1.介绍
目的：使用redis缓存数据。第一次需要从数据库获得数据，第二次直接从redis中获取。通常用在缓存不常变化的数据。
需求：
1. 提供index.html页面，页面中有一个省份 下拉列表
2. 当 页面加载完成后 发送ajax请求，加载所有省份
流程：
2.代码展示
2.1.index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<script src="js/jquery-3.3.1.min.js"></script>
<script>
$(function () {
//发送ajax请求，加载所有省份数据
$.get("provinceServlet",{},function (data) {
//[{"id":1,"name":"北京"},{"id":2,"name":"上海"},{"id":3,"name":"广州"},{"id":4,"name":"陕西"}]
//1.获取select
var province = $("#province");
//2.遍历json数组
//$(data).each(function () {
$.each(data, function () {
//3.创建<option>
var option = "<option value='"+this.id+"'>"+this.name+"</option>";
//4.调用select的append追加option
province.append(option);
});
});
});
</script>
</head>
<body>
<select id="province">
<option>--请选择省份--</option>
</select>
</body>
</html>
2.2.创建数据库
CREATE DATABASE RP; -- 创建数据库 USE RP; -- 使用数据库 CREATE TABLE province( -- 创建表 id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20) NOT NULL ); -- 插入数据 INSERT INTO province VALUES(NULL,'北京'); INSERT INTO province VALUES(NULL,'上海'); INSERT INTO province VALUES(NULL,'广州'); INSERT INTO province VALUES(NULL,'陕西');
2.3.ProvinceDaoImpl
public class ProvinceDaoImpl implements ProvinceDao {
//1.声明成员变量 jdbctemplement
private JdbcTemplate template = new JdbcTemplate(JDBCUtils.getDataSource());
@Override
public List<Province> findAll() {
//1.定义sql
String sql = "select * from province ";
//2.执行sql
List<Province> list = template.query(sql, new BeanPropertyRowMapper<Province>(Province.class));
return list;
}
}
2.4.ProvinceServiceImpl
public class ProvinceServiceImpl implements ProvinceService {
//声明dao
private ProvinceDao dao = new ProvinceDaoImpl();
/**
使用redis缓存
*/
@Override
public String findAllJson() {
//1.先从redis中查询数据
//1.1获取redis客户端连接
Jedis jedis = JedisPoolUtils.getJedis();
String province_json = jedis.get("province");
//2判断 province_json 数据是否为null
if(province_json == null || province_json.length() == 0){
//redis中没有数据
System.out.println("redis中没数据，查询数据库...");
//2.1从数据中查询
List<Province> ps = dao.findAll();
//2.2将list序列化为json
ObjectMapper mapper = new ObjectMapper();
try {
province_json = mapper.writeValueAsString(ps);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
//2.3 将json数据存入redis
jedis.set("province",province_json);
//归还连接
jedis.close();
}else{
System.out.println("redis中有数据，查询缓存...");
}
return province_json;
}
}
2.5.web.servelt
@WebServlet("/provinceServlet")
public class ProvinceServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.调用service查询
ProvinceService service = new ProvinceServiceImpl();
String json = service.findAllJson();
System.out.println(json);
//3.响应结果
response.setContentType("application/json;charset=utf-8");
response.getWriter().write(json);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}