Ankur Mhatre
958b401f0f
Adds spring-boot-startup-time/, the companion project for BLOG-618: a runnable Spring Boot 4.1.1 application on JDK 25 that installs BufferingApplicationStartup and FlightRecorderApplicationStartup behind a system property, and a /diag/startup endpoint that computes step self time -- the number /actuator/startup does not give you and the one that names the actual culprits. Captured under docs/output/: the step tree sorted both ways, the same startup as JFR events, a +5000-class experiment putting 0.11 ms per scanned class on the classpath scan tax, the silent truncation a 2048-step buffer performs, and JDK 25 AOT cache timings (6.93 s to 4.82 s). Post body and metadata live in post/. Moves the existing Actuator project into actuator-in-production/ so the repository holds one directory per article; the root README is now an index.
108 lines
4.4 KiB
Markdown
108 lines
4.4 KiB
Markdown
[← 01 What Actuator exposes](01-what-actuator-exposes.md) · **02 · What changed in Spring Boot 4** · [03 The endpoint catalogue →](03-endpoint-catalogue.md)
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# 02 — What changed in Spring Boot 4
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Every claim below was checked against the 4.1.1 jars with `javap`, or against the 3.5.16 jars
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for the "before" side. None of it came from a migration blog.
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## `HealthIndicator` moved module and package
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This is the one that breaks every custom health indicator ever written.
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```
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Boot 3.5.16 org.springframework.boot.actuate.health.HealthIndicator (spring-boot-actuator)
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Boot 4.1.1 org.springframework.boot.health.contributor.HealthIndicator (spring-boot-health)
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```
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`org.springframework.boot.actuate.health` does not exist in Boot 4.1.1 at all — not deprecated,
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absent. `Health`, `Status`, `AbstractHealthIndicator`, `HealthContributor` and the composites
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all moved with it, into a new `spring-boot-health` module.
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Two neighbouring packages in the same new module are worth knowing:
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- `org.springframework.boot.health.application` — `DiskSpaceHealthIndicator`,
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`LivenessStateHealthIndicator`, `ReadinessStateHealthIndicator`, `SslHealthIndicator`
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- `org.springframework.boot.health.registry` — `HealthContributorRegistry`, which is how
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[`DiagnosticsEndpoint`](../src/main/java/com/ankurm/actuator/web/DiagnosticsEndpoint.java)
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enumerates contributors at runtime
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## The interface method was renamed
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```java
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// Boot 3.5.16
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public interface HealthIndicator extends HealthContributor {
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default Health getHealth(boolean includeDetails);
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Health health();
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}
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// Boot 4.1.1
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public interface HealthIndicator extends HealthContributor {
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default Health health(boolean includeDetails);
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Health health();
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}
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```
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If you overrode `getHealth(boolean)` — which people do to control detail rendering — it now
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silently stops being an override. Add `@Override` and let the compiler find it.
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`Health` also stopped extending `HealthComponent`; that class is gone from Boot 4.1.1 entirely.
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## `EndpointRequest` moved too
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```
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Boot 3.5.16 org.springframework.boot.actuate.autoconfigure.security.servlet.EndpointRequest
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Boot 4.1.1 org.springframework.boot.security.autoconfigure.actuate.web.servlet.EndpointRequest
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```
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Same class, same static methods (`toAnyEndpoint()`, `to(Class...)`, `to(String...)`,
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`toLinks()`, `toAdditionalPaths(...)`), new package, and it now ships in `spring-boot-security`
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rather than `spring-boot-actuator-autoconfigure`. The reactive variant made the equivalent move.
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## `RestClient` is not in the web starter any more
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Boot 4 split the framework into fine-grained modules, and `RestClient` auto-configuration went
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with it. Adding `spring-boot-starter-webmvc` and injecting `RestClient.Builder` fails at
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startup:
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```
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Parameter 0 of constructor in com.ankurm.actuator.health.ExternalApiHealthIndicator
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required a bean of type 'org.springframework.web.client.RestClient$Builder' that could not be found.
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```
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The fix is one dependency:
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```xml
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-restclient</artifactId>
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</dependency>
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```
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This cost a startup cycle while building this repository, which is why it is documented here
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rather than glossed over.
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## Liveness and readiness probes are on by default
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From the 4.0 migration guide, and confirmed by running the app with no configuration at all —
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`/actuator/health` reports `"groups":["liveness","readiness"]` out of the box. Turn them off
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with `management.endpoint.health.probes.enabled=false` if you genuinely do not want them.
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## Nullability annotations
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Actuator endpoint parameters can no longer use `org.springframework.lang.Nullable` to mark a
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parameter optional. Migrate to `org.jspecify.annotations.Nullable`.
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## There is no Micrometer 2
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Several migration write-ups claim Boot 4 replaces "legacy Actuator endpoints" with a
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"Micrometer 2 observability stack". Spring Boot 4.1.1 resolves **Micrometer 1.17.1**
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(`docs/output/00-versions.txt`), and `maven-metadata.xml` for `micrometer-core` shows 1.17.1 as
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the newest GA with 1.18.0-M1 as a milestone. Metrics *did* move to their own module
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(`spring-boot-micrometer-metrics`, which `spring-boot-starter-actuator` still pulls in), and
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there is a new `spring-boot-starter-opentelemetry`. Neither of those is a major Micrometer
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release.
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---
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[← 01](01-what-actuator-exposes.md) · **02** · [03 The endpoint catalogue →](03-endpoint-catalogue.md)
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