’s orchestration. Introduction Building reliable distributed applications can be challenging. System crash, network fail, and processes can get stuck halfway through execution. This is where Temporal comes in. It is an open-source workflow orchestration platform. When combined with Spring Boot, it helps you build robust apps. These apps can handle real-world challenges. Why should you care about Temporal? If you’ve worked with distributed systems, you’ve likely faced process failures. They can leave your system inconsistent. They processed a payment but didn’t update the order. Or, they sent an email but didn’t update the database. Temporal solve these problems. It provides durable execution, automatic retries, and state management. With Spring Boot, Temporal gives you tools for complex processes. It also keeps familiar Spring ecosystem you know. You get the best of both worlds. You get Spring’s dependency injection and configuration. You also get Temporal’s workflow management features.
December 12, 2024
Master Java Release with GitHub Actions and Maven Release plugin
Introduction In software development, automating the release process is key. It ensures efficiency and consistency in a fast-paced field. Many Java developer struggle with manual release. They face issues with version management and Git tagging. This article will show you how to automate your release process using GitHub Actions and the Maven Release plugin Prerequisites Before diving into the implementation, ensure you have
December 5, 2024
Build a MatterMost Bot with Java - Practical guide
Introduction Weather info in your team chat can help with office planning and casual chats. This article will build a simple, practical MatterMost bot. It will post daily weather updates using Java, Spring Boot, and weather API. What we will build Spring Boot application that: Connects to MatterMost via webhooks. Fetches weather data from OpenWeatherMap API. Posts daily weather updates at 9:00 AM. Prerequisites Java 17 Maven or Gradle Docker Implementation Let’s start bot development using the MatterMost server on our local environment. Create a docker-compose file with the following content.
November 28, 2024
Pulumi for Java Developer - Getting started with IaC
Introduction In today’s cloud-native world, managing infrastructure by hand is no longer practical. Infrastructure as Code (IaC) has emerged as the de facto standard for managing cloud resources. Terraform has dominated this space with its domain-specific language. Pulumi takes a different approach, which benefits Java Developers. What is Pulumi? Pulumi is a modern Infrastructure as Code platform. It lets developers use familiar programming languages instead of domain specific one like HCL or YAML. For Java developers, this means using their knowledge of Java, strong typing, and OOP. They must use the whole Java ecosystem to manage cloud infrastructure.
November 21, 2024
Mastering Error Handling in Spring Boot with ProblemDetails
Image by author Introduction Hello everyone! In this article I will try to cover a game — changer for API error handling in Spring Boot — the ProblemDetails RFC. If you spent a long time wrestling with inconsistent error responses or scratching your head over how to structure your API’s error message, you’re in for a treat. What is the deal with ProblemDetails? Spring Boot + ProblemDetails First of all the ProblemDetails is not just another Spring Boot feature — it is an IETF standard (RFC 9457) that defines a “problem detail” as a way to carry machine-readable details error in a HTTP response.
September 26, 2024
Automate your business processes with Temporal.io and Java
Introduction Today the world is a fast-paced business environment, and automating processes is crucial for staying competitive. Temporal.io, a powerful open — source platform, simplifies the development, of scalable workflow automation. Temporal.io enables developers to create efficient, resilient business process automation not only with Java but with a wide — range of different programming languages. In this article, we will explore how to leverage Temporal.io and Java to streamline your operations.
September 24, 2024
Mastering JUnit 5 - Advanced Techniques for Efficient and Powerful testing
Meme about unit tests Hello everyone in this article we will dive into note-worthy JUnit 5 annotations which help you to write extensive unit tests. Before starting to start writing unit tests we have to add required dependencies to our pom.xml or build.gradle. pom.xml<?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> <groupId>me.vrnsky</groupId> <artifactId>mastering-junit</artifactId> <version>1.0-SNAPSHOT</version> <properties> <maven.compiler.source>17</maven.compiler.source> <maven.compiler.target>17</maven.compiler.target> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-params</artifactId> <version>5.11.0</version> <scope>test</scope> </dependency> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-engine</artifactId> <version>5.11.0</version> <scope>test</scope> </dependency> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-api</artifactId> <version>5.11.0</version> <scope>test</scope> </dependency> </dependencies> </project> Parametrized test This article will follow test — driven development approach, so first, we will write a unit test. Most of the examples of test units contain examples of testing simple calculators, but for this example, we will develop a String utility class.
