spring-aop源码解析：declare-parent

spring-aop源码解析：declare-parent

借助Aop的引入，我们可以不侵入性的改变现有的实现，对现有实现类无侵入性的增加方法。

1、举个例子：Einstein从小爱发明，是个发明家，我们创建一个Einstein类，实现发明家（Inventor）接口。随着知识的积累，Einstein也成为了数学家，我们可以在不改变Eistein类的前提下使用declare-parent为Eistein添加数学家的特性。

package com.zhc.aop.declareparent;public interface Inventor {public void invent();}

 

package com.zhc.aop.declareparent;public class Einstein implements Inventor {@Overridepublic void invent() {// TODO Auto-generated method stubSystem.out.println("create new thing");}}

 

package com.zhc.aop.declareparent;public interface Mathematician {public void calculate();}

 

package com.zhc.aop.declareparent;public class MathematicianImpl implements Mathematician {@Overridepublic void calculate() {System.out.println("calculate the result of the formulae");}}

 

spring-aop.xml配置declare-parent，为Einstein添加特性

 <bean id="Einstein" class="com.zhc.aop.declareparent.Einstein"></bean> <aop:config> <aop:aspect> <aop:declare-parents types-matching="com.zhc.aop.declareparent.Einstein"  implement-interface="com.zhc.aop.declareparent.Mathematician" default-impl="com.zhc.aop.declareparent.MathematicianImpl"/> </aop:aspect> </aop:config>

 测试类：

import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class DeclareParentTest {@Testpublic void testEinstein(){String xml = "classpath:spring-aop.xml";    ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { xml });    Inventor inventor = (Inventor) context.getBean("Einstein");    inventor.invent();    Mathematician mathematician = (Mathematician) context.getBean("Einstein");    mathematician.calculate();    }}

 

2、源码分析

 ConfigBeanDefinitionParser同过parseDeclareParents方法来解析declare-parents 标签

/** * Parse a '<code>declare-parents</code>' element and register the appropriate * DeclareParentsAdvisor with the BeanDefinitionRegistry encapsulated in the * supplied ParserContext. * 解析一个declare-parents标签，并且使用BeanDefinitionRegistry注册一个合适的DeclareParentsAdvisor * BeanDefinitionRegistry封装在了parserContext中 */private AbstractBeanDefinition parseDeclareParents(Element declareParentsElement, ParserContext parserContext) {//BeanDefinition是由BeanDefinitionBuilder创建的，在builder创建BeanDefinition之前，//要设置根bean定义（rootBeanDefinition），它指定了bean的Class//declare-parents标签内部实现方式是创建了一个切面BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(DeclareParentsAdvisor.class);//添加构造函数的参数//这里的构造函数是指DeclareParentsAdvisor的构造函数builder.addConstructorArgValue(declareParentsElement.getAttribute(IMPLEMENT_INTERFACE));//新加的接口builder.addConstructorArgValue(declareParentsElement.getAttribute(TYPE_PATTERN));//类型匹配表达式String defaultImpl = declareParentsElement.getAttribute(DEFAULT_IMPL);//新加接口的默认实现String delegateRef = declareParentsElement.getAttribute(DELEGATE_REF);//新加接口的实现引用//新接口实现类和实现引用指定一个即可，且只能指定一个if (StringUtils.hasText(defaultImpl) && !StringUtils.hasText(delegateRef)) {builder.addConstructorArgValue(defaultImpl);}else if (StringUtils.hasText(delegateRef) && !StringUtils.hasText(defaultImpl)) {builder.addConstructorArgReference(delegateRef);}else {parserContext.getReaderContext().error("Exactly one of the " + DEFAULT_IMPL + " or " + DELEGATE_REF + " attributes must be specified",declareParentsElement, this.parseState.snapshot());}//获取bean定义AbstractBeanDefinition definition = builder.getBeanDefinition();definition.setSource(parserContext.extractSource(declareParentsElement));//注册bean定义parserContext.getReaderContext().registerWithGeneratedName(definition);return definition;}