Lifecycle callbacks

Definition

Spring creates a bean, injects its dependencies, then calls your @PostConstruct method. When the application stops it calls your @PreDestroy method. Use them to open and close resources instead of doing that work in the constructor.

Example code

The order: constructor, init, use, destroy

import jakarta.annotation.PostConstruct;
import jakarta.annotation.PreDestroy;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;

@Component
class ConnectionPool {
    ConnectionPool() { System.out.println("1. constructor"); }

    @PostConstruct
    void open() { System.out.println("2. @PostConstruct: open connections"); }

    void use() { System.out.println("3. in use"); }

    @PreDestroy
    void close() { System.out.println("4. @PreDestroy: close connections"); }
}

@ComponentScan
class Demo {
    public static void main(String[] args) {
        try (var context = new AnnotationConfigApplicationContext(Demo.class)) {
            context.getBean(ConnectionPool.class).use();
        }                                                      // closing the context destroys the beans
    }
}

// Output:
// 1. constructor
// 2. @PostConstruct: open connections
// 3. in use
// 4. @PreDestroy: close connections