redis缓存的的使用

Posted 2022-01-07 uoshuan

注意： 使用redis缓存一些不经常发生变化的数据。
* 数据库的数据一旦发生改变，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缓存数据清空，再次存入
* 在service对应的增删改方法中，将redis数据删除。

项目结构

jar包

数据库

CREATE TABLE province(  
	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');

JDBCUtil

import com.alibaba.druid.pool.DruidDataSourceFactory;

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

/**
 * 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();
    

JedisPoolUtils

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;

/**
 JedisPool工具类
    加载配置文件，配置连接池的参数
    提供获取连接的方法

 */
public class JedisPoolUtils 

    private static JedisPool jedisPool;

    static
        //读取配置文件
        InputStream is = JedisPoolUtils.class.getClassLoader().getResourceAsStream("jedis.properties");
        //创建Properties对象
        Properties pro = new Properties();
        //关联文件
        try 
            pro.load(is);
         catch (IOException e) 
            e.printStackTrace();
        
        //获取数据，设置到JedisPoolConfig中
        JedisPoolConfig config = new JedisPoolConfig();
        config.setMaxTotal(Integer.parseInt(pro.getProperty("maxTotal")));
        config.setMaxIdle(Integer.parseInt(pro.getProperty("maxIdle")));

        //初始化JedisPool
        jedisPool = new JedisPool(config,pro.getProperty("host"),Integer.parseInt(pro.getProperty("port")));



    


    /**
     * 获取连接方法
     */
    public static Jedis getJedis()
        return jedisPool.getResource();
    

Province

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;
    

ProvinceServlet

import cn.itcast.service.ProvinceService;
import cn.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);
    

ProvinceDao

import java.util.List;
public interface ProvinceDao 
    public List<Province> findAll();

ProvinceDaoImpl

import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;

import java.util.List;

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;
    

ProvinceService

import java.util.List;

public interface ProvinceService 

    public List<Province> findAll();

    public String findAllJson();

ProvinceServiceImpl

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;
    

<!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>