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 * * * */@Componentpublic 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; }} |
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); } |
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; }} |
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(); } }} |
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
