Spring中SmartLifecycle的用法解读

Spring中SmartLifecycle的用法解读

目录Spring SmartLifecycle用法SmartLifecycle 是一个接口SmartLifecycle 解读1、接口定义2、应用

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）。

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

* 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。

* 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。

* 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。

* 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。

//

//

//

//

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。

* 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。

* 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;

}

}

SmartLifecycle 解读

org.springframework.context.SmartLifecycle解读

1、接口定义

/**

* 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 must invoke the

* callback's run() method upon shutdown completion to avoid unnecessary delays

* in the overall ApplicationContext shutdown.

*

*

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 lowest

* phase value and ends with the highest 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.

*

*

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.

*

*

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.

*

*

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.

*

*

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.

*

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.

*

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 must be executed after

* the {@code SmartLifecycle} component does indeed stop.

*

The {@link LifecycleProcessor} will call only 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);

}

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

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;

}

}

启动类

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();

}

}

}

可以发现，类SmartLifecycleImpl提交给spring容器后，启动后，会输出 start() 方法的方法体。

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