Spring攻略学习笔记(3.05)重用切入点定义

一、知识点

       在编写AspectJ aspect时，可以直接在通知注解中嵌入切入点表达式。但是，相同的切入点表达式可能在多个通知中重复。

       和其它许多AOP实现一样，AspectJ也允许独立地定义切入点，在多个通知中重用。

二、代码示例

       在AspectJ aspect中，切入点可以声明为一个带有@Pointcut注解的简单方法。切入点的方法体通常为空，因为将切入点定义与应用程序逻辑混合在一起是不合理的。切入点方法的访问修饰符控制切入点的可见性。其他通知可以用方法名称引用这个切入点。

package com.codeproject.jackie.springrecipesnote.springaop;

import java.util.Arrays;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;

/**
 * @author jackie
 * 
 */
@Aspect
public class CalculatorLoggingAspect {
	private Log log = LogFactory.getLog(this.getClass());

	@Pointcut("execution(* *.*(..))")
	private void loggingOperation() {
	}

	@Before("loggingOperation()")
	public void logBefore(JoinPoint joinPoint) {
		log.info("The method " + joinPoint.getSignature().getName()
				+ "() begins with " + Arrays.toString(joinPoint.getArgs()));
	}

	@After("loggingOperation()")
	public void logAfter(JoinPoint joinPoint) {
		log.info("The method " + joinPoint.getSignature().getName() + "() ends");
	}

	@AfterReturning(pointcut = "loggingOperation())", returning = "result")
	public void logAfterReturning(JoinPoint joinPoint, Object result) {
		log.info("The method " + joinPoint.getSignature().getName() + "() ends with " + result);
	}

	@AfterThrowing(pointcut = "loggingOperation())", throwing = "e")
	public void logAfterThrowing(JoinPoint joinPoint, Throwable e) {
		log.error("An exception " + e + " has been thrown in " + joinPoint.getSignature().getName() + "()");
	}

	@Around("loggingOperation()")
	public Object logAround(ProceedingJoinPoint joinPoint) throws Throwable {
		log.info("The method " + joinPoint.getSignature().getName() + "() begins with " + Arrays.toString(joinPoint.getArgs()));
		try {
			Object result = joinPoint.proceed();
			log.info("The method " + joinPoint.getSignature().getName() + "() ends with " + result);
			return result;
		} catch (IllegalArgumentException e) {
			log.error("Illegal argument " + Arrays.toString(joinPoint.getArgs()) + " in " + joinPoint.getSignature().getName() + "()");
			throw e;
		}
	}
}

通常，如果切入点在多个aspect之间共享，最好将它们集中到一个公共类中。在这种情况下，它们必须声明为public。

package com.codeproject.jackie.springrecipesnote.springaop;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;

/**
 * @author jackie
 * 
 */
@Aspect
public class CalculatorPointcuts {
	@Pointcut("execution(* *.*(..))")
	public void loggingOperation() {
	}
}

当引用这个切入点时，必须包含类名。如果类不在与这个aspect相同的包中，还必须包含包名。

        @Before("CalculatorPointcuts.loggingOperation()")
	public void logBefore(JoinPoint joinPoint) {
		log.info("The method " + joinPoint.getSignature().getName()
				+ "() begins with " + Arrays.toString(joinPoint.getArgs()));
	}

	@After("CalculatorPointcuts.loggingOperation()")
	public void logAfter(JoinPoint joinPoint) {
		log.info("The method " + joinPoint.getSignature().getName() + "() ends");
	}

	@AfterReturning(pointcut = "CalculatorPointcuts.loggingOperation())", returning = "result")
	public void logAfterReturning(JoinPoint joinPoint, Object result) {
		log.info("The method " + joinPoint.getSignature().getName() + "() ends with " + result);
	}

	@AfterThrowing(pointcut = "CalculatorPointcuts.loggingOperation())", throwing = "e")
	public void logAfterThrowing(JoinPoint joinPoint, Throwable e) {
		log.error("An exception " + e + " has been thrown in " + joinPoint.getSignature().getName() + "()");
	}

	@Around("CalculatorPointcuts.loggingOperation()")
	public Object logAround(ProceedingJoinPoint joinPoint) throws Throwable {
		log.info("The method " + joinPoint.getSignature().getName() + "() begins with " + Arrays.toString(joinPoint.getArgs()));
		try {
			Object result = joinPoint.proceed();
			log.info("The method " + joinPoint.getSignature().getName() + "() ends with " + result);
			return result;
		} catch (IllegalArgumentException e) {
			log.error("Illegal argument " + Arrays.toString(joinPoint.getArgs()) + " in " + joinPoint.getSignature().getName() + "()");
			throw e;
		}
	}