观察者模式实际应用：监听线程，意外退出线程后自动重启
摘要: 观察者模式，定义对象之间的一种一对多的依赖关系，当对象的状态发生改变时，所有依赖于它的对象都得到通知并且被自动更新。观察者模式在JDK中有现成的实现，java.util.Obserable。
《设计模式就该这么学系列》文章:
首先说下需求：通过ftp上传约定格式的文件到服务器指定目录下，应用程序能实时监控该目录下文件变化，如果上传的文件格式符合要求，将将按照每一行读取解析再写入到数据库，解析完之后再将文件改名。（这个是原先已经实现了的功能，请看我的一篇文章java利用WatchService实时监控某个目录下的文件变化并按行解析（注：附源代码））
但项目上线一段时间后，发现再利用FileZilla登陆上传文件，文件不能被解析，而重启tomcat之后再上传，又能解析，于是判定是监控指定目录的那个线程挂掉了，导致上传后的文件不能被检测到，故也不能被解析。之后查看日志也最终验证了我推断。
所以关键的问题就是：如何监听线程，当意外退出线程后进行自动重启，这也是本文所要利用观察者模式实现的。
下面请看实现过程（尤其见红色注解部分）：
1、web.xml监听器配置文件监控监听器，初始化创建一个监控指定目录的线程
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:root-context.xml</param-value>
</context-param>
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<param-name>forceEncoding</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
<filter-name>sitemesh</filter-name>
<filter-class>com.opensymphony.sitemesh.webapp.SiteMeshFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>sitemesh</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>appServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:servlet-context.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>appServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
<!-- 配置spring监听器 -->
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- 配置监控文件变化监听器 -->
<listener>
<listener-class>com.zealer.ad.listener.ThreadStartUpListenser</listener-class>
</listener>
<listener>
<listener-class>com.zealer.ad.listener.SessionLifecycleListener</listener-class>
</listener>
<jsp-config>
<taglib>
<taglib-uri>/tag</taglib-uri>
<taglib-location>/WEB-INF/tag/tag.tld</taglib-location>
</taglib>
</jsp-config>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<session-config>
<session-timeout>45</session-timeout>
</session-config>
</web-app>
2、观察者对象：编写一个观察者实现类
当“监控指定目录线程”，即WatchFilePathTask 挂掉后，会调用doBusiness(),doBusiness()调用notifyObservers()，notifyObservers()调用所有的具体观察者的update()方法，也就是下面这个实现的重启线程的方法
package com.zealer.ad.listener; import java.util.Observable; import java.util.Observer;
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import com.zealer.ad.task.WatchFilePathTask; public class ObserverListener implements Observer{ private Log log = LogFactory.getLog(ObserverListener.class); @Override public void update(Observable o, Object arg) { log.info("WatchFilePathTask挂掉"); WatchFilePathTask run = new WatchFilePathTask(); run.addObserver(this); new Thread(run).start(); log.info("WatchFilePathTask重启"); } }
3、编写一个ThreadStartUpListenser类，实现ServletContextListener，tomcat启动时创建后台线程
package com.zealer.ad.listener; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.stereotype.Component; import com.zealer.ad.task.WatchFilePathTask; @Component public class ThreadStartUpListenser implements ServletContextListener { private static WatchFilePathTask r = new WatchFilePathTask(); private Log log = LogFactory.getLog(ThreadStartUpListenser.class); @Override public void contextDestroyed(ServletContextEvent paramServletContextEvent) { // r.interrupt(); } @Override public void contextInitialized(ServletContextEvent paramServletContextEvent) { ObserverListener listen = new ObserverListener();
//给“监控指定目录下的线程”(被观察者)，添加一个观察者 r.addObserver(listen); new Thread(r).start(); // r.start(); log.info("ImportUserFromFileTask is started!"); } }
4、主题对象：创建指定目录文件变化监控类WatchFilePathTask，当
package com.zealer.ad.task; import java.io.File; import java.io.FileFilter; import java.nio.file.FileSystems; import java.nio.file.Path; import java.nio.file.StandardWatchEventKinds; import java.nio.file.WatchEvent; import java.nio.file.WatchKey; import java.nio.file.WatchService; import java.util.Observable; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.joda.time.DateTime; import com.zealer.ad.util.ConfigUtils; import com.zealer.ad.util.SpringUtils; /** * 指定目录文件变化监控类 * @author cancer * */ public class WatchFilePathTask extends Observable implements Runnable { private Log log = LogFactory.getLog(WatchFilePathTask.class); private static final String filePath = ConfigUtils.getInstance().getValue("userfile_path"); private WatchService watchService; // 此方法一经调用，立马可以通知观察者，在本例中是监听线程 public void doBusiness()
{ if(true)
{ super.setChanged(); }
