????? 在一些项目可能配置文件经常变化，配置文件的类型可能为xml，或者properties文件等，我们系统会自动检测到配置文件的变化，自动更新到内存等中，可以采用Apache 的commons-confiugrations实现相关的功能。如在Tomcat中web.xml配置文件的变化，tomcat会自动加载。

?????? 在commons-configuration中自动保存代码如下：

PropertiesConfiguration config = new PropertiesConfiguration("usergui.properties");
config.setAutoSave(true);
config.setProperty("colors.background", "#000000); // the configuration is saved after this call

?

?自动加载代码如下：

PropertiesConfiguration config = new PropertiesConfiguration("usergui.properties");
config.setReloadingStrategy(new FileChangedReloadingStrategy());

??

?FileChangedReloadingStrategy中重点代码如下：

	public boolean reloadingRequired() {
		if (!reloading) {
			long now = System.currentTimeMillis();
			if (now > lastChecked + refreshDelay) {
				lastChecked = now;
				if (hasChanged())
					reloading = true;
			}
		}
		return reloading;
	}

?

?

?

在web项目写一个servlet类测试属性文件变化，并自动加载。

package com.easyway.app.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.configuration.ConfigurationException;
import org.apache.commons.configuration.PropertiesConfiguration;
import org.apache.commons.configuration.reloading.FileChangedReloadingStrategy;

public class ConfigurationServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public ConfigurationServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		//从上下文中获取
		PropertiesConfiguration propconfig=(PropertiesConfiguration)this.getServletContext().getAttribute("propconfig");
		//打印信息到页面
		String username=propconfig.getString("username");
		
		out.println("用户的名称为：username ="+username);
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		PropertiesConfiguration propconfig=(PropertiesConfiguration)this.getServletContext().getAttribute("propconfig");
		String username=propconfig.getString("username");
		out.println("username ="+username);
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occure
	 */
	public void init() throws ServletException {
		//读取配置的文件的名称
		ServletContext servletContext = this.getServletContext();
		String filename=servletContext.getInitParameter("appconfig");
		System.out.println("filename"+filename);
		//创建自动加载的机制
		PropertiesConfiguration