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中介者在 Java 中的实现

分类: 文章 • 2024-08-13 15:49:52

中介者是一种行为设计模式， 让程序组件通过特殊的中介者对象进行间接沟通， 达到减少组件之间依赖关系的目的。

中介者能使得程序更易于修改和扩展， 而且能更方便地对独立的组件进行复用， 因为它们不再依赖于很多其他的类。

在 Java 中使用模式

复杂度：⭐⭐

流行度：⭐⭐

使用示例： 中介者模式在 Java 代码中最常用于帮助程序 GUI 组件之间的通信。 在 MVC 模式中， 控制器是中介者的同义词。

下面是核心 Java 程序库中该模式的一些示例：

笔记程序

本例展示了如何将许多 GUI 元素组织起来， 使其在中介者的帮助下无需相互依赖就能合作。

 components: Colleague classes

 components/Component.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;

/**
 * Common component interface.
 */
public interface Component {
    void setMediator(Mediator mediator);
    String getName();
}

 components/AddButton.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;
import refactoring_guru.mediator.example.mediator.Note;

import javax.swing.*;
import java.awt.event.ActionEvent;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class AddButton extends JButton implements Component {
    private Mediator mediator;

    public AddButton() {
        super("Add");
    }

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void fireActionPerformed(ActionEvent actionEvent) {
        mediator.addNewNote(new Note());
    }

    @Override
    public String getName() {
        return "AddButton";
    }
}

 components/DeleteButton.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;
import java.awt.event.ActionEvent;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class DeleteButton extends JButton  implements Component {
    private Mediator mediator;

    public DeleteButton() {
        super("Del");
    }

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void fireActionPerformed(ActionEvent actionEvent) {
        mediator.deleteNote();
    }

    @Override
    public String getName() {
        return "DelButton";
    }
}

 components/Filter.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;
import refactoring_guru.mediator.example.mediator.Note;

import javax.swing.*;
import java.awt.event.KeyEvent;
import java.util.ArrayList;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class Filter extends JTextField implements Component {
    private Mediator mediator;
    private ListModel listModel;

    public Filter() {}

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void processComponentKeyEvent(KeyEvent keyEvent) {
        String start = getText();
        searchElements(start);
    }

    public void setList(ListModel listModel) {
        this.listModel = listModel;
    }

    private void searchElements(String s) {
        if (listModel == null) {
            return;
        }

        if (s.equals("")) {
            mediator.setElementsList(listModel);
            return;
        }

        ArrayList<Note> notes = new ArrayList<>();
        for (int i = 0; i < listModel.getSize(); i++) {
            notes.add((Note) listModel.getElementAt(i));
        }
        DefaultListModel<Note> listModel = new DefaultListModel<>();
        for (Note note : notes) {
            if (note.getName().contains(s)) {
                listModel.addElement(note);
            }
        }
        mediator.setElementsList(listModel);
    }

    @Override
    public String getName() {
        return "Filter";
    }
}

 components/List.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;
import refactoring_guru.mediator.example.mediator.Note;

import javax.swing.*;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
@SuppressWarnings("unchecked")
public class List extends JList implements Component {
    private Mediator mediator;
    private final DefaultListModel LIST_MODEL;

    public List(DefaultListModel listModel) {
        super(listModel);
        this.LIST_MODEL = listModel;
        setModel(listModel);
        this.setLayoutOrientation(JList.VERTICAL);
        Thread thread = new Thread(new Hide(this));
        thread.start();
    }

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    public void addElement(Note note) {
        LIST_MODEL.addElement(note);
        int index = LIST_MODEL.size() - 1;
        setSelectedIndex(index);
        ensureIndexIsVisible(index);
        mediator.sendToFilter(LIST_MODEL);
    }

    public void deleteElement() {
        int index = this.getSelectedIndex();
        try {
            LIST_MODEL.remove(index);
            mediator.sendToFilter(LIST_MODEL);
        } catch (ArrayIndexOutOfBoundsException ignored) {}
    }

    public Note getCurrentElement() {
        return (Note)getSelectedValue();
    }

    @Override
    public String getName() {
        return "List";
    }

    private class Hide implements Runnable {
        private List list;

