JDBC工具类
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概述：JDBCUtils，目的简化书写
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抽取JDBC工具类
// 建立Properties配置文件 url=jdbc:mysql:///db2 user=root password=root driver=com.mysql.jdbc.Driver/*JDBC工具类提取*/ public class JDBCUtils { private static String url; private static String user; private static String password; private static String driver; /*文件的读取只需要读取一次即可拿到数据，使用静态代码*/ static { // 读取文件资源，获取值 // 1.创建Properties集合对象 Properties properties = new Properties(); try { // 获取src路径下的文件的方式-->ClassLoader类加载器 ClassLoader classLoader = JDBCUtils.class.getClassLoader(); URL resource = classLoader.getResource("jdbc.properties"); String path = resource.getPath(); // 获取觉得路径 // 2.加载文件 properties.load(new FileReader(path)); // 3.获取数据，复制 url=properties.getProperty("url"); user=properties.getProperty("user"); password=properties.getProperty("password"); driver=properties.getProperty("driver"); // 4.注册驱动 Class.forName(driver); } catch (Exception e) { e.printStackTrace(); } } /*获取连接对象*/ public static Connection getConnection() throws SQLException { return DriverManager.getConnection(url,user,password); } /*释放资源方法*/ public static void close(Statement stmt,Connection con){ if(stmt!=null){ try { stmt.close(); } catch (SQLException e) { e.printStackTrace(); } } if(con!=null){ try { con.close(); } catch (SQLException e) { e.printStackTrace(); } } } public static void close(ResultSet rs,Statement stmt, Connection con){ if(rs!=null){ try { rs.close(); } catch (SQLException e) { e.printStackTrace(); } } if(stmt!=null){ try { stmt.close(); } catch (SQLException e) { e.printStackTrace(); } } if(con!=null){ try { con.close(); } catch (SQLException e) { e.printStackTrace(); } } } }// 实现JDBC工具类 public static void main(String[] args) { List<Account> all = findAll(); System.out.println(all); System.out.println(all.get(0).getName()); } public static List<Account> findAll(){ /* 查询所有Account对象*/ Connection con=null; Statement stmt =null; ArrayList<Account> accounts = new ArrayList<>(); ResultSet rs=null; try { // 2.获取连接 con = JDBCUtils.getConnection(); // 3.定义sql语句 String sql="select * from account"; // 4.获取执行sql的对象 stmt = con.createStatement(); // 5.执行sql语句 rs = stmt.executeQuery(sql); // 6.遍历结果集，封装对象，装载 while (rs.next()){ int id=rs.getInt(1); String name=rs.getString(2); double money=rs.getDouble(3); accounts.add(new Account(id,name,money)); } } catch (Exception e) { e.printStackTrace(); }finally { JDBCUtils.close(rs,stmt,con); } return accounts; }
练习
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通过键盘录入用户名和密码，判断用户是否登录成功
-- 1.创建数据表users CREATE TABLE users( id INT PRIMARY KEY AUTO_INCREMENT, username VARCHAR(30), PASSWORD VARCHAR(30) ) SELECT * FROM users; -- 数据表users添加数据 INSERT INTO users(username,PASSWORD) VALUES('zhangsan','123'),('lisi','456'); DROP TABLE users;// 2.创建登录的类 public class JDBCDemo2 { /*登录方法*/ public boolean login(String username,String password){ if(username==null||password==null) return false; Connection connection=null; Statement statement=null; ResultSet resultSet=null; try { // 1.获取连接 connection = JDBCUtils.getConnection(); // 2.定义sql语句 String sql="select * from users where username='"+username+"' and password= '"+password+"'"; // 3.获取执行sql的对象 statement = connection.createStatement(); // 4.执行sql对象 resultSet = statement.executeQuery(sql); // 5.判断 return resultSet.next(); } catch (SQLException e) { e.printStackTrace(); }finally { JDBCUtils.close(resultSet,statement,connection); } return true; } public static void main(String[] args) { // 1.键盘输入 Scanner scanner = new Scanner(System.in); System.out.println("请输入用户名："); // 获取输入的用户名 String username = scanner.nextLine(); System.out.println("请输入密码："); // 获取输入的用户名密码 String password=scanner.nextLine(); // 2.调用方法，判断成功或者失败 if(new JDBCDemo2().login(username,password)){ System.out.println("登录成功"); }else{ System.out.println("登录失败"); } } }// 使用PreparedStatement对象防止sql的注入问题 /*登录方法*/ public boolean login(String username,String password){ if(username==null||password==null) return false; Connection connection=null; PreparedStatement preparedStatement=null; ResultSet resultSet=null; try { // 1.获取连接 connection = JDBCUtils.getConnection(); // 2.定义sql语句 String sql="select * from users where username=? and password=?"; // 3.获取执行sql的对象 preparedStatement = connection.prepareStatement(sql); // 4.给?赋值 preparedStatement.setString(1,username); preparedStatement.setString(2,password); // 5.执行sql对象 resultSet = preparedStatement.executeQuery(); // 6.判断 return resultSet.next(); } catch (SQLException e) { e.printStackTrace(); }finally { JDBCUtils.close(resultSet,preparedStatement,connection); } return true; } public static void main(String[] args) { // 1.键盘输入 Scanner scanner = new Scanner(System.in); System.out.println("请输入用户名："); // 获取输入的用户名 String username = scanner.nextLine(); System.out.println("请输入密码："); // 获取输入的用户名密码 String password=scanner.nextLine(); // 2.调用方法，判断成功或者失败 if(new JDBCDemo3().login(username,password)){ System.out.println("登录成功"); }else{ System.out.println("登录失败"); } } -
转账
public static void main(String[] args) { Connection connection =null; PreparedStatement preparedStatementSub =null; PreparedStatement preparedStatementAdd =null; try { // 1.获取连接 connection = JDBCUtils.getConnection(); // 开启事务 connection.setAutoCommit(false); // 2.定义sql String sqlSub="update account set money = money - ? where id=?"; String sqlAdd="update account set money = money + ? where id=?"; // 3.获取执行sql对象 preparedStatementSub = connection.prepareStatement(sqlSub); preparedStatementAdd = connection.prepareStatement(sqlAdd); // 4.设置参数 preparedStatementSub.setDouble(1,500); preparedStatementSub.setInt(2,1); preparedStatementAdd.setDouble(1,500); preparedStatementAdd.setDouble(2,2); // 5.执行sql preparedStatementSub.executeUpdate(); int i=3/0; preparedStatementAdd.executeUpdate(); // 提交事务 connection.commit(); } catch (Exception e) { // 回滚事务 try { if(connection!=null)connection.rollback(); } catch (SQLException ex) { ex.printStackTrace(); } e.printStackTrace(); }finally { JDBCUtils.close(preparedStatementSub,null); JDBCUtils.close(preparedStatementAdd,connection); } }
