关于Java Web的Servlet+JDBC(封装)+JSP的登录（送给入门的你）

package cn.com.DaoTier; import java.sql.*; import java.util.ArrayList; import java.util.List; /** * Created by Jmlc on 2017/8/22. */ public class DBHelper { private static final String DRIVENAME = "com.mysql.jdbc.Driver"; private static final String URL = "jdbc:mysql://localhost:3306/Jsp_Servlet"; private static final String USER = "root"; private static final String PASSWORD = "root"; private int columnCount = 0; private int affectedLine = 0;//受影响的行数 private Connection connection = null; private Statement statement = null; private PreparedStatement preparedStatement = null; private ResultSet resultSet = null; private ResultSetMetaData resultSetMetaData = null; /** * 加载驱动 */ static { try { Class.forName(DRIVENAME); System.out.println("驱动加载成功。"); } catch (Exception e) { System.out.println("驱动加载失败：" + e.getMessage()); } } /** * 连接数据库 * * @return */ public Connection gainConnection() { try { connection = DriverManager.getConnection(URL, USER, PASSWORD); System.out.println("连接数据库成功。"); } catch (SQLException e) { System.out.println("连接数据库失败!--" + e.getMessage()); } return connection; } /** * 查询（有参、无参） * * @param sql * @param params * @return */ public List<Object> gainQuery(String sql, Object[] params) { List<Object> list = new ArrayList<>(); if (params != null) { resultSet = gainResultSet(sql, params); } else { resultSet = gainResultSet(sql); System.out.println(sql); } try { while (resultSet.next()) { //rs.get+数据库中对应的类型+(数据库中对应的列别名) String username = resultSet.getString("username"); String password = resultSet.getString("password"); if (username == null && password == null) { list.add("error"); return list; } else { list.add(username); list.add(password); System.out.println("结果集解析成功。"); return list; } } } catch (SQLException e) { System.out.println("结果集解析出错!--" + e.getMessage()); list.add("error"); } finally { closeConnection(); } return list; } /** * 获取结果集（无参） * * @param sql * @return */ private ResultSet gainResultSet(String sql) { connection = this.gainConnection(); try { statement = connection.createStatement(); resultSet = statement.executeQuery(sql); System.out.println("获取结果集（无参）成功。"); } catch (SQLException e) { System.out.println("获取结果集（无参）失败!--" + e.getMessage()); } return resultSet; } /** * 获取结果集（有参） * * @param sql * @param params * @return */ private ResultSet gainResultSet(String sql, Object[] params) { connection = this.gainConnection(); try { preparedStatement = connection.prepareStatement(sql); if (params != null) { for (int i = 0; i < params.length; i++) { preparedStatement.setObject(i + 1, params[i]); } } resultSet = preparedStatement.executeQuery(); System.out.println("获取结果集（有参）成功。"); } catch (SQLException e) { System.out.println("获取结果集（有参）失败!--" + e.getMessage()); } finally { closeConnection(); } return resultSet; } /** * 更新（无参） * * @param sql */ public int gainUpdate(String sql) { connection = this.gainConnection(); try { statement = connection.createStatement(); affectedLine = statement.executeUpdate(sql); System.out.println("更新（无参）成功。"); } catch (SQLException e) { System.out.println("更新（无参）失败!--" + e.getMessage()); } finally { closeConnection(); } return affectedLine; } /** * 更新（有参） * * @param sql * @param params * @return */ public int gainUpdate(String sql, Object[] params) { connection = this.gainConnection(); try { preparedStatement = connection.prepareStatement(sql); if (params != null) { for (int i = 0; i < params.length; i++) { preparedStatement.setObject(i + 1, params[i]); } } affectedLine = preparedStatement.executeUpdate(); System.out.println("更新（有参）成功。"); } catch (SQLException e) { System.out.println("更新失败!--" + e.getMessage()); } finally { closeConnection(); } return affectedLine; } private void closeConnection() { if (resultSet != null) { try { resultSet.close(); System.out.println("资源关闭成功。"); } catch (SQLException e) { System.out.println(e.getMessage()); } } if (statement != null) { try { statement.close(); System.out.println("资源关闭成功。"); } catch (SQLException e) { System.out.println(e.getMessage()); } } if (preparedStatement != null) { try { preparedStatement.close(); System.out.println("资源关闭成功。"); } catch (SQLException e) { System.out.println(e.getMessage()); } } if (connection != null) { try { connection.close(); System.out.println("资源关闭成功。"); } catch (SQLException e) { System.out.println(e.getMessage()); } } } }