Spring AOP

• 面向切面编程；

启动AspectJ

• 添加AspectJ类库；

<!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-aspects -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.aspectj/aspectjweaver -->
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjweaver</artifactId>
    <version>1.9.5</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.aopalliance/com.springsource.org.aopalliance -->
<dependency>
    <groupId>org.aopalliance</groupId>
    <artifactId>com.springsource.org.aopalliance</artifactId>
    <version>1.0.0</version>
</dependency>

• 在配置文件中定义一个空的xml元素；

<aop:aspectj-autoproxy/>

• 编写类，需要加入扫描，标注@Aspect

@Aspect
@Component
public class AopLogging {
//    //声明该方法是一个前置通知，在方法执行之前执行
//    @Before("execution(public int ArithmeticCalculator.add(int,int))")
//    public void before(JoinPoint joinPoint) {
//        String methodName = joinPoint.getSignature().getName();
//        List args = Arrays.asList(joinPoint.getArgs());
//        System.out.println("The method" + methodName + " begins with " + args);
//    }
//    @After("execution(public int ArithmeticCalculator.*(int,int))")
//    public void after(JoinPoint joinPoint) {
//        String methodName = joinPoint.getSignature().getName();
//        List args = Arrays.asList(joinPoint.getArgs());
//        System.out.println("The method" + methodName + " end with " + args);
//    }
//
//    @AfterReturning(value = "execution(public int ArithmeticCalculator.*(int,int))",returning = "result")
//    public void afterReturn(JoinPoint joinPoint,Object result) {
//        String methodName = joinPoint.getSignature().getName();
//        System.out.println("The method" + methodName + " returns with " + result);
//    }
//
//    @AfterThrowing(value = "execution(public int ArithmeticCalculator.*(int,int))",throwing = "ex")
//    public void afterThrow(JoinPoint joinPoint, Exception ex) {
//        String methodName = joinPoint.getSignature().getName();
//        System.out.println("The method" + methodName + " occurs: " + ex);
//    }

    @Around("execution(public int ArithmeticCalculator.*(..))")
    public Object around(ProceedingJoinPoint point) {
        String methodName = point.getSignature().getName();
        Object result = null;

        try {
            System.out.println("This method starts with name: " + methodName);
            result = point.proceed();
            System.out.println("This method return result: " + result);
        } catch (Throwable throwable) {
            System.out.println("This method occurs with" + throwable);
            throwable.printStackTrace();
        }

        System.out.println("This method ends with name: " + methodName);
        return result;
    }
}

• 在类中声明各种通知：
  • @Before：前置通知；
  • @After：目标方法执行后，无论是否发生异常；
  • @AfterReturning：携带方法的返回值；
  • @AfterThrowing：抛出异常时执行，可获取异常对象；
  • @Around：环绕，功能最强大，包含以上几种；

切面的优先级

@Order(1)
@Aspect
@Component
public class AopLogging {

• 使用@Order指定优先级，值越小，优先级越高；

切面表达式重用

• 定义方法来指定相同的切面表达式;
• 使用时，直接引用方法名；
• 外部使用需要全类名.方法名；

@Pointcut("execution(public int ArithmeticCalculator.*(..))")
public void declarePoint(){}

@Before("declarePoint()")
public void before(JoinPoint joinPoint) {
    String methodName = joinPoint.getSignature().getName();
    List args = Arrays.asList(joinPoint.getArgs());
    System.out.println("The method" + methodName + " begins with " + args);
}

使用基于配置文件的使用

<bean id="aopLogging" class="com.llds.aop2.AopLogging"/>
<bean id="calculator" class="com.llds.aop2.ArithmeticCalculatorImpl"/>

<aop:config>
    <aop:pointcut id="pointcut" expression="execution(* com.llds.aop2.ArithmeticCalculator.*(..))"/>
    <aop:aspect ref="aopLogging" >
        <aop:before method="before" pointcut-ref="pointcut"/>
    </aop:aspect>
</aop:config>