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 cache.com;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 cache.com;/** * 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