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
3.列表中的省份保持不变，则之后每次刷新页面都是从redis中获取
* 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缓存数据清除，再次存入
* 在service对应的增删改方法中，将redis数据删除。
前端页面：
<!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>
jar包：
provinceServlet:
@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);
}
}
provinceService接口 和 provinceServiceImpl代码：
public interface ProvinceService { public List<Province> findAll(); public String findAllJson(); }
===================================================================
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; } }
provinceDao接口 和 provinceDaoImpl代码：
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; } }
JDBCUtils:
/** * 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:
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(); } }
druid.properties 和 jedis.properties以及sql文件:
演示界面：
