JDBC_DBUtils

• 把建立连接和释放连接封装到工具类中，代码如下：

• public class DBUtils {
      // 不变的东西
      private static String driverclass = "com.mysql.cj.jdbc.Driver";
      private static String url = "jdbc:mysql://localhost:3306/test";
      private static String user = "root";
      private static String password = "123456";
      // static语句块，该类被加载的时候会被执行且只执行一次，驱动注册
      static {
          try {
              Class.forName(driverclass);
          } catch (ClassNotFoundException e) {
              e.printStackTrace();
          }
      }
  
      // 建立连接
      public static Connection getConnection() throws SQLException {
          return DriverManager.getConnection(url, user, password);
      }
  
      // 释放连接
      public static void close(ResultSet resultSet, Statement statement, Connection connection) {
          if (resultSet != null) {
              try {
                  resultSet.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
          if (statement != null) {
              try {
                  statement.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
          if (connection != null) {
              try {
                  connection.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
      }
  }

   

• 新的查询数据类，代码如下：

• public class JDBC_01 {
  
      public static void main(String[] args) {
          Connection connection = null;
          Statement statement = null;
          ResultSet resultSet = null;
          try {
  //          // 1.注册驱动。现在这一句不需要了，DBUtils类被加载的时候会执行static块
  //            Class.forName("com.mysql.cj.jdbc.Driver");
              // 2.创建连接
              connection = DBUtils.getConnection();
              // 3.创建执行SQL语句的对象
              statement = connection.createStatement();
              // 4.执行SQL语句并返回结果集
              resultSet = statement.executeQuery("select * from user;");
              // 5.遍历
              while (resultSet.next()) {
                  System.out.print(resultSet.getObject(1) + "   ");
                  System.out.print(resultSet.getObject(2) + "   ");
                  System.out.print(resultSet.getObject(3) + "   ");
                  System.out.print(resultSet.getObject(4) + "   ");
                  System.out.println(resultSet.getObject(5) + "   ");
              }
          } catch (Exception e) {
              // TODO: handle exception
          } finally {
              DBUtils.close(resultSet, statement, connection);
          }
      }
  }