The document discusses software architecture patterns and principles. It provides examples of how to apply Model-View-Controller (MVC), client-server, and other patterns to Android and web application development. Key strategies mentioned include refactoring existing code, separating concerns, and using patterns like observer and strategy to reduce coupling between architectural components.

1. 超級全能危樓改造王
增建、改建、打掉重建你的軟體架構？
Spirit Tu
Senior Program Analyst, GSS
White Day, 2013

2. 2
• Sorry, this is an English slide
• I am a good man
– Don’t ask where the (bad) examples come from
• The patterns and methods mentioned today
can be found in the following books
Taking the Teddy’s courses is one of the fastest ways
DP POSA RF PEAA
Warning

3. 3
Alien?
Do you believe
evolutional software
architecture?
I want to believe

4. 4
• Before the doom, I received the Ph. D. degree
About me

5. 5
• Recently, I updated my profile on Link-in
– Six-year teaching assist
(Saw many bad examples)
– A distributed wireless communication protocol
(WiMAX) simulator and emulator
(Project Manager, Aug 2006 – July 2009)
– An embedded DVB-H transport stream decoder
(Scrum Master, Aug 2009 – July 2011)
– A configurable conference management system &
A distributed load testing framework
(Consultant and test planner, Aug 2011 – July 2012)
– An Android game framework for teaching OOP Lab
(Major refactoring for release, Jan 2012 – Apr 2012)
The experiences

6. 6
Snapshots of the WiMAX emulator

7. 7
• Recall the first year of the first project
– Chaos, spaghetti, etc.
• Starting of the second year
– Requirement change: 802.16d  802.16e
– Throw away vs. refactoring
– I played both the PM and SA roles.
– The architecture design took almost three months.
– However, it did work!!
– In addition, we were happy to add new functions
in the third year.
“Big design up front” won this time

8. 8
Mobile Station
Base Station
Application
Application Socket
Socket Driver
Driver
MAC Single Layer
Simulation
MAC SECU
Gateway UI & Console
SECU Agent
PHY1
Agent SYS UI
PHY1 Agent MAC PHY Agent
PHY2
PHY2 CHN CHN MIMO Routing Table Conf. SPMT
Plug-in Plug-in
Data Control Data Control Data Control Data Control
Socket Socket Socket Socket Socket Socket Socket Socket Control Socket
2 sheets of A2 paper class diagram, 15 sheets of A4
paper sequence diagrams, and totally over 180k LOC
The architecture

9. 9
• In the second project
– I was the scrum master of a sub-project, but was
compelled to be the SA of the main project
– The architecture design took almost four months
– Well, it did work, again!!
• In our sub-project, all features completed near 2-month
before the due day
Signal 1
Signal 2
具DVB-H訊號接受器與
具Bluetooth或WiFi之
DVB-H訊號源 Bluetooth或WiFi之裝置A
平板B (需使用本套件)
(需使用本套件)
“Big design up front” won, again

10. 10
• In the following projects
– When I involved, chaos or close to chaos
– “Throw away” is forbidden
– Refactoring  adding new features  chaos 
refactoring  adding new features  chaos 
refactoring, ...
– Evolutional software architecture also works?
• Especially, after I refactored the Android game
framework
The things that changed my mindset

11. 11
always
usually
often
• I sometimes use MVC in a GUI application
rarely
never
• Why do we use MVC? POSA
– Separation of concern
– Focus on the problem domain
– Reusable model, etc.
Starting from the MVC pattern

12. 12
• Do we implement the MVC correctly?
– Are you kidding?
– In Android, Activity is a model, view, or controller?
An Activity is an application component that provides a screen with which
users can interact in order to do something, such as dial the phone, take a
photo, send an email, or view a map. Each activity is given a window in which
to draw its user interface. The window typically fills the screen, but may be
smaller than the screen and float on top of other windows.
http://developer.android.com/guide/components/activities.html
MVC implementation is easy?

13. 13
• I don’t how to test my Android App quickly!!
– I know the advantages of unit tests, but I wrote all
the logics in the activities.
– Using the Android testing and Instrumentation
framework is very slow.
ATMTextConsole ATMSwingApp ATMAndroidApp
ATMCore ATMCore ATMCore
(100% Tested) (100% Tested) (100% Tested)
How to test an Android App?

