how2j.cn

步骤 1 : UserDAO.java   
步骤 2 : 基本的CRUD   
步骤 3 : 非CRUD方法   
步骤 4 : 相关界面功能截图-注册验证账号是否重复   

UserDAO用于建立对于User对象的ORM映射
package tmall.dao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.ArrayList; import java.util.List; import tmall.bean.User; import tmall.util.DBUtil; public class UserDAO { public int getTotal() { int total = 0; try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement();) { String sql = "select count(*) from User"; ResultSet rs = s.executeQuery(sql); while (rs.next()) { total = rs.getInt(1); } } catch (SQLException e) { e.printStackTrace(); } return total; } public void add(User bean) { String sql = "insert into user values(null ,? ,?)"; try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql);) { ps.setString(1, bean.getName()); ps.setString(2, bean.getPassword()); ps.execute(); ResultSet rs = ps.getGeneratedKeys(); if (rs.next()) { int id = rs.getInt(1); bean.setId(id); } } catch (SQLException e) { e.printStackTrace(); } } public void update(User bean) { String sql = "update user set name= ? , password = ? where id = ? "; try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql);) { ps.setString(1, bean.getName()); ps.setString(2, bean.getPassword()); ps.setInt(3, bean.getId()); ps.execute(); } catch (SQLException e) { e.printStackTrace(); } } public void delete(int id) { try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement();) { String sql = "delete from User where id = " + id; s.execute(sql); } catch (SQLException e) { e.printStackTrace(); } } public User get(int id) { User bean = null; try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement();) { String sql = "select * from User where id = " + id; ResultSet rs = s.executeQuery(sql); if (rs.next()) { bean = new User(); String name = rs.getString("name"); bean.setName(name); String password = rs.getString("password"); bean.setPassword(password); bean.setId(id); } } catch (SQLException e) { e.printStackTrace(); } return bean; } public List<User> list() { return list(0, Short.MAX_VALUE); } public List<User> list(int start, int count) { List<User> beans = new ArrayList<User>(); String sql = "select * from User order by id desc limit ?,? "; try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql);) { ps.setInt(1, start); ps.setInt(2, count); ResultSet rs = ps.executeQuery(); while (rs.next()) { User bean = new User(); int id = rs.getInt(1); String name = rs.getString("name"); bean.setName(name); String password = rs.getString("password"); bean.setPassword(password); bean.setId(id); beans.add(bean); } } catch (SQLException e) { e.printStackTrace(); } return beans; } public boolean isExist(String name) { User user = get(name); return user!=null; } public User get(String name) { User bean = null; String sql = "select * from User where name = ?"; try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) { ps.setString(1, name); ResultSet rs =ps.executeQuery(); if (rs.next()) { bean = new User(); int id = rs.getInt("id"); bean.setName(name); String password = rs.getString("password"); bean.setPassword(password); bean.setId(id); } } catch (SQLException e) { e.printStackTrace(); } return bean; } public User get(String name, String password) { User bean = null; String sql = "select * from User where name = ? and password=?"; try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) { ps.setString(1, name); ps.setString(2, password); ResultSet rs =ps.executeQuery(); if (rs.next()) { bean = new User(); int id = rs.getInt("id"); bean.setName(name); bean.setPassword(password); bean.setId(id); } } catch (SQLException e) { e.printStackTrace(); } return bean; } }
基本的CRUD操作与CategoryDAO的CRUD一样,在此不做赘述
除开CRUD之外,UserDAO还提供了一些其他用于支持业务的方法。

在业务上,注册的时候,需要判断某个用户是否已经存在,账号密码是否正确等操作,UserDAO特别提供如下方法进行支持:
根据用户名获取对象
public User get(String name)


以boolean形式返回某个用户名是否已经存在
public boolean isExist(String name)


根据账号和密码获取对象,这才是合理的判断账号密码是否正确的方式,而不是一下把所有的用户信息查出来,在内存中进行比较。
public User get(String name,String password)



注:部分非CRUD的业务方法,需要结合业务场景才能更好的理解,现在理解不透彻也很正常,在后续学习到相关场景的时候,再回过头来看,就明白了。
步骤 4 :

相关界面功能截图-注册验证账号是否重复

edit
相关界面功能截图-注册验证账号是否重复


HOW2J公众号,关注后实时获知最新的教程和优惠活动,谢谢。


提问之前请登陆
提问已经提交成功,正在审核。 请于 我的提问 处查看提问记录,谢谢