《Spring Recipes》第三章笔记2：Declaring Aspects

 《Spring Recipes》第三章笔记2：Declaring Aspects

Spring容器支持的AspectJ注解：@Aspect，@Before，@After，@AfterReturning，@AfterThrowing，@Around。

注意：切面必须让Spring容器管理（使用注解或者在配置文件中声明切面）才能生效。

1、@Aspect：声明一个切面。

2、@Before：定义在切入点之前执行特定代码。

@Aspect
public class CalculatorLoggingAspect {
  private Log log = LogFactory.getLog(this.getClass());
  @Before("execution(* ArithmeticCalculator.add(..))")
  public void logBefore() {
    log.info("The method add() begins");
  }
}

可以通知方法中添加JoinPoint类型的参数，获取JoinPoint的信息：

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

3、@After：定义在切入点之后 执行特定代码，无论切入点是成功返回还是抛出异常。

@Aspect
public class CalculatorLoggingAspect {
...
  @After("execution(* *.*(..))")
  public void logAfter(JoinPoint joinPoint) {
    log.info("The method " + joinPoint.getSignature().getName()
    + "() ends");
  }
}

4、@AfterReturning：定义在切入点成功返回后执行特定代码。

@Aspect
public class CalculatorLoggingAspect {
... ...
  @AfterReturning("execution(* *.*(..))")
  public void logAfterReturning(JoinPoint joinPoint) {
  log.info("The method " + joinPoint.getSignature().getName()+ "() ends");
  }
}

可以在@ AfterReturning注解中添加returning，在通知中添加Object类型的参数获取方法的返回信息：

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

5、@AfterThrowing：定义在切入点抛出异常后执行特定代码，可以指定抛出的异常类型。

@Aspect
public class CalculatorLoggingAspect {
... ...
  @AfterThrowing("execution(* *.*(..))")
  public void logAfterThrowing(JoinPoint joinPoint) {
    log.error("An exception has been thrown in "+ joinPoint.getSignature().getName() + "()");
  }
}

可以通过在 @AfterThrowing 中添加throwing获取异常，在通知中添加Throwable类型的参数：

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

可以通过在通知中指定异常类型，来只捕获特定类型的异常：

@Aspect
public class CalculatorLoggingAspect {
... ...
  @AfterThrowing(pointcut = "execution(* *.*(..))",
                 throwing = "e")
  public void logAfterThrowing(JoinPoint joinPoint,IllegalArgumentException e) {
    log.error("Illegal argument " + Arrays.toString(joinPoint.getArgs())+ " in " + joinPoint.getSignature().getName() + "()");
  }
}

6、@Around：对切入点具有完全的控制，可以在一个通知中定义上面5中类型的通知。

@Around通知的参数必须为ProceedingJoinPoint类型。

@Aspect
public class CalculatorLoggingAspect {
...
@Around("execution(* *.*(..))")
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;
   }
 }
}