Question

我在此网站上获得此计划：（ http://danielniko.wordpress.com/2012/04/17/simple-crud-using-jsp-servlet-and-mysql/ ）。我怀疑他们为什么使用这个公共用户getUserById（int userId）也许我们可以生活这部分，输出没有任何改变然后，为什么他们使用？最重要的伙伴是什么？任何人都把我从这个问题中解脱出来，......

package com.daniel.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 com.daniel.model.User;
import com.daniel.util.DbUtil;

public class UserDao {

    private Connection connection;

    public UserDao() {
        connection = DbUtil.getConnection();
    }

    public void addUser(User user) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("insert into users(firstname,lastname,dob,email) values (?, ?, ?, ? )");
            // Parameters start with 1
            preparedStatement.setString(1, user.getFirstName());
            preparedStatement.setString(2, user.getLastName());
            preparedStatement.setDate(3, new java.sql.Date(user.getDob().getTime()));
            preparedStatement.setString(4, user.getEmail());
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void deleteUser(int userId) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("delete from users where userid=?");
            // Parameters start with 1
            preparedStatement.setInt(1, userId);
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void updateUser(User user) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("update users set firstname=?, lastname=?, dob=?, email=?" +
                            "where userid=?");
            // Parameters start with 1
            preparedStatement.setString(1, user.getFirstName());
            preparedStatement.setString(2, user.getLastName());
            preparedStatement.setDate(3, new java.sql.Date(user.getDob().getTime()));
            preparedStatement.setString(4, user.getEmail());
            preparedStatement.setInt(5, user.getUserid());
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public List<User> getAllUsers() {
        List<User> users = new ArrayList<User>();
        try {
            Statement statement = connection.createStatement();
            ResultSet rs = statement.executeQuery("select * from users");
            while (rs.next()) {
                User user = new User();
                user.setUserid(rs.getInt("userid"));
                user.setFirstName(rs.getString("firstname"));
                user.setLastName(rs.getString("lastname"));
                user.setDob(rs.getDate("dob"));
                user.setEmail(rs.getString("email"));
                users.add(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return users;
    }

    **public User getUserById(int userId) {
        User user = new User();
        try {
            PreparedStatement preparedStatement = connection.
                    prepareStatement("select * from users where userid=?");
            preparedStatement.setInt(1, userId);
            ResultSet rs = preparedStatement.executeQuery();

            if (rs.next()) {
                user.setUserid(rs.getInt("userid"));
                user.setFirstName(rs.getString("firstname"));
                user.setLastName(rs.getString("lastname"));
                user.setDob(rs.getDate("dob"));
                user.setEmail(rs.getString("email"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return user;
    }**
}

Answer 1

是的，需要这个功能。因为java有封装机制＆amp;对于batter arcitacture，他们使用MVC，其中User类是这里的模型。

这里public User getUserById(int userId)只是收集数据库中的所有信息。返回为变量User（其行为类似于模型）现在无需重新连接到数据库以获取更多详细信息。

他们为什么使用这个'public User getUserById（int userId）'？

1 个答案: