002.Redis与Mysql的联动

 项目结构：

package com.redis.pojo;


/**
 * 1.pojo对应的数据库表的实体类
 * 2.Shop对应数据库shop表对应的实体类
 */
public class Shop
{
    private Integer id;
    private Double price;
    private Integer stock;

    public Shop(Integer id, Double price, Integer stock)
    {
        this.id = id;
        this.price = price;
        this.stock = stock;
    }

    public Shop()
    {
    }

    public Integer getId()
    {
        return id;
    }

    public void setId(Integer id)
    {
        this.id = id;
    }

    public Double getPrice()
    {
        return price;
    }

    public void setPrice(Double price)
    {
        this.price = price;
    }

    public Integer getStock()
    {
        return stock;
    }

    public void setStock(Integer stock)
    {
        this.stock = stock;
    }

    @Override
    public String toString()
    {
        return "Shop{" + "id=" + id + ", price=" + price + ", stock=" + stock + '}';
    }
}

package com.redis.servlet;

import com.redis.utils.GsonListMapUtil;
import com.redis.utils.JedisUtil;
import redis.clients.jedis.Jedis;

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;
import java.sql.SQLException;
import java.util.List;

@WebServlet("/helloServlet")
public class HelloServlet extends HttpServlet
{
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
    {
        super.doPost(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
    {
        req.setCharacterEncoding("utf-8"); //设置对客户端请求和数据库取值时的编码
        resp.setContentType("text/html;charset=utf-8");//指定服务器响应给浏览器的编码
        Jedis jedis = JedisUtil.getJedis();
        /**
         * 1.查询redis中的所有数剧
         * 2.list!=null（相当于先判断有没有杯子）和list.size()>0（判断杯子里面有没有水）的区别：
         */
        List<String> shopIdList = jedis.lrange("shopId", 0, -1);
        if (shopIdList != null && shopIdList.size() != 0)
        {
            for (String shopIdListString : shopIdList)
            {
                resp.getWriter().write(shopIdListString);
                System.out.println("redis中有数据");
            }
        }
        else
        {
            String gsonString = null;
            try
            {
                gsonString = GsonListMapUtil.gsonString();
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }
            jedis.rpush("shopId", gsonString);
            resp.getWriter().write(gsonString);
            System.out.println("程序先在Mysql中查询数据然后在存放到redis中！");
        }
        JedisUtil.closeJedis(jedis);
    }
}

package com.redis.utils;

import com.google.gson.Gson;

import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;


/**
 * 1.将数据库中的数据转换成json形式
 */
public class GsonListMapUtil
{
    public static PreparedStatement preparedStatement = null;
    public static Connection connection = null;
    public static ResultSet resultSet = null;


    /**
     * 1.1.将数据库中的数据转换成json形式
     */
    public static String gsonString() throws SQLException
    {
        connection = JdbcUtil.getConnection();
        String sql = "select * from shop".trim();
        preparedStatement = connection.prepareStatement(sql);
        resultSet = preparedStatement.executeQuery();
        ResultSetMetaData keyName = resultSet.getMetaData();//获取键名
        int columnCount = keyName.getColumnCount();//获取行的数量
        ArrayList arrayList = new ArrayList<Object>();// 定义一个list，用来存放数据
        while (resultSet.next())
        {
            Map map = new HashMap();
            for (int i = 1; i <= columnCount ; i++)
            {
                map.put(keyName.getColumnName(i), resultSet.getObject(i));
            }
            arrayList.add(map);
        }
        Gson gson = new Gson();
        String gsonString = gson.toJson(arrayList);
        JdbcUtil.close(preparedStatement,connection,resultSet);
        return gsonString;
    }

}

package com.redis.utils;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import javax.sql.DataSource;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

public class JdbcUtil
{

    private  static  DataSource dataSource;

    static
    {
        try
        {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Properties properties = new Properties();
            InputStream inputStream= JdbcUtil.class.getClassLoader().getResourceAsStream("com/redis/properties/druid.properties");
            properties.load(inputStream);
            dataSource = DruidDataSourceFactory.createDataSource(properties);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    /**
     * 1.获取一个 Connection 对象
     */
    public static Connection getConnection() throws SQLException
    {
        return dataSource.getConnection();
    }

    /**
     * 1.关闭资源
     */
    /**
     * 1.关闭资源
     */
    public static void close(PreparedStatement preparedStatement2, Connection connection, ResultSet resultSet) throws SQLException
    {
        if (preparedStatement2 != null)
        {
            preparedStatement2.close();
        }
        if (connection != null)
        {
            connection.close();
        }
        if (resultSet != null)
        {
            resultSet.close();
        }
    }





}

package com.redis.utils;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class JedisUtil
{
    private static final  JedisPool JEDIS_POOL;

    static
    {
        /**
         * 1.getResourceAsStream()从resource目录读取文件变成输入流
         * 2. prop.load()将输入流中转化复制到Properties中
         */
        InputStream resourceAsStream = JedisUtil.class.getClassLoader().getResourceAsStream("com/redis/properties/jedis.properties");
        Properties pro = new Properties();
        try
        {
            pro.load(resourceAsStream);
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        JedisPoolConfig config =new JedisPoolConfig();
        config.setMaxTotal(Integer.parseInt(pro.getProperty("maxTotal")));
        config.setMaxIdle(Integer.parseInt(pro.getProperty("maxIdle")));
        JEDIS_POOL =new JedisPool(config,pro.getProperty("host"), Integer.parseInt(pro.getProperty("port")));
    }

    public static Jedis getJedis()
    {
        return JEDIS_POOL.getResource();
    }

    public static void closeJedis(Jedis jedis) {
        if (jedis != null) {
            jedis.close();

        }
    }
}