14. 14
• Extract method and extract class RF
View
View
View
Controller
Controller
Model
View
View
Controller Presentation Controller
Model
Model
Evolution to MVC

15. 15
public class CalculatorModel {
public Number LeftOperand { get; };
public Number RightOperand { get; };
public Number Result { get; };
public void InputDigit(Button button, TextBox result) {
// Append the value of the button to the right operand
// Update the text displayed on the text box
}
}
public class CalculatorView : Form { Any problem?
public CalculatorView(CalculatorModel model) {
...
Nine.Click += new EventHandler(DigitPressed);
}
private void DigitPressed(object sender, EventArgs e) {
Model.InputDigit((Button)sender, ResultTextBox);
}
}
An example

16. 16
• Observer and Strategy pattern DP
– Hollywood Principle: don't call us, we'll call you
View
Strategy Observer Strategy & Observer
Presentation Controller
Program to abstraction Program to abstraction
Model
Direct
Indirect
Dependencies between MVC

17. 17
• In the O’Reilly head first series, you often see
– “lots of customers love your program, and your
boss wants a better program that has ...”
– The boss wants a cloud-based App
• Client server pattern is a good choice POSA
– Who is on the server and who is on the client?
Client Server
View
Model
Controller
Client-server architecture

18. 18
• How do the model in the server side notify the
observer (view) in the client slide?
– Assume a connection is always kept between a
client and the server
– Remote proxy DP
Client Server
View
Model
Controller
Model Proxy Observer Stub Observer Proxy Model Stub
Methods won’t be like methods

19. 19
• Web application – one of the most popular
connectionless client-server architecture
– Decode the URLs
– Call the correct methods
– Keep the model state Server
– Object creation
Model
Client (Browser) Session (Container)
View Command (Struts 2 Action) DP
(AJAX Controller) Front Controller (Container) PEAA
Connectionless client server

20. 20
• Two different models
– Object domain model (class diagram)
• Behavior, inheritance, and polymorphism
• Composition with collection (list, map, etc.)
• Direct (dot) navigation
– Data model (ERD for relational databases)
• Composition with foreign key mapping (and relation
tables)
• SQL join
– Data mapper PEAA
• Extract the persistence logic from the domain model
Persistence

21. 21
<<interface>>
core::PreferencesManager
<<interface>>
core::Preferences +loadPreferences(in preferences : Preferences)
1 +savePreferences(in preferences : Preferences)
+setPreference(in key : string, in value : string)
+getPreference(in key : string) : string
+getPreferenceKeys() : string[] 1
+addPreferencesListener(in listener : PreferencesListener) 1
+removePreferencesListener(in listener : PreferencesListener)
<<interface>>
1 core::ComicSurferModel
<<interface>>
core::LanguageManager +initialize()
+exit()
+initialize(in path : string)
1 +getNavigator() : NavigationModel
+loadLanguage(in name : String) : bool 1
+getDisplayModel() : ImageDisplayModel
+getLocalizedText(in key : string) : string
+getMotionController() : MotionController
+getCurrentLanguage() : string
1 +getLanguageManager() : LanguageManager
+setCurrentLanguage(in name : string) : string
+getPreferences() : Preferences
+getAvailableLanguages() : Set<string>
+getViewHistory() : ViewHistory
+addLanguageChangeListener(in listener : LanguageChangeListener)
+getReaderManager() : ComicBookSuiteReaderManager
+removeLanguageChangeListener(in listener : LanguageChangeListener)
+getParallelTaskQueue() : BlockingQueue<Runnable>
<<interface>> 1
core::ViewHistory 1 1
+getRecordCount() : int
+getMaximumRecordCapacity() : int <<interface>>
+getLastRecord() : ViewRecord core::ViewHistoryManager
+getRecord(in index : int) : ViewRecord +saveHistory(in history : ViewHistory)
+getRecord(in name : string) : ViewRecord +loadHistory(in history : ViewHistory)
+getRecords() : Iterator<ViewRecord>
+setLastViewRecord(in name : string, in uri : URI, in volume : int, in page : int)
+setMaximumRecordCapacity() : int
+addViewHistoryListener()
Data mapper example

22. 22
• Comic surfer supports many formats
– How about ISO, RAR, or comic books on the web?
Comic Surfer readers

23. 23
• Plug-in pattern can be seen is many software
and platforms PEAA
– Eclipse, Firefox, Chrome, etc.
– Extend additional functionalities
• Plug-in can be designed with many techniques
– Reflection for instantiating objects
– Factory method for plug-in initialization DP
– Strategy for utilizing plug-ins DP
– Command for invoking functions DP
– Mediator for plug-in communication DP
Plug-in architecture pattern

24. 24
Plug-in
<<interface>>
core::ComicBookSuite <<interface>>
+getComicBookCount() : int core::ComicBook
+getComicBook(in index : int) : ComicBook +open()
+getSuitePath() : string +close()
+getSuitePath() : URI 1..*
1 +getPageCount() : int
+close() +getPage(in index : int) : Page
+open()
1
1..*
<<interface>>
<<interface>> core::Page
<<interface>>
core::ComicBookSuiteReader +getContent() : InputStream
core::ComicBookSuiteReaderManager
+getDescription() : string +close()
+addReader(in reader : ComicBookSuiteReader)
+getExtension(in file : File) : string
+addReaders(in readers : ComicBookSuiteReader[])
+getSupportedSchemes() : string[]
+loadThirdPartyReaders(in path : string) 1* +isFolderReader() : bool Strategy
+read(in uri : URI) : ComicBookSuite
+canRead(in uri : URI) : bool
+getBestFitReader(in uri : URI) : ComicBookSuiteReader
+read(in uri : URI) : ComicBookSuite
<<interface>>
core::ComicBookSuiteReaderFactory Factory method
+createReaders() : ComicBookSuiteReader[]
3rd-party readers management

