package com.DesignPatterns.ad.factory6;

public interface BeanFactory {
    Object getBean(String id);
}

package com.DesignPatterns.ad.factory6;

public interface Moveable {
    void run();
}

package com.DesignPatterns.ad.factory6;


public class Car implements Moveable{
    
    
 
public void run() {
        System.out.println("冒著煙奔跑中car.......");
    }
}

package com.DesignPatterns.ad.factory6;

public class Train implements Moveable{

    @Override
    public void run() {
        System.out.println("小火車嗚嗚嗚");
    }
    
}

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans>

  <bean id="v" class="com.DesignPatterns.ad.factory6.Train">
  
  </bean>
   <bean id="n" class="com.DesignPatterns.ad.factory6.Car">
  
  </bean>
  <!--  //v=com.bjsxt.spring.factory.Car  -->


</beans>

package com.DesignPatterns.ad.factory6;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.jdom.Document;
import org.jdom.Element;
import org.jdom.input.SAXBuilder;
import org.jdom.xpath.XPath;

public class ClassPathXmlApplicationContext implements BeanFactory  {
    private Map<String, Object> container = new HashMap<String, Object>();
    
    public ClassPathXmlApplicationContext(String fileName) throws Exception{
        //解析xml的不用太關心這裡。主要是理解spring的bean的工廠機制。
        SAXBuilder sb = new SAXBuilder();
          Document doc = sb.build(this.getClass().getClassLoader()
                  .getResourceAsStream(fileName));
          Element root = doc.getRootElement();
          List list = XPath.selectNodes(root, "/beans/bean");
          System.out.println(list.size());
          
          for (int i = 0; i < list.size(); i++) { 
           Element bean = (Element) list.get(i);
           String id = bean.getAttributeValue("id");
           String clazz = bean.getAttributeValue("class");
           Object o = Class.forName(clazz).newInstance();
           //最關鍵的就是在這把它的id和物件全部放到一個map中來，所謂的容器其實就是一個map，
           //當專案啟動的時候就會把所有的在xml配置檔案中配置的物件全部都載入一遍，等用到的時候就會從map中取出來
           //
           container.put(id, o);
           System.out.println(id + " " + clazz);
          }

    }
    
    @Override
    public Object getBean(String id) {
        
        return container.get(id);
    }

}

package com.DesignPatterns.ad.factory6;

import java.io.IOException;
import java.util.Properties;

public class Test {

    /**
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws Exception {
        BeanFactory f = new ClassPathXmlApplicationContext("com/DesignPatterns/ad/factory6/applicationContext.xml");
        //這裡就和我們平常用的set注入進來的目的是一樣的。
        Object o1 = f.getBean("v");
        Moveable m = (Moveable)o1;
        m.run();
        Object o2 = f.getBean("n");
        Moveable n = (Moveable)o2;
        n.run();
    }

}

 只需要修改配置檔案就可以實現注入的邏輯。建立物件是不是變的更加簡單了好多。

它的原理就是通過獲取xml中class的字串的路徑,然後在通過反射獲取物件，最後在使用這個物件，這樣就免去了來回new物件產生的不必要的剪不斷理還亂的物件的依賴的關係。