Map实现java缓存机制的简单实例

Posted 2020-10-05 Henu丶雨巷

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