单个和多个对象的 MVC 模式的实现

Question

我已经使用 MVC 模式实现了学生管理（教程：Link）。我决定将学生分为“SingleStudentModel”和“MultipleStudentModel”，但我不确定这对我来说是否有意义。总的来说，我对我的解决方案不满意。是否可以使用一个控制器处理单个学生和多个学生？ 如果将模型导入视图类（参见 StudentsView.java）可以吗？

我该如何改进这个项目？

提前致谢。

Student.java（模型，数据类（？））

public class Student {

    private String name;
    private int nr;

    public Student(String _name, int _nr){
        this.name = _name;
        this.nr = _nr;
    }

    // get set
}

SingleStudentModel.java（模型）

public class SingleStudentModel {
    private Student student;

    // get set
}

StudentController.java（控制器 -> SingleStudentModel）

public class StudentController {
    private SingleStudentModel model;
    private StudentView view;

    public StudentController(SingleStudentModel _model, StudentView _view){
        this.model = _model;
        this.view = _view;
    }

   // set get

    public void updateView(){
        view.printStudentDetails(model.getStudent().getName(), model.getStudent().getNr());
    }
}

MultipleStudentModel.java（模型）

public class MultipleStudentModel {
    private Collection<Student> students = new ArrayList<Student>();

    public Collection<Student> getStudents() {
        return students;
    }

    public void setStudents(Student student){
        this.students.add(student);
    }
}

StudentsController.java（控制器 -> StudentsModel）

public class StudentsController {
    private MultipleStudentModel model;
    private StudentsView view;

    public StudentsController(MultipleStudentModel _model, StudentsView _view){
        this.model = _model;
        this.view = _view;
    }

    public void updateView(){
        view.printStudentList(model.getStudents());
    }
}

StudentView.java

public class StudentView {
    public void printStudentDetails(String _name, int _nr){
        System.out.println("Student: ");
        System.out.println("name: " + _name);
        System.out.println("nr: " + _nr);
    }
}

StudentsView.java

import com.mvc.model.Student;

import java.util.Collection;

public class StudentsView {

    public void printStudentList(Collection<Student> students){

        System.out.println("\nStudent list");

        for(Student item : students){
            System.out.println("name: " + item.getName());
            System.out.println("nr: " + item.getNr());
        }
    }
}

Main.java

 public class Main {

       public static void main(String [] args){

            //Single student
            SingleStudentModel model = new SingleStudentModel();
            StudentView view = new StudentView();
            StudentController controller = new StudentController(model, view);

            model.setStudent(new Student("John", 1));

            controller.updateView();

            //Multiple student
            MultipleStudentModel model2 = new MultipleStudentModel();
            StudentsView view2 = new StudentsView();
            StudentsController controller2 = new StudentsController(model2, view2);

            model2.setStudents(new Student("Zelda", 2));
            model2.setStudents(new Student("Link", 3));

            controller2.updateView();

            }
      }

Answer 1

您可以创建一个model 的接口，这样MultipleStudentModel 和SingleStudentModel 两个类都会实现

所以你不需要定义两个基本共享相同逻辑的控制器，这也可以让你在运行时使用setModel改变控制器行为

这还将创建一个合同，将您的模型绑定到特定方法，例如 get 等（插入/更新/删除）

public class StudentController {
    private Model model;
    private StudentView view;

    public StudentController(Model _model, StudentView _view){
        this.model = _model;
        this.view = _view;
    }

    public setModel(Model model){
         this.model = model;
    }


}

您也可以使用 View 类来做到这一点

另外，基本上一个学生只是一个学生列表，只包含 一个元素，你可以去掉那个冗余

Answer 2

有一些建议：

1。使用接口而不是类。

您可能听说过Interface-based programming，如果您有多个同种对象的实现，这是一种更好的方法，例如本例中的model 和view。所以更好的方法是将这两个抽象为接口而不是类：

StudentView.java

import java.util.List;

public interface StudentView {
    void printStudentList(List<Student> students);
}

