（十六）解耦合

<?xml version="1.0" encoding="UTF-8"?>
<beans>
    <bean id="CategoryService" class="com.louis.service.impl.CategoryServiceImpl"></bean>
    <bean id="ProductService" class="com.louis.service.impl.ProductServiceImpl"></bean>
    <bean id="UserService" class="com.louis.service.impl.UserServiceImpl"></bean>

   <bean id="ProductDao" class="com.louis.dao.impl.ProductDaoImpl"/>
   <bean id="UserDao" class="com.louis.dao.impl.UserDaoImpl"/>
   <bean id="CategoryDao" class="com.louis.dao.impl.CategoryDaoImpl"/>
</beans>

package com.louis.utils;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class BeanFactory {
    public static Object getBean(String id) {
        //通过id获取一个指定的实现类
        //1、导入jar包
        
        
        try {
            //2、获取document对象
            Document document = new SAXReader().read(BeanFactory.class.getClassLoader().getResourceAsStream("beans.xml"));
        
            //3、获取指定的bean对象
            Element element = (Element) document.selectSingleNode("//bean[@id=‘"+id+"‘]");
            //4、获取bean对象的class属性
            String value = element.attributeValue("class");
            //5、反射
            return Class.forName(value).newInstance();
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return null;
    }
}

    CategoryService categoryService = (CategoryService) BeanFactory.getBean("CategoryService");