Facade(门面)模式

一、模式简介
      外观模式(Facade Pattern）可以将一系列复杂的类包装成一个简单的封闭接口。也称门面模式.

二、模式意图
      facade（门面）模式的作用在于降低客户端操作与Server之间的耦合度，提供统一的访问
入口供客户端使用。减少回底层变化给客户端使用带来的不便。

它适用于一组相对固定且有实际意义的操作，如去医院看病分为挂号、门诊、划价、化验、
收费、取药等。这些操作都可以由Facade来处理，病人只需要与Facade交互就可以了。

在Facade中，我们实现的只是一种事务处理的抽象，并不涉及具体的事务处理逻辑。比如
挂号，我们只需要告诉Facade我们需要挂号，Facade再去联系具体实现挂号的护士，由
护士最终实现具体挂号操作。
     
三、模式UML（下图转自http://www.dofactory.com/）


       
四、模式参与者
      门面(Facade)角色:客户端可以调用这个角色的方法。
          此角色知晓相关的(一个或者多个)子系统的功能和责任。
          在正常情况下，本角色会将所有从客户端发来的请求委派到相应的子系统去。
         
      子系统(SubSystem)角色:可以同时有一个或者多个子系统。
          实现子系统的功能，处理由Facade对象指派的任务。
          每一个子系统都不是一个单独的类，而是一个类的集合。
          每一个子系统都可以被客户端直接调用，或者被门面角色调用。
          子系统并不知道门面的存在，对于子系统而言，门面仅仅是另外一个客户端而已。

五、示例代码


1.子系统代码

public class Account {
	String firstName;
	String lastName;
	final String ACCOUNT_DATA_FILE = "AccountData.txt";
	
	
	public Account(String fname, String lname) {
	firstName = fname;
	lastName = lname;
	}
	public boolean isValid() {
		/*
		Let's go with simpler validation
		here to keep the example simpler.
		*/
		return false;
	}
	public boolean save() {
		String dataLine = getLastName() + "," + getFirstName();
		try {
			FileUtils.writeStringToFile(new File(ACCOUNT_DATA_FILE), dataLine);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return false;
		}
		return true;
	}
	public String getFirstName() {
		return firstName;
	}
	public String getLastName() {
		return lastName;
	}
}



public class Address {
	String address;
	String city;
	String state;
	final String ADDRESS_DATA_FILE = "Address.txt";
	
	public Address(String add, String cty, String st) {
		address = add;
		city = cty;
		state = st;
	}
	public boolean isValid() {
		/*
		The address validation algorithm
		could be complex in real-world
		applications.
		Let's go with simpler validation
		here to keep the example simpler.
		*/
		if (getState().trim().length() < 2)
			return false;
		return true;
	}
	public boolean save() {
		String dataLine = getAddress() + "," + getCity() + "," +
		getState();
		try {
			FileUtils.writeStringToFile(new File(ADDRESS_DATA_FILE), dataLine);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return false;
		}
		return true;
	}
	public String getAddress() {
		return address;
	}
	public String getCity() {
		return city;
	}
	public String getState() {
		return state;
	}
}


public class CreditCard {
	String cardType;
	String cardNumber;
	String cardExpDate;
	final String CC_DATA_FILE = "CC.txt";
	
	public CreditCard(String ccType, String ccNumber,
		String ccExpDate) {
		cardType = ccType;
		cardNumber = ccNumber;
		cardExpDate = ccExpDate;
	}
	public boolean isValid() {
		/*
		Let's go with simpler validation
		here to keep the example simpler.
		*/
		if (getCardType().equals(AccountManager.VISA)) {
			return (getCardNumber().trim().length() == 16);
		}
		if (getCardType().equals(AccountManager.DISCOVER)) {
			return (getCardNumber().trim().length() == 15);
		}
		if (getCardType().equals(AccountManager.MASTER)) {
			return (getCardNumber().trim().length() == 16);
		}
		return false;
	}
	public boolean save() {
		String dataLine =
		getCardType() + "," + getCardNumber() + "," +
		getCardExpDate();
		try {
			FileUtils.writeStringToFile(new File(CC_DATA_FILE), dataLine);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return false;
		}
		return true;
	}
	public String getCardType() {
		return cardType;
		}
		public String getCardNumber() {
		return cardNumber;
		}
		public String getCardExpDate() {
		return cardExpDate;
	}
}

