Mastering Spring Boot 4: From New Features to 3.x Migration

Hello, I’m Jjanggu (may9noy).

I’ve opened the new course I’ve been preparing for a long time today.

Creating a blog takes just 10 minutes. The question is whether you’ll still be writing three months later.

Over the past 8 years, I’ve written 1,211 posts on Tistory, and the cumulative number of visitors has reached 570,000. I’ve never run ads or participated in reciprocal promotion. Most visitors came through search.

This course was created by reverse-engineering those eight years. Rather than focusing on how to create a blog, it focuses on how to keep going.

Recommended for people like this

• Those who want to start a technical blog but are stuck on their first post

• Those who created a blog but have left it abandoned for several months

• Those who feel discouraged because they write posts but no one reads them

• Those who want to document their technical work for a career change or portfolio.

What We’ll Create Together in the Course

• A category structure that holds up even after surpassing 1,000 posts

• A collection routine that never runs out of topics and the "trial-and-error log" technique

• Reusable article templates and a 30-minute publishing workflow

• Google Search Console Integration and Indexing Request (We’ll Do It Together While Looking at the Screen)

• A weekly publishing rhythm and backup system you can maintain without burnout

• How to Use Your Blog Effectively in Resumes and Interviews

I don’t exaggerate AdSense earnings. For 1,000 posts, a monthly income of 10,000–30,000 won is the reality of a tech blog, and I tell you exactly that in the course as well.

📦 I’m providing article templates, a collection of head tags, and a 30-day action plan for free as course materials.

🎁 Launch celebration discount: [30%]

🔗 Go to the course: https://inf.run/PJYkm

Even 1,211 posts started with a first post that had just 3 views. Two of those were from me checking it myself. Your first post can be enough for today, too.

Hello! I've launched a new course.

Open-source support for Spring Boot 3.5 ended in June 2026. Now is the time to upgrade, not say, “I’ll upgrade someday.” But when you actually look for examples, most blog posts use code from the 4.0 milestone releases, so they often don’t work with the official release.

Therefore, I created a course based on the official releases of Spring Boot 4.1.1, Spring Framework 7, and Java 25, with all code compiled and all tests passing.

✅ Features Unique to This Course

• All figures were measured directly.

  • With a single line of virtual thread configuration, I reduced the time to process 2,000 requests from 5.2 seconds to 0.7 seconds.

  • I also directly verified that the number of auto-configuration candidates decreased from 279 to 92.

  • Using the JVM AOT cache makes startup approximately 2.4 times faster.

• We’ll complete one project from start to finish. Over 26 lessons, we’ll build up a library shelving API and verify all its behavior with 36 tests.

• I’ll show you the actual migration process. We’ll cover the three causes behind the 20 compilation errors encountered while upgrading a 3.5 project to 4.1, along with the subtle configuration changes that the tools don’t tell you about.

• We always compare 3.x and 4 code side by side.

📚 What You’ll Learn

• A new modularized starter system, Java 25, and virtual threads

• Jackson 3, Hibernate 7, RFC 9457 ProblemDetail

• Official API versioning: @GetMapping(version = "2.0"), Deprecation and Sunset headers

• @Retryable and @ConcurrencyLimit integrated into the core, HTTP Service Client, BeanRegistrar

• Null safety using JSpecify and NullAway, JUnit 6, @MockitoBean, RestTestClient, and Testcontainers 2

• OpenTelemetry, health probes, container images, and AOT

• Migration strategies and hands-on practice for moving from 3.x to 4.

👉 Recommended for those who:

• Those who have used Spring Boot 3 and want to properly understand what has changed in version 4

• Those who need to upgrade a 3.x service currently in operation to 4.

📦 A total of 26 lessons, approximately 8 hours and 40 minutes of content, along with all the practice code, a configuration cheat sheet, and a migration checklist.

🎁 [To celebrate the launch, a 30% discount will be available for one month.]

🔗 [Course link] https://inf.run/o9pF2

We appreciate your interest! 🙏