设计模式笔记 – 传输对象模式

传输对象模式（Transfer Object Pattern）用于从客户端向服务器一次性传递带有多个属性的数据。传输对象也被称为数值对象。传输对象是一个具有 getter/setter 方法的简单的 POJO 类，它是可序列化的，所以它可以通过网络传输。它没有任何的行为。服务器端的业务类通常从数据库读取数据，然后填充 POJO，并把它发送到客户端或按值传递它。对于客户端，传输对象是只读的。客户端可以创建自己的传输对象，并把它传递给服务器，以便一次性更新数据库中的数值。以下是这种设计模式的实体。

• 业务对象（Business Object） – 为传输对象填充数据的业务服务。
• 传输对象（Transfer Object） – 简单的 POJO，只有设置/获取属性的方法。
• 客户端（Client） – 客户端可以发送请求或者发送传输对象到业务对象。

示例

我们将创建一个作为业务对象的 StudentBO 和作为传输对象的 StudentVO，它们都代表了我们的实体。

TransferObjectPatternDemo，我们的演示类在这里是作为一个客户端，将使用 StudentBO 和 Student 来演示传输对象设计模式。

Java 实现

创建传输对象

public class StudentVO {
    private String name;
    private int rollNo;
    StudentVO(String name, int rollNo) {
        this.name = name;
        this.rollNo = rollNo;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getRollNo() {
        return rollNo;
    }
    public void setRollNo(int rollNo) {
        this.rollNo = rollNo;
    }
}

创建业务对象

import java.util.ArrayList;
import java.util.List;

public class StudentBO {
    List<StudentVO> students;
    public StudentBO() {
        students = new ArrayList<StudentVO>();
        StudentVO student1 = new StudentVO("Robert", 0);
        StudentVO student2 = new StudentVO("John", 1);
        students.add(student1);
        students.add(student2);
    }
    public void deleteStudent(StudentVO student) {
        students.remove(student.getRollNo());
        System.out.println("Student: Roll No "+student.getRollNo()+", deleted from database");
    }
    public List<StudentVO> getAllStudents() {
        return students;
    }
    public StudentVO getStudent(int rollNo) {
        return students.get(rollNo);
    }
    public void updateStudent(StudentVO student) {
        students.get(student.getRollNo()).setName(student.getName());
        System.out.println("Student: Roll No "+student.getRollNo()+", updated in the database");
    }
}

使用 StudentBO 来演示传输对象设计模式

public class TransferObjectPatternDemo {
    public static void main(String[] args) {
        StudentBO studentBusinessObject = new StudentBO();
        for (StudentVO student : studentBusinessObject.getAllStudents()) {
            System.out.println("Student: [RollNo: "+student.getRollNo()+", Name: "+student.getName()+"]");
        }
        StudentVO student = studentBusinessObject.getAllStudents().get(0);
        student.setName("Michael");
        studentBusinessObject.updateStudent(student);
        student = studentBusinessObject.getStudent(0);
        System.out.println("Student: [RollNo: "+student.getRollNo()+", Name: "+student.getName()+"]");
    }
}

Python 实现

from typing import Tuple

class StudentVO:
    def __init__(self, name: str, roll_no: int):
        self.name = name
        self.roll_no = roll_no

    def get_name(self) -> str:
        return self.name

    def set_name(self, name: str):
        self.name = name

    def get_roll_no(self) -> int:
        return self.roll_no

    def set_roll_no(self, roll_no: int):
        self.roll_no = roll_no

class StudentBO:
    def __init__(self):
        self.students = []
        student1 = StudentVO("Robert", 0)
        student2 = StudentVO("John", 1)
        self.students.append(student1)
        self.students.append(student2)

    def delete_student(self, student: StudentVO):
        self.students.remove(student)
        print(f"Student: Roll No {student.get_roll_no()}, deleted from database")

    def get_all_students(self) -> Tuple[StudentVO, ...]:
        return self.students

    def get_student(self, roll_no: int) -> StudentVO:
        return self.students[roll_no]

    def update_student(self, student: StudentVO):
        self.students[student.get_roll_no()].set_name(student.get_name())
        print(f"Student: Roll No {student.get_roll_no()}, updated in the database")

if __name__ == "__main__":
    student_business_object = StudentBO()
    for student in student_business_object.get_all_students():
        print(f"Student: [RollNo: {student.get_roll_no()}, Name: {student.get_name()}]")

    student = student_business_object.get_all_students()[0]
    student.set_name("Michael")
    student_business_object.update_student(student)

    student = student_business_object.get_student(0)
    print(f"Student: [RollNo: {student.get_roll_no()}, Name: {student.get_name()}]")