Speed Up Spring Boot Startup with Actuator’s Startup Endpoint

Background

As a Spring Boot project adds more middleware, its startup time gradually increases. The author notes that many non‑official starters do not disable the default proxyBeanMethods attribute of @Configuration, which can hurt performance. Serial initialization logic, such as an inefficient Druid datasource pool, also slows startup.

Spring Boot 2.4 provides a startup monitoring endpoint that lets developers observe each component’s initialization time, which is far more precise than parsing raw startup logs.

Getting Started

Add the actuator dependency:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Expose the startup endpoint:

management:
  endpoints:
    web:
      exposure:
        include: startup

Configure the main class to use a buffering startup recorder (increase the buffer size if many beans are present):

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        // Enable buffering only during development or troubleshooting
        new SpringApplicationBuilder(DemoApplication.class)
            .applicationStartup(new BufferingApplicationStartup(20480))
            .run(args);
    }
}

Query the endpoint (POST) to obtain the JSON report:

curl -XPOST http://localhost:8080/actuator/startup
{
  "springBootVersion":"2.4.0",
  "timeline":{
    "startTime":"2020-12-04T01:38:15.028114Z",
    "events":[
      {
        "startupStep":{
          "name":"spring.event.invoke-listener",
          "id":296,
          "parentId":0,
          "tags":[
            {"key":"event","value":"ServletRequestHandledEvent: url=[/actuator/startup]; client=[0:0:0:0:0:0:0:1]; method=[POST]; servlet=[dispatcherServlet]; session=[null]; user=[null]; time=[83ms]; status=[OK]"},
            {"key":"listener","value":"org.springframework.boot.context.config.DelegatingApplicationListener@2053d869"}
          ]
        },
        "startTime":"2020-12-04T01:38:28.402870279Z",
        "endTime":"2020-12-04T01:38:28.402929390Z",
        "duration":"PT0.000059111S"
      }
    ]
  }
}

Test Case

Create a bean that deliberately delays initialization to see its impact:

@Configuration(proxyBeanMethods = false)
public class DemoConfiguration {
    @Bean
    public RestTemplate restTemplate() throws InterruptedException {
        // Simulate a costly initialization step
        Thread.sleep(5000);
        return new RestTemplate();
    }
}

After starting the application, request /actuator/startup and verify that the RestTemplate bean appears with a ~5‑second duration.

Sorting by Duration

The endpoint returns events in startup order. To sort them by elapsed time, export the JSON and use an online tool such as bejson.com .

Select the option to sort by duration to quickly identify the slowest initialization steps.

References

Spring Boot 2.4 release notes: https://www.oschina.net/news/120443/spring-boot-2-4-0-released

Druid connection‑pool issue: https://github.com/alibaba/druid/issues/1368