/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
public abstract class Config {
    /**
     * the  supper  class  for  parse  the xml  files

    */
    protected Element root;

    protected void init(ServletContext sctx, String xmlFile) throws Exception {
        InputStream  is=null;
        try{
            is=sctx.getResourceAsStream(xmlFile);
            DocumentBuilderFactory  factory=DocumentBuilderFactory.newInstance();
            DocumentBuilder  builder=factory.newDocumentBuilder();
            Document  doc=builder.parse(new InputSource(is));
            root=doc.getDocumentElement();
            System.out.println("root:   "+root );
           
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            if(is!=null){
                is.close();
            }
        }
    }
    protected  String getElementText(Element parent,String name){
        NodeList  nodeList=parent.getElementsByTagName(name);
        if(nodeList.getLength()==0){
            return null;
        }
       
        Element  element=(Element)nodeList.item(0);
        StringBuffer sb=new StringBuffer();
        for(Node child=element.getFirstChild();child!=null;child=child.getNextSibling()){
            if(child.getNodeType()==Node.TEXT_NODE){
                sb.append(child.getNodeValue());
            }
        }
        return sb.toString().trim();

    }
    protected  void cleanup(){
        root=null;
    }
}
(三)    定义解析我们自定义配置文件（XML文件）的 抽象类，此处我们定义了DataSourceConfig.java,文件内容如下：
/*
 * Created on 2005-8-29
 *
 *reading  the  JDBC  datasource  properties from  xml  files
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package zy.pro.wd.xml;

import javax.sql.DataSource;
import javax.servlet.ServletContext;

/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
public abstract class DataSourceConfig extends Config {
    private static final String DATABASE_USER = "DatabaseUser";

    private static final String DATABASE_PASSWORD = "DatabasePassword";

    private static final String SERVER_NAME = "ServerName";

    private static final String DATABASE_NAME = "DatabaseName";

    private static final String SERVER_PORT = "ServerPort";
   
   
    protected  DataSource ds;
    protected String databaseUser;
    protected String databasePassword;
    protected String serverName;
    protected String  portNumber;
    protected String databaseName;
   
   
    public void  init(ServletContext sctx,String xmlFile) throws Exception{
        super.init(sctx,xmlFile);
        databaseUser=this.getElementText(root,DATABASE_USER);
        System.out.println("< br>databaseUser:           "+databaseUser);
        databasePassword=this.getElementText(root,DATABASE_PASSWORD);
        System.out.println("< br>databasePassword:         "+databasePassword);

        databaseName=this.getElementText(root,DATABASE_NAME);
        System.out.println("< br>databaseName:       "+databaseName);
        serverName=this.getElementText(root,SERVER_NAME);
        System.out.println("< br>serverName:         "+serverName);
        portNumber=this.getElementText(root,SERVER_PORT);
        System.out.println("< br>portNumber:           "+portNumber);
    }
    public  DataSource  getDataSource(){
        return ds;
    }
}
(四)    定义我们解析数据源配置文件的实现类
（1）    定义解析MS SQL 数据源的实现类MSSQLConfig.java.内容如下：
/*
 * Created on 2005-8-31
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package zy.pro.wd.xml;

import javax.servlet.ServletContext;

import org.apache.commons.dbcp.BasicDataSource;
import com.microsoft.jdbc.base.BaseConnectionPool;

/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
public class MSSQLConfig extends DataSourceConfig {
   
    private static final String MAX_CONNECTIONS = "MaxConnections";

    public void init(ServletContext ctx, String xmlFile) throws Exception {
        super.init(ctx, xmlFile);
        String databaseURL = "jdbc:microsoft:sqlserver://" + this.serverName + ":"
                + this.portNumber + ";databaseName=" + this.databaseName;
        System.out.println("< br> databaseURL :        " + databaseURL);
        ds = new BasicDataSource();
    /*
    *此处使用的是apache 给提供的DBCP数据源

    */
        System.out.println("< br>ds:           " + ds);
        ((BasicDataSource) ds).setUrl(databaseURL);
        ((BasicDataSource) ds).setUsername(this.databaseUser);
        ((BasicDataSource) ds).setPassword(this.databasePassword);

        try {
            int maxConnections = Integer.parseInt(this.getElementText(root,
                    MAX_CONNECTIONS));
            ((BasicDataSource) ds).setMaxActive(maxConnections);
        } catch (Exception e) {
            e.printStackTrace();
        }
        this.cleanup();

    }
}
（2）    定义实现解析oracle数据源的实现类OracleConfig.java,内容如下：
/*
 * Created on 2005-8-29
 *
 *parse  the  xml  file  of  the  oracle  configure
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package zy.pro.wd.xml;

import javax.sql.DataSource;
import javax.servlet.ServletContext;
import oracle.jdbc.pool.OracleConnectionCacheImpl;