        Hide(List list) {
            this.list = list;
        }

        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(300);
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
                if (list.isSelectionEmpty()) {
                    mediator.hideElements(true);
                } else {
                    mediator.hideElements(false);
                }
            }
        }
    }
}

 components/SaveButton.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;
import java.awt.event.ActionEvent;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class SaveButton extends JButton implements Component {
    private Mediator mediator;

    public SaveButton() {
        super("Save");
    }

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void fireActionPerformed(ActionEvent actionEvent) {
        mediator.saveChanges();
    }

    @Override
    public String getName() {
        return "SaveButton";
    }
}

 components/TextBox.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;
import java.awt.event.KeyEvent;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class TextBox extends JTextArea implements Component {
    private Mediator mediator;

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void processComponentKeyEvent(KeyEvent keyEvent) {
        mediator.markNote();
    }

    @Override
    public String getName() {
        return "TextBox";
    }
}

 components/Title.java

package refactoring_guru.mediator.example.components;

import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;
import java.awt.event.KeyEvent;

/**
 * Concrete components don't talk with each other. They have only one
 * communication channel–sending requests to the mediator.
 */
public class Title extends JTextField implements Component {
    private Mediator mediator;

    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    protected void processComponentKeyEvent(KeyEvent keyEvent) {
        mediator.markNote();
    }

    @Override
    public String getName() {
        return "Title";
    }
}

 mediator

 mediator/Mediator.java: 定义通用的中介者接口

package refactoring_guru.mediator.example.mediator;

import refactoring_guru.mediator.example.components.Component;

import javax.swing.*;

/**
 * Common mediator interface.
 */
public interface Mediator {
    void addNewNote(Note note);
    void deleteNote();
    void getInfoFromList(Note note);
    void saveChanges();
    void markNote();
    void clear();
    void sendToFilter(ListModel listModel);
    void setElementsList(ListModel list);
    void registerComponent(Component component);
    void hideElements(boolean flag);
    void createGUI();
}

 mediator/Editor.java: 具体中介者

package refactoring_guru.mediator.example.mediator;

import refactoring_guru.mediator.example.components.*;
import refactoring_guru.mediator.example.components.Component;
import refactoring_guru.mediator.example.components.List;

import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.*;

/**
 * Concrete mediator. All chaotic communications between concrete components
 * have been extracted to the mediator. Now components only talk with the
 * mediator, which knows who has to handle a request.
 */
public class Editor implements Mediator {
    private Title title;
    private TextBox textBox;
    private AddButton add;
    private DeleteButton del;
    private SaveButton save;
    private List list;
    private Filter filter;

    private JLabel titleLabel = new JLabel("Title:");
    private JLabel textLabel = new JLabel("Text:");
    private JLabel label = new JLabel("Add or select existing note to proceed...");
  
    /**
     * Here the registration of components by the mediator.
     */
    @Override
    public void registerComponent(Component component) {
        component.setMediator(this);
        switch (component.getName()) {
            case "AddButton":
                add = (AddButton)component;
                break;
            case "DelButton":
                del = (DeleteButton)component;
                break;
            case "Filter":
                filter = (Filter)component;
                break;
            case "List":
                list = (List)component;
                this.list.addListSelectionListener(listSelectionEvent -> {
                    Note note = (Note)list.getSelectedValue();
                    if (note != null) {
                        getInfoFromList(note);
                    } else {
                        clear();
                    }
                });
                break;
            case "SaveButton":
                save = (SaveButton)component;
                break;
            case "TextBox":
                textBox = (TextBox)component;
                break;
            case "Title":
                title = (Title)component;
                break;
        }
    }

    /**
     * Various methods to handle requests from particular components.
     */
    @Override
    public void addNewNote(Note note) {
        title.setText("");
        textBox.setText("");
        list.addElement(note);
    }

    @Override
    public void deleteNote() {
        list.deleteElement();
    }

    @Override
    public void getInfoFromList(Note note) {
        title.setText(note.getName().replace('*', ' '));
        textBox.setText(note.getText());
    }

    @Override
    public void saveChanges() {
        try {
            Note note = (Note) list.getSelectedValue();
            note.setName(title.getText());
            note.setText(textBox.getText());
            list.repaint();
        } catch (NullPointerException ignored) {}
    }

