大话设计模式最新章节_吴强著

4.4　例子

大B:“我给你举个例子来说明吧。”

小A：“嗯。好的。”

大B：“让我们建立一个应用：1、接受客户的详细资料（账户、地址和信用卡信息）2、验证输入的信息3、保存输入的信息到相应的文件中。这个应用有三个类：Account、Address和CreditCard。每一个类都有自己的验证和保存数据的方法。”

Listing1: AccountClass
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.
*/
}
public boolean save() {
FileUtil futil = new FileUtil();
String dataLine = getLastName() + ”," + getFirstName();
return futil.writeToFile(ACCOUNT_DATA_FILE, dataLine,true, true);
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
}
Listing2: Address Class
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() {
FileUtil futil = new FileUtil();
String dataLine = getAddress() + ”," + getCity() + ”," + getState();
return futil.writeToFile(ADDRESS_DATA_FILE, dataLine,true, true);
}
public String getAddress() {
return address;
}
public String getCity() {
return city;
}
public String getState() {
return state;
}
}
Listing3: CreditCard Class
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() {
FileUtil futil = new FileUtil();
String dataLine = getCardType() + ,”" + getCardNumber() + ”," + getCardExpDate();
return futil.writeToFile(CC_DATA_FILE, dataLine, true, true);
}
public String getCardType() {
return cardType;
}
public String getCardNumber() {
return cardNumber;
}
public String getCardExpDate() {
return cardExpDate;
}
}

图4-3　验证并保存客户数据

大B：“建立一个客户AccountManager，它提供用户输入数据的用户界面。”

Listing4: Client AccountManager Class
public class AccountManager extends JFrame {
public static final -0*963String newline = "\n";
public static final String VALIDATE_SAVE = "Validate & Save";
public AccountManager() {
super(" Facade Pattern - Example ");
cmbCardType = new JComboBox();
cmbCardType.addItem(AccountManager.VISA);
cmbCardType.addItem(AccountManager.MASTER);
cmbCardType.addItem(AccountManager.DISCOVER);
//Create buttons
JButton validateSaveButton = new JButton(AccountManager.VALIDATE_SAVE);
}
public String getFirstName() {
return txtFirstName.getText();
}
}//End of class AccountManager

当客户AccountManage运行的时候，展示的用户接口如下：

图4-4　用户接口

大B：“为了验证和保存输入的数据，客户AccountManager需要：1、建立Account、Address和CreditCard对象。 2、用这些对象验证输入的数据3、用这些对象保存输入的数据。”

图4-5是对象间的交互顺序图：

图4-5　对象间的交互顺序图

大B：“在这个例子中应用外观模式是一个很好的设计，它可以降低客户和子系统组件（Address、Account和CreditCard）之间的耦合度。应用外观模式，定义一个外观类CustomerFacade (Figure6 and Listing5)。它为由客户数据处理类（Address、Account和CreditCard）所组成的子系统提供一个高层次的、简单的接口。 ”

CustomerFacade
address:String
city:String
state:String
cardType:String
cardNumber:String
cardExpDate:String
fname:String
lname:String
setAddress(inAddress:String)
setCity(inCity:String)
setState(inState:String)
setCardType(inCardType:String)
setCardNumber(inCardNumber:String)
setCardExpDate(inCardExpDate:String)
setFName(inFName:String)
setLName(inLName:String)
saveCustomerData()

图4-6　外观类

Listing5: CustomerFacade Class
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;
}
}
}

大B：“CustomerFacade类以saveCustomData方法的形式提供了业务层次上的服务。客户AccountManager不是直接和子系统的每一个组件交互，而是使用了由CustomFacade对象提供的验证和保存客户数据的更高层次、更简单的接口(如图4-7所示)。”

图4-7　验证和保存客户数据

大B：“在新的设计中，为了验证和保存客户数据，客户需要：1、建立或获得外观对象CustomFacade的一个实例。2、传递数据给CustomFacade实例进行验证和保存。3、调用CustomFacade实例上的saveCustomData方法。CustomFacade处理创建子系统中必要的对象并且调用这些对象上相应的验证、保存客户数据的方法这些细节问题。客户不再需要直接访问任何的子系统中的对象。”

图4-8展示了新的设计的消息流图：

图4-8　新的设计的消息流图

4.4 例子

4.4　例子