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

巴特西

Map实现java缓存机制的简单实例

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