Redis數據庫緩存，提高性能。

ProvinceServlet.java

package cn.itcast.web.servlet;

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.調用service查詢
        ProvinceService service = new ProvinceServiceImpl();
        List<Province> list = service.findAll();
        //2.序列化list爲json
        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(list);*/

        //1.調用service查詢
        ProvinceService service = new ProvinceServiceImpl();
        String json = service.findAllJson();


        System.out.println(json);
        //3.響應結果
        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);
    }
}

核心代碼
ProvinceServiceImpl.java

package cn.itcast.service.impl;

import cn.itcast.dao.ProvinceDao;
import cn.itcast.dao.impl.ProvinceDaoImpl;
import cn.itcast.domain.Province;
import cn.itcast.jedis.util.JedisPoolUtils;
import cn.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 {
    //聲明dao
    private ProvinceDao dao = new ProvinceDaoImpl();

    @Override
    public List<Province> findAll() {
        return dao.findAll();
    }

    /**
     使用redis緩存
     */

    @Override
    public String findAllJson() {
        //1.先從redis中查詢數據
        //1.1獲取redis客戶端連接
        Jedis jedis = JedisPoolUtils.getJedis();
        String province_json = jedis.get("province");

        //2判斷 province_json 數據是否爲null
        if(province_json == null || province_json.length() == 0){
            //redis中沒有數據
            System.out.println("redis中沒數據，查詢數據庫...");
            //2.1從數據中查詢
            List<Province> ps = dao.findAll();
            //2.2將list序列化爲json
            ObjectMapper mapper = new ObjectMapper();
            try {
                province_json = mapper.writeValueAsString(ps);
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }

            //2.3 將json數據存入redis
            jedis.set("province",province_json);
            //歸還連接
            jedis.close();

        }else{
            System.out.println("redis中有數據，查詢緩存...");
        }


        return province_json;
    }
}