DaoFactory的问题！求教！
package org.yeeku.factory;

import org.yeeku.dao.base.Dao;
import org.yeeku.consttool.*;

import org.dom4j.*;
import org.dom4j.io.*;

import java.util.*;
import java.io.*;


public class DaoFactory
{
private Map<String , Dao> daoMap = new HashMap<String , Dao>();

private static DaoFactory df;

private DaoFactory()throws Exception
{
Document doc = new SAXReader().read(new File(ConstantsUtil.realPath + "\\daoContext.xml"));
Element root = doc.getRootElement();
List el = root.elements();
for (Iterator it = el.iterator();it.hasNext() ; )
{
Element em = (Element)it.next();
String id = em.attributeValue("id");
String impl = em.attributeValue("class");
Class implClazz = Class.forName(impl);
Dao d = (Dao)implClazz.newInstance();
daoMap.put(id , d);
}
}

public static DaoFactory instance()throws Exception
{
if (df == null)
{
df = new DaoFactory();
}
return df;
}

public Dao getDao(String id)
{
return daoMap.get(id);
}
}
这段代码是STRUTS2和HIBERNATE里的，但我实在是看不出来他的作用，请各位高手指教！
最好能把每句代码，为什么说一下！好的话，我在加分！多谢！


[解决办法]
//这个好像是自己手动的去读XML文件
package org.yeeku.factory;

import org.yeeku.dao.base.Dao;
import org.yeeku.consttool.*;

import org.dom4j.*;
import org.dom4j.io.*;

import java.util.*;
import java.io.*;


public class DaoFactory
{
private Map <String , Dao> daoMap = new HashMap <String , Dao>();

private static DaoFactory df;

private DaoFactory()throws Exception
{
Document doc = new SAXReader().read(new File(ConstantsUtil.realPath + "\\daoContext.xml")); //读XML文件
Element root = doc.getRootElement(); //得到xml根结点
List el = root.elements(); //得到根结点下的所有元素集合
for (Iterator it = el.iterator();it.hasNext() ; ) //读取某一子结点下的结点
{
Element em = (Element)it.next();
String id = em.attributeValue("id"); //得到属性结点 名为ID
String impl = em.attributeValue("class"); //得到属性结点 名为class
Class implClazz = Class.forName(impl); //加载驱动属性结点 名为class的值
Dao d = (Dao)implClazz.newInstance(); //创建这个类的实例
daoMap.put(id , d); //放入Map中
}
}




public static DaoFactory instance()throws Exception
{
if (df == null)
{
df = new DaoFactory();
}
return df;
}



public Dao getDao(String id)
{
return daoMap.get(id);
}
}
[解决办法]

Java code

package org.yeeku.factory;import org.yeeku.dao.base.Dao;import org.yeeku.consttool.*;import org.dom4j.*;import org.dom4j.io.*;import java.util.*;import java.io.*;public class DaoFactory{    private Map <String , Dao> daoMap = new HashMap <String , Dao>();    private static DaoFactory df;    private DaoFactory()throws Exception    {//读取xml文件        Document doc = new SAXReader().read(new File(ConstantsUtil.realPath + "\\daoContext.xml"));        Element root = doc.getRootElement();        List el =  root.elements();        //循环遍历所有xml元素        for (Iterator it = el.iterator();it.hasNext() ; )        {            Element em = (Element)it.next();            //获得id,class属性            String id = em.attributeValue("id");            String impl = em.attributeValue("class");            //通过反射加载class属性指定的类            Class implClazz = Class.forName(impl);            //实例话该类，该类一定要实现Dao接口。            Dao d = (Dao)implClazz.newInstance();            //把id作为key,dao作为value放到map里面            daoMap.put(id , d);                   }    }    //没有实例话就先实例化，然后就返回factory实例，否则直接返回facotory实例    public static DaoFactory instance()throws Exception    {        if (df == null)        {            df = new DaoFactory();        }        return df;    }    //根据id 来取dao，对应的语句->>>daoMap.put(id , d);    public Dao getDao(String id)    {        return daoMap.get(id);    }} 
 
[解决办法]
楼上已经解释的很清楚了!
建议楼主:
  1,了解下工厂模式;
  2,此处就是通过配置得到DAO类的实例对象;