How to secure a Spring Security client application with OIDC (using pac4j)
If you already have Spring Security in your application, with hasRole rules, @PreAuthorize on services and code reading SecurityContextHolder and yo…
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A Kafka Streams topology starts in a sandbox, not on your cluster
Somebody owns the Kafka cluster you need, and it is not you. You have a topology in mind: read orders , keep the big ones, write them somewhere. You…
Request lifecycle: HandlerMapping HandlerAdapter resolvers
🧠 The big idea in one line Spring finds the handler, prepares its arguments, calls it, and handles the result. Why this exists — an HTTP request con…
🚀 Building Spring by Example: Completing the Advanced Spring Module
When I started learning Spring, I noticed something about many of the tutorials I found. They often showed how to use a feature, but not always why…
Week 13 of #100DaysOfCode: Completing Spring Microservices and Starting JUnit 5
Introduction This week was another challenging but rewarding part of my #100DaysOfCode journey. I started the week by learning about Docker and cont…
sync = true protects one JVM, not the cluster
Originally published at bitsar.net . Twelve pods, one Redis, and @Cacheable(sync = true) on the method. I read that as a protected endpoint. It coor…
Week 12 of #100DaysOfCode: Exploring Spring Cloud and Microservices Infrastructure
Introduction This week was another challenging but rewarding part of my #100DaysOfCode journey. I continued going deeper into Microservices with Spr…
Starter dependencies — how they work
What a starter actually is When you build a real application, you rarely need just one library. To expose a web endpoint in the Spring world, for ex…
What Boot adds over plain Spring
What Boot actually is If you have written any Spring at all, you have met the container — the engine that reads your classes, builds one object per…
AOP: aspect / pointcut / advice / weaving
Every codebase grows a set of chores that have nothing to do with the actual job of a method, yet somehow end up inside every method anyway. Logging…
What I gave up to run Spring static analysis in a browser
There is a question that costs me half an hour every time I have to answer it: If I change this controller method, what else breaks? The honest proc…
Week 10 of #100DaysOfCode: Exploring Microservices and Modern Architecture
Introduction This has been one of the toughest weeks I've experienced since starting this challenge. There were moments when I doubted myself , ques…
Spring proxies: JDK dynamic vs CGLIB
You put @Transactional on a method and a database transaction opens before it runs and commits when it returns — yet you never wrote a line to start…
BeanPostProcessor & BeanFactoryPostProcessor
Two hooks with nearly the same name Spring's container builds your objects so you don't have to. You mark a class, and a fully-wired object — a bean…
Claude's System Prompt Grew From 358 to 3,235 Words. Here's What It Teaches Production AI Teams
This week, Anthropic's system-prompt release notes became the top story on Hacker News. The page is where Anthropic publishes the exact instructions…
Week 9 of #100DaysOfCode: A Week of Deep Spring Learning
Introduction This week, I decided to slow down and go deeper into the Spring Framework . Instead of focusing heavily on building new features, I spe…
DeepSeek Now Prices Tokens Like Electricity: 50% Off-Peak Discount and a Spring Boot Pattern to Profit From It
Three days ago I knew exactly what a DeepSeek call cost me. I had wired DeepSeek V4 Pro 0813 into a Spring Boot app with Spring AI, and the math was…
🚀 Building Spring by Example: Completing the Bean Lifecycle Module
When I started learning Spring, I noticed something about many of the tutorials I found. They often showed how to use a feature, but not always why…
From Querydsl to Spring Filter: One Syntax, Three Backends
Querydsl is one of those libraries that everyone used for years and then quietly stopped updating. The 5.0 release has been "coming soon" since 2019…
MCP Goes Stateless: Building AI Agent Servers with Spring AI 2.0
Last month, I was building an AI assistant for an e-commerce system. The idea was simple: let users ask natural-language questions about orders and…
Spring AI vs LangChain4j: Which Java AI Framework Should You Choose in 2026?
Earlier this year, I needed to add an AI assistant to a Spring Boot application I maintain. Nothing exotic -- just a chat interface that could answe…
SpringBoot + mybatis-plus项目的SQL映射问题（完全萌新？
完全的萌新第一个SpringBoot项目，主要爆红问题是： MyBatis-Plus尝试执行某个 Mapper 方法，却找不到与之对应的 SQL 映射 具体爆红日志如下： 2026-07-29T16:57:48.976+08:00 ERROR 38512 --- [nio-8080-exec-6…
Running Snyk on Real Legacy Java Code — The Full Unfiltered Results
Numbers are easy to skim. 10 Critical. 99 High. 59 Medium. 20 Low. 188 total. Those numbers appeared in the first article and they're striking — but…
Rod Johnson Is Back - and He's Bringing AI Agents to Java
If you have written enterprise Java in the last 20 years, you know the name Rod Johnson. He created Spring Framework back in 2003 - the thing that m…
Explain the Concept of "Convention over Configuration" in Spring Boot
If you've ever started a Java project, you probably know how much configuration is usually required. You need to configure XML files, register beans…
Your Keycloak roles aren't working in Spring Security. Here's the actual reason.
If you've wired up a Spring Boot resource server behind Keycloak and your @PreAuthorize("hasRole('ADMIN')") is silently returning 403 for a user you…
Stop Begging Your LLM for Valid JSON: Self-Correcting Structured Output in Spring AI 2.0
Every developer who has worked with LLMs has been there. You ask the model for JSON. You describe the schema. You say "please only respond with vali…
How does Spring Boot simplify the development of Java applications?
Introduction Imagine you're assembling a new piece of furniture. One option is to buy every screw, bolt, plank, and tool separately, then spend hour…
Four Bugs Stood Between Me amd "Sign in with Google"
Summary: I had a rough time adding Google login to my app, Kenning. It took me a while to figure out four issues that were causing problems. These i…
I Built a Tool That Shows the SQL Behind Any Spring Data Method Name
Spring Data JPA has one genuinely magical feature: you declare a query by naming a method . No SQL, no @Query , no implementation. interface OrderRe…