Spring学习(十六)----- Spring AOP实例(Pointcut(切点),Advisor)

在上一个Spring AOP通知的例子，一个类的整个方法被自动拦截。但在大多数情况下，可能只需要一种方式来拦截一个或两个方法，这就是为什么引入'切入点'的原因。它允许你通过它的方法名来拦截方法。另外，一个“切入点”必须具有“Advisor' 相关联。

在Spring AOP中，有三个非常专业术语- Advices, Pointcut , Advisor，把它在非官方的方式...

• Advice(通知) – 指示之前或方法执行后采取的行动。
• Pointcut(切点)– 指明哪些方法应该拦截，通过方法的名称或正则表达式模式。
• Advisor – 分组"通知"和”切点“成为一个单元，并把它传递到代理工厂对象。

再次回顾上一个 Spring AOP通知的例子。

File : CustomerService.java

package com.yiibai.customer.services;

public class CustomerService
{
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName(){
        System.out.println("Customer name : " + this.name);
    }
    
    public void printURL(){
        System.out.println("Customer website : " + this.url);
    }
    
    public void printThrowException(){
        throw new IllegalArgumentException();
    }
    
}

File : applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yong Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackAroundMethodBeanAdvice" class="com.yiibai.aop.HijackAroundMethod" />

    <bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackAroundMethodBeanAdvice</value>
            </list>
        </property>
    </bean>
</beans>

File : HijackAroundMethod.java

package com.yiibai.aop;

import java.util.Arrays;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class HijackAroundMethod implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation methodInvocation) throws Throwable {

        System.out.println("Method name : "
                + methodInvocation.getMethod().getName());
        System.out.println("Method arguments : "
                + Arrays.toString(methodInvocation.getArguments()));

        System.out.println("HijackAroundMethod : Before method hijacked!");

        try {
            Object result = methodInvocation.proceed();
            System.out.println("HijackAroundMethod : Before after hijacked!");

            return result;

        } catch (IllegalArgumentException e) {

            System.out.println("HijackAroundMethod : Throw exception hijacked!");
            throw e;
        }
    }
}

执行它

package com.yiibai.common;

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

import com.yiibai.customer.services.CustomerService;

public class App {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext(
                new String[] { "applicationContext.xml" });

        CustomerService cust = (CustomerService) appContext
                .getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {
        }
    }
}

输出

*************************
Method name : printName
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer name : Yiibai
HijackAroundMethod : Before after hijacked!
*************************
Method name : printURL
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer website : http://www.yiibai.com
HijackAroundMethod : Before after hijacked!
*************************
Method name : printThrowException
Method arguments : []
HijackAroundMethod : Before method hijacked!
HijackAroundMethod : Throw exception hijacked!

客户服务类的全部方法被截获。后来，我们展示如何使用“切入点”只拦截printName()方法。

切入点的例子

可以通过以下两种方式相匹配的方法：

1. 名称匹配
2. 正则表达式匹配

1.切入点 - 名称匹配的例子

通过“切入点”和“advisor”拦截printName()方法。创建NameMatchMethodPointcut切入点bean，并提出要在“mappedName”属性值来拦截方法名。

<bean id="customerPointcut"
        class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName" />
    </bean>

创建 DefaultPointcutAdvisor 通知 bean，通知和切入点相关联。

<bean id="customerAdvisor"
        class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut" />
        <property name="advice" ref="hijackAroundMethodBeanAdvice" />
    </bean>

更换代理“interceptorNames”到“customerAdvisor”（它是“hijackAroundMethodBeanAdvice”）。

<bean id="customerServiceProxy"
        class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />
        
        <property name="interceptorNames">
            <list>
                <value>customerAdvisor</value>
            </list>
        </property>
    </bean>

全部bean配置文件

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yiibai" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackAroundMethodBeanAdvice" class="com.yiibai.aop.HijackAroundMethod" />

    <bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>customerAdvisor</value>
            </list>
        </property>
    </bean>

    <bean id="customerPointcut" 
                class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName" />
    </bean>

    <bean id="customerAdvisor" 
                 class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut" />
        <property name="advice" ref="hijackAroundMethodBeanAdvice" />
    </bean>

</beans>

再次运行，输出

*************************
Method name : printName
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer name : Yiibai
HijackAroundMethod : Before after hijacked!
*************************
Customer website : http://www.yiibai.com
*************************

现在，只拦截 printName()方法。

PointcutAdvisor

Spring提供了PointcutAdvisor类来保存工作声明advisor和切入点到不同的bean，可以使用 NameMatchMethodPointcutAdvisor 两者结合成一个 bean。

<bean id="customerAdvisor"
        class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor">
    
        <property name="mappedName" value="printName" />
        <property name="advice" ref="hijackAroundMethodBeanAdvice" />
    
    </bean>

2.切入点 - 正则表达式的例子

也可以通过使用正则表达式匹配切入点方法的名称  – RegexpMethodPointcutAdvisor.

<bean id="customerAdvisor"
        class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
        <property name="patterns">
            <list>
                <value>.*URL.*</value>
            </list>
        </property>

        <property name="advice" ref="hijackAroundMethodBeanAdvice" />
    </bean> 

现在，它拦截方法名称中有“URL”的方法。在实践中，可以用它来管理DAO层，声明“.*DAO.*” 拦截所有的DAO类来支持事务。