//通知观察者调用update()方法，重启线程 notifyObservers(); } @Override public void run() { try { //获取监控服务 watchService = FileSystems.getDefault().newWatchService(); log.debug("获取监控服务"+watchService); Path path = FileSystems.getDefault().getPath(filePath); log.debug("@@@:Path:"+path); final String todayFormat = DateTime.now().toString("yyyyMMdd"); File existFiles = new File(filePath); //启动时检查是否有未解析的符合要求的文件 if(existFiles.isDirectory()) { File[] matchFile = existFiles.listFiles(new FileFilter() { @Override public boolean accept(File pathname) { if((todayFormat+".txt").equals(pathname.getName())) { return true; } else { return false; } } }); if(null != matchFile) { for (File file : matchFile) { //找到符合要求的文件，开始解析 ImportUserFromFileTask task = (ImportUserFromFileTask) SpringUtils.getApplicationContext().getBean("importUserFromFileTask"); task.setFileName(file.getAbsolutePath()); task.start(); } } } //注册监控服务，监控新增事件 WatchKey key = path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE); while (true) { key = watchService.take(); for (WatchEvent<?> event : key.pollEvents()) { //获取目录下新增的文件名 String fileName = event.context().toString(); //检查文件名是否符合要求 if((todayFormat+".txt").equals(fileName)) { String filePath = path.toFile().getAbsolutePath()+File.separator+fileName; log.info("import filePath:"+filePath); //启动线程导入用户数据 ImportUserFromFileTask task = (ImportUserFromFileTask) SpringUtils.getApplicationContext().getBean("importUserFromFileTask");//new ImportUserFromFileTask(filePath); task.setFileName(filePath); task.start(); log.debug("启动线程导入用户数据"+task); } } key.reset(); } }
catch (Exception e) { e.printStackTrace(); System.out.println("已经到这里来了"); doBusiness();//在抛出异常时调用，通知观察者，让其重启线程 } } }
5、创建解析用户文件及导入数据库线程，由WatchFilePathTask启动
package com.zealer.ad.task; import com.zealer.ad.entity.AutoPutUser; import com.zealer.ad.entity.Bmsuser; import com.zealer.ad.service.AutoPutUserService; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.joda.time.DateTime; import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.InputStreamReader; import java.util.Date; import javax.annotation.Resource; /** * 解析用户文件及入库线程,由WatchFilePathTask启动 * @author cancer * */ public class ImportUserFromFileTask extends Thread { private Log log = LogFactory.getLog(ImportUserFromFileTask.class); private String fileName; @Resource(name = "autoPutUserService") private AutoPutUserService autoPutUserService; @Override public void run() { File file = new File(fileName); if (file.exists() && file.isFile()) { log.debug("：@@@准备开始休眠10秒钟：" + file); //休眠十分钟，防止文件过大还没完全拷贝到指定目录下，这里的线程就开始读取文件 try { sleep(10000); } catch (InterruptedException e1) { e1.printStackTrace(); } InputStreamReader read; try { read = new InputStreamReader(new FileInputStream(file), "UTF-8"); BufferedReader bufferedReader = new BufferedReader(read); String lineTxt = null; int count = 0; Boolean f = false; while ((lineTxt = bufferedReader.readLine()) != null) { if ((null == lineTxt) || "".equals(lineTxt)) { continue; } if (lineTxt.startsWith("'")) { lineTxt = lineTxt.substring(1, lineTxt.length()); } //解析分隔符为', ' String[] lines = lineTxt.split("', '"); int length = lines.length; if (length < 2) { continue; } Bmsuser bmsuser = new Bmsuser(); bmsuser.setName(lines[0]);if (!"".equals(lines[1])) { bmsuser.setCity(lines[1]); } //根据唯一索引已经存在的数据则不插入 f = autoPutUserService.insertIgnore(bmsuser); if (f) { count++; } } //汇总数据 AutoPutUser autoPutUser = new AutoPutUser(); autoPutUser.setTotalCount(autoPutUserService.getUserCount()); autoPutUser.setCount(count); autoPutUser.setCountDate(new Date(System.currentTimeMillis())); String today = DateTime.now().toString("yyyy-MM-dd"); Integer oldCount = autoPutUserService.getOldCount(today); //如果今天导入过了就更新否则插入 if (!oldCount.equals(0)) { autoPutUserService.updateUserData(autoPutUser, today, oldCount); } else { autoPutUserService.gatherUserData(autoPutUser); } //注意：要关闭流 read.close(); } catch (Exception e) { log.error(e.getMessage(), e); } File newFile = new File(file.getPath() + System.currentTimeMillis() + ".complate"); file.renameTo(newFile); } else { log.error(fileName + " file is not exists"); } } public String getFileName() { return fileName; } public void setFileName(String fileName) { this.fileName = fileName; } public AutoPutUserService getAutoPutUserService() { return autoPutUserService; } public void setAutoPutUserService(AutoPutUserService autoPutUserService) { this.autoPutUserService = autoPutUserService; } }
附带：
1、sql脚本
CREATE TABLE `bmsuser` (
`id` int(255) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(32) DEFAULT NULL ,
`city` varchar(32) DEFAULT NULL COMMENT ,
PRIMARY KEY (`bmsid`),
UNIQUE KEY `bbLoginName` (`bbLoginName`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
2、文件格式，命名为yyyyMMdd.txt
'张三', '深圳'
每一个你不满意的当下，都有一个你不曾努力的过去