/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
public class OracleConfig extends DataSourceConfig {

    private static final String MAX_CONNECTIONS = "MaxConnections";

    public void init(ServletContext ctx, String xmlFile) throws Exception {
        super.init(ctx, xmlFile);
        String databaseURL = "jdbc:oracle:thin:@" + this.serverName + ":"
                + this.portNumber + ":" + this.databaseName;

        System.out.println("< br> databaseURL :        " + databaseURL);
    /*
    *此处使用的Oracle给提供的数据源，也可以使用DBCP数据源
    */
        ds = new OracleConnectionCacheImpl();
        System.out.println("< br>ds:           " + ds);
        ((OracleConnectionCacheImpl) ds).setURL(databaseURL);
        ((OracleConnectionCacheImpl) ds).setUser(this.databaseUser);
        ((OracleConnectionCacheImpl) ds).setPassword(this.databasePassword);

        try {
            int maxConnections = Integer.parseInt(this.getElementText(root,
                    MAX_CONNECTIONS));
            ((OracleConnectionCacheImpl) ds).setMaxLimit(maxConnections);
        } catch (Exception e) {
            e.printStackTrace();
        }
        this.cleanup();

    }

}
(五)    编写Context的侦听器
（1）    编写MSSQL 数据源的侦听器类：MSSQLDataSourceListener.java,内容如下：
/*
 * Created on 2005-8-30
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package zy.pro.wd.listener;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.naming.*;
import zy.pro.wd.xml.*;

/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
public class MSSQLDataSourceListener implements ServletContextListener {
    /*
     * this  is  a  listener   class  for  mssql  datasource  registing  in  the  web.xml

*
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package zy.pro.wd.listener;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.naming.*;
import zy.pro.wd.xml.*;

/**
 * @author zhangyi
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
public class OracleDataSourceListener implements ServletContextListener {

    public  static String  JNDI_NAME;
    private ServletContext sctx;
   
    public void contextInitialized(ServletContextEvent event){
        sctx=event.getServletContext();
        System.out.println("< br>sctx  in listener :        "+sctx);
        try{
            Class  cls=Class.forName(sctx.getInitParameter("OracleDataSourceConfig"));
           
            OracleConfig  cfig=(OracleConfig)cls.newInstance();
            System.out.println("< br>OracleConfig:   "+cfig);
       
            cfig.init(sctx,sctx.getInitParameter("OracleDataSourceConfigXML"));
           
            InitialContext ctx=new InitialContext();
            JNDI_NAME=sctx.getInitParameter("OracleDataSourceConfig");
            System.out.println("oracle  DataSouce  JNDI_NAME:     "+JNDI_NAME);
            ctx.bind(JNDI_NAME,cfig.getDataSource());
           
        }catch(Exception e){
            sctx.log("DataSourceListener",e);

            e.printStackTrace();
        }
    }
    /* (non-Javadoc)
     * @see javax.servlet.ServletContextListener#contextDestroyed(javax.servlet.ServletContextEvent)
     */
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        sctx=null;
    }
}

(六)    在Web.xml中配置数据源，配置代码如下：

    < !--  configure  the  oracle  datasource  by  XML  files  -->
    < context-param>
        < param-name>OracleDataSourceConfigXML< /param-name>
        < param-value>/WEB-INF/oracle.xml< /param-value>
    < /context-param>
    < context-param>
        < param-name>OracleDataSourceConfig< /param-name>
        < param-value>zy.pro.wd.xml.OracleConfig< /param-value>
    < /context-param>
    < listener>
        < listener-class>zy.pro.wd.listener.OracleDataSourceListener< /listener-class>
    < /listener>
   
    < !-- configure  the  MSSQL  datasource  using  XML files -->
    < context-param>
        < param-name>MSSQLDataSourceConfigXML< /param-name>
        < param-value>/WEB-INF/mssql.xml< /param-value>
    < /context-param>
    < context-param>
        < param-name>MSSQLDataSourceConfig< /param-name>
        < param-value>zy.pro.wd.xml.MSSQLConfig< /param-value>
    < /context-param>
    < listener>
        < listener-class>zy.pro.wd.listener.MSSQLDataSourceListener< /listener-class>
    < /listener>

(七)    测试配置是否成功，我们在jsp中测试
（1）    测试MS SQL SERVER的JSP页面mssqlDataSourceDemo.jsp,代码如下：
< %@ page language="java" import="javax.naming.*" %>

< %@ page language="java" import="java.util.*" %>
< %@ page language="java" import="java.sql.*" %>
< %@ page language="java" import="javax.sql.*" %>
< %@ page import ="zy.pro.wd.listener.MSSQLDataSourceListener"%>