25. 25
• When the plug-in API is published
– Any modification could make the existing plug-ins
not compatible with the host application
• Eclipse 3.8  Eclipse 4.2
– Adapter
• Great, but whose responsibility?
Compatibility issue

26. 26
• This method is NOT silver bullet
– Change interfaces and adapt changes on the
abstract classes
<<interface>>
<<interface>>
core::ComicBookSuite
core::ComicBook <<interface>>
+getComicBookCount() : int core::Page
+open()
+getComicBook(in index : int) : ComicBook
+close() +getContent() : InputStream
+getSuitePath() : string 1 1..* 1 1..*
+getPageCount() : int +close()
+getSuitePath() : URI
+getPage(in index : int) : Page
+close()
core::AbstractComicBookSuite core::AbstractComicBook core::AbstractPage
ThirdPartyComicBookSuite ThirdPartyComicBook ThirdPartyPage
How to adapt the changes?

27. 27
• When the model becomes more complicated
– The components in the model can be organized in
different logical layers POSA
http://docs.oracle.com/javase/7/docs/
Layer architecture pattern

28. 28
• Ideally, clients access only the top layer
– For some reasons, clients access the lower layer
– Even the world is not perfect,
• Law of Demeter (Façade) DP
Layer 1 Layer 1
Layer 2 Layer 2
Layer 3 Layer 3
Layer 4 Layer 4
Ideal case Real case
Visibility in layer

29. 29
• Layer substitution
– I want to change one of the layers, but it is difficult
because the upper layer depends on it directly
• Strong dependency between layers
– Why does TCP/IP works?
• Really?
• If you write a C/C++ network program, the TCP
interfaces are in different platforms (Unix/Linux socket
API vs. WinSocket API)
Dependency in layers

30. 30
• Decouple the dependency between layers
– Extract interface RF
• Two façade, one for the upper client and another for
the lower service provider
• Factory or dependency injection (Spring framework)
Façade for the upper client Adapter to the upper layer
Layer N
Interfaces for the lower service provider
Façade for the upper client Adapter to the upper layer
Layer N + 1
Interfaces for the lower service provider
Dependency inversion principle

31. 31
• The reader layer and streaming layer
nsc::MediaReader
<<interface>>
-DEFAULT_IO_SLEEP_TIME : unsigned int nsc::InputStream
-_sleepTime : unsigned int nsc::TransportStream +close()
-_stream : TransportStream*
+open() : bool
+run() +read() : char
#synchronize()
+stop() * 1 +read(in buffer : char*, in length : int) : int
+readPacket() : TransportPacket
+pause() +isAvaliable() : bool
+isRunning() : bool +isOpened() : bool
+setSleepTime(in time : unsigned int)
nsc::NetworkTransportStream nsc::FileInputStream
-_dataSocket : Socket*
<<interface>>
network::Socket
+connect(in host : string, in port : int)
+read(in data : void*, in length : int) : int
+write(in data, in length : int) : int
+close()
network::BluetoothTCPSocket network::BluetoothUDPSocket network::EthernetSocket
Dependency inversion example

32. 32
• Layers vs. tiers
– A tier is a physical deployment unit
– Web services
– Dependency inversion principle
Presentation tier
Layer 1
Layer 2
Layer 1
Layer 2
Layer 3
Layer 4 Model Service tier
Layer 3
Layer 4
From layers to tiers

33. 33
• Which machine should keep the model state?
– May the client cookie or server session help you?
– Duplicate states?
• Database state PEAA Presentation tier
• Disposable model objects Layer 1
Layer 2
– Reduce network overhead
• Data transfer objects PEAA
– Transaction Model Service tier
• Unit of work PEAA Layer 3
Layer 4
Model state

34. 34
• Concurrency vs. transaction
– Martin Fowler’s first law of distributed object
design: don’t distribute your objects!
Presentation tier Load Balancer
Layer 1
Layer 2
Model Service tier Load Balancer
Layer 3
Layer 4
Scale up

35. 35
http://tedxtaipei.com/talks/2012-simon-chang/
Cloud dream

36. 36
• Evolutional software architecture is not easy
– Does big design at the start of the project avoid
changing the software architecture?
• It depends on the characters of the projects
• Requirements always change
– The following things will help you
• Why do we start from MVC? Domain model design
• Design principles and design patterns
• Unit tests, integration tests, and regression tests
• Continuous integration
• Utilize the frameworks, not be used by them
http://zh.wikipedia.org/wiki/Think_Different
Think different

37. 37
• Evolutional software architecture (refactoring)
is an endless story and harmless, not like...
Keep on the correct direction