MVC的一个例子

首先是创建一个模型（Model）。PropertyChangeSupport成员变量，是事件委托模型中的发布订阅机制。它允许试图注册给Model，并接收Model状态的变化通告。

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

public class Model
    ...{
        private PropertyChangeSupport changeSupport = new PropertyChangeSupport(this);
        private boolean loginStatus;
        private String login;
        private String password;
        public Model()
            ...{
                loginStatus = false;
            }
        public void setLogin(String login)
            ...{
                this.login = login;
            }
        public void setPassword(String password)
            ...{
                this.password = password;
            }
        public boolean getLoginStatus()
            ...{
                return loginStatus;
            }
        public boolean getAllowed()
            ...{
                boolean allowed = false;
                if (login == "abc" && password == "abc")
                    allowed = true;
                else
                    allowed = false;
                return allowed;
            }
        public void setLoginStatus(boolean status)
            ...{
                boolean old = this.loginStatus;
                this.loginStatus = status;
                changeSupport.firePropertyChange("model.loginStatus", old, status);
            }
        public void login(String login,String password)
            ...{
                setLogin(login);
                setPassword(password);
                
                if (getAllowed())
                    ...{
                        if (getLoginStatus())
                            ...{
                                setLoginStatus(false);
                            } else
                            ...{
                                setLoginStatus(true);
                            }
                    }
                else
                    setLoginStatus(false); 
            }
        public void addPropertyChangeListener(PropertyChangeListener listener)
            ...{
                changeSupport.addPropertyChangeListener(listener);
            }
    }

 然后是创建视图。CenterPanel用来输入用户数据。WorkPanel实现了PropertyChangeListener接口，这就使得WorkPanel可以注册到应用程序Model，并且当Model变化时使修改通告被发布给它。WorkPanel被作为PropertyChangeListener被注册到Model。这将在界面和域逻辑之间提供了低耦合，允许视图在Model发生变化时被修改。

import java.awt.GridLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.JPasswordField;

public class CenterPanel extends JPanel
    ...{
        static final long serialVersionUID = 1L;
        private JTextField login = new JTextField(15);
        private JPasswordField password = new JPasswordField(15);
        
        public CenterPanel()
            ...{
                setLayout(new GridLayout(2,2));
                add(new JLabel("Login:"));
                add(login);
                add(new JLabel("Password:"));
                add(password);
            }
        public String getLogin()
            ...{
                return login.getText();
            }
        public String getPassword()
            ...{
                return password.getText();
            }
    }

 

import java.awt.BorderLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.Action;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class WorkPanel extends JPanel implements PropertyChangeListener
    ...{
        static final long serialVersionUID = 1L;
        private Model model;
        private JPanel center;
        private JPanel buttonPanel = new JPanel();
        private JLabel loginStatusLabel = new JLabel("  ");
        
        public WorkPanel(JPanel center, Model model)
            ...{
                this.center = center;
                this.model = model;
                init();
            }
        private void init()
            ...{
                setLayout(new BorderLayout());
                add(center ,BorderLayout.CENTER);
                add(buttonPanel, BorderLayout.SOUTH);
                add(loginStatusLabel , BorderLayout.NORTH);
            }
        public void propertyChange(PropertyChangeEvent evt)
            ...{
                if (evt.getPropertyName().equals("model.loginStatus"))
                    ...{
                        Boolean status = (Boolean)evt.getNewValue();
                        if (status.booleanValue())
                            ...{
                                loginStatusLabel.setText("Login is sucessful");
                            }
                        else 
                            ...{
                                loginStatusLabel.setText("Login Failed");
                            }
                    }
            }
        public void addButton (String name , Action action)
            ...{
                JButton button = new JButton(name);
                button.addActionListener(action);
                buttonPanel.add(button);
            }
    }

接着是控制器。控制器的目的是作为模型修改的入口来提供服务。Action类通过组件addActionListener()方法注册到一个或者多个图形组件中。以下两个Action，一个尝试使用Model进行登录，一个用于退出应用程序。 

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

public class LoginAction extends AbstractAction
    ...{
        static final long serialVersionUID = 1L;
        private Model model;
        private CenterPanel panel;
        
        public LoginAction(Model model,CenterPanel panel)
            ...{
                this.model = model;
                this.panel = panel;
            }
        
        public void actionPerformed(ActionEvent e)
            ...{
                System.out.println("Login Action:" + panel.getLogin() + " " + panel.getPassword());
                model.login(panel.getLogin(), panel.getPassword());
            }
    }

 

import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class ExitAction extends AbstractAction
    ...{
        static final long serialVersionUID = 1L;
        public void actionPerformed(ActionEvent e)
            ...{
                JFrame frame = new JFrame();
                int response = JOptionPane.showConfirmDialog(frame, "Exit Application?", "Exit", JOptionPane.OK_CANCEL_OPTION);
                if (JOptionPane.YES_OPTION == response)
                    ...{
                        System.exit(0);
                    }
            }
    }

 最后，Application类用来初始化。它创建关联，建立起了MVC逻辑设计原则。
1、创建到Model类的关联；
2、创建View来显示Swing接口；
3、创建Action类，表示控制器并且将通过命令按钮来注册它们；
4、最后用Swing来显示应用程序； 

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class Application extends JFrame
    ...{
        static final long serialVersionUID = 1L;
        private Model model;
        public Application(Model model)
            ...{
                this.model = model;
                CenterPanel center = new CenterPanel();
                WorkPanel work = new WorkPanel(center,model);
                work.addButton("login", new LoginAction(model,center));
                work.addButton("exit", new ExitAction());
                model.addPropertyChangeListener(work);
                setTitle("MVC Pattern Application");
                
                getContentPane().add(work);
                pack();
                setVisible(true);
                addWindowListener(new WindowAdapter()
                ...{
                    public void windowClosing(WindowEvent e)
                        ...{
                            int response = JOptionPane.showConfirmDialog(null, "Exit Application?", "Exit", JOptionPane.OK_CANCEL_OPTION);
                            if (JOptionPane.YES_OPTION == response)
                                ...{
//                                    dispose();
//                                    finalize();
                                    System.exit(0);
                                }
                        }
                });
            }
        public static void main(String[] args)
            ...{
                Model model = new Model();
                Application application = new Application(model);
            }
    }