Spring之AOP适配器模式

  Spring架构中涉及了很多设计模式，本文来介绍下Spring中在AOP实现时Adapter模式的使用。AOP本质上是Java动态代理模式的实现和适配器模式的使用，关于这两种设计模式的具体介绍烦请参考我之前的文章

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Java代理模式
Java适配器模式(adapter)

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Spring中适配器模式

一、AOP案例

  Spring中的AOP的实现方式有多种，而且每种实现方式中的通知类型也比较多，本文以Spring自带的Schema-base方式中的前置通知来说明。详细介绍移步 Spring之AOP详解

1.相关依赖

<dependency>
	<groupId>org.springframeworkgroupId>
	<artifactId>spring-contextartifactId>
	<version>4.3.21.RELEASEversion>
dependency>
<dependency>
	<groupId>junitgroupId>
	<artifactId>junitartifactId>
	<version>4.12version>
dependency>
<dependency>
	<groupId>aopalliancegroupId>
	<artifactId>aopallianceartifactId>
	<version>1.0version>
dependency>

2.创建目标对象

/**
 * 目标对象 接口
 * @author 波波烤鸭
 * @email [email protected]
 *
 */
public interface SomeService {

	public void doSome();
}

/**
 * 目标对象
 * @author 波波烤鸭
 * @email [email protected]
 *
 */
public class SomeServiceImpl implements SomeService {

	@Override
	public void doSome() {
		System.out.println("目标对象....方法执行了");
	}
}

3.创建通知

/**
 * 前置通知
 * 		需要实现MethodBeforeAdvice接口
 * @author 波波烤鸭
 * @email [email protected]
 *
 */
public class MyMethodBeforeAdvice implements MethodBeforeAdvice {

	/**
	 * method 目标方法
	 * args 目标方法参数列表
	 * target 目标对象
	 */
	@Override
	public void before(Method method, Object[] args, Object target) throws Throwable {
		System.out.println("前置通知执行了....");
	}
}

4.配置文件

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">
	
	<bean id="someServiceImpl" class="com.dpb.service.SomeServiceImpl" >bean>
	
	<bean class="com.dpb.schema.MyMethodBeforeAdvice" id="myMethodBeforeAdvice">bean>

	
	<bean id="proxyFactoryBean" class="org.springframework.aop.framework.ProxyFactoryBean">
		
		<property name="target" ref="someServiceImpl"/>
		
		<property name="interfaces" value="com.dpb.service.SomeService"/>
		
		<property name="interceptorNames" >
			<list>
				<value>myMethodBeforeAdvicevalue>
			list>
		property>
	bean>
beans>

5.测试

@Test
public void test1() {
	ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
	// 注意通过getBean获取增强的代理类！！！
	SomeService some = ac.getBean("proxyFactoryBean",SomeService.class);
	some.doSome();
}

输出:

说明我们配置的前置通知生效了，在目标方法执行之前执行了。

二、适配器应用解析

1.Advice体系结构

说明：

1. advice的类型有:BeforeAdvice,AfterReturningAdvice,ThrowsAdvice等
2. 每个类型的通知都有对应的拦截器

advice	拦截器
BeforeAdvice	MethodBeforeAdviceInterceptor
AfterAdvice	AfterReturningAdviceInterceptor
AfterAdvice	ThrowsAdviceInterceptor

3. Spring容器需要将每个具体的advice封装成对应的拦截器，返回给容器，这里对advice转换就需要用到适配器模式。

2.适配器的实现

  以前置通知为例

2.1Adaptee

  MethodBeforeAdvice

public interface MethodBeforeAdvice extends BeforeAdvice {

	void before(Method method, Object[] args, Object target) throws Throwable;

}

2.2target

  Adapter的接口 AdvisorAdapter

public interface AdvisorAdapter {
	// 判断通知类型是否匹配
	boolean supportsAdvice(Advice advice);
	// 获取对应的拦截器
	MethodInterceptor getInterceptor(Advisor advisor);

}

2.3Adapter

  MethodBeforeAdviceAdapter

class MethodBeforeAdviceAdapter implements AdvisorAdapter, Serializable {

	@Override
	public boolean supportsAdvice(Advice advice) {
		return (advice instanceof MethodBeforeAdvice);
	}

	@Override
	public MethodInterceptor getInterceptor(Advisor advisor) {
		MethodBeforeAdvice advice = (MethodBeforeAdvice) advisor.getAdvice();
		// 通知类型匹配对应的拦截器
		return new MethodBeforeAdviceInterceptor(advice);
	}
}

2.4Client

  代理类通过DefaultAdvisorAdapterRegistry类来注册相应的适配器。

public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {

	private final List<AdvisorAdapter> adapters = new ArrayList<AdvisorAdapter>(3);


	/**
	 * Create a new DefaultAdvisorAdapterRegistry, registering well-known adapters.
	 */
	public DefaultAdvisorAdapterRegistry() {
		// 注册相应的适配器
		registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
		registerAdvisorAdapter(new AfterReturningAdviceAdapter());
		registerAdvisorAdapter(new ThrowsAdviceAdapter());
	}

	// 包装类  将通知转换为了 对应的适配器
	// 本案例中将 MyMethodBeforeAdvice转换为了MethodBeforeAdviceAdapter
	@Override
	public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {
		if (adviceObject instanceof Advisor) {
			return (Advisor) adviceObject;
		}
		if (!(adviceObject instanceof Advice)) {
			throw new UnknownAdviceTypeException(adviceObject);
		}
		Advice advice = (Advice) adviceObject;
		if (advice instanceof MethodInterceptor) {
			// So well-known it doesn't even need an adapter.
			return new DefaultPointcutAdvisor(advice);
		}
		for (AdvisorAdapter adapter : this.adapters) {
			// Check that it is supported.
			if (adapter.supportsAdvice(advice)) {
				return new DefaultPointcutAdvisor(advice);
			}
		}
		throw new UnknownAdviceTypeException(advice);
	}
	// 获取适配器对应的所有的拦截器
	@Override
	public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
		List<MethodInterceptor> interceptors = new ArrayList<MethodInterceptor>(3);
		Advice advice = advisor.getAdvice();
		if (advice instanceof MethodInterceptor) {
			interceptors.add((MethodInterceptor) advice);
		}
		for (AdvisorAdapter adapter : this.adapters) {
			if (adapter.supportsAdvice(advice)) {
								// 调用了适配器的方法
				interceptors.add(adapter.getInterceptor(advisor));
			}
		}
		if (interceptors.isEmpty()) {
			throw new UnknownAdviceTypeException(advisor.getAdvice());
		}
		return interceptors.toArray(new MethodInterceptor[interceptors.size()]);
	}

	@Override
	public void registerAdvisorAdapter(AdvisorAdapter adapter) {
		this.adapters.add(adapter);
	}
}

本案例中的适配器中的方法是

@Override
public Object invoke(MethodInvocation mi) throws Throwable {
	// 前置通知方法
	this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
	// 目标对象的方法
	return mi.proceed();
}

~ 好了 AOP中的适配器的分析就到此了。关于AOP中的代理的实现抽空再来分析