赞
踩
先用代码讲一下什么是传统的AOP(面向切面编程)编程
需求:实现一个简单的计算器,在每一步的运算前添加日志。最传统的方式如下:
Calculator.java
- package cn.limbo.spring.aop.calculator;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public interface Calculator {
- int add(int i , int j);
- int sub(int i , int j);
- int mul(int i , int j);
- int div(int i , int j);
- }
CalculatorImpl.java
- package cn.limbo.spring.aop.calculator;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public class CalculatorImpl implements Calculator {
- @Override
- public int add(int i, int j) {
- System.out.println("The method add begin with [ "+ i +"," + j+" ]");
- System.out.println("The method add end with [ "+ i +"," + j+"]");
- return i + j;
- }
-
- @Override
- public int sub(int i, int j) {
- System.out.println("The method sub begin with [ "+ i +"," + j+" ]");
- System.out.println("The method sub end with [ "+ i +"," + j+" ]");
- return i - j;
- }
-
- @Override
- public int mul(int i, int j) {
- System.out.println("The method mul begin with [ "+ i +"," + j+" ]");
- System.out.println("The method mul end with [ "+ i +"," + j+" ]");
- return i * j;
- }
-
- @Override
- public int div(int i, int j) {
- System.out.println("The method div begin with [ "+ i +"," + j+" ]");
- System.out.println("The method div end with [ "+ i +"," + j+" ]");
- return i / j;
- }
- }
这样就完成了需求,但是我们发现,倘若是要修改日志的信息,那么就需要在具体方法里面改,这样做很麻烦,而且把原本清爽的方法改的十分混乱,方法应该表现的是核心功能,而不是这些无关紧要的关注点,下面用原生的java的方式实现在执行方法时,动态添加输出日志方法
CalculatorImpl.java
- package cn.limbo.spring.aop.calculator;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public class CalculatorImpl implements Calculator {
- @Override
- public int add(int i, int j) {
- return i + j;
- }
-
- @Override
- public int sub(int i, int j) {
- return i - j;
- }
-
- @Override
- public int mul(int i, int j) {
- return i * j;
- }
-
- @Override
- public int div(int i, int j) {
- return i / j;
- }
- }
- package cn.limbo.spring.aop.calculator;
-
-
- import java.lang.reflect.InvocationHandler;
- import java.lang.reflect.Method;
- import java.lang.reflect.Proxy;
- import java.util.Arrays;
- import java.util.Objects;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public class CalculatorLoggingProxy {
-
- //要代理的对象
- private Calculator target;
-
- public CalculatorLoggingProxy(Calculator target) {
- this.target = target;
- }
-
- public Calculator getLoggingProxy(){
-
- //代理对象由哪一个类加载器负责加载
- ClassLoader loader = target.getClass().getClassLoader();
- //代理对象的类型,即其中有哪些方法
- Class[] interfaces = new Class[]{Calculator.class};
- // 当调用代理对象其中的方法时,执行改代码
- InvocationHandler handler = new InvocationHandler() {
- @Override
- /**
- * proxy:正在返回的那个对象的代理,一般情况下,在invoke方法中不使用该对象
- * method:正在被调用的方法
- * args:调用方法时,传入的参数
- */
- public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
- String methodName = method.getName();
- System.out.println("The method " + methodName + " begins with " + Arrays.asList(args));
- //日志
- Object result = method.invoke(target,args);
- System.out.println("The method " + methodName + " ends with " + result);
-
- return result;
- }
- };
- Calculator proxy = (Calculator) Proxy.newProxyInstance(loader,interfaces,handler);
-
- return proxy;
- }
-
- }
- package cn.limbo.spring.aop.calculator;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public class Main {
- public static void main(String[] args) {
- Calculator calculator = new CalculatorImpl();
- Calculator proxy = new CalculatorLoggingProxy(calculator).getLoggingProxy();
-
- int result = proxy.add(1,2);
- System.out.println("--->" + result);
-
- result = proxy.sub(1,2);
- System.out.println("--->" + result);
-
- result = proxy.mul(3,2);
- System.out.println("--->" + result);
-
- result = proxy.div(14,2);
- System.out.println("--->" + result);
- }
- }
下面我们使用spring自带的aop包实现但是要加入
com.springsource.org.aopalliance-1.0.0.jar
com.springsource.org.aspectj.weaver-1.8.5.RELEASE.jar
这两个额外的包
下面看代码,要点全部卸载代码里面了
Calculator.java
- package cn.limbo.spring.aop.impl;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- public interface Calculator {
- int add(int i, int j);
- int sub(int i, int j);
- int mul(int i, int j);
- int div(int i, int j);
- }
CalculatorImpl.java
- package cn.limbo.spring.aop.impl;
-
- import org.springframework.stereotype.Component;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- @Component("calculatorImpl")
- public class CalculatorImpl implements Calculator {
- @Override
- public int add(int i, int j) {
- return i + j;
- }
-
- @Override
- public int sub(int i, int j) {
- return i - j;
- }
-
- @Override
- public int mul(int i, int j) {
- return i * j;
- }
-
- @Override
- public int div(int i, int j) {
- return i / j;
- }
- }
LoggingAspect.java
- package cn.limbo.spring.aop.impl;
-
- import org.aspectj.lang.JoinPoint;
- import org.aspectj.lang.ProceedingJoinPoint;
- import org.aspectj.lang.annotation.*;
- import org.springframework.core.annotation.Order;
- import org.springframework.stereotype.Component;
-
- import java.util.Arrays;
- import java.util.List;
- import java.util.Objects;
-
- /**
- * Created by Limbo on 16/7/14.
- */
- //把这个类声明为切面:需要该类放入IOC容器中,再声明为一个切面
- @Order(0)//指定切面优先级,只越小优先级越高
- @Aspect
- @Component
- public class LoggingAspect {
-
- /**
- * 定义一个方法,用于声明切入点表达式,一般的,该方法中再不需要添加其他代码
- * 主要是为了重用路径,使用@Pointcut来声明切入点表达式
- * 后面的其他通知直接使用方法名来引用当前的切入点表达式
- */
- @Pointcut("execution(* cn.limbo.spring.aop.impl.Calculator.*(..))")
- public void declareJointPointExpression()
- {
-
- }
-
-
- //声明该方法是一个前置通知:在目标方法之前执行
- @Before("declareJointPointExpression()")
- // @Before("execution(* cn.limbo.spring.aop.impl.*.*(..))") 该包下任意返回值,任意类,任意方法,任意参数类型
- public void beforeMethod(JoinPoint joinPoint)
- {
- String methodName = joinPoint.getSignature().getName();
- List<Object> args = Arrays.asList(joinPoint.getArgs());
- System.out.println("The Method "+ methodName+" Begins With " + args);
- }
- //在目标方法执行之后执行,无论这个方法是否出错
- //在后置通知中还不能访问目标方法的返回值,只能通过返回通知访问
- @After("execution(* cn.limbo.spring.aop.impl.Calculator.*(int,int))")
- public void afterMethod(JoinPoint joinPoint)
- {
- String methodName = joinPoint.getSignature().getName();
- System.out.println("The Method "+ methodName+" Ends ");
- }
-
- /**
- * 在方法正常结束后执行的代码
- * 返回通知是可以访问到方法的返回值
- */
- @AfterReturning(value = "execution(* cn.limbo.spring.aop.impl.Calculator.*(..))",returning = "result")
- public void afterReturning(JoinPoint joinPoint , Object result)
- {
- String methodName = joinPoint.getSignature().getName();
- System.out.println("The Method " + methodName + " Ends With " + result);
- }
-
-
- /**
- *在目标方法出现异常的时候执行代码
- * 可以访问异常对象,且可以指定出现特定异常时再执行通知
- */
- @AfterThrowing(value = "execution(* cn.limbo.spring.aop.impl.Calculator.*(..))",throwing = "ex")
- public void afterThrowing(JoinPoint joinPoint,Exception ex)//Exception 可以改成 NullPointerException等特定异常
- {
- String methodName = joinPoint.getSignature().getName();
- System.out.println("The Method " + methodName + " Occurs With " + ex);
- }
-
- /**
- * 环绕通知需要ProceedingJoinPoint 类型参数 功能最强大
- * 环绕通知类似于动态代理的全过程:ProceedingJoinPoint 类型的参数可以决定是否执行目标方法
- * 且环绕通知必须有返回值,返回值即为目标方法的返回值
- */
- @Around("execution(* cn.limbo.spring.aop.impl.Calculator.*(..))")
- public Object aroundMethod(ProceedingJoinPoint proceedingJoinPoint)
- {
- Object result =null;
- String methodName = proceedingJoinPoint.getSignature().getName();
- try {
- //前置通知
- System.out.println("The Method " + methodName + " Begins With " + Arrays.asList(proceedingJoinPoint.getArgs()));
- result = proceedingJoinPoint.proceed();
- // 返回通知
- System.out.println("The Method " + methodName + " Ends With " + result);
- } catch (Throwable throwable) {
- //异常通知
- throwable.printStackTrace();
- }
- System.out.println("The Method " + methodName + " Ends ");
- return result;
- }
- }
applicationContext.xml
- <?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/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
- <!--配置自动扫描的包-->
- <context:component-scan base-package="cn.limbo.spring.aop.impl"></context:component-scan>
-
- <!--使Aspect注解起作用,自动为匹配的类生成代理对象-->
- <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
-
-
- </beans>
用xml来配置aop
application-config.xml
- <?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"
- xmlns:tx="http://www.springframework.org/schema/tx"
- xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
- http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
- http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">
-
-
- <bean id="userManager" class="com.tgb.aop.UserManagerImpl"/>
-
- <!--<bean id="aspcejHandler" class="com.tgb.aop.AspceJAdvice"/>-->
- <bean id="xmlHandler" class="com.tgb.aop.XMLAdvice" />
- <aop:config>
- <aop:aspect id="aspect" ref="xmlHandler">
- <aop:pointcut id="pointUserMgr" expression="execution(* com.tgb.aop.*.find*(..))"/>
-
- <aop:before method="doBefore" pointcut-ref="pointUserMgr"/>
- <aop:after method="doAfter" pointcut-ref="pointUserMgr"/>
- <aop:around method="doAround" pointcut-ref="pointUserMgr"/>
- <aop:after-returning method="doReturn" pointcut-ref="pointUserMgr"/>
- <aop:after-throwing method="doThrowing" throwing="ex" pointcut-ref="pointUserMgr"/>
-
- </aop:aspect>
- </aop:config>
- </beans>
一共有5类的通知,其中around最为强大,但是不一定最常用,aspect的底层实现都是通过代理来实现的,只能说这个轮子造的不错
最近在实际项目中配置aop发现了几个问题,实际的项目配置的的模式是ssh即Spring4+SpringMVC+Hibernate4的模式。
基于注解的方式配置方式有些坑点:
1.发现SpringMVC中aop不起任何作用
经过排查和查找网上的资料,发现问题如下:
Spring MVC启动时的配置文件,包含组件扫描、url映射以及设置freemarker参数,让spring不扫描带有@Service注解的类。为什么要这样设置?因为springmvc.xml与applicationContext.xml不是同时加载,如果不进行这样的设置,那么,spring就会将所有带@Service注解的类都扫描到容器中,等到加载applicationContext.xml的时候,会因为容器已经存在Service类,使得cglib将不对Service进行代理,直接导致的结果就是在applicationContext 中的事务配置不起作用,发生异常时,无法对数据进行回滚。以上就是原因所在。
所以改进后的applicationContext.xml如下(只是更改自动扫描包的那个配置):
- <context:component-scan base-package="cn.limbo">
- <!--不要将Controller扫进来,否则aop无法使用-->
- <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller" />
- </context:component-scan>
- <context:component-scan base-package="cn.limbo">
- <!--不要将Service扫进来,否则aop无法使用-->
- <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Service" />
- </context:component-scan>
这样就可以成功解决ssh配置下不能使用aop的情况。看来扫描包的时候不能暴力直接全部扫描进来啊,真是成也扫描,败也扫描,手动哭笑不得。
Copyright © 2003-2013 www.wpsshop.cn 版权所有,并保留所有权利。