Spring AOP通知实例 – Advice

Spring AOP通知实例 – Advice

Spring AOP(面向方面编程)框架,用于在模块化方面的横切关注点。简单得说,它只是一个拦截器拦截一些过程,例如,当一个方法执行,Spring AOP 可以劫持一个执行的方法,在方法执行之前或之后添加额外的功能。
在Spring AOP中,有 4 种类型通知(advices)的支持:
  • 通知(Advice)之前 - 该方法执行前运行
  • 通知(Advice)返回之后 – 运行后,该方法返回一个结果
  • 通知(Advice)抛出之后 – 运行方法抛出异常后,
  • 环绕通知 – 环绕方法执行运行,结合以上这三个通知。
下面的例子显示Spring AOP 通知如何工作。

简单的 Spring 例子

创建一个简单的客户服务类及一个print方法作为演示。
package com.zyiz.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 – 一个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.zyiz.customer.services.CustomerService">
		<property name="name" value="zyizi Mook Kim" />
		<property name="url" value="http://www.zyiz.net" />
	</bean>

</beans>

执行它

package com.zyiz.netmon;

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

import com.zyiz.customer.services.CustomerService;

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

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

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

		}

	}
}

输出

*************************
Customer name : zyiz Mook Kim
*************************
Customer website : http://www.zyiz.net
*************************
一个简单的Spring项目用来注入(DI)bean和输出一些字符串。

Spring AOP 通知

现在,附加 Spring AOP 建议到上述的客户服务。

1. 之前通知

它会在方法执行之前执行。创建一个实现 MethodBeforeAdvice 接口的类。
package com.zyiz.aop;

import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;

public class HijackBeforeMethod implements MethodBeforeAdvice
{
	@Override
	public void before(Method method, Object[] args, Object target)
		throws Throwable {
	        System.out.println("HijackBeforeMethod : Before method hijacked!");
	}
}
在 bean 配置文件(applicationContext.xml),创建一个 bean 的 HijackBeforeMethod 类,并命名为“customerServiceProxy” 作为一个新的代理对象。
  • ‘target’ – 定义你想拦截的bean。
  • ‘interceptorNames’ – 定义要应用这个代理/目标对象的类(通知)。
<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.zyiz.customer.services.CustomerService">
		<property name="name" value="zyiz Mook Kim" />
		<property name="url" value="http://www.zyiz.net" />
	</bean>

	<bean id="hijackBeforeMethodBean" class="com.zyiz.aop.HijackBeforeMethod" />

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

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

		<property name="interceptorNames">
			<list>
				<value>hijackBeforeMethodBean</value>
			</list>
		</property>
	</bean>
</beans>
再次运行它,现在得到新的 customerServiceProxy bean,而不是原来的CustomerService bean。
package com.zyiz.netmon;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.zyiz.customer.services.CustomerService;

public class App {
	public static void main(String[] args) {
		ApplicationContext appContext = new ClassPathXmlApplicationContext(
				new String[] { "Spring-Customer.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) {

		}

	}
}

输出结果

*************************
HijackBeforeMethod : Before method hijacked!
Customer name : zyiz Mook Kim
*************************
HijackBeforeMethod : Before method hijacked!
Customer website : http://www.zyiz.net
*************************
HijackBeforeMethod : Before method hijacked!
它将运行 HijackBeforeMethod 的 before() 方法,在每个 CustomerService 的方法之前执行。

2.返回后通知

该方法返回一个结果之后它将执行。创建一个实现AfterReturningAdvice接口的类。
package com.zyiz.aop;

import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;

public class HijackAfterMethod implements AfterReturningAdvice
{
	@Override
	public void afterReturning(Object returnValue, Method method,
		Object[] args, Object target) throws Throwable {
	        System.out.println("HijackAfterMethod : After method hijacked!");
	}
}
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.zyiz.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.zyiz.net" />
	</bean>

	<bean id="hijackAfterMethodBean" class="com.zyiz.aop.HijackAfterMethod" />

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

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

		<property name="interceptorNames">
			<list>
				<value>hijackAfterMethodBean</value>
			</list>
		</property>
	</bean>
</beans>
再次运行,输出
*************************
Customer name : zyiz Mook Kim
HijackAfterMethod : After method hijacked!
*************************
Customer website : http://www.zyiz.net
HijackAfterMethod : After method hijacked!
*************************
它将运行 HijackAfterMethod 的 afterReturning()方法,在每次 CustomerService 方法返回结果之后。

3.抛出后通知

它将在执行方法抛出一个异常后。创建一个实现ThrowsAdvice接口的类,并创建一个afterThrowing方法拦截抛出:IllegalArgumentException异常。
package com.zyiz.aop;

import org.springframework.aop.ThrowsAdvice;

public class HijackThrowException implements ThrowsAdvice {
	public void afterThrowing(IllegalArgumentException e) throws Throwable {
		System.out.println("HijackThrowException : Throw exception hijacked!");
	}
}
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.zyiz.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.zyiz.net" />
	</bean>

	<bean id="hijackThrowExceptionBean" class="com.zyiz.aop.HijackThrowException" />

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

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

		<property name="interceptorNames">
			<list>
				<value>hijackThrowExceptionBean</value>
			</list>
		</property>
	</bean>
</beans>
再次运行,输出
*************************
Customer name : zyiz Mook Kim
*************************
Customer website : http://www.zyiz.net
*************************
HijackThrowException : Throw exception hijacked!
它将运行 HijackThrowException 的 afterThrowing()方法,如果 CustomerService 的方法抛出异常。

4.环绕通知

它结合了上面的三个通知,在方法执行过程中执行。创建一个实现了MethodInterceptor接口的类。必须调用“methodInvocation.proceed();” 继续在原来的方法执行,否则原来的方法将不会执行。

package com.zyiz.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()));

		// same with MethodBeforeAdvice
		System.out.println("HijackAroundMethod : Before method hijacked!");

		try {
			// proceed to original method call
			Object result = methodInvocation.proceed();

			// same with AfterReturningAdvice
			System.out.println("HijackAroundMethod : Before after hijacked!");

			return result;

		} catch (IllegalArgumentException e) {
			// same with ThrowsAdvice
			System.out.println("HijackAroundMethod : Throw exception hijacked!");
			throw e;
		}
	}
}
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.zyiz.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.zyiz.net" />
	</bean>

	<bean id="hijackAroundMethodBean" class="com.zyiz.aop.HijackAroundMethod" />

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

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

		<property name="interceptorNames">
			<list>
				<value>hijackAroundMethodBean</value>
			</list>
		</property>
	</bean>
</beans>
再次运行,输出
*************************
Method name : printName
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer name : zyiz Mook Kim
HijackAroundMethod : Before after hijacked!
*************************
Method name : printURL
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer website : http://www.zyiz.net 
HijackAroundMethod : Before after hijacked!
*************************
Method name : printThrowException
Method arguments : []
HijackAroundMethod : Before method hijacked!
HijackAroundMethod : Throw exception hijacked!

它将运行HijackAroundMethod 的 invoke()方法,在每一个 CustomerService 方法执行后。

总结

大部分的 Spring 开发者都只是实现了“环绕通知”,因为它可以对所有通知类型,但更好的做法应该是选择最合适的通知类型来满足要求。
切入点
在这个例子中,在一客户服务类中的所有方法都自动拦截(通知)。但在大多数情况下,可能需要使用切入点和Advisor通过它的方法名拦截它的方法。

下载代码 – 

目录

Spring与其它Web框架集成