单例模式（兼谈Java读取xml配置文件）

配置文件如下：

<?xml version="1.0" encoding="utf-8" ?> 
<config>
	<db-config>
		<db-driver>com.microsoft.jdbc.sqlserver.SQLServerDriver</db-driver>
		<url>jdbc:microsoft:sqlserver://192.168.1.200:1433;databaseName=user_data</url>
		<user-name>sa</user-name>
		<password>master</password>
	</db-config>
</config>

读取配置文件xml:

package com.bjpowernode.drp.util;

import java.io.InputStream;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
/**
 *采用单例模式来解析sys-config.xml文件
 * @author jsly
 *
 */
public class XMLConfigReader {
	
	/**
	 * 饿汉模式
	 * @param args
	 */
	/*private static XMLConfigReader instance = new XMLConfigReader();
	
	private XMLConfigReader(){	
	}
	public static XMLConfigReader getInstance(){
		return instance;
	}*/
	
	/**
	 * 懒汉模式
	 */
	
	private static XMLConfigReader instance = null;
	
	private XMLConfigReader(){
		SAXReader reader = new SAXReader();
		InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("sys-config.xml");
		try {
			Document document=reader.read(in);
			Element driverElt = (Element)document.selectObject("/config/db-info/driver-name");
			Element urlElt = (Element)document.selectObject("/config/db-info/url");
			Element userNameElt = (Element)document.selectObject("/config/db-info/user-name");
			Element passwordElt = (Element)document.selectObject("/config/db-info/password");
			
			
			String driver = driverElt.getStringValue();
			String url = urlElt.getStringValue();
			String username = userNameElt.getStringValue();
			String password = passwordElt.getStringValue();
			System.out.println(driver);
			
		} catch (DocumentException e) {
			e.printStackTrace();
		}
	}
	
	public static synchronized XMLConfigReader getInstance(){
		if(instance==null){
			instance = new XMLConfigReader();
		}
		return instance;
	}
	
	public static void main(String args[]){
		XMLConfigReader reader = XMLConfigReader.getInstance();
	}
}