    @Override
    public void markNote() {
        try {
            Note note = list.getCurrentElement();
            String name = note.getName();
            if (!name.endsWith("*")) {
                note.setName(note.getName() + "*");
            }
            list.repaint();
        } catch (NullPointerException ignored) {}
    }

    @Override
    public void clear() {
        title.setText("");
        textBox.setText("");
    }

    @Override
    public void sendToFilter(ListModel listModel) {
        filter.setList(listModel);
    }

    @SuppressWarnings("unchecked")
    @Override
    public void setElementsList(ListModel list) {
        this.list.setModel(list);
        this.list.repaint();
    }

    @Override
    public void hideElements(boolean flag) {
        titleLabel.setVisible(!flag);
        textLabel.setVisible(!flag);
        title.setVisible(!flag);
        textBox.setVisible(!flag);
        save.setVisible(!flag);
        label.setVisible(flag);
    }

    @Override
    public void createGUI() {
        JFrame notes = new JFrame("Notes");
        notes.setSize(960, 600);
        notes.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        JPanel left = new JPanel();
        left.setBorder(new LineBorder(Color.BLACK));
        left.setSize(320, 600);
        left.setLayout(new BoxLayout(left, BoxLayout.Y_AXIS));
        JPanel filterPanel = new JPanel();
        filterPanel.add(new JLabel("Filter:"));
        filter.setColumns(20);
        filterPanel.add(filter);
        filterPanel.setPreferredSize(new Dimension(280, 40));
        JPanel listPanel = new JPanel();
        list.setFixedCellWidth(260);
        listPanel.setSize(320, 470);
        JScrollPane scrollPane = new JScrollPane(list);
        scrollPane.setPreferredSize(new Dimension(275, 410));
        listPanel.add(scrollPane);
        JPanel buttonPanel = new JPanel();
        add.setPreferredSize(new Dimension(85, 25));
        buttonPanel.add(add);
        del.setPreferredSize(new Dimension(85, 25));
        buttonPanel.add(del);
        buttonPanel.setLayout(new FlowLayout());
        left.add(filterPanel);
        left.add(listPanel);
        left.add(buttonPanel);
        JPanel right = new JPanel();
        right.setLayout(null);
        right.setSize(640, 600);
        right.setLocation(320, 0);
        right.setBorder(new LineBorder(Color.BLACK));
        titleLabel.setBounds(20, 4, 50, 20);
        title.setBounds(60, 5, 555, 20);
        textLabel.setBounds(20, 4, 50, 130);
        textBox.setBorder(new LineBorder(Color.DARK_GRAY));
        textBox.setBounds(20, 80, 595, 410);
        save.setBounds(270, 535, 80, 25);
        label.setFont(new Font("Verdana", Font.PLAIN, 22));
        label.setBounds(100, 240, 500, 100);
        right.add(label);
        right.add(titleLabel);
        right.add(title);
        right.add(textLabel);
        right.add(textBox);
        right.add(save);
        notes.setLayout(null);
        notes.getContentPane().add(left);
        notes.getContentPane().add(right);
        notes.setResizable(false);
        notes.setLocationRelativeTo(null);
        notes.setVisible(true);
    }
}

 mediator/Note.java: 笔记类

package refactoring_guru.mediator.example.mediator;

/**
 * Note class.
 */
public class Note {
    private String name;
    private String text;

    public Note() {
        name = "New note";
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getName() {
        return name;
    }

    public String getText() {
        return text;
    }

    @Override
    public String toString() {
        return name;
    }
}

 Demo.java: 初始化代码

package refactoring_guru.mediator.example;

import refactoring_guru.mediator.example.components.*;
import refactoring_guru.mediator.example.mediator.Editor;
import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {
    public static void main(String[] args) {
        Mediator mediator = new Editor();

        mediator.registerComponent(new Title());
        mediator.registerComponent(new TextBox());
        mediator.registerComponent(new AddButton());
        mediator.registerComponent(new DeleteButton());
        mediator.registerComponent(new SaveButton());
        mediator.registerComponent(new List(new DefaultListModel()));
        mediator.registerComponent(new Filter());

        mediator.createGUI();
    }
}

 OutputDemo.png: 执行结果

中介者在 Java 中的实现

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