OSCache缓存技术（6）【实例】
本实例将模仿一个JSP页面从数据库中取得一个LIST集合的数据，模型是模拟一个新闻发布页面去后台取得信息，系统设定10秒钟更新一次缓存，而前台页面每隔5秒打印一次集合信息。
<1>POJO缓存实现
1.缓存的基类BaseCache
package com.test;
import java.util.Date;
import com.opensymphony.oscache.base.NeedsRefreshException;
import com.opensymphony.oscache.general.GeneralCacheAdministrator;
public class BaseCache extends GeneralCacheAdministrator {
// 过期时间(单位为秒);
private int refreshPeriod;
// 关键字前缀字符;
private String keyPrefix;
private static final long serialVersionUID = -4397192926052141162L;
public BaseCache(String keyPrefix, int refreshPeriod) {
super();
this.keyPrefix = keyPrefix;
this.refreshPeriod = refreshPeriod;
}
// 添加被缓存的对象;
public void put(String key, Object value) {
this.putInCache(this.keyPrefix + "_" + key, value);
}
// 删除被缓存的对象;
public void remove(String key) {
this.flushEntry(this.keyPrefix + "_" + key);
}
// 删除所有被缓存的对象;
public void removeAll(Date date) {
this.flushAll(date);
}
public void removeAll() {
this.flushAll();
}
// 获取被缓存的对象;
public Object get(String key) throws Exception {
try {
return this.getFromCache(this.keyPrefix + "_" + key,
this.refreshPeriod);
} catch (NeedsRefreshException e) {
this.cancelUpdate(this.keyPrefix + "_" + key);
throw e;
}
}
private static BaseCache cache;
public static BaseCache getInstance()
{
if(cache==null)
{
cache = new BaseCache("count",10);
}
return cache;
}
}
2.缓存的管理类CacheUser
package com.test;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
public class CacheUser {
private BaseCache newsCache;
private static CacheUser instance;
private static Object lock = new Object();
private CacheUser() {
//这个根据配置文件来，初始BaseCache而已;
newsCache = new BaseCache("news",10); //在这里10表示的10秒钟更新一次缓存
}
public List<String> getUser(String newsID) {
try {
List<String> list = null;
list = (List<String>) newsCache.get(newsID);
return list;
//因为是10秒钟更新一次缓存，所以每隔10秒后newsCache.get(newsID)就会为空,抛出异常，重新去数据库取得数据
} catch (Exception e) {
System.out.println("getNews>>newsID["+newsID+"]>>"+e.getMessage());
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8";
String user = "root";
String pwd = "root";
List<String> lists =new ArrayList<String>();
try
{
String sql = "select * from kindergarden_user";
Class.forName(driver);
con = DriverManager.getConnection(url,user,pwd);
stmt = con.createStatement();
rs = stmt.executeQuery(sql);
while(rs.next())
{
String name = rs.getString("Name");
lists.add(name);
}
newsCache.put("userlist",lists); //重新取得数据以后，放到缓存中
}
catch(Exception e3)
{
e3.printStackTrace();
}
finally
{
try
{
}
catch(Exception ee)
{
try {
rs.close();
stmt.close();
con.close();
} catch (Exception exx) {
exx.printStackTrace();
}
}
}
return lists;
}
}
public void putUser(User news) { newsCache.put(news.getId()+"",news); }
//通过单线程的方式取得缓存的对象
public static CacheUser getInstance(){
if (instance == null){
synchronized( lock ){
if (instance == null){
instance = new CacheUser();
}
}
}
return instance;
}
public void removeUser(String newsID) { newsCache.remove(newsID); }
public void removeAllUsers() {
newsCache.removeAll();
}
}
3.前端的JSP页面userlist.jsp
<%@ page language="java" import="java.util.*,java.sql.*,com.test.*" pageEncoding="GB2312" isELIgnored="false"%>
<%@ taglib prefix="s" uri="/WEB-INF/classes/oscache.tld" %>
<%
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>
<%
%>
<%
List<String> list = null;
CacheUser cm=CacheUser.getInstance();
//通过单利模式取得缓存对象，然后从缓存中取得LIST集合，前端页面就不用管集合是从数据库还是缓存中得到了，由缓存管理的类去进行管理
for (int i = 0; i < 1000; i++) {
try {
list = (List<String>)cm.getUser("userlist");
System.out.println(list);
if(i==10){
//删除缓存id的对象
cm.removeUser("userlist");
}
if(i==20){
//删除所有缓存的对象
cm.removeAllUsers();
}
Thread.sleep(5000);
} catch (Exception e) {
}
}
%>
</body>
</html>
<2>JSP页面缓存实现
1.在WEB.XML文件中配置
<taglib>
<taglib-uri>oscache</taglib-uri>
<taglib-location>/WEB-INF/classes/oscache.tld</taglib-location>
</taglib>
2.编写index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
<%@ taglib prefix="cache" uri="oscache" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<body>
没有缓存的日期: <%= new Date() %><p>
<!--自动刷新-->
<cache:cache time="10">
每30秒刷新缓存一次的日期: <%= new Date() %>
<!--该段代码处的时期是10秒钟清空一次，也就是10秒钟取得一次，你在10秒内刷新index.jsp该时间是不变的。-->
</cache:cache>
<!--手动刷新-->
<cache:cache key="testcache">
手动刷新缓存的日期: <%= new Date() %> <p>
<!--该段代码处的时间永远都不变，除非你手动刷新该处的时间，要么该时间永远保存在缓存中。-->
</cache:cache>
<a href="cache2.jsp">手动刷新</a>
</body>
</html>
3.cache2.jsp
<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
<%@ taglib prefix="cache" uri="oscache" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<body>
缓存已刷新...<p>
<cache:flush key="testcache" scope="application"/>
<a href="index.jsp">返回</a>
</body>
</html>