UML软件工程组织

SpringFramework中的AOP简单使用
 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>

 
  嗯,要想彻底理解Spring的AOP,最好还是多看看源码,开源就是好啊!

 

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