javaweb开发（十二）：jdbc工具类与池化思想

• src目录下编写配置类db.properties

url=jdbc:mysql://127.0.0.1:3306/jdbc?useUnicode=true&characterEncoding=utf-8&useSSL=false
username=root
password=123456
driver=com.mysql.cj.jdbc.Driver

• 编写工具类

public class CustomDBUtil {

    private static String url;

    private static String username;

    private static String password;

    private static String driver;

    static {
        try {
            Properties properties = new Properties();
            properties.load(CustomDBUtil.class.getClassLoader().getResourceAsStream("db.properties"));
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
            driver = properties.getProperty("driver");
            //加载JDBC驱动程序
            Class.forName(driver);
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    /**
     * 获取连接
     * @return
     * @throws Exception
     */
    public static Connection getConnection() throws Exception{
        Connection connection = DriverManager.getConnection(url,username,password);
        return connection;
    }

    /**
     * 关闭数据库资源
     * @param resultSet
     * @param ps
     * @param connection
     */
    public static void close(ResultSet resultSet, PreparedStatement ps, Connection connection){
        try{

            if(resultSet!=null){
                resultSet.close();
            }
            if(ps!=null){
                ps.close();
            }
            if(connection!=null){
                connection.close();
            }
        }catch (SQLException e){
            throw  new RuntimeException();
        }
    }

}

• 编写测试类

@WebServlet("/jdbc")
public class TestServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String idStr =  req.getParameter("id");
        int id = Integer.parseInt(idStr);
        try {
            Connection connection = CustomDBUtil.getConnection();
            PreparedStatement ps = connection.prepareStatement("select  * from user where  id=?");
            ps.setInt(1,id);
            ResultSet resultSet = ps.executeQuery();
            while (resultSet.next()){
                System.out.println("用户名称 name="+ resultSet.getString("username") + "  联系方式 wechat="+ resultSet.getString("wechat"));
            }
            CustomDBUtil.close(resultSet,ps,connection);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

• 测试

# 浏览器
http://localhost:8081/jdbc?id=1

# 控制台
�û����� name=jack  ��ϵ��ʽ wechat=xdclass6

• 数据库连接池

数据库建⽴Connection⽐较耗时，频繁的创建和释放连接引起的⼤量性能开销
如果数据库连接得到重⽤，避免这些开销，也提⾼了系统稳定
数据库连接池在初始化过程中，往往已经创建了若⼲数据库连接置于池中备⽤，对于业务请求处理⽽⾔，直接利⽤现有可⽤连接，缩减了系统整体响应时间
统⼀的连接管理，避免数据库连接泄漏、超时占⽤等问题