什么时候自己创建工具类
      如果一个功能经常用到 我们建议把这个功能做成工具类
      创建JdbcUtils包含三个方法
      1: 把几个字符串 定义为常量
      2：得到数据库连接getConnection();
    3  关闭和打开资源

package JdbcUtils;

import java.sql.*;

public class JdbcUtilsDemo {
    public static final String USER = "root";
    public static final String PSW = "root";
    public static final String URL = "jdbc:mysql://localhost:3306/qy97";
    public static final String DRIVER = "com.mysql.jdbc.Driver";

    static {
        try {
            Class.forName(DRIVER);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(URL,USER,PSW);
    }
      /*public static void close(Statement st,Connection con){
        if (st!=null){
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(con!=null){
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
      }
    public static void close(Connection con, Statement st, ResultSet rs){
          if(rs!=null){
              try {
                  rs.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
          if (st!=null){
              try {
                  st.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
          if (con!=null){
              try {
                  con.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
    }*/

      public  static  void close(AutoCloseable... ca){
          for (AutoCloseable c:ca){
              if(c!=null){
                  try {
                      c.close();
                  } catch (Exception e) {
                      e.printStackTrace();
                  }
              }
          }
      }

}


调用工具类方法进行查询

package cn.lideng.dbc;

import JdbcUtils.JdbcUtilsDemo;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JdbcDemo5 {

    private static Connection connection;
    private static Statement statement;
    private static ResultSet rs;

    public static void main(String[] args){
        try {
            connection = JdbcUtilsDemo.getConnection();
            String sql="select * from users";
            statement = connection.createStatement();
            rs = statement.executeQuery(sql);
            while(rs.next()){
                int id = rs.getInt(1);
                String name = rs.getString(2);
                String address = rs.getString(3);
                System.out.println(id+"   "+name+"   "+address);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            JdbcUtilsDemo.close(rs,statement,connection);
        }


    }
}