Spring Cleaning: What Boot 4 Lets You Delete - ConFoo 2027

A tour of the code and libraries Spring Boot 4 lets you remove, from Spring Retry and Feign to custom versioning filters, with a clear upgrade path.

Spring Boot 4 can help you delete more than old dependencies. Built-in resilience may replace Spring Retry. HTTP interfaces can replace Feign. API versioning can replace custom filters. RestTestClient can simplify test setup.

We'll also cover JSpecify, Jackson 3, modular auto-configuration, and the smaller changes worth knowing. You'll leave with less code to maintain and a clear upgrade path.

What You'll Learn

Built-in resilience with @Retryable and @ConcurrencyLimit, so Spring Retry can go
HTTP interfaces as a replacement for Feign clients
API versioning in the framework instead of custom filters
RestTestClient for simpler test setup
JSpecify null safety and what it means for your code
Jackson 3 and the new tools.jackson packages
Modular auto-configuration and the starters that changed
A clear upgrade path from Spring Boot 3 to 4