Map實現java快取機制的簡單例項
阿新 • • 發佈：2019-02-11
快取是java中主要的內容，主要目的是緩解專案訪問資料庫的壓力以及提升訪問資料的效率，以下是通過Map實現java快取的功能，並沒有用cache相關框架。
一、快取管理類 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; /** * 快取管理類 * @author Administrator * */ public class CacheMgr { private static Map cacheMap = new HashMap(); private static Map cacheConfMap = new HashMap(); private static CacheMgr cm = null; //構造方法 private CacheMgr(){ } public static CacheMgr getInstance(){ if(cm==null){ cm = new CacheMgr(); Thread t = new ClearCache(); t.start(); } return cm; } /** * 增加快取 * @param key * @param value * @param ccm 快取物件 * @return */ public boolean addCache(Object key,Object value,CacheConfModel ccm){ System.out.println("開始增加快取－－－－－－－－－－－－－"); boolean flag = false; try { cacheMap.put(key, value); cacheConfMap.put(key, ccm); System.out.println("增加快取結束－－－－－－－－－－－－－"); System.out.println("now addcache=="+cacheMap.size()); flag=true; } catch (Exception e) { e.printStackTrace(); } return flag; } /** * 獲取快取實體 */ public Object getValue(String key){ Object ob=cacheMap.get(key); if(ob!=null){ return ob; }else{ return null; } } /** * 獲取快取資料的數量 * @return */ public int getSize(){ return cacheMap.size(); } /** * 刪除快取 * @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; } /** * 清除快取的類 * 繼承Thread執行緒類 */ 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); //比較是否需要清除 if(!ccm.isForever()){ if((new Date().getTime()-ccm.getBeginTime())>= ccm.getDurableTime()*60*1000){ //可以清除，先記錄下來 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、快取屬性類 CacheConfModel.java
package cache.com; /** * 快取屬性類 * @author Administrator * */ public class CacheConfModel implements java.io.Serializable{ private long beginTime;//快取開始時間 private boolean isForever = false;//是否持久 private int durableTime;//持續時間 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、配置啟動專案時自動載入 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、自動載入快取的類 LoadCache.java
在此類中實現你想要初始化的快取資料
package cache.com;
import java.util.Date;
import javax.servlet.http.HttpServlet;
import cache.com.CacheConfModel;
import cache.com.CacheMgr;
/**
* 專案啟動時預設載入快取資料類
* @author Administrator
*/
public class LoadCache extends HttpServlet{
public void init(){
addData();
}
/**
* 專案啟動時載入快取
*/
public void addData(){
System.out.println("進入載入快取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);//在快取加值
}
}
五、寫一個測試類 Cservlet.java，我在這裡寫了一個servlet類進行測試的
package cache.com;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 測試讀取、新增快取資料等
* @author Administrator
*/
public class Cservlet extends HttpServlet{
public void service(HttpServletRequest request,HttpServletResponse response){
try {
System.out.println("進入servlet類............");
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8"); //3.設定響應型別
PrintWriter out = response.getWriter();
CacheMgr cm=CacheMgr.getInstance();
int numm=cm.getSize();//獲取快取個數
Object ob=cm.getValue("kk");
System.out.println("numm===========//======"+numm);
out.println("快取個數為："+numm);
out.println("快取數值：value===="+ob);
} catch (Exception e) {
e.printStackTrace();
}
}
}
六、寫一個簡單的按鈕頁面 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" >獲取快取資料</button>
</form>
</body>
</html>
啟動專案後點擊按鈕 “獲取快取資料”後，出現如下圖說明快取成功併成功取值了
