浅谈Spring @Order注解的使用（转）

注解@Order或者接口Ordered的作用是定义Spring IOC容器中Bean的执行顺序的优先级，而不是定义Bean的加载顺序，Bean的加载顺序不受@Order或Ordered接口的影响；

1.@Order的注解源码解读

@Retention(RetentionPolicy.RUNTIME)

@Target({ElementType.TYPE, ElementType.METHOD, ElementType.FIELD})

@Documented

public @interface Order {

    /**

     * 默认是最低优先级,值越小优先级越高

     */

    int value() default Ordered.LOWEST_PRECEDENCE;

}

注解可以作用在类(接口、枚举)、方法、字段声明（包括枚举常量）；
注解有一个int类型的参数，可以不传，默认是最低优先级；
通过常量类的值我们可以推测参数值越小优先级越高；

2.Ordered接口类

package org.springframework.core;

public interface Ordered {

    int HIGHEST_PRECEDENCE = -2147483648;

    int LOWEST_PRECEDENCE = 2147483647;

    int getOrder();

}

3.创建BlackPersion、YellowPersion类，这两个类都实现CommandLineRunner
实现CommandLineRunner接口的类会在Spring IOC容器加载完毕后执行，适合预加载类及其它资源；也可以使用ApplicationRunner,使用方法及效果是一样的。

package com.yaomy.common.order;

import org.springframework.boot.CommandLineRunner;

import org.springframework.core.annotation.Order;

import org.springframework.stereotype.Component;

/**

 * @Description: Description

 * @ProjectName: spring-parent

 * @Version: 1.0

 */

@Component

@Order(1)

public class BlackPersion implements CommandLineRunner {

    @Override

    public void run(String... args) throws Exception {

        System.out.println("----BlackPersion----");

    }

}

package com.yaomy.common.order;

import org.springframework.boot.CommandLineRunner;

import org.springframework.core.annotation.Order;

import org.springframework.stereotype.Component;

/**

 * @Description: Description

 * @ProjectName: spring-parent

 * @Version: 1.0

 */

@Component

@Order(0)

public class YellowPersion implements CommandLineRunner {

    @Override

    public void run(String... args) throws Exception {

        System.out.println("----YellowPersion----");

    }

}

4.启动应用程序打印出结果

----YellowPersion----

----BlackPersion----

我们可以通过调整@Order的值来调整类执行顺序的优先级，即执行的先后；当然也可以将@Order注解更换为Ordered接口，效果是一样的

5.到这里可能会疑惑IOC容器是如何根据优先级值来先后执行程序的，那接下来看容器是如何加载component的

看如下的启动main方法

@SpringBootApplication

public class CommonBootStrap {

    public static void main(String[] args) {

        SpringApplication.run(CommonBootStrap.class, args);

    }

}

这个不用过多的解释，进入run方法。。

    public ConfigurableApplicationContext run(String... args) {

        StopWatch stopWatch = new StopWatch();

        stopWatch.start();

        ConfigurableApplicationContext context = null;

        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();

        this.configureHeadlessProperty();

        SpringApplicationRunListeners listeners = this.getRunListeners(args);

        listeners.starting();

        Collection exceptionReporters;

        try {

            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);

            this.configureIgnoreBeanInfo(environment);

            Banner printedBanner = this.printBanner(environment);

            context = this.createApplicationContext();

            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);

            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);

            this.refreshContext(context);

            this.afterRefresh(context, applicationArguments);

            stopWatch.stop();

            if (this.logStartupInfo) {

                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);

            }

            listeners.started(context);

            //这里是重点，调用具体的执行方法

            this.callRunners(context, applicationArguments);

        } catch (Throwable var10) {

            this.handleRunFailure(context, var10, exceptionReporters, listeners);

            throw new IllegalStateException(var10);

        }

        try {

            listeners.running(context);

            return context;

        } catch (Throwable var9) {

            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);

            throw new IllegalStateException(var9);

        }

    }

   private void callRunners(ApplicationContext context, ApplicationArguments args) {

        List<Object> runners = new ArrayList();

        runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());

        runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());

        //重点来了，按照定义的优先级顺序排序

        AnnotationAwareOrderComparator.sort(runners);

        Iterator var4 = (new LinkedHashSet(runners)).iterator();

        //循环调用具体方法

        while(var4.hasNext()) {

            Object runner = var4.next();

            if (runner instanceof ApplicationRunner) {

                this.callRunner((ApplicationRunner)runner, args);

            }

            if (runner instanceof CommandLineRunner) {

                this.callRunner((CommandLineRunner)runner, args);

            }

        }

    }

    private void callRunner(ApplicationRunner runner, ApplicationArguments args) {

        try {

            //执行方法

            runner.run(args);

        } catch (Exception var4) {

            throw new IllegalStateException("Failed to execute ApplicationRunner", var4);

        }

    }

    private void callRunner(CommandLineRunner runner, ApplicationArguments args) {

        try {

            //执行方法

            runner.run(args.getSourceArgs());

        } catch (Exception var4) {

            throw new IllegalStateException("Failed to execute CommandLineRunner", var4);

        }

    }

到这里优先级类的示例及其执行原理都分析完毕；不过还是要强调下@Order、Ordered不影响类的加载顺序而是影响Bean加载如IOC容器之后执行的顺序（优先级）；

原文地址：https://blog.csdn.net/yaomingyang/article/details/86649072

巴特西

浅谈Spring @Order注解的使用（转）

1.@Order的注解源码解读

2.Ordered接口类

4.启动应用程序打印出结果

5.到这里可能会疑惑IOC容器是如何根据优先级值来先后执行程序的，那接下来看容器是如何加载component的

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