AOP 示例

现在您已经了解了所有组成部分的工作原理，我们可以将它们组合在一起以完成一些有用的操作。

业务服务的执行有时可能会由于并发问题（例如，死锁失败者）而失败。如果重试操作，则很可能在下一次尝试中成功。对于在这些情况下适合重试的业务服务（不需要返回给用户进行冲突解决的幂等操作），我们希望透明地重试操作，以避免客户端看到PessimisticLockingFailureException。这是一个显然跨越服务层中多个服务的必需条件，因此，非常适合通过方面来实现。

因为我们希望重试操作，所以我们需要使用环绕通知，以便我们可以多次调用proceed。以下清单显示了基本的方面实现

  • Java

  • Kotlin

@Aspect
public class ConcurrentOperationExecutor implements Ordered {

	private static final int DEFAULT_MAX_RETRIES = 2;

	private int maxRetries = DEFAULT_MAX_RETRIES;
	private int order = 1;

	public void setMaxRetries(int maxRetries) {
		this.maxRetries = maxRetries;
	}

	public int getOrder() {
		return this.order;
	}

	public void setOrder(int order) {
		this.order = order;
	}

	@Around("com.xyz.CommonPointcuts.businessService()")
	public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {
		int numAttempts = 0;
		PessimisticLockingFailureException lockFailureException;
		do {
			numAttempts++;
			try {
				return pjp.proceed();
			}
			catch(PessimisticLockingFailureException ex) {
				lockFailureException = ex;
			}
		} while(numAttempts <= this.maxRetries);
		throw lockFailureException;
	}
}
@Aspect
class ConcurrentOperationExecutor : Ordered {

	companion object {
		private const val DEFAULT_MAX_RETRIES = 2
	}

	var maxRetries = DEFAULT_MAX_RETRIES

	private var order = 1

	override fun getOrder(): Int {
		return this.order
	}

	fun setOrder(order: Int) {
		this.order = order
	}

	@Around("com.xyz.CommonPointcuts.businessService()")
	fun doConcurrentOperation(pjp: ProceedingJoinPoint): Any {
		var numAttempts = 0
		var lockFailureException: PessimisticLockingFailureException?
		do {
			numAttempts++
			try {
				return pjp.proceed()
			} catch (ex: PessimisticLockingFailureException) {
				lockFailureException = ex
			}
		} while (numAttempts <= this.maxRetries)
		throw lockFailureException!!
	}

@Around("com.xyz.CommonPointcuts.businessService()") 引用在共享命名切点定义中定义的名为businessService的切点。

请注意，该方面实现了Ordered接口，以便我们可以将该方面的优先级设置为高于事务通知（我们希望每次重试时都使用新的事务）。maxRetries和order属性都由 Spring 配置。主要操作发生在doConcurrentOperation环绕通知中。请注意，目前，我们将重试逻辑应用于每个businessService。我们尝试继续执行，如果我们遇到PessimisticLockingFailureException失败，我们会再次尝试，除非我们已用尽所有重试尝试。

相应的 Spring 配置如下

  • Java

  • Kotlin

  • Xml

@Configuration
@EnableAspectJAutoProxy
public class ApplicationConfiguration {

	@Bean
	public ConcurrentOperationExecutor concurrentOperationExecutor() {
		ConcurrentOperationExecutor executor = new ConcurrentOperationExecutor();
		executor.setMaxRetries(3);
		executor.setOrder(100);
		return executor;

	}
}
@Configuration
@EnableAspectJAutoProxy
class ApplicationConfiguration {

	@Bean
	fun concurrentOperationExecutor() = ConcurrentOperationExecutor().apply {
		maxRetries = 3
		order = 100
	}
}
<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xmlns:aop="http://www.springframework.org/schema/aop"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans
			https://www.springframework.org/schema/beans/spring-beans.xsd
			http://www.springframework.org/schema/aop
			https://www.springframework.org/schema/aop/spring-aop.xsd">

	<aop:aspectj-autoproxy />

	<bean id="concurrentOperationExecutor"
		  class="com.xyz.service.impl.ConcurrentOperationExecutor">
		<property name="maxRetries" value="3"/>
		<property name="order" value="100"/>
	</bean>

</beans>

为了改进该方面，使其仅重试幂等操作，我们可以定义以下Idempotent注解

  • Java

  • Kotlin

@Retention(RetentionPolicy.RUNTIME)
// marker annotation
public @interface Idempotent {
}
@Retention(AnnotationRetention.RUNTIME)
// marker annotation
annotation class Idempotent

然后，我们可以使用该注解来注解服务操作的实现。对该方面的更改，使其仅重试幂等操作，包括改进切点表达式，以便仅匹配@Idempotent操作，如下所示

  • Java

  • Kotlin

@Around("execution(* com.xyz..service.*.*(..)) && " +
		"@annotation(com.xyz.service.Idempotent)")
public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {
	// ...
	return pjp.proceed(pjp.getArgs());
}
@Around("execution(* com.xyz..service.*.*(..)) && " +
		"@annotation(com.xyz.service.Idempotent)")
fun doConcurrentOperation(pjp: ProceedingJoinPoint): Any? {
	// ...
	return pjp.proceed(pjp.args)
}