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