Spring @Order注解的使用
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;
@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
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----"); } }
----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);
个人理解是加载代码的底层要支持优先级执行程序,否则即使配置上Ordered、@Order也是不起任何作用的。