数据库连接

//创建一个工具类
public class DbUtil {
    private static String name;
    private static String pwd;
    private static String url;
    static{
        Properties properties=new Properties();
        try {    
                 properties.load(Thread.currentThread().getContextClassLoader()
                .getResourceAsStream("sql.properties"));
            name=properties.getProperty("name");
            pwd=properties.getProperty("pwd");
            url=properties.getProperty("url");
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static Connection getConnection(){
        Connection conn=null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn=DriverManager.getConnection(url,name,pwd);
        } catch (ClassNotFoundException | SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return conn;
    }
    public static void closeConn(Connection conn){
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

//创建配置文件.propertites的配置文件，创建在WEB-INF/classes
name:root
pwd:admin
url:jdbc:mysql://127.0.0.1:3306/j121?useUnicode=true&characterEncoding=UTF-8


public class UserDaoImpl implements UserDAO {

    @Override
    public User findUser(String name, String pwd) {
        //链接数据库
        Connection conn=DbUtil.getConnection();
        String sql="select * from users where user_name=? and user_pwd=?";
        User user=null; 
        try {
            PreparedStatement ptmt=conn.prepareStatement(sql);
            ptmt.setString(1, name);
            ptmt.setString(2, pwd);
            ResultSet rs= ptmt.executeQuery();
            if(rs.next()){
                user=new User();
                user.setUserId(rs.getInt("user_id"));
                user.setUserName(rs.getString("user_name"));
                user.setUserPwd(rs.getString("user_pwd"));
                user.setUserType(rs.getInt("user_type"));
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return user;
    }
    public static void main(String[] args) {
        UserDAO userDao=new UserDaoImpl();
        System.out.println(userDao.findUser("lisi", "admin"));
    }
}