2.Facade代码

public class CustomerFacade {
	private String address;
	private String city;
	private String state;
	private String cardType;
	private String cardNumber;
	private String cardExpDate;
	private String fname;
	private String lname;
	
	public void setAddress(String inAddress) {
		address = inAddress;
	}
	public void setCity(String inCity) {
		city = inCity;
	}
	public void setState(String inState) {
		state = inState;
	}
	public void setFName(String inFName) {
		fname = inFName;
	}
	public void setLName(String inLName) {
		lname = inLName;
	}
	public void setCardType(String inCardType) {
		cardType = inCardType;
	}
	public void setCardNumber(String inCardNumber) {
		cardNumber = inCardNumber;
	}
	public void setCardExpDate(String inCardExpDate) {
		cardExpDate = inCardExpDate;
	}
	public boolean saveCustomerData() {
		Address objAddress;
		Account objAccount;
		CreditCard objCreditCard;
		/*
		client is transparent from the following
		set of subsystem related operations.
		*/
		boolean validData = true;
		String errorMessage = "";
		objAccount = new Account(fname, lname);
		if (objAccount.isValid() == false) {
			validData = false;
			errorMessage = "Invalid FirstName/LastName";
		}
		objAddress = new Address(address, city, state);
		if (objAddress.isValid() == false) {
			validData = false;
				errorMessage = "Invalid Address/City/State";
		}
		objCreditCard = new CreditCard(cardType, cardNumber,
		cardExpDate);
		if (objCreditCard.isValid() == false) {
			validData = false;
			errorMessage = "Invalid CreditCard Info";
		}
		if (!validData) {
			System.out.println(errorMessage);
			return false;
		}
		if (objAddress.save() && objAccount.save() && objCreditCard.save()) {
			return true;
		} else {
			return false;
		}
	}
}

3.客户端代码

public class AccountManager extends JFrame {
	public static final String VISA = "VISA";
	public static final String MASTER = "MASTER";
	public static final String DISCOVER = "DISCOVER"; 
	public static final String newline = "\n";
	public static final String VALIDATE_SAVE = "Validate & Save";
	private JComboBox cmbCardType;
	private JTextField txtFirstName = new JTextField();
	private JTextField txtLastName = new JTextField();
	private JTextField txtAddress = new JTextField();
	private JTextField txtCity = new JTextField();
	private JTextField txtState = new JTextField();
	private JTextField txtCardNumber = new JTextField();
	private JTextField txtDate = new JTextField();
	private JButton submit = new JButton("submit");
	
	
	private CustomerFacade customer;

	public AccountManager() {
		super(" Facade Pattern - Example ");
		cmbCardType = new JComboBox();
		cmbCardType.addItem(AccountManager.VISA);
		cmbCardType.addItem(AccountManager.MASTER);
		cmbCardType.addItem(AccountManager.DISCOVER);
		
		submit.addActionListener(new ActionListener(){

			@Override
			public void actionPerformed(ActionEvent e) {
				// TODO Auto-generated method stub
				customer = new CustomerFacade();
				if(txtFirstName.getText() != null || txtFirstName.getText() != ""){
					customer.setFName(txtFirstName.getText());
				}
				{
					//赋值操作
				}
				customer.saveCustomerData();
			}
			
		});
		GridLayout layout = new GridLayout(9,2);
		
		setLayout(layout);
		add(new JLabel("txtFirstName"));
		add(txtFirstName);
		add(new JLabel("txtLastName"));
		add(txtLastName);
		add(new JLabel("txtAddress"));
		add(txtAddress);
		add(new JLabel("txtCity"));
		add(txtCity);
		add(new JLabel("cmbCardType"));
		add(cmbCardType);
		add(new JLabel("txtCardNumber"));
		add(txtCardNumber);
		add(new JLabel("txtDate"));
		add(txtDate);
		add(new JLabel());
		add(submit);
		

	}

	public static void main(String[]args){
		JFrame f = new AccountManager();
		f.setBounds(100, 100, 600, 800);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setVisible(true);
	}
}