Spring中的Lifecycle接口使用与源码分析

2023-05-20 05:05:31 分析 源码 接口

LifeCycle接口定义了spring容器的生命周期,任何被Spring管理的对象都可以实现该接口。当Spring容器本身启动和停止时,会回调LifeCycle接口中定义的方法。

Lifecycle接口的声明

org.springframework.context.Lifecycle

public interface Lifecycle {
	    
	void start();
	    
	void stop();
	    
	boolean isRunning();
}

Lifecycle的使用

自定义一个Lifecycle需要实现Lifecycle接口:

package com.morris.spring.demo.lifecycle;
import org.springframework.context.Lifecycle;

public class MyLifecycle implements Lifecycle {
	private boolean isRunning;
	@Override
	public void start() {
		System.out.println("MyLifecycle start");
		isRunning = true;
	}
	@Override
	public void stop() {
		System.out.println("MyLifecycle stop");
		isRunning = false;
	}
	@Override
	public boolean isRunning() {
		return isRunning;
	}
}

测试类:

public class LifecycleDemo {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
		applicationContext.reGISter(MyLifecycle.class);
		applicationContext.refresh();
	}
}

启动main()方法后发现并没有调用MyLifecycle的start()和stop()方法。

把测试类改为如下,主动调用applicationContext容器的start()和stop()方法:

public class LifecycleDemo {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
		applicationContext.register(MyLifecycle.class);
		applicationContext.refresh();
		applicationContext.start();
		applicationContext.stop();
	}
}

运行结果如下:

DEBUG main DefaultLifecycleProcessor:356 - Starting beans in phase 0
MyLifecycle start
DEBUG main DefaultLifecycleProcessor:188 - Successfully started bean 'myLifecycle'
DEBUG main DefaultLifecycleProcessor:369 - Stopping beans in phase 0
MyLifecycle stop
DEBUG main DefaultLifecycleProcessor:253 - Successfully stopped bean 'myLifecycle'

这时我们看到Spring容器回调了Lifecycle生命周期的方法。

SmartLifecycle接口的声明

常规的LifeCycle接口只能在容器上下文显式的调用start()或stop()方法时,才会去回调LifeCycle的实现类的start()或stop()方法逻辑,并不意味着在容器上下文刷新时自动回调。

org.springframework.context.SmartLifecycle

public interface SmartLifecycle extends Lifecycle, Phased {
	int DEFAULT_PHASE = Integer.MAX_VALUE;
	
	default boolean isAutoStartup() {
		return true;
	}
	default void stop(Runnable callback) {
		stop();
		callback.run();
	}
	@Override
	default int getPhase() {
		return DEFAULT_PHASE;
	}
}

SmartLifecycle的使用

自定义SmartLifecycle需要实现SmartLifecycle接口:

package com.morris.spring.demo.lifecycle;
import org.springframework.context.SmartLifecycle;

public class MySmartLifecycle implements SmartLifecycle {
	private boolean isRunning;
	@Override
	public void start() {
		System.out.println("MyLifecycle start");
		isRunning = true;
	}
	@Override
	public void stop() {
		System.out.println("MyLifecycle stop");
		isRunning = false;
	}
	@Override
	public boolean isRunning() {
		return isRunning;
	}
}

测试类:

package com.morris.spring.demo.lifecycle;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class SmartLifecycleDemo {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
		applicationContext.register(MySmartLifecycle.class);
		applicationContext.refresh();
	}
}

运行结果如下:

DEBUG main DefaultListableBeanFactory:228 - Creating shared instance of singleton bean 'mySmartLifecycle'
DEBUG main DefaultLifecycleProcessor:357 - Starting beans in phase 2147483647
MyLifecycle start
DEBUG main DefaultLifecycleProcessor:189 - Successfully started bean 'mySmartLifecycle'

容器中多个实现了Lifecycle的类如果希望有顺序的进行回调时,那么启动和关闭调用的顺序可能很重要。如果任何两个对象之间存在依赖关系,那么依赖方将在依赖后开始,在依赖前停止。然而,有时直接依赖关系是未知的。您可能只知道某个类型的对象应该在另一个类型的对象之前开始。在这些情况下,SmartLifecycle接口定义了另一个选项,即在其超接口上定义的getPhase()方法。

当开始时,getPhase()返回值最小的对象先开始,当停止时,遵循相反的顺序。因此,实现SmartLifecycle的对象及其getPhase()方法返回Integer.MIN_VALUE将在第一个开始和最后一个停止。相反,MAX_VALUE将指示对象应该在最后启动并首先停止。

源码解读

Lifecycle的调用时机

Lifecycle中的方法只有在主动调用容器的start()和stop()方法时才会触发,所以直接看容器的start()或stop()方法即可。

org.springframework.context.support.AbstractApplicationContext#start

public void start() {
	// 获取DefaultLifecycleProcessor
	
	getLifecycleProcessor().start();
	publishEvent(new ContextStartedEvent(this));
}

org.springframework.context.support.DefaultLifecycleProcessor#start

public void start() {
	startBeans(false);
	this.running = true;
}

最后会调用DefaultLifecycleProcessor的startBeans()方法。

SmartLifecycle的调用时机

SmartLifecycle的调用时机发生在容器refresh()时。

org.springframework.context.support.AbstractApplicationContext#finishRefresh

protected void finishRefresh() {
	// Clear context-level resource caches (such as ASM metadata from scanning).
	clearResourceCaches();
	// Initialize lifecycle processor for this context.
	// 注入DefaultLifecycleProcessor
	initLifecycleProcessor();
	// Propagate refresh to lifecycle processor first.
	getLifecycleProcessor().onRefresh();
	// Publish the final event.
	publishEvent(new ContextRefreshedEvent(this));
	// Participate in LiveBeansView MBean, if active.
	LiveBeansView.registerApplicationContext(this);
}

DefaultLifecycleProcessor的创建并调用onRefresh()方法。

org.springframework.context.support.DefaultLifecycleProcessor#onRefresh

public void onRefresh() {
	startBeans(true);
	this.running = true;
}

通用最后会调用DefaultLifecycleProcessor的startBeans()方法,只不过参数传入true。

DefaultLifecycleProcessor.startBeans()

private void startBeans(boolean autoStartupOnly) {
	// 拿到容器中所有的Lifecycle
	Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
	Map<Integer, LifecycleGroup> phases = new HashMap<>();
	lifecycleBeans.forEach((beanName, bean) -> {
		if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
			// autoStartupOnly=false,表示调用的Lifecycle
			// autoStartupOnly=true,表示调用的SmartLifecycle
			int phase = getPhase(bean);
			// 根据phase进行分组
			LifecycleGroup group = phases.get(phase);
			if (group == null) {
				group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
				phases.put(phase, group);
			}
			group.add(beanName, bean);
		}
	});
	if (!phases.isEmpty()) {
		List<Integer> keys = new ArrayList<>(phases.keySet());
		Collections.sort(keys);
		for (Integer key : keys) {
			// 调用start()
			phases.get(key).start();
		}
	}
}

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