How does Lifecycle interface work in Spring? What are “top-level singleton beans”?

Question

It is said in Spring javadoc, that \"Note that the Lifecycle interface is only supported on top-level singleton beans.\" Here URL

My LifecycleBeanTest.xml d

Answer 1

I never used Lifecycle interface and I am not sure how it is suppose to work. But it looks like simply calling start() on context calls these callbacks:

AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("...");
ctx.start();

However typically I use @PostConstruct/@PreDestroy annotations or implement InitializingBean or DisposableBean:

public class LifecycleBean implements InitializingBean, DisposableBean {

    @Override
    public void afterPropertiesSet() {
        //...
    }

    @Override
    public void destroy() {
        //...
    }

}

Notice I don't call close() on application context. Since you are creating non-daemon thread in LifecycleBean the JVM remains running even when main exits.

When you stop that thread JVM exists but does not close application context properly. Basically last non-daemon thread stops, causing the whole JVM to terminate. Here is a bit hacky workaround - when your background non-daemon thread is about to finish, close the application context explicitly:

public class LifecycleBean implements ApplicationContextAware /* ... */ {

    private AbstractApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = (AbstractApplicationContext)applicationContext;
    }

    public void run() {
        for(int i=0; i<10 && !isInterrupted(); ++i) {
            log.info("Hearbeat {}", i);
            try {
                sleep(1000);
            } catch (InterruptedException e) {
            }
        }
        applicationContext.close();
    }

}