自定义注解

自定义注解：

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TestAnnotation {
    String value() default "";
    String name() default "";
}

使用自定义注解：

@Service
public class TestAnnotationService {

    @TestAnnotation(value = "myTestAnnotation")
    public String test(String s) {
        return s;
    }
}

要实现的功能是：在类加载后打印自定义注解的值

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if(beanName.equals("testAnnotationService")){
            Class clazz = bean.getClass();
            Method[] methods=clazz.getDeclaredMethods();
            if(methods.length>0){
                for(Method method:methods){
                    TestAnnotation annotation=method.getAnnotation(TestAnnotation.class);
                    if(annotation!=null){
                        System.out.println("222222"+annotation.value());
                    }
                }
            }
        }
        return bean;
    }
}

 这样在方法加载的时候就会打印222222myTestAnnotation

注：

BeanPostProcessor也称为Bean后置处理器，它是Spring中定义的接口，在Spring容器的创建过程中（具体为Bean初始化前后）会回调BeanPostProcessor中定义的两个方法。BeanPostProcessor的源码如下：

public interface BeanPostProcessor {

    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName)     throws BeansException {
        return bean;
    }

    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

在方法调用前后，或者调用方法时获取注解并写相应的业务逻辑，可以使用切面的方式。

@Aspect
@Component
public class TestAspect {
    @Before("@annotation(com.tkp.coupon.web.myself.annotation.TestAnnotation)")
    public void before(JoinPoint joinPoint) {
        System.out.println("before the method");
    }
}