StudentModel.java

import java.util.List;

public interface StudentModel {
    List<Student> getStudents();
}

随时可以方便地实现它们。

2。如果您想在一个控制器中控制多个模型视图对，可以使用 Map 访问。

StudentController.java

import java.util.HashMap;
import java.util.Map;

public class StudentController {
    //    private StudentModel model;
    //    private StudentView view;

    private Map<StudentModel, StudentView> modelAndViews;  // store model-view couple

    public StudentController() {
        this.modelAndViews = new HashMap<>();
    }
    public void updateView(StudentModel model) {
        StudentView v = this.modelAndViews.get(model);
        if (v == null)  return; 
        v.printStudentList(model.getStudents());
    }
    public void addModelAndView(StudentModel model, StudentView view) {
        // validate for null pointer
        // if (...)
        this.modelAndViews.put(model, view); // add new model-view couple
    }
    // other methods
}

3。实现 POJO 的 toString() 方法是测试代码的好方法，而不是在其他方法中进行。

学生.java

public class Student {
    private String name;
    private int rollNo;
    public Student(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;
    }
    @Override
    public String toString() {
        return "Student (name=" + name + ", rollNo=" + rollNo + ")";  // for testing
    }
}

这里是model 和view 的实现：

SingleStudentModel.java

import java.util.List;

public class SingleStudentModel implements StudentModel {

    private List<Student> students; // store one student;   

    public SingleStudentModel(List<Student> students) {
        this.students = students;
    }
    @Override
    public List<Student> getStudents() {
        return this.students;
    }
}

MultipleStudentModel.java

import java.util.List;

public class MultipleStudentModel implements StudentModel {

    private List<Student> students;

    public MultipleStudentModel(List<Student> students) {
        this.students = students;
    }
    @Override
    public List<Student> getStudents() {
        return this.students;
    }
}

SingleStudentView.java

import java.util.List;

public class SingleStudentView implements StudentView {

    @Override
    public void printStudentList(List<Student> students) {
        Student s = students.get(0);
        System.out.println(s);
    }
}

MultipleStudentView.java

import java.util.List;

public class MultipleStudentView implements StudentView {

    @Override
    public void printStudentList(List<Student> students) {
        for (Student s : students) {
            System.out.println(s);
        }
    }
}

（这两个视图可以合二为一，两个更容易理解：）

终于是主类了：

Main.java

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

public class Main {
    public static void main(String[] args) {

        List<Student> student = new ArrayList<>();
        List<Student> students = new ArrayList<>();
        // add test cases
        student.add(new Student("s1", 1));
        for (int i = 0; i < 5; i++) {
            students.add(new Student("s" + i, i));
        }

        StudentModel singleStudentModel = new SingleStudentModel(student);
        StudentModel multipleStudentModel = new MultipleStudentModel(students);

        StudentView singleStudentView = new SingleStudentView();
        StudentView multipleStudentView = new MultipleStudentView();


        StudentController controller = new StudentController();

        controller.addModelAndView(singleStudentModel, singleStudentView);
        controller.addModelAndView(multipleStudentModel, multipleStudentView);

        System.out.println("---------- update single student's view ---------------");
        controller.updateView(singleStudentModel);
        System.out.println("---------- update multiple students' views ---------------");
        controller.updateView(multipleStudentModel);
    }
}

解决方案：

---------- update single student's view ---------------
Student (name=s1, rollNo=1)
---------- update multiple students' views ---------------
Student (name=s0, rollNo=0)
Student (name=s1, rollNo=1)
Student (name=s2, rollNo=2)
Student (name=s3, rollNo=3)
Student (name=s4, rollNo=4)

代码结构：

-src
├ view
│  ├ MultipleStudentView.java
│  ├ SingleStudentView.java
│  └ StudentView.java
├ model
│  ├ MultipleStudentModel.java
│  ├ SingleStudentModel.java
│  ├ Student.java
│  └ StudentModel.java
├ controller
│  └ StudentController.java
└ Main.java

这些都是这里的代码，希望有所帮助~

（顺便说一下，在典型的JavaEE开发中，model只是POJO，而view更常见的是像String这样的逻辑视图。这只是一个MVC的例子，便于理解。）