[學習小結]Spring_通知的那些事和基於配置文件的方式來配置AOP

Spring_通知的那些事：

說道Spring，肯定都會想到IOC和AOP，這次就是圍繞AOP來講，同時也不得要說AspectJ。

AspectJ的瞭解：

代碼示例：

準備一個接口：

public interface ArithmeticCalculator {

	int add(int i, int j);
	int sub(int i, int j);
	
	int mul(int i, int j);
	int div(int i, int j);
	
}

準備一個接口的實現類：

import org.springframework.stereotype.Component;

@Component("arithmeticCalculator")
public class ArithmeticCalculatorImpl implements ArithmeticCalculator {

	@Override
	public int add(int i, int j) {
		int result = i + j;
		return result;
	}

	@Override
	public int sub(int i, int j) {
		int result = i - j;
		return result;
	}

	@Override
	public int mul(int i, int j) {
		int result = i * j;
		return result;
	}

	@Override
	public int div(int i, int j) {
		int result = i / j;
		return result;
	}

}

配置文件：applicationContext.xml

配置前別忘記了勾選Namespaces：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">

	<!-- 配置自動掃描的包 -->
	<context:component-scan base-package="com.atguigu.spring.aop"></context:component-scan>
	
	<!-- 配置自動爲匹配 aspectJ 註解的 Java 類生成代理對象 -->
	<aop:aspectj-autoproxy></aop:aspectj-autoproxy>
	
</beans>

首先來看一下環繞通知：

/**
	 * 環繞通知需要攜帶 ProceedingJoinPoint 類型的參數. 
	 * 環繞通知類似於動態代理的全過程: ProceedingJoinPoint 類型的參數可以決定是否執行目標方法.
	 * 且環繞通知必須有返回值, 返回值即爲目標方法的返回值
	 */
	
	@Around("execution(public int com.atguigu.spring.aop.ArithmeticCalculator.*(..))")
	public Object aroundMethod(ProceedingJoinPoint pjd){
		
		Object result = null;
		String methodName = pjd.getSignature().getName();
		
		try {
			//前置通知
			System.out.println("The method " + methodName + " begins with " + Arrays.asList(pjd.getArgs()));
			//執行目標方法
			result = pjd.proceed();
			//返回通知
			System.out.println("The method " + methodName + " ends with " + result);
		} catch (Throwable e) {
			//異常通知
			System.out.println("The method " + methodName + " occurs exception:" + e);
			throw new RuntimeException(e);
		}
		//後置通知
		System.out.println("The method " + methodName + " ends");
		
		return result;
	}

前置通知，後置通知，異常通知，返回通知

import java.util.Arrays;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

/**
 * 可以使用 @Order 註解指定切面的優先級, 值越小優先級越高
 */
@Order(2)
@Aspect
@Component
public class LoggingAspect {
	
	/**
	 * 定義一個方法, 用於聲明切入點表達式. 一般地, 該方法中再不需要添入其他的代碼. 
	 * 使用 @Pointcut 來聲明切入點表達式. 
	 * 後面的其他通知直接使用方法名來引用當前的切入點表達式. 
	 */
	@Pointcut("execution(public int com.atguigu.spring.aop.ArithmeticCalculator.*(..))")
	public void declareJointPointExpression(){}
	
	/**
	 * 在 com.atguigu.spring.aop.ArithmeticCalculator 接口的每一個實現類的每一個方法開始之前執行一段代碼
	 */
	@Before("declareJointPointExpression()")
	public void beforeMethod(JoinPoint joinPoint){
		String methodName = joinPoint.getSignature().getName();
		Object [] args = joinPoint.getArgs();
		
		System.out.println("The method " + methodName + " begins with " + Arrays.asList(args));
	}
	
	/**
	 * 在方法執行之後執行的代碼. 無論該方法是否出現異常
	 */
	@After("declareJointPointExpression()")
	public void afterMethod(JoinPoint joinPoint){
		String methodName = joinPoint.getSignature().getName();
		System.out.println("The method " + methodName + " ends");
	}
	
