SmartLifecycle 解讀

org.springframework.context.SmartLifecycle解讀

一、接口定義

/**
 * An extension of the {@link Lifecycle} interface for those objects that require to
 * be started upon ApplicationContext refresh and/or shutdown in a particular order.
 * The {@link #isAutoStartup()} return value indicates whether this object should
 * be started at the time of a context refresh. The callback-accepting
 * {@link #stop(Runnable)} method is useful for objects that have an asynchronous
 * shutdown process. Any implementation of this interface <i>must</i> invoke the
 * callback's run() method upon shutdown completion to avoid unnecessary delays
 * in the overall ApplicationContext shutdown.
 *
 * <p>This interface extends {@link Phased}, and the {@link #getPhase()} method's
 * return value indicates the phase within which this Lifecycle component should
 * be started and stopped. The startup process begins with the <i>lowest</i>
 * phase value and ends with the <i>highest</i> phase value (Integer.MIN_VALUE
 * is the lowest possible, and Integer.MAX_VALUE is the highest possible). The
 * shutdown process will apply the reverse order. Any components with the
 * same value will be arbitrarily ordered within the same phase.
 *
 * <p>Example: if component B depends on component A having already started, then
 * component A should have a lower phase value than component B. During the
 * shutdown process, component B would be stopped before component A.
 *
 * <p>Any explicit "depends-on" relationship will take precedence over
 * the phase order such that the dependent bean always starts after its
 * dependency and always stops before its dependency.
 *
 * <p>Any Lifecycle components within the context that do not also implement
 * SmartLifecycle will be treated as if they have a phase value of 0. That
 * way a SmartLifecycle implementation may start before those Lifecycle
 * components if it has a negative phase value, or it may start after
 * those components if it has a positive phase value.
 *
 * <p>Note that, due to the auto-startup support in SmartLifecycle,
 * a SmartLifecycle bean instance will get initialized on startup of the
 * application context in any case. As a consequence, the bean definition
 * lazy-init flag has very limited actual effect on SmartLifecycle beans.
 *
 * @author Mark Fisher
 * @since 3.0
 * @see LifecycleProcessor
 * @see ConfigurableApplicationContext
 */
public interface SmartLifecycle extends Lifecycle, Phased {

	/**
	 * Returns {@code true} if this {@code Lifecycle} component should get
	 * started automatically by the container at the time that the containing
	 * {@link ApplicationContext} gets refreshed.
	 * <p>A value of {@code false} indicates that the component is intended to
	 * be started through an explicit {@link #start()} call instead, analogous
	 * to a plain {@link Lifecycle} implementation.
	 * @see #start()
	 * @see #getPhase()
	 * @see LifecycleProcessor#onRefresh()
	 * @see ConfigurableApplicationContext#refresh()
	 */
	boolean isAutoStartup();

	/**
	 * Indicates that a Lifecycle component must stop if it is currently running.
	 * <p>The provided callback is used by the {@link LifecycleProcessor} to support
	 * an ordered, and potentially concurrent, shutdown of all components having a
	 * common shutdown order value. The callback <b>must</b> be executed after
	 * the {@code SmartLifecycle} component does indeed stop.
	 * <p>The {@link LifecycleProcessor} will call <i>only</i> this variant of the
	 * {@code stop} method; i.e. {@link Lifecycle#stop()} will not be called for
	 * {@code SmartLifecycle} implementations unless explicitly delegated to within
	 * the implementation of this method.
	 * @see #stop()
	 * @see #getPhase()
	 */
	void stop(Runnable callback);

}

從註釋文檔裏可以看出：

1、是接口 Lifecycle 的拓展，且會在應用上下文類ApplicationContext 執行 refresh and/or shutdown 時會調用

2、方法 isAutoStartup() 返回的值會決定，當前實體對象是否會被調用，當應用上下文類ApplicationContext 執行 refresh

3、stop(Runnable) 方法用於調用Lifecycle的stop方法

4、getPhase() 返回值用於設置LifeCycle的執行優先度：值越小優先度越高

5、isRunning() 決定了start()方法的是否調用

二、應用

public class SmartLifecycleImpl implements SmartLifecycle {
    private Boolean isRunning = false;
    @Override
    public boolean isAutoStartup() {
        return true;
    }

    @Override
    public void stop(Runnable callback) {
        callback.run();
    }

    @Override
    public void start() {
        System.out.println("SmartLifecycleImpl is starting ....");
        isRunning = true;
    }

    @Override
    public void stop() {
        System.out.println("SmartLifecycleImpl is stopped.");
    }
    /**
     * 執行start()方法前會用它來判斷是否執行，返回爲true時，start()方法不執行
     */
    @Override
    public boolean isRunning() {
        return isRunning;
    }

    @Override
    public int getPhase() {
        return 0;
    }
}

啓動類

public class ProviderBootstrap {

    public static void main(String[] args) throws Exception {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ProviderConfiguration.class);
        context.start();
        System.in.read();
    }

    @Configuration
    static class ProviderConfiguration {

        @Bean
        public SmartLifecycleImpl getSmartLifecycleImpl(){
            return new SmartLifecycleImpl();
        }
    }
}

可以發現，類SmartLifecycleImpl提交給spring容器後，啓動後，會輸出 start() 方法的方法體。