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Teemitze
Asked:2020-12-12 14:54:06 +0000 UTC2020-12-12 14:54:06 +0000 UTC

Java中的DTO是什么？

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您能否使用简单的 JAVA 代码示例来解释 DTO 是什么？为什么需要这个？

这段代码会是 DTO 吗？有两个类客户和银行

顾客

    import java.sql.Date;

class Customer {
    private String first_name;
    private String last_name;
    private String gedner;
    private Date age;
    private String address;


    Customer(String first_name, String last_name, String gedner, Date age, String address) {
        this.first_name = first_name;
        this.last_name = last_name;
        this.gedner = gedner;
        this.age = age;
        this.address = address;
    }

    public String getLast_name() {
        return last_name;
    }

    public String getFirst_name() {
        return first_name;
    }

    public String getGedner() {
        return gedner;
    }

    public Date getAge() {
        return age;
    }

    public String getAddress() {
        return address;
    }
}

银行

import java.sql.*;
import java.util.Scanner;


public class Bank {
    private static final String URL = "jdbc:mysql://localhost/bank?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC";
    private static final String USER = "root";
    private static final String PASSWORD = "root";

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    Scanner in = new Scanner(System.in);

    public void connect() {
        try {
            connection = DriverManager.getConnection(URL, USER, PASSWORD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    Customer readCustomer() {
        Customer customer = null;
        try {
            preparedStatement = connection.prepareStatement("SELECT * FROM customers WHERE id_customer = ?");
            System.out.print("Введите id пользователя: ");
            preparedStatement.setInt(1, Integer.parseInt(in.next()));
            preparedStatement.execute();
            ResultSet rs = preparedStatement.executeQuery();
            String first_name = rs.getString("first_name");
            String last_name = rs.getString("last_name");
            String gender = rs.getString("gender");
            Date age = rs.getDate("age");
            String address = rs.getString("address");
            customer = new Customer(first_name, last_name, gender, age, address);
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                preparedStatement.close();
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return customer;
    }
}

在 read 方法中，我将 ResultSet 变成了一个客户对象。这是DTO吗？

java

1 个回答

  1. Best Answer

    对象Customer- DTO。

    DTO 对象是不包含方法的对象。它只能包含字段、getter/setter 和构造函数。

    数据传输对象 - 传输数据的对象。数据是类中的字段。

    一个真实的例子是跳棋游戏。您必须有一个对象Checker（检查器）。它不应该有方法，只有字段。

    public class Checker {
    private COLOR checkerColor;
    private Coordinate coordinate; //show checker coordinate
    private boolean isQueen; //show is the checker queen

    public Checker(COLOR checkerColor, int xCoordinate, int yCoordinate) {
        this.checkerColor = checkerColor;
        coordinate = new Coordinate(xCoordinate, yCoordinate);
        isQueen = false;
    }

    public Checker() {}

    public COLOR getColor() {
        return checkerColor;
    }

    public Coordinate getCoordinate() {
        return coordinate;
    }

    public boolean isQueen() {
        return isQueen;
    }

    public void setCoordinate(Coordinate coordinate) {
        this.coordinate.setCoordinates(coordinate.getX(), coordinate.getY());
    }

    public void setQueen() {
        isQueen = true;
    }
}

    或一类Cell（棋盘）。

    public class Cell {

    private boolean isBusy; //shows does the field is occupied with the checker
    private Coordinate coordinate; //show field coordinate

    public Cell(boolean isBusy, int x, int y) {
        coordinate = new Coordinate(x, y);
        this.isBusy = isBusy;
    }

    public Cell() {}

    public boolean isBusy() {
        return isBusy;
    }

    public void setBusy(boolean isBusy) {
        this.isBusy = isBusy;
    }

    public Coordinate getCoordinate() {
        return coordinate;
    }
}

    或类Board（板）：

    public class Board {

    private List<Cell> cells; //list with 64 Fields()
    private List<Checker> checkers; //list with Checkers(), whose number falls from 24 to 0

    public Board() {
        cells = new LinkedList<>();
        checkers = new LinkedList<>();
    }

    public List<Cell> getCells() {
        return cells;
    }

    public List<Checker> getCheckers() {
        return checkers;
    }
}

    还是一类Coordinate。虽然它有方法（重写equals和compare），但这些是来自的方法Object，它也可以被认为是一个 DTO 对象，因为 它仅用于存储数据（坐标）。

    public class Coordinate {

    private int x; //x coordinate
    private int y; //y coordinate


    public Coordinate(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    public void setCoordinates(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Coordinate that = (Coordinate) o;

        return x == that.x && y == that.y;
    }

    public boolean compare(Coordinate that, int xMove, int yMove) {
        return x == that.getX() + xMove
                && y == that.getY() + yMove;
   }
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