AOP作为Spring这个轻量级的容器中很重要的一部分,得到越来越多的关注,Spring的Transaction就是用AOP来管理的,今天就通过简单的例子来看看Spring中的AOP的基本使用方法。 首先确定将要Proxy的目标,在Spring中默认采用JDK中的dynamic proxy,它只能够实现接口的代理,如果想对类进行代理的话,需要采用CGLIB的proxy。显然,选择“编程到接口”是更明智的做法,下面是将要代理的接口: public interface FooInterface { public void printFoo(); public void dummyFoo(); } 以及其一个简单的实现: public class FooImpl implements FooInterface { public void printFoo() { System.out.println("In FooImpl.printFoo"); } public void dummyFoo() { System.out.println("In FooImpl.dummyFoo"); } } 接下来创建一个Advice,在Spring中支持Around,Before,After returning和Throws四种Advice,这里就以简单的Before Advice举例: public class PrintBeforeAdvice implements MethodBeforeAdvice { public void before(Method arg0, Object[] arg1, Object arg2) throws Throwable { System.out.println("In PrintBeforeAdvice"); } } 有了自己的business interface和advice,剩下的就是如何去装配它们了,首先利用ProxyFactory以编程方式实现,如下: public class AopTestMain { public static void main(String[] args) { FooImpl fooImpl = new FooImpl(); PrintBeforeAdvice myAdvice = new PrintBeforeAdvice(); ProxyFactory factory = new ProxyFactory(fooImpl); factory.addBeforeAdvice(myAdvice); FooInterface myInterface = (FooInterface)factory.getProxy(); myInterface.printFoo(); myInterface.dummyFoo(); } } 现在执行程序,神奇的结果就出现了: In PrintBeforeAdvice In FooImpl.printFoo In PrintBeforeAdvice In FooImpl.dummyFoo 虽然这样能体会到Spring中AOP的用法,但这决不是值得推荐的方法,既然使用了Spring,在ApplicationContext中装配所需要 的bean才是最佳策略,实现上面的功能只需要写个简单的applicationContext就可以了,如下: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <beans> <description>The aop application context</description> <bean id="fooTarget" class="FooImpl"/> <bean id="myAdvice" class="PrintBeforeAdvice"/> <bean id="foo" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces"> <value>FooInterface</value> </property> <property name="target"> <ref local="fooTarget"/> </property> <property name="interceptorNames"> <list> <value>myAdvice</value> </list> </property> </bean> </beans> 当然,main中的代码也要进行相应的修改: public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); FooInterface foo = (FooInterface)context.getBean("foo"); foo.printFoo(); foo.dummyFoo(); } 现在运行一下,结果将和上面的运行结果完全一样,这样是不是更优雅?当需要更改实现时,只需要修改配置文件就可以了,程序中的代码不需任何改动。 但是,这时候会发现被proxy的object中的所有方法调用时都将运行advice中的before,这显然不能满足绝大多数情况下的需要,此时,只 需借用Advisor就可以了,当然要在Advisor中利用pattern设置好哪些方法需要advice,更改applicationContext 如下: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <beans> <description>The springeva application context</description> <bean id="fooTarget" class="FooImpl"/> <bean id="printBeforeAdvice" class="PrintBeforeAdvice"/> <bean id="myAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> <property name="advice"> <ref local="printBeforeAdvice"/> </property> <property name="pattern"> <value>.*print.*</value> </property> </bean> <bean id="foo" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces"> <value>FooInterface</value> </property> <property name="target"> <ref local="fooTarget"/> </property> <property name="interceptorNames"> <list> <value>myAdvisor</value> </list> </property> </bean> </beans> 主程序不需进行任何修改,运行结果已经变样了: In PrintBeforeAdvice In FooImpl.printFoo In FooImpl.dummyFoo 至此,应该已经理解了Spring中AOP的使用方法,当然Spring中AOP最重要的应用是Transaction Manager,举个这方面的applicationContext例子看看: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "spring-beans.dtd"> <beans> <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="location"> <value>/WEB-INF/jdbc.properties</value> </property> </bean> <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName"> <value>${jdbc.driverClassName}</value> </property> <property name="url"> <value>${jdbc.url}</value> </property> <property name="username"> <value>${jdbc.username}</value> </property> <property name="password"> <value>${jdbc.password}</value> </property> </bean> <bean id="sessionFactory" class="org.springframework.orm.hibernate.LocalSessionFactoryBean"> <property name="dataSource"> <ref local="dataSource"/> </property> <property name="mappingResources"> <value>smartmenu.hbm.xml</value> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">${hibernate.dialect}</prop> </props> </property> </bean> <bean id="transactionManager" class="org.springframework.orm.hibernate.HibernateTransactionManager"> <property name="sessionFactory"> <ref local="sessionFactory"/> </property> </bean> <bean id="smartmenuTarget" class="SmartMenuHibernate"> <property name="sessionFactory"> <ref local="sessionFactory"/> </property> </bean> <bean id="smartMenu" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager"> <ref local="transactionManager"/> </property> <property name="target"> <ref local="smartmenuTarget"/> </property> <property name="transactionAttributes"> <props> <prop key="get*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="find*">PROPAGATION_REQUIRED,readOnly</prop> </props> </property> </bean> </beans> 要实现自动代理exmaple如下: <beans>
<!-- Transaction manager for a single Hibernate SessionFactory (alternative to JTA) -->
<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory">
<ref bean="sessionFactory"/>
</property>
</bean>
<bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor">
<property name="transactionManager" ref="transactionManager"/>?
<property name="transactionAttributes">
<props>
<prop key="*">PROPAGATION_REQUIRED</prop>
<prop key="find*">PROPAGATION_REQUIRED,readOnly</prop>
</props>
</property>
</bean>
<bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
<property name="beanNames">
<value>*Service,*Manager</value>
</property>
<property name="interceptorNames">
<list>
<value>transactionInterceptor</value>
<!-- 此处增加新的Interceptor or advisor or advice -->
</list>
</property>
</bean>
<bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor">
<property name="transactionInterceptor" ref="transactionInterceptor"/>?
</bean>
<bean id="userManager" class="some.package.UserManagerImpl" autoWire="byName"/>
</beans> |