注册登陆的方法

package com.zhiyou.dao;
import com.zhiyou.entity.User;
import com.zhiyou.util.BaseDao;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;




public class LoginDao extends BaseDao {
	//新增一个用户
	public int insertUser() throws Exception {
		int i=0;
		super.getConnection();//创建链接
		
		Scanner sc=new Scanner(System.in);
		System.out.println("输入要添加的用户名");
		String username=sc.next();
		System.out.println("输入密码");
		String password=sc.next();
		/*System.out.println("输入id");
		int id = Integer.valueOf(sc.next()).intValue();*/
		String sql = "insert into login values('"+username+"','"+password+"')";
		this.st=conn.createStatement();
		i=st.executeUpdate(sql);
		closeAll();
		return i;
	}
	//新增一个用户
		public int insertUser2(String username,String password) throws Exception {
			int i=0;
			super.getConnection();//创建链接
			
			String sql = "insert into login values('"+username+"','"+password+"')";
			this.st=conn.createStatement();
			i=st.executeUpdate(sql);
			closeAll();
			return i;
		}
	
	// 查
	public List<User> getAll() {
		List<User> list = new ArrayList<User>();
		this.getConnection();
		try {
			this.st = conn.createStatement();
			String sql = "select * from login";
			rs=st.executeQuery(sql);
			while(rs.next()) {
				User user = new User();
				user.setUsername(rs.getString("username"));
				user.setPassword(rs.getString("password"));
				list.add(user);
			}
			this.closeAll();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return list;
	}
	// 查 根据输入的username返回用户user
	public User getById(String username) throws Exception {
		User user = null;
		this.getConnection();
		// 建立SQL语句
		String sql = "select username,password from login where username='"+ username +"'";
		System.out.println("sql语句：" + sql);
		// 建立执行语句
		this.st = conn.createStatement();
		// 执行SQL语句，返回结果集
		rs = st.executeQuery(sql);
		// 遍历结果集
		if(rs.next()) {
			user = new User();
			user.setUsername(rs.getString("username")); 
			user.setPassword(rs.getString("password"));
		}
		// 关闭资源
		this.closeAll();
		// 返回对象user
		return user;
	}
	// 删
	public int deleteDao () throws Exception {
		int j = 0;
		// 得到链接
		super.getConnection();
		Scanner sc = new Scanner(System.in);
		System.out.println("输入要删除的用户名");
		String username=sc.next();
		// 建立SQL语句
		String sql = "delete from login where username='"+username+"'";
		// 建立执行语句
		this.st = conn.createStatement();
		// 执行SQL语句，返回结果
		j = st.executeUpdate(sql);
		// 关闭资源
		closeAll();
		// 返回删除结果
		return j;
	}
	// 改
	public int updateDao() throws Exception {
		int a = 0;
		// 得到链接
		super.getConnection();
		
		Scanner sc = new Scanner(System.in);
		System.out.println("修改用户名输入：1          修改密码请输入：2");
		String num = sc.next();
		if(num != null && num.equals("1")) {
			System.out.println("输入要修改姓名的用户名");
			String username1 = sc.next();
			System.out.println("输入新的用户名");
			String username2 = sc.next();
			// SQL语句
			String sql = "update login set username='"+username2+"' where username='"+username1+"' ";
			// 得到执行语句
			this.st = conn.createStatement();
			// 执行修改用户名语句
			int k = st.executeUpdate(sql);
			a = k;
			// 关闭资源
			closeAll();
		}else if(num != null && num.equals("2")) {
			System.out.println("输入要修改密码的用户名");
			String username1 = sc.next();
			System.out.println("输入新的密码");
			String password = sc.next();
			// SQL语句
			String sql = "update login set password='"+password+"' where username='"+username1+"' ";
			// 得到执行语句
			this.st = conn.createStatement();
			// 执行修改用户名语句
			int k = st.executeUpdate(sql);
			a = k;
			// 关闭资源
			closeAll();
		}
		// 返回结果
		return a;
		
	}
	// 登陆
	public User login(String username,String password) {
		User user = null;
		this.getConnection();
		try {
			st=conn.createStatement();
			String sql = "select username,password from login where username='"+username+"' and password='"+ password+"'";
			System.out.println("sql: "+sql);
			rs = st.executeQuery(sql);
			// 遍历结果集
			if(rs.next()) {
				user = new User();
				user.setUsername(rs.getString("username")); 
				user.setPassword(rs.getString("password"));
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}finally { // 不管是否出现异常，都会执行finally中的代码
			closeAll();
		}
		return user;
	}
	// 登陆 ：使用preparedStatement 避免SQL注入
		public User login2(String username,String password) {
			User user = null;
			this.getConnection();
			try {
				// SQL语句
				String sql = "select username,password from login where username=? and password=?";
				System.out.println("sql: "+sql);
				// 准备执行语句
				ps = conn.prepareStatement(sql);
				// 设置第一个通配符为username, 至关于 给第一个通配符? 赋值
				ps.setString(1, username);
				// 设置第二个通配符为password
				ps.setString(2, password);
				// 执行SQL语句，返回结果集
				rs = ps.executeQuery();
				// 遍历结果集
				if(rs.next()) {
					user = new User();
					user.setUsername(rs.getString("username")); 
					user.setPassword(rs.getString("password"));
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}finally { // 不管是否出现异常，都会执行finally中的代码
				closeAll();
			}
			return user;
		}
}