September 24, 2024
Advanced Java Garbage Collection — G1 and ZGC
Garbage collector Hello everyone! In this article, we discuss advanced Java Garbage Collection: G1 and ZGC. Introduction Both garbage collectors are designed to optimize memory management in large-scale applications by improving the efficiency of memory allocation, deallocation, and garbage collection. Both G1 and ZGC are designed to reduce pauses while performing the garbage collection cycle and improve overall system performance. G1 or Garbage First G1 is a fully incremental garbage collector that divides memory into multiple regions. The G1 garbage collector is concurrent. The division approach brings more efficient usage of memory by dynamically allocating objects in different regions based on their usage patterns.
August 15, 2024
Spring Boot & Infisical - Managing your sensitive configuration
Hello everyone! In this article, I’ll show you how to employ Infisical in your Spring Boot application. But last year, HashiCorp changed Terraform’s license to non-open source. This could also happen to Vault, or not. The second reason why I chose Infisical for this article is because IBM acquired Terraform this year. Introduction Like the HashiCorp Vault, Infisical is a secret management platform. Let’s start by starting up the Infisical instance locally with the docker-compose file provided by the documentation. First, we need to download it with the following command.
May 30, 2024
Spring Boot - How to build layered jar
In this article, I will show you how you can build a simple CRUD application and create a layered jar. The inventory service manages inventory, such as left stocks, i.e., some drinks, merch, or something else that can be stored in the warehouse. Reasons for choosing layered jar: If you have an extensive application with different dependencies If you need flexibility in layer updates Reasons for choosing Uber Jar: If you have a simple application with a relatively small number of dependencies If you need simplicity in the deployment process DockerfileFROM eclipse-temurin:17 as JAR_EXTRACT WORKDIR /app ARG JAR_FILE=*.jar COPY ./target/${JAR_FILE} ./app.jar RUN java -Djarmode=layertools -jar ./app.jar extract FROM eclipse-temurin:17 WORKDIR /application COPY --from=JAR_EXTRACT /app/dependencies ./ COPY --from=JAR_EXTRACT /app/spring-boot-loader ./ COPY --from=JAR_EXTRACT /app/snapshot-dependencies ./ COPY --from=JAR_EXTRACT /app/application ./ ENTRYPOINT ["java", "org.springframework.boot.loader.launch.JarLauncher"] EXPOSE 8080 Access full article MediumFollow & read SubstackSubscribe & read
January 6, 2024
Spring Boot and gRPC - Boost your service communication
Introduction In this article, I will describe gRPC and how you can employ it in your project. The motivation creation of gRPC The motivation behind creating gRPC was that developers and businesses require faster and more efficient solutions. The existing technologies utilize HTTP 1/1.1. The Spring Boot supports Undertow, but Tomcat requires some additional changes. It is why creators employed HTTP 2 in gRPC. This article will create another CRUD service to manage restaurant reservations.
January 6, 2024
Spring Boot and JOOQ - Getting started
This article will show how to use jOOQ in your spring boot projects. Why do we need jOOQ? There is a lot of pain using JPA and Hibernate. That is why we have something jOOQ. First, we need to create a database schema. In this article, we will develop a simple CRUD (create, read, update, and delete) application to manage goods. The first step is to design our database. The application will contain only one table — goods. The table looks like below.
