Spring Boot startup time: bean-by-bean diagnosis, and one directory per post

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.
2026-09-05 00:17:37 +05:30
parent 4b6cefa60a
commit 958b401f0f
112 changed files with 2744 additions and 154 deletions
@@ -0,0 +1,24 @@
+package com.ankurm.startup;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup;
+import org.springframework.core.metrics.jfr.FlightRecorderApplicationStartup;
+
+@SpringBootApplication
+public class StartupDiagnosisApplication {
+
+    public static void main(String[] args) {
+        SpringApplication app = new SpringApplication(StartupDiagnosisApplication.class);
+        String mode = System.getProperty("startup.tracking", "buffering");
+        // The capacity is the number of *steps*, not beans, and there is no way to change it
+        // after construction. See docs/07-failure-modes.md for what a too-small buffer does.
+        int capacity = Integer.getInteger("startup.buffer", 16384);
+        switch (mode) {
+            case "buffering" -> app.setApplicationStartup(new BufferingApplicationStartup(capacity));
+            case "jfr" -> app.setApplicationStartup(new FlightRecorderApplicationStartup());
+            default -> { }
+        }
+        app.run(args);
+    }
+}