Spring中的Lifecycle接口使用与源码分析
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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