January 3, 2024
JUnit 5 - How to write more test with less code
Introduction In this article, I will show and explain how you can write more tests with relatively small changes in your code. Recently, one of my colleagues wrote a massive test with repetitive code. The difference between test cases was only data that was submitted to the service. I will use JUnit 5 in this article, but feel free to check the library docs you use for writing tests.
December 31, 2023
Spring Cloud Functions, Kafka - How to interact asynchronous
Introduction This article will show how to use the Spring Cloud Functions projects. The Spring Cloud Functions is the best approach to implementing a straightforward business logic. Nowadays, the usage of message brokers such as Kafka has increased. I will implement a simple system in this article, as shown below. Diagram of developing system Implementation I will start with a simple example of a cloud function, which is the same as a rest endpoint in the classical spring boot web application. You can create a project from your favorite IDE or from Spring Initliazr.
December 24, 2023
Spring Cloud Config, Spring Cloud Bus & Kafka - How to set up automatic updates of your configuration
Introduction In this article, I will show you how to achieve automatic updates with Spring Cloud Bus and Kafka The Spring Cloud Bus, according to documentation: Spring Cloud Bus links nodes of a distributed system with a lightweight message broker. This can then broadcast state changes (e.g., configuration changes) or other management instructions. AMQP and Kafka broker implementations are included in the project. Alternatively, any Spring Cloud Stream binder on the classpath will work out of the box as a transport.
December 21, 2023
Spring Boot Mutation testing with JUnit5, Testcontainers, and Pit
What is mutation testing? Mutation testing is a type of testing that validates new and existing tests. More formal definition from Wikipedia: Mutation testing (or mutation analysis or program mutation) is used to design new software tests and evaluate the quality of existing software tests. Why do we need mutation testing? The problem that solves mutation testing is checking the validity of the existing and new tests. I often have met invalid unit tests that have covered only the happy path and no other paths.
December 13, 2023
Digital Image Processing Basics
Introduction Digital image processing is the acquisition, analysis, and performing of a wide range of operations on an image. In digital image processing, there are three types of images: Binary Grayscale RGB The digital image can be represented within the two-dimensional array. A binary image is represented by a dimensional array where each cell stores 0 (black) and 1 (white) values. A grayscale image is a two-dimensional array where values in the array lay in a range from 0 to 255
November 26, 2023
Write your Spring Boot (3.x) starter with Kotlin & Maven
Some companies use Camunda(TM) BPMN Engine for managing the business automatization process. Most of the functionality provided out of the box is enough for most cases. But recently I have realized that we have always written our service to send messages to the engine. So, I decided to write my starter. The native language for Camunda is Java, but it supports many other languages. Since I want programming experience in Java, I have decided to write my starter with Kotlin. For those who are already tired — the full code is available on the GitHub There are no breaking backward capability changes in writing spring boot starters.
January 23, 2023
Spring Boot interaction with Kafka with HTTPS
In this article, we will be developing a Spring Boot application that works with Kafka and terminates traffic via HTTPS. So first of all we have to generate self-signed certificates by following the bash script. #!/bin/bash set -o nounset \ -o errexit \ -o verbose \ -o xtrace # Generate CA key openssl req -new -x509 -keyout snakeoil-ca-1.key -out snakeoil-ca-1.crt -days 365 -subj ‘/CN=localhost/OU=TEST/O=MEDIUM/L=PaloAlto/S=Ca/C=US’ -passin pass:medium -passout pass:medium # openssl req -new -x509 -keyout snakeoil-ca-2.key -out snakeoil-ca-2.crt -days 365 -subj ‘/CN=ca2.test.confluent.io/OU=TEST/O=MEDIUM/L=PaloAlto/S=Ca/C=US’ -passin pass:meduim -passout pass:medium # Kafkacat openssl genrsa -des3 -passout “pass:medmium” -out kafkacat.client.key 1024 openssl req -passin “pass:medium” -passout “pass:medium” -key kafkacat.client.key -new -out kafkacat.client.req -subj ‘/CN=localhost/OU=TEST/O=MEDIUM/L=PaloAlto/S=Ca/C=US’ openssl x509 -req -CA snakeoil-ca-1.crt -CAkey snakeoil-ca-1.key -in kafkacat.client.req -out kafkacat-ca1-signed.pem -days 9999 -CAcreateserial -passin “pass:medium” for i in broker1 consumer # we are going to generate certs for broker(zookeper) and cosumer(our app) do echo $i # Create keystores keytool -genkey -noprompt \ -alias $i \ -dname “CN=localhost, OU=TEST, O=MEDIUM, L=PaloAlto, S=Ca, C=US” \ -keystore kafka.