889~891 分析，环境搭建，实现查询数据库，redis缓存优化
案例：
案例需求：
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，加载说有省份
CREATE DATABASE day23; -- 创建数据库 USE day23; -- 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');
public class Province {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public interface ProvinceDao {
public List<Province> findAll();
}
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;
}
}
/**
* JDBC工具类 使用Durid连接池
*/
public class JDBCUtils {
private static DataSource ds ;
static {
try {
//1.加载配置文件
Properties pro = new Properties();
//使用ClassLoader加载配置文件，获取字节输入流
InputStream is = JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties");
pro.load(is);
//2.初始化连接池对象
ds = DruidDataSourceFactory.createDataSource(pro);
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 获取连接池对象
*/
public static DataSource getDataSource(){
return ds;
}
/**
* 获取连接Connection对象
*/
public static Connection getConnection() throws SQLException {
return ds.getConnection();
}
}
public interface ProvinceService {
public List<Province> findAll();
public String findAllJson();
}
<!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 () {
//3.创建<option>
var option = "<option name='"+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>
package com.example.itcast.service.impl;
import com.example.itcast.dao.ProvinceDao;
import com.example.itcast.dao.impl.ProvinceDaoImpl;
import com.example.itcast.domain.Province;
import com.example.itcast.jedis.util.JedisPoolUtils;
import com.example.itcast.service.ProvinceService;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import redis.clients.jedis.Jedis;
import java.util.List;
public class ProvinceServiceImpl implements ProvinceService {
//声明dao
private ProvinceDao dao = new ProvinceDaoImpl();
@Override
public List<Province> findAll() {
return dao.findAll();
}
/**
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;
}
}
package com.example.itcast.web.servlet;
import com.example.itcast.service.ProvinceService;
import com.example.itcast.service.impl.ProvinceServiceImpl;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@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();
List<Province> list = service.findAll();
//2.序列化list为json
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(list);*/
//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);
}
}
注意：使用redis缓存一些不经常发生变化的数据。
数据库的数据一旦改变，则需要更新缓存
数据库的表执行 增删改的相关操作，需要将redis缓存数据情况，再次存入
在service对应的增删改方法中，将redis数据删除
