Spring SmartLifecycle用法
Spring SmartLifecycle 在容器所有bean加载和初始化完毕执行
在使用Spring开发时，我们都知道，所有bean都交给Spring容器来统一管理，其中包括每一个bean的加载和初始化。
有时候我们需要在Spring加载和初始化所有bean后，接着执行一些任务或者启动需要的异步服务，这样我们可以使用 SmartLifecycle 来做到。
SmartLifecycle 是一个接口
当Spring容器加载所有bean并完成初始化之后，会接着回调实现该接口的类中对应的方法（start()方法）。
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import org.springframework.context.SmartLifecycle;
import org.springframework.stereotype.Component;
/**
* SmartLifecycle测试
*
*
*
*/
@Component
public class TestSmartLifecycle implements SmartLifecycle {
private boolean isRunning = false;
/**
* 1. 我们主要在该方法中启动任务或者其他异步服务，比如开启MQ接收消息<br/>
* 2. 当上下文被刷新（所有对象已被实例化和初始化之后）时，将调用该方法，默认生命周期处理器将检查每个SmartLifecycle对象的isAutoStartup()方法返回的布尔值。
* 如果为“true”，则该方法会被调用，而不是等待显式调用自己的start()方法。
*/
@Override
public void start() {
System.out.println("start");
// 执行完其他业务后，可以修改 isRunning = true
isRunning = true;
}
/**
* 如果工程中有多个实现接口SmartLifecycle的类，则这些类的start的执行顺序按getPhase方法返回值从小到大执行。<br/>
* 例如：1比2先执行，-1比0先执行。 stop方法的执行顺序则相反，getPhase返回值较大类的stop方法先被调用，小的后被调用。
*/
@Override
public int getPhase() {
// 默认为0
return 0;
}
/**
* 根据该方法的返回值决定是否执行start方法。<br/>
* 返回true时start方法会被自动执行，返回false则不会。
*/
@Override
public boolean isAutoStartup() {
// 默认为false
return true;
}
/**
* 1. 只有该方法返回false时，start方法才会被执行。<br/>
* 2. 只有该方法返回true时，stop(Runnable callback)或stop()方法才会被执行。
*/
@Override
public boolean isRunning() {
// 默认返回false
return isRunning;
}
/**
* SmartLifecycle子类的才有的方法，当isRunning方法返回true时，该方法才会被调用。
*/
@Override
public void stop(Runnable callback) {
System.out.println("stop(Runnable)");
// 如果你让isRunning返回true，需要执行stop这个方法，那么就不要忘记调用callback.run()。
// 否则在你程序退出时，Spring的DefaultLifecycleProcessor会认为你这个TestSmartLifecycle没有stop完成，程序会一直卡着结束不了，等待一定时间（默认超时时间30秒）后才会自动结束。
// PS：如果你想修改这个默认超时时间，可以按下面思路做，当然下面代码是springmvc配置文件形式的参考，在SpringBoot中自然不是配置xml来完成，这里只是提供一种思路。
// <bean id="lifecycleProcessor" class="org.springframework.context.support.DefaultLifecycleProcessor">
// <!-- timeout value in milliseconds -->
// <property name="timeoutPerShutdownPhase" value="10000"/>
// </bean>
callback.run();
isRunning = false;
}
/**
* 接口Lifecycle的子类的方法，只有非SmartLifecycle的子类才会执行该方法。<br/>
* 1. 该方法只对直接实现接口Lifecycle的类才起作用，对实现SmartLifecycle接口的类无效。<br/>
* 2. 方法stop()和方法stop(Runnable callback)的区别只在于，后者是SmartLifecycle子类的专属。
*/
@Override
public void stop() {
System.out.println("stop");
isRunning = false;
}
}
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SmartLifecycle 解读
org.springframework.context.SmartLifecycle解读
1、接口定义
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/**
* 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);
}
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从注释文档里可以看出：
1、是接口 Lifecycle 的拓展，且会在应用上下文类ApplicationContext 执行 refresh and/or shutdown 时会调用
2、方法 isAutoStartup() 返回的值会决定，当前实体对象是否会被调用，当应用上下文类ApplicationContext 执行 refresh
3、stop(Runnable) 方法用于调用Lifecycle的stop方法
4、getPhase() 返回值用于设置LifeCycle的执行优先度：值越小优先度越高
5、isRunning() 决定了start()方法的是否调用
2、应用
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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.");
}
/**
* 执行start()方法前会用它来判断是否执行，返回为true时，start()方法不执行
*/
@Override
public boolean isRunning() {
return isRunning;
}
@Override
public int getPhase() {
return 0;
}
}
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启动类
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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();
}
}
}
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可以发现，类SmartLifecycleImpl提交给spring容器后，启动后，会输出 start() 方法的方法体。
以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：https://www.jianshu.com/p/7b8f2a97c8f5