聊聊dubbo的AwaitingNonWebApplicationListener

public class AwaitingNonWebApplicationListener implements SmartApplicationListener {
​
    private static final String[] WEB_APPLICATION_CONTEXT_CLASSES = new String[]{
            "org.springframework.web.context.WebApplicationContext",
            "org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext"
    };
​
    private static final Logger logger = LoggerFactory.getLogger(AwaitingNonWebApplicationListener.class);
​
    private static final Class<? extends ApplicationEvent>[] SUPPORTED_APPLICATION_EVENTS =
            of(ApplicationReadyEvent.class, ContextClosedEvent.class);
​
    private static final AtomicBoolean awaited = new AtomicBoolean(false);
​
    private static final Lock lock = new ReentrantLock();
​
    private static final Condition condition = lock.newCondition();
​
    private static final ExecutorService executorService = newSingleThreadExecutor();
​
    private static <T> T[] of(T... values) {
        return values;
    }
​
    static AtomicBoolean getAwaited() {
        return awaited;
    }
​
    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return containsElement(SUPPORTED_APPLICATION_EVENTS, eventType);
    }
​
    @Override
    public boolean supportsSourceType(Class<?> sourceType) {
        return true;
    }
​
    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationReadyEvent) {
            onApplicationReadyEvent((ApplicationReadyEvent) event);
        } else if (event instanceof ContextClosedEvent) {
            onContextClosedEvent((ContextClosedEvent) event);
        }
    }
​
    @Override
    public int getOrder() {
        return LOWEST_PRECEDENCE;
    }
​
    protected void onApplicationReadyEvent(ApplicationReadyEvent event) {
​
        final ConfigurableApplicationContext applicationContext = event.getApplicationContext();
​
        if (!isRootApplicationContext(applicationContext) || isWebApplication(applicationContext)) {
            return;
        }
​
        await();
    }
​
    private boolean isRootApplicationContext(ApplicationContext applicationContext) {
        return applicationContext.getParent() == null;
    }
​
    private boolean isWebApplication(ApplicationContext applicationContext) {
        boolean webApplication = false;
        for (String contextClass : WEB_APPLICATION_CONTEXT_CLASSES) {
            if (isAssignable(contextClass, applicationContext.getClass(), applicationContext.getClassLoader())) {
                webApplication = true;
                break;
            }
        }
        return webApplication;
    }
​
    private static boolean isAssignable(String target, Class<?> type, ClassLoader classLoader) {
        try {
            return ClassUtils.resolveClassName(target, classLoader).isAssignableFrom(type);
        } catch (Throwable ex) {
            return false;
        }
    }
​
    protected void onContextClosedEvent(ContextClosedEvent event) {
        release();
        shutdown();
    }
​
    protected void await() {
​
        // has been waited, return immediately
        if (awaited.get()) {
            return;
        }
​
        if (!executorService.isShutdown()) {
            executorService.execute(() -> executeMutually(() -> {
                while (!awaited.get()) {
                    if (logger.isInfoEnabled()) {
                        logger.info(" [Dubbo] Current Spring Boot Application is await...");
                    }
                    try {
                        condition.await();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            }));
        }
    }
​
    protected void release() {
        executeMutually(() -> {
            while (awaited.compareAndSet(false, true)) {
                if (logger.isInfoEnabled()) {
                    logger.info(" [Dubbo] Current Spring Boot Application is about to shutdown...");
                }
                condition.signalAll();
            }
        });
    }
​
    private void shutdown() {
        if (!executorService.isShutdown()) {
            // Shutdown executorService
            executorService.shutdown();
        }
    }
​
    private void executeMutually(Runnable runnable) {
        try {
            lock.lock();
            runnable.run();
        } finally {
            lock.unlock();
        }
    }
}

public class AwaitingNonWebApplicationListenerTest {
​
    @Test
    public void init() {
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        awaited.set(false);
​
    }
​
    @Test
    public void testSingleContextNonWebApplication() {
        new SpringApplicationBuilder(Object.class)
                .web(false)
                .run().close();
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        Assert.assertTrue(awaited.get());
    }
​
    @Test
    public void testMultipleContextNonWebApplication() {
        new SpringApplicationBuilder(Object.class)
                .parent(Object.class)
                .web(false)
                .run().close();
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        Assert.assertTrue(awaited.get());
    }
​
}