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。

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脚本之家。