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

Warning

• 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

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DP POSA RF PEAA

Taking the Teddy’s courses is one of the fastest ways

I want to believe

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Alien?

Do you believe evolutional software

architecture?

About me

• Before the doom, I received the Ph. D. degree

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The experiences

• 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)

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Snapshots of the WiMAX emulator

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“Big design up front” won this time

• 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.

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The architecture

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MAC

PHY1

SECU

PHY2

Data Socket

Socket

Application

Driver

Control Socket

Data Socket

Control Socket

Mobile Station

Base Station

Agent

MAC

PHY1

SECU

PHY2

Socket

Application

Driver

Control Socket

Data Socket

CHN

Single Layer Simulation

UI & Console

SYS UI

Control Socket

Agent

Agent

Conf.Plug-in

SPMTPlug-in

Data Socket

Control Socket

Gateway

Agent

Routing TableMIMO

PHYMAC

CHN

2 sheets of A2 paper class diagram, 15 sheets of A4 paper sequence diagrams, and totally over 180k LOC

“Big design up front” won, again

• 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

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DVB-H訊號源

具DVB-H訊號接受器與

Bluetooth或WiFi之裝置A

(需使用本套件)

具Bluetooth或WiFi之

平板B (需使用本套件)

Signal 1

Signal 2

The things that changed my mindset

• 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

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Starting from the MVC pattern

• I use MVC in a GUI application

• Why do we use MVC?

– Separation of concern

– Focus on the problem domain

– Reusable model, etc.

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always usually often sometimes rarely never

POSA

MVC implementation is easy?

• Do we implement the MVC correctly?

– Are you kidding?

– In Android, Activity is a model, view, or controller?

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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

How to test an Android App?

• 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.

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ATMCore (100% Tested)

ATMTextConsole ATMSwingApp ATMAndroidApp

ATMCore (100% Tested)

ATMCore (100% Tested)

Evolution to MVC

• Extract method and extract class

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View

View

Controller

View

Controller

Model

View Controller

Model

View

Controller Presentation

Model

RF

An example

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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 { public CalculatorView(CalculatorModel model) { ... Nine.Click += new EventHandler(DigitPressed); } private void DigitPressed(object sender, EventArgs e) { Model.InputDigit((Button)sender, ResultTextBox); } }

Any problem?

Dependencies between MVC

• Observer and Strategy pattern

– Hollywood Principle: don't call us, we'll call you

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View

Controller Presentation

Model

Direct

Indirect

Strategy & Observer