《Spring Recipes》第三章筆記2：Declaring Aspects

 《Spring Recipes》第三章筆記2：Declaring Aspects

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

注意：切面必須讓Spring容器管理（使用註解或者在配置文件中聲明切面）才能生效。

一、@Aspect：聲明一個切面。

二、@Before：定義在切入點以前執行特定代碼。

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

能夠通知方法中添加JoinPoint類型的參數，獲取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()));
  }
}

三、@After：定義在切入點以後 執行特定代碼，不管切入點是成功返回仍是拋出異常。

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

四、@AfterReturning：定義在切入點成功返回後執行特定代碼。

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

能夠在@ AfterReturning註解中添加returning，在通知中添加Object類型的參數獲取方法的返回信息：

@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);
  }
}

五、@AfterThrowing：定義在切入點拋出異常後執行特定代碼，能夠指定拋出的異常類型。

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

能夠經過在 @AfterThrowing 中添加throwing獲取異常，在通知中添加Throwable類型的參數：

@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() + "()");
  }
}

能夠經過在通知中指定異常類型，來只捕獲特定類型的異常：

@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() + "()");
  }
}

六、@Around：對切入點具備徹底的控制，能夠在一個通知中定義上面5中類型的通知。

@Around通知的參數必須爲ProceedingJoinPoint類型。

@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;
   }
 }
}