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 加载所有省份

java代码实现

配置文件

数据库配置文件：druid.properties

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///day23
username=root
password=root
initialSize=5
maxActive=10
maxWait=3000

实体类

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;
    }
}

ProvinceDao接口

public interface ProvinceDao {

    public List<Province> findAll();
}

ProvinceDaoImpl类

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接口

public interface ProvinceService {

    public List<Province> findAll();

    public String findAllJson();
}

ProvinceServiceImpl类

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;
    }
}

工具类：JDBCUtils

 

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();
    }
}

ProvinceServlet类

@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);
    }
}

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 () {
                    //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>