Spring中SmartLifecycle的用法是怎样的

这期内容当中小编将会给大家带来有关Spring中SmartLifecycle的用法是怎样的，文章内容丰富且以专业的角度为大家分析和叙述，阅读完这篇文章希望大家可以有所收获！

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 * *  *  */@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
     * 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。

上述就是小编为大家分享的Spring中SmartLifecycle的用法是怎样的了，如果刚好有类似的疑惑，不妨参照上述分析进行理解。如果想知道更多相关知识，欢迎关注行业资讯频道。