以 Annotation 执行顺序来探究 AOP闲文杂记以 Annotation 执行顺序来探究 AOP 导航前往主站应用闲文杂记代码在线代码魔方房价浅析

/**
 * <Description> Description for A <br>
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface A {

}



/**
 * <Description> Description for B <br>
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface B {

}



/**
 * <Description> Description for 注解顺序 <br>
 */
@Component
public class AnnotationOrderDemo extends AbstractDemoFactory {

    @A
    @B
    public void testABeforeB() {

    }

    @B
    @A
    public void testAAfterB() {

    }
}



@Component
@Aspect
public class AspectA {

    /**
     * logger
     */
    private static final Logger LOGGER = LoggerFactory.getLogger(AspectA.class);

    @Around("@annotation(com.jansora.demo.annotation.lib.annotation.A)")
    public Object a(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        LOGGER.debug("aspect a.");
        return proceedingJoinPoint.proceed();
    }


    @Around("@annotation(com.jansora.demo.annotation.lib.annotation.B)")
    public Object b(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        LOGGER.debug("aspect b.");
        return proceedingJoinPoint.proceed();
    }

}




@SpringBootApplication
public class AnnotationApplication implements ApplicationRunner {

    @Autowired
    AnnotationOrderDemo annotationOrderDemo;

    private String[] args;

    public static void main(String[] args) throws Throwable {
        SpringApplication.run(AnnotationApplication.class, args);
    }


    @Override
    public void run(ApplicationArguments args) throws Exception {
        this.args = args.getSourceArgs();
        System.out.println("testABeforeB: ");
        annotationOrderDemo.testABeforeB();
        System.out.println("testAAfterB: ");
        annotationOrderDemo.testAAfterB();
    }
}

默认情况(不作任何干预)

2022-08-04 11:03:11.429  INFO 32664 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 19932 (http) with context path ''
2022-08-04 11:03:11.443  INFO 32664 --- [  restartedMain] c.j.d.annotation.AnnotationApplication   : Started AnnotationApplication in 2.217 seconds (JVM running for 2.65)
testABeforeB: 
2022-08-04 11:03:11.449 DEBUG 32664 --- [  restartedMain] c.j.demo.annotation.lib.aspect.AspectA   : aspect a.
2022-08-04 11:03:11.450 DEBUG 32664 --- [  restartedMain] c.j.demo.annotation.lib.aspect.AspectA   : aspect b.
testAAfterB: 
2022-08-04 11:03:11.454 DEBUG 32664 --- [  restartedMain] c.j.demo.annotation.lib.aspect.AspectA   : aspect a.
2022-08-04 11:03:11.454 DEBUG 32664 --- [  restartedMain] c.j.demo.annotation.lib.aspect.AspectA   : aspect b.

结论: 不管 A 在 B 前, 还是 A 在 B 后, 默认情况下显示, A 的执行顺序都在 B 前.

那么问题来了

问题 1: 为什么两次执行结果不一致?

问题 2: 为什么两次执行结果都是 A 在 B 前, 而不是 B 在 A 前?

带着这两个问题, 我们来 DEBUG 一下