简单用户管理系统--Manage设计

package UserManager; /**
 * Created by mff on 2017/10/31.
 */

import java.sql.*;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * 采用单例管理用户
 *
 * @author mff
 */
public class UserManager {
    private static UserManager instance = new UserManager();

    private UserManager() {
    }

    /**
     * 提供一个入口方法
     *
     * @return
     */
    public static UserManager getInstance() {
        return instance;
    }

    /**
     * 取得用户列表
     *
     * @return
     */
    public List getUsers() {//如果不是static 我们取用户的时候可能要new 一个新的用户
        String sql = "select * from t_user";
        Connection conn = null;
        Statement pstmt = null;
        ResultSet rs = null;
        User user = null;
        List users = new ArrayList();
        try {
            // Statement,createStatement用来执行SQL语句
            conn = MysqlConnect.connectMysql();
            pstmt = conn.createStatement();
            rs = pstmt.executeQuery(sql);
            while (rs.next()) {
                user = new User();
                user.setUserId(rs.getString("user_id"));
                user.setUserName(rs.getString("user_name"));
                user.setPassword(rs.getString("password"));
                user.setContactTel(rs.getString("contact_tel"));
                user.setEmail(rs.getString("email"));
                user.setCreateDate(rs.getTimestamp("create_date"));
                users.add(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            MysqlConnect.close(rs);
            //UserManager.UserManager.MysqlConnect.close(pstmt);
            MysqlConnect.close(conn);
        }
        return users;
    }


    /**
     * 添加用户的方法
     *
     * @param user
     */
    public void addUser(User user) {
        String sql = "insert into t_user (user_id, user_name, password, contact_tel, email, create_date) values (?,?,?,?,?,?)";
        Connection conn = null;
        PreparedStatement pstmt = null;

        try {

            conn = MysqlConnect.connectMysql();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getUserId());
            pstmt.setString(2, user.getUserName());
            pstmt.setString(3, user.getPassword());
            pstmt.setString(4, user.getContactTel());
            pstmt.setString(5, user.getEmail());
            pstmt.setTimestamp(6, new Timestamp(new Date().getTime()));//能保存年月日 时分秒
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            MysqlConnect.close(pstmt);
            MysqlConnect.close(conn);
        }
    }

    /**
     * 修改用户
     *
     * @param user
     */
    public void modifyUser(User user) {
        StringBuilder sbSql = new StringBuilder();
        sbSql.append("update t_user ")
                .append("set    user_name   = ?, ")
                .append("password    = ?, ")
                .append("contact_tel = ?, ")
                .append("email       = ? ")
                .append("where  user_id     = ? ");
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = MysqlConnect.connectMysql();
            pstmt = conn.prepareStatement(sbSql.toString());
            pstmt.setString(1, user.getUserName());
            pstmt.setString(2, user.getPassword());
            pstmt.setString(3, user.getContactTel());
            pstmt.setString(4, user.getEmail());
            pstmt.setString(5, user.getUserId());
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            MysqlConnect.close(pstmt);
            MysqlConnect.close(conn);
        }
    }

    /**
     * 根据用户代码删除
     *
     * @param userId
     */
    public void delUser(String userId) {
        String sql = "delete from t_user where user_id=?";
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = MysqlConnect.connectMysql();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, userId);
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            MysqlConnect.close(pstmt);
            MysqlConnect.close(conn);
        }
    }

    /**
     * 根据用户代码查询
     *
     * @param userId
     * @return 如果存在返回User对象，否则返回null
     */
    public User findUserById(String userId) {
        String sql = "select user_id, user_name, password, contact_tel, email, create_date from t_user where user_id=?";
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        User user = null;
        try {
            conn = MysqlConnect.connectMysql();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, userId);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                user = new User();
                user.setUserId(rs.getString("user_id"));
                user.setUserName(rs.getString("user_name"));
                user.setPassword(rs.getString("password"));
                user.setContactTel(rs.getString("contact_tel"));
                user.setEmail(rs.getString("email"));
                user.setCreateDate(rs.getTimestamp("create_date"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            MysqlConnect.close(rs);
            MysqlConnect.close(pstmt);
            MysqlConnect.close(conn);
        }
        return user;
    }

    /**
     * 取得总记录数
     *
     * @param conn
     * @return
     */
    private int getTotalRecords(Connection conn)
            throws SQLException {
        String sql = "select count(*) from t_user where user_id <> 'root'";
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        int count = 0;
        try {
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            rs.next();
            count = rs.getInt(1);
        } finally {
            MysqlConnect.close(rs);
            MysqlConnect.close(pstmt);
        }
        return count;
    }
}