	/**
	 * 在方法法正常結束受執行的代碼
	 * 返回通知是可以訪問到方法的返回值的!
	 */
	@AfterReturning(value="declareJointPointExpression()",
			returning="result")
	public void afterReturning(JoinPoint joinPoint, Object result){
		String methodName = joinPoint.getSignature().getName();
		System.out.println("The method " + methodName + " ends with " + result);
	}
	
	/**
	 * 在目標方法出現異常時會執行的代碼.
	 * 可以訪問到異常對象; 且可以指定在出現特定異常時在執行通知代碼
	 */
	@AfterThrowing(value="declareJointPointExpression()",
			throwing="e")
	public void afterThrowing(JoinPoint joinPoint, Exception e){
		String methodName = joinPoint.getSignature().getName();
		System.out.println("The method " + methodName + " occurs excetion:" + e);
	}
}

測試用例：

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {
	
	public static void main(String[] args) {
		
		ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
		ArithmeticCalculator arithmeticCalculator = (ArithmeticCalculator) ctx.getBean("arithmeticCalculator");
		
		System.out.println(arithmeticCalculator.getClass().getName());
		
		int result = arithmeticCalculator.add(1, 2);
		System.out.println("result:" + result);
		
		result = arithmeticCalculator.div(1000, 10);
		System.out.println("result:" + result);
	}

測試結果：

1.沒有出現異常的情況

com.sun.proxy.$Proxy12
-->validate:[1, 2]
The method add begins with [1, 2]
The method add ends
The method add ends with 3
result:3
-->validate:[1000, 10]
The method div begins with [1000, 10]
The method div ends
The method div ends with 100
result:100

2.出現異常的情況：

com.sun.proxy.$Proxy12
-->validate:[1, 2]
The method add begins with [1, 2]
The method add ends
The method add ends with 3
result:3
-->validate:[1000, 0]
The method div begins with [1000, 0]
The method div ends
The method div occurs excetion:java.lang.ArithmeticException: / by zero

基於配置文件的方式來配置AOP

瞭解概述：

代碼示例：

與上面所述的一樣需要接口和一個接口實現類（但這次只有實現類稍微改動一點），取消了註釋

public class ArithmeticCalculatorImpl implements ArithmeticCalculator {

	@Override
	public int add(int i, int j) {
		int result = i + j;
		return result;
	}

	@Override
	public int sub(int i, int j) {
		int result = i - j;
		return result;
	}

	@Override
	public int mul(int i, int j) {
		int result = i * j;
		return result;
	}

	@Override
	public int div(int i, int j) {
		int result = i / j;
		return result;
	}

}

配置文件：applicationContext-xml.xml（關鍵在這裏）

<?xml version="1.0" encoding="UTF-8"?>
<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 http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd">

	<!-- 配置 bean -->
	<bean id="arithmeticCalculator" 
		class="com.atguigu.spring.aop.xml.ArithmeticCalculatorImpl"></bean>

	<!-- 配置切面的 bean. -->
	<bean id="loggingAspect"
		class="com.atguigu.spring.aop.xml.LoggingAspect"></bean>

	<bean id="vlidationAspect"
		class="com.atguigu.spring.aop.xml.VlidationAspect"></bean>





	<!-- 配置 AOP -->
	<aop:config>
		<!-- 配置切點表達式 -->
		<aop:pointcut expression="execution(* com.atguigu.spring.aop.xml.ArithmeticCalculator.*(int, int))" 
			id="pointcut"/>
		<!-- 配置切面及通知 -->
		<aop:aspect ref="loggingAspect" order="2">
			<aop:before method="beforeMethod" pointcut-ref="pointcut"/>
			<aop:after method="afterMethod" pointcut-ref="pointcut"/>
			<aop:after-throwing method="afterThrowing" pointcut-ref="pointcut" throwing="e"/>
			<aop:after-returning method="afterReturning" pointcut-ref="pointcut" returning="result"/>
			<!--  
			<aop:around method="aroundMethod" pointcut-ref="pointcut"/>
			-->
		</aop:aspect>	
		<aop:aspect ref="vlidationAspect" order="1">
			<aop:before method="validateArgs" pointcut-ref="pointcut"/>
		</aop:aspect>
	</aop:config>

</beans>

測試用例與測試結果與上面一樣