What’s New in Spring Boot Admin 4.0.0? Deep Dive into Core, UI, and RestClient Upgrade

What Is Spring Boot Admin?

Spring Boot Admin (SBA) is an open‑source monitoring and management console for Spring Boot applications. It consists of a single Admin Server that aggregates health, JVM metrics, logs, environment, and thread information from multiple Admin Clients via Actuator endpoints, presenting them in a unified web UI.

Core Framework Upgrade

SBA 4.0.0 upgrades its underlying stack to the latest versions:

Core framework: Spring Framework 6 → Spring Framework 7

Jakarta EE: 10 → 11 (Servlet 6.1)

Java baseline: Java 17 (minimum) – recommends Java 25, which brings virtual‑thread support that dramatically reduces I/O‑blocking costs for large‑scale monitoring.

Kotlin support: 1.9+ → 2.2+

GraalVM: 23+ → 25+

A typical scenario is monitoring 200 micro‑service instances, each polled every 10 seconds. With virtual threads on Java 25, the thread‑blocking overhead becomes negligible, allowing the same hardware to handle a much larger monitoring load.

UI Overhaul

The UI layer receives a major redesign. A new PrimeUI theme ( @primeuix/themes) provides a more consistent visual style, tighter accordion panels, expanded instance‑detail screens, and a refreshed wallboard layout for large‑screen dashboards. A bug causing column‑width overflow in the thread‑dump table has also been fixed.

SBOM Visualization Improvements

Software Bill‑of‑Materials (SBOM) support now makes the path configuration optional, shows alerts when data is missing, and adds legends to charts, helping security auditors quickly see dependencies and potential risks across services.

Communication Protocol Shift: RestClient Takes Over

Clients previously used RestTemplate or WebClient. SBA 4.0.0 now auto‑configures only RestClient, a synchronous HTTP client introduced in Spring Framework 6.1 and refined in 7. It combines the simplicity of RestTemplate with the fluent, streaming API of WebClient without pulling in the full Reactor stack.

<dependency>
    <groupId>de.codecentric</groupId>
    <artifactId>spring-boot-admin-starter-client</artifactId>
    <version>4.0.0</version>
</dependency>

If you customized SBA to use RestTemplate, replace those configurations with the new RestClient approach.

Null‑Safety Annotation Migration

SBA now adopts JSpecify’s @Nullable annotation instead of Spring’s proprietary one, aligning with the broader Java ecosystem. The change is a single import line:

// Before (SBA 3.x)
import org.springframework.lang.Nullable;

// After (SBA 4.0.0)
import org.jspecify.annotations.Nullable;

This enables tools like NullAway to detect potential null‑pointer issues at compile time.

Jackson 3 Adaptation

Jackson has moved from version 2 to version 3, changing the base package from com.fasterxml.jackson to tools.jackson. Update any custom serializers or deserializers accordingly.

Known Issue: Jolokia Compatibility

Jolokia does not yet support Spring Boot 4. SBA temporarily downgrades Jolokia to 2.1.0, offering only basic functionality. The team awaits Jolokia 2.5.0 for full compatibility. If your monitoring heavily relies on Jolokia’s JMX‑over‑HTTP features, evaluate the impact before upgrading.

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