$i.keystore.jks \ -keyalg RSA \ -storepass confluent \ -keypass confluent # Create CSR, sign the key and import back into keystore keytool -keystore kafka.$i.keystore.jks -alias $i -certreq -file $i.csr -storepass confluent -keypass medium openssl x509 -req -CA snakeoil-ca-1.crt -CAkey snakeoil-ca-1.key -in $i.csr -out $i-ca1-signed.crt -days 9999 -CAcreateserial -passin pass:medium keytool -keystore kafka.$i.keystore.jks -alias CARoot -import -file snakeoil-ca-1.crt -storepass meduim -keypass medium keytool -keystore kafka.$i.keystore.jks -alias $i -import -file $i-ca1-signed.crt -storepass medium -keypass medium # Create truststore and import the CA cert. keytool -keystore kafka.$i.truststore.jks -alias CARoot -import -file snakeoil-ca-1.crt -storepass medium -keypass medium echo “medium” > ${i}_sslkey_creds echo “medium” > ${i}_keystore_creds echo “medium” > ${i}_truststore_creds done This script eventually generated for us following files
January 22, 2023
HashiCorp Vault - Getting started
Hi, there! It is a text version of the Vault webinar Let’s go! First of all, we have to download Vault or install it via your favorite packet manager. You can download the latest version of Vault from the official website — https://www.vaultproject.io/downloads Or simply install it via brew brew tap hashicorp/tap brew install hashicorp/tap/vault After successful installation, we can check that Vault in the PATH
February 23, 2022
Stop writing code inside main method
Introduction Greetings to everyone who reads this post! Due to my work, I often run into novice programmers and look at their code. Sometimes it is beautiful, sometimes not, but I understand that a person learns, and the further he masters the best practices and technologies, the better his code becomes. But I would still like to pay some attention to such a simple task that almost all novice programmers face — writing a calculator.
November 29, 2020
Software architecture, 2
My previous blogpost start from the house picture — as analogy about architecture. But I found some problems with this analogy: There is no software construction industry in the same degree that there is for buildings. The building industry has substantial substructure, reflection numerous specialisations, skill sets, training paths, corporate organisations, standards bodies, and regulations. While the software industry has some structure, including that seen in offshore development practices, it is much less differentiated than the building industry The discipline off architecture does not have anything akin to the issue of deployment in software: Software is built in one place, but deployed for use in many places, often with specialisation and localisation. Manufactured building, otherwise known as trailers, are somewhat similar, but still there is no corresponding notion to dynamic distributed, mobile architectures, as there is with software Software is a machine; building are not (notwithstanding Le Corbusier’s declaration that, “A house is machine for living in”). The dynamic character of software — the observation that led to Edsger Dijkstra’s famous “goto statement considers harmful” paper (Dijkstra 1968), provides a profoundly difficult challenge to designers, for which there is not counterpart in building design Fundamental understanding There are three fundamental understandings of architecture, the recognition of which helps situate architecture with respect to rest of software engineering:
November 28, 2020
Software architecture
Introduction In this article I will try to explain what is architecture, clean architecture, architector role in project Examples of web architecture application Let’s consider an example of a service with one architectural level (Single Tier) In an application with one architectural level, the user interface, business logic, that is, the backend part of the application and the database are on the same server An example of an application with one architectural level are applications such as MS Office, GIMP
November 24, 2020