| AOP作為Spring這個(gè)輕量級(jí)的容器中很重要的一部分，得到越來(lái)越多的關(guān)注，Spring的Transaction就是用AOP來(lái)管理的，今天就通過(guò)簡(jiǎn)單的例子來(lái)看看Spring中的AOP的基本使用方法。
首先確定將要Proxy的目標(biāo)，在Spring中默認(rèn)采用JDK中的dynamic proxy，它只能夠?qū)崿F(xiàn)接口的代理，如果想對(duì)類(lèi)進(jìn)行代理的話(huà)，需要采用CGLIB的proxy。顯然，選擇“編程到接口”是更明智的做法，下面是將要代理的接口：
public interface FooInterface {
public void printFoo();
public void dummyFoo();
}
以及其一個(gè)簡(jiǎn)單的實(shí)現(xiàn)：
public class FooImpl implements FooInterface {
public void printFoo() {
System.out.println("In FooImpl.printFoo");
}
public void dummyFoo() {
System.out.println("In FooImpl.dummyFoo");
}
}
接下來(lái)創(chuàng)建一個(gè)Advice，在Spring中支持Around,Before,After returning和Throws四種Advice，這里就以簡(jiǎn)單的Before Advice舉例：
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，剩下的就是如何去裝配它們了，首先利用ProxyFactory以編程方式實(shí)現(xiàn)，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();
}
}
現(xiàn)在執(zhí)行程序，神奇的結(jié)果就出現(xiàn)了：
In PrintBeforeAdvice
In FooImpl.printFoo
In PrintBeforeAdvice
In FooImpl.dummyFoo
雖然這樣能體會(huì)到Spring中AOP的用法，但這決不是值得推薦的方法，既然使用了Spring，在ApplicationContext中裝配所需要 的bean才是最佳策略，實(shí)現(xiàn)上面的功能只需要寫(xiě)個(gè)簡(jiǎn)單的applicationContext就可以了，如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www./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>
當(dāng)然，main中的代碼也要進(jìn)行相應(yīng)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();
}
現(xiàn)在運(yùn)行一下，結(jié)果將和上面的運(yùn)行結(jié)果完全一樣，這樣是不是更優(yōu)雅？當(dāng)需要更改實(shí)現(xiàn)時(shí)，只需要修改配置文件就可以了，程序中的代碼不需任何改動(dòng)。
但是，這時(shí)候會(huì)發(fā)現(xiàn)被proxy的object中的所有方法調(diào)用時(shí)都將運(yùn)行advice中的before，這顯然不能滿(mǎn)足絕大多數(shù)情況下的需要，此時(shí)，只 需借用Advisor就可以了，當(dāng)然要在Advisor中利用pattern設(shè)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./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>
主程序不需進(jìn)行任何修改，運(yùn)行結(jié)果已經(jīng)變樣了：
In PrintBeforeAdvice
In FooImpl.printFoo
In FooImpl.dummyFoo
至此，應(yīng)該已經(jīng)理解了Spring中AOP的使用方法，當(dāng)然Spring中AOP最重要的應(yīng)用是Transaction Manager，舉個(gè)這方面的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>
嗯，要想徹底理解Spring的AOP，最好還是多看看源碼，開(kāi)源就是好??！
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