设计模式之工厂模式（3）

奔主题：模拟SpringBean工厂：

先来一个简单的interface：beanFactory

package cn.asto.spring;

public interface BeanFactory {

    public Object getBean();
}

一个最简单的Spring配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<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-3.0.xsd">

  <bean id="v" class="cn.asto.spring.Car">
  </bean>


</beans>

现在我们已经有了配置文件，有了BeanFactroy接口，接下来要做的就是实现一个BeanFactory的接口。
这个实现中做那么几件事情：

• 读入配置文件
• 利用反射将类名字符串实例化成对象
• 将对象注入Map(这个Map就是Spring的Bean容器)
• 通过<key,value>的形式获取对象

---

• 读入配置文件

我这里使用JDOM（利用了XPath语法）:

package cn.asto.spring;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.filter.Filters;
import org.jdom2.input.SAXBuilder;
import org.jdom2.xpath.XPathExpression;
import org.jdom2.xpath.XPathFactory;




public class ClassPathXmlApplicationContext implements BeanFactory{
    
    
 public ClassPathXmlApplicationContext(String xml) throws Exception{
        //读入XML文件
        
        SAXBuilder sax = new SAXBuilder();  
        Document doc = sax.build(ClassPathXmlApplicationContext.class.getClassLoader().getResource(xml));  
        XPathFactory xFactory = XPathFactory.instance();
        XPathExpression<Element> expr = xFactory.compile("/beans/bean", Filters.element());
        List<Element> beans = expr.evaluate(doc);
        for (Element bean : beans) {
            String id = bean.getAttributeValue("id");
            String value = bean.getAttributeValue("class");
    
        }
    }
    @Override
    public Object getBean(String key) {
       
        return null;
    }

}

• 利用反射将类名 字符串实例化成对象
• 将对象注入Map(这个Map就是Spring的Bean容器)
• 通过<key,value>的形式获取对象

  package cn.asto.spring;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import org.jdom2.Document;
  import org.jdom2.Element;
  import org.jdom2.filter.Filters;
  import org.jdom2.input.SAXBuilder;
  import org.jdom2.xpath.XPathExpression;
  import org.jdom2.xpath.XPathFactory;
  public class ClassPathXmlApplicationContext implements BeanFactory{
      
      
      private Map<String,Object> map = new HashMap<String,Object>();
      public ClassPathXmlApplicationContext(String xml) throws Exception{
          //读入XML文件
          
          SAXBuilder sax = new SAXBuilder();  
          Document doc = sax.build(ClassPathXmlApplicationContext.class.getClassLoader().getResource(xml));  
          XPathFactory xFactory = XPathFactory.instance();
          XPathExpression<Element> expr = xFactory.compile("/beans/bean", Filters.element());
          List<Element> beans = expr.evaluate(doc);
          for (Element bean : beans) {
              String id = bean.getAttributeValue("id");
              String value = bean.getAttributeValue("class");
              System.out.println(value);
              //反射实例化对象
              Object o = Class.forName(value).newInstance();
              //经典IOC注入容器
              map.put(id, o);
          }
      }
      @Override
      public Object getBean(String key) {
          //得到Bean
          return map.get(key);
      }
  
  }

测试一下：

package cn.asto.spring;

public class Test {

    public static void main(String args[]) throws Exception {
        BeanFactory factory = new ClassPathXmlApplicationContext("cn/asto/spring/applicationContext.xml");
        Car car = (Car)factory.getBean("v");
        car.move();
    }
}

输出：

car is running.

ok,spring的IOC模拟完成！

哦。忘记把Car类放上来了：

package cn.asto.spring;

public class Car {

    public void move(){
        System.out.println("car is running");
    }
}