Map实现java缓存机制的简单实例
缓存是Java中主要的内容，主要目的是缓解项目访问数据库的压力以及提升访问数据的效率，以下是通过Map实现java缓存的功能，并没有用cache相关框架。
一、缓存管理类 CacheMgr.java
package com.henu.util; import java.util.Date; import java.util.HashMap; import java.util.HashSet; import java.util.Iterator; import java.util.Map; import java.util.Set; /** * 缓存管理类 * * @author Administrator * */ public class CacheMgr { private static Map cacheMap = new HashMap(); private static Map cacheConfMap = new HashMap(); private static CacheMgr cm = null; // 构造方法 private CacheMgr() { } public static CacheMgr getInstance() { if (cm == null) { cm = new CacheMgr(); Thread t = new ClearCache(); t.start(); } return cm; } /** * 增加缓存 * * @param key * @param value * @param ccm * 缓存对象 * @return */ public boolean addCache(Object key, Object value, CacheConfModel ccm) { System.out.println("开始增加缓存－－－－－－－－－－－－－"); boolean flag = false; try { cacheMap.put(key, value); cacheConfMap.put(key, ccm); System.out.println("增加缓存结束－－－－－－－－－－－－－"); System.out.println("now addcache==" + cacheMap.size()); flag = true; } catch (Exception e) { e.printStackTrace(); } return flag; } /** * 获取缓存实体 */ public Object getValue(String key) { Object ob = cacheMap.get(key); if (ob != null) { return ob; } else { return null; } } /** * 获取缓存数据的数量 * * @return */ public int getSize() { return cacheMap.size(); } /** * 删除缓存 * * @param key * @return */ public boolean removeCache(Object key) { boolean flag = false; try { cacheMap.remove(key); cacheConfMap.remove(key); flag = true; } catch (Exception e) { e.printStackTrace(); } return flag; } /** * 清除缓存的类 继承Thread线程类 */ private static class ClearCache extends Thread { public void run() { while (true) { Set tempSet = new HashSet(); Set set = cacheConfMap.keySet(); Iterator it = set.iterator(); while (it.hasNext()) { Object key = it.next(); CacheConfModel ccm = (CacheConfModel) cacheConfMap.get(key); // 比较是否需要清除 if (!ccm.isForever()) { if ((new Date().getTime() - ccm.getBeginTime()) >= ccm .getDurableTime() * 60 * 1000) { // 可以清除，先记录下来 tempSet.add(key); } } } // 真正清除 Iterator tempIt = tempSet.iterator(); while (tempIt.hasNext()) { Object key = tempIt.next(); cacheMap.remove(key); cacheConfMap.remove(key); } System.out.println("now thread================>" + cacheMap.size()); // 休息 try { Thread.sleep(60 * 1000L); } catch (InterruptedException e) { e.printStackTrace(); } } } } }
二、缓存属性类 CacheConfModel.java
package com.henu.util; /** * 缓存属性类 * * @author Administrator * */ public class CacheConfModel implements java.io.Serializable { private long beginTime;// 缓存开始时间 private boolean isForever = false;// 是否持久 private int durableTime;// 持续时间 public long getBeginTime() { return beginTime; } public void setBeginTime(long beginTime) { this.beginTime = beginTime; } public boolean isForever() { return isForever; } public void setForever(boolean isForever) { this.isForever = isForever; } public int getDurableTime() { return durableTime; } public void setDurableTime(int durableTime) { this.durableTime = durableTime; } }
三、配置启动项目时自动加载 web.xml
<?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"> <servlet> <servlet-name>testCache</servlet-name> <servlet-class>cache.com.Cservlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>testCache</servlet-name> <url-pattern>/testCache.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>cacheinitservlet</servlet-name> <servlet-class>cache.com.LoadCache</servlet-class> <load-on-startup>2</load-on-startup> </servlet> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>
四、自动加载缓存的类 LoadCache.java，在此类中实现你想要初始化的缓存数据
package cache.com; import java.util.Date; import javax.servlet.http.HttpServlet; import cache.com.CacheConfModel; import cache.com.CacheMgr; /** * 项目启动时默认加载缓存数据类 * @author Administrator */ public class LoadCache extends HttpServlet{ public void init(){ addData(); } /** * 项目启动时加载缓存 */ public void addData(){ System.out.println("进入加载缓存addData()………………。"); CacheMgr cm=CacheMgr.getInstance(); CacheConfModel cModel=new CacheConfModel(); Date d=new Date(); cModel.setBeginTime(d.getTime()); cModel.setDurableTime(60); cModel.setForever(true); cm.addCache("kk", "123", cModel);//在缓存加值 } }
五、写一个测试类 Cservlet.java，我在这里写了一个servlet类进行测试的
package cache.com; import java.io.PrintWriter; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * 测试读取、添加缓存数据等 * @author Administrator */ public class Cservlet extends HttpServlet{ public void service(HttpServletRequest request,HttpServletResponse response){ try { System.out.println("进入servlet类............"); request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=UTF-8"); //3.设置响应类型 PrintWriter out = response.getWriter(); CacheMgr cm=CacheMgr.getInstance(); int numm=cm.getSize();//获取缓存个数 Object ob=cm.getValue("kk"); System.out.println("numm===========//======"+numm); out.println("缓存个数为："+numm); out.println("缓存数值：value===="+ob); } catch (Exception e) { e.printStackTrace(); } } }
六、写一个简单的按钮页面 index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> <form action="testCache.do" method="post"> <button type="submit" >获取缓存数据</button> </form> </body> </html>
启动项目后点击按钮 “获取缓存数据” 后，出现如下图说明缓存成功并成功取值了
