Java 实现自动监听并更新配置文件内容 （转自高手）

Java 实现自动监听并更新配置文件内容

Posted on 2007-02-28 11:49 广氏波罗猫 Kelvin Wong 阅读(1096) 评论(0) 编辑 收藏

自动监听器 PropertiesListener

package org.stephencat.listener;

import javax.servlet. * ;

/**
* 自动监听器
* @author stephen
*
*/
public class PropertiesListener implements ServletContextListener {

/**
* 自动监听时钟
*/
private PropertiesTimer rt = null ;

public void contextInitialized(ServletContextEvent event) {
String status = " Properties listener start . " ;
event.getServletContext().log(status);
System.out.println(status);

// 激活自动监听时钟
rt = new PropertiesTimer( 15 , event.getServletContext());
rt.start();
}

public void contextDestroyed(ServletContextEvent event) {
String status = " Properties listener stop . " ;
event.getServletContext().log(status);
System.out.println(status);

// 停止自动监听时钟
if (rt != null ) {
rt.stop();
}
}
}

自动监听时钟 PropertiesTimer

package org.stephencat.listener;
import java.util. * ;
import javax.servlet. * ;


/**
* 自动监听时钟
* @author stephen
*
*/
public class PropertiesTimer {

private final Timer timer = new Timer();
private final int sec;
private ServletContext context = null ;

public PropertiesTimer( int seconds, ServletContext context) {
sec = seconds;
this .context = context;
}

/**
* 启动自动监听任务
*/
public void start() {

// 取得当前日期时间
Date date = new Date();

// 执行自动监听计划
timer.schedule( new PropertiesTask( this .context), date, sec * 1000 );
}

/**
* 停止自动监听任务
*/
public void stop() {
timer.cancel();

}

}

自动监听任务 PropertiesTask

package org.stephencat.listener;
import java.io.IOException;
import java.io. * ;
import java.util. * ;

import javax.servlet. * ;
/**
* 自动监听任务
* @author stephen
*
*/
public class PropertiesTask extends TimerTask {

private ServletContext context = null ;
/**
* 配置文件的最后更新时间
*/
private long lastModified = 0 ;

/**
* 构造一个自动更新任务
* @param context
*/
public PropertiesTask(ServletContext context){
this .context = context;
System.out.println( " A task instance is created now. " ); // 任务在整个 application 周期内只创建一次。
}

/**
* 每次执行任务时显示一个随机数。
*/
public void todoTestRandom(){
System.out.println( " Task running " );
context.setAttribute( " random " , String.valueOf(Math.random()));
System.out.println((String)context.getAttribute( " random " ));
}

/**
* 监听配置文件是否被更新。
*/
public void todoTestFileStatus(){
System.out.println( " Getting file status " );
System.out.println( this .isFileUpdated( " WEB-INF/platforms/test.properties " ));
}

/**
* 监听配置文件是否被更新，自动更新文件中的配置项存储到 application 变量中。
*/
public void todo(){
String filename = " WEB-INF/platforms/test.properties " ;
if ( this .isFileUpdated(filename)){

System.out.println( " Getting properties " );
try {
this .loadProperties( " test " , filename);
} catch (IOException ioe){
System.err.println(ioe.getMessage());
}
}
System.out.println( " Test value is: " + this .getTestProperty( " name " ));
}

public void run() {
todoTestRandom();
todo();
// todo();
}

/**
* 判断物理文件是否已被更新
* @param filename 物理文件名
* @return 是 true 否 false
*/
private boolean isFileUpdated(String filename){
File file = new File(context.getRealPath(filename));
if (file.isFile()){
long lastUpdateTime = file.lastModified();
if (lastUpdateTime > this .lastModified){
System.out.println( " The properties file was modified. " );
this .lastModified = lastUpdateTime;
return true ;
} else {
System.out.println( " The properties file was not modified. " );
return false ;
}
} else {
System.out.println( " The path does not point to a file. " );
return false ;
}
}

/**
* 获取配置文件
* @param key
* @param filename
* @return
*/
public void loadProperties(String key, String filename) throws IOException{
Properties prop = new Properties();
InputStream stream = context.getResourceAsStream(filename);
prop.load(stream);
if (stream != null ){
stream.close();
}
context.setAttribute(key, prop);
}

/**
* 从 application 取配置项的值
* @param key 配置项的键名
* @return 配置项的值
*/
public String getTestProperty(String key){
Properties prop = (Properties)context.getAttribute( " test " );
if (prop == null ){
return null ;
} else {
return (String)prop.get(key);
}
}

}

web.xml 配置

xml version="1.0" encoding="GB18030" ?>
< web-app version ="2.4"
xmlns ="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation ="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" >

< listener >
< listener-class > org.stephencat.listener.PropertiesListener listener-class >
listener >
web-app >

在 WEB-INF 目录下增加 platforms/test.properties 文件

name = Stephen Wong

启动应用服务器，控制台输出如下：

11:30:31,000 INFO [TomcatDeployer] undeploy, ctxPath=/ServerTest, warUrl=.../deploy/ServerTest.war/
11:30:31,000 INFO [[/ServerTest]] Properties listener stop .
11:30:31,000 INFO [STDOUT] Properties listener stop .
11:30:31,046 INFO [TomcatDeployer] deploy, ctxPath=/ServerTest, warUrl=.../deploy/ServerTest.war/
11:30:31,359 INFO [[/ServerTest]] Properties listener start .
11:30:31,359 INFO [STDOUT] Properties listener start .
11:30:31,375 INFO [STDOUT] A task instance is created now.
11:30:31,390 INFO [STDOUT] Task running
11:30:31,390 INFO [STDOUT] 0.9924364802139768
11:30:31,390 INFO [STDOUT] The properties file was modified.
11:30:31,390 INFO [STDOUT] Getting properties
11:30:31,390 INFO [STDOUT] Test value is: Stephen
11:30:46,390 INFO [STDOUT] Task running
11:30:46,390 INFO [STDOUT] 0.24869896604923036
11:30:46,390 INFO [STDOUT] The properties file was not modified.
11:30:46,390 INFO [STDOUT] Test value is: Stephen
11:31:01,390 INFO [STDOUT] Task running
11:31:01,390 INFO [STDOUT] 0.47994173379307203
11:31:01,390 INFO [STDOUT] The properties file was not modified.
11:31:01,390 INFO [STDOUT] Test value is: Stephen
11:31:16,390 INFO [STDOUT] Task running
11:31:16,390 INFO [STDOUT] 0.6379331056768383
11:31:16,390 INFO [STDOUT] The properties file was modified.
11:31:16,390 INFO [STDOUT] Getting properties
11:31:16,390 INFO [STDOUT] Test value is: Stephen Wong
11:31:31,390 INFO [STDOUT] Task running
11:31:31,390 INFO [STDOUT] 0.30415561271978353
11:31:31,390 INFO [STDOUT] The properties file was not modified.
11:31:31,390 INFO [STDOUT] Test value is: Stephen Wong
11:31:46,390 INFO [STDOUT] Task running
11:31:46,390 INFO [STDOUT] 0.03696303208126983
11:31:46,390 INFO [STDOUT] The properties file was not modified.
11:31:46,390 INFO [STDOUT] Test value is: Stephen Wong