JAVA基础篇（7）-自定义注解（实践）

JAVA && Spring && SpringBoot2.x — 学习目录

Spring AOP与Hystrix自定义注解结合案例。

AOP-Spring实际项目中面向切面编程(含工具类)

1. 相关maven依赖

       
        
            com.netflix.hystrix
            hystrix-javanica
            1.5.18
        

2. 注解解析

本质上是使用Spring的AOP去解析自定义的Java注解。

注解源码：com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface HystrixCommand {
    String groupKey() default "";
    String commandKey() default "";
    String threadPoolKey() default "";
    String fallbackMethod() default "";
    HystrixProperty[] commandProperties() default {};
    HystrixProperty[] threadPoolProperties() default {};
    Class[] ignoreExceptions() default {};
    ObservableExecutionMode observableExecutionMode() default ObservableExecutionMode.EAGER;
    HystrixException[] raiseHystrixExceptions() default {};
    String defaultFallback() default "";
}

解析源码：com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect

1. 定义切面

    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
    public void hystrixCommandAnnotationPointcut() {
    }

    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
    public void hystrixCollapserAnnotationPointcut() {
    }

2. 环绕通知

    @Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
    public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {
        Method method = getMethodFromTarget(joinPoint);
        Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);
        if (method.isAnnotationPresent(HystrixCommand.class) && method.isAnnotationPresent(HystrixCollapser.class)) {
            throw new IllegalStateException("method cannot be annotated with HystrixCommand and HystrixCollapser " +
                    "annotations at the same time");
        }
        MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
        MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
        HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);
        ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
                metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();

        Object result;
        try {
            if (!metaHolder.isObservable()) {
                result = CommandExecutor.execute(invokable, executionType, metaHolder);
            } else {
                result = executeObservable(invokable, executionType, metaHolder);
            }
        } catch (HystrixBadRequestException e) {
            throw e.getCause();
        } catch (HystrixRuntimeException e) {
            throw hystrixRuntimeExceptionToThrowable(metaHolder, e);
        }
        return result;
    }

我们可以通过JoinPoint对象获取到Method对象，然后获取到对象中的注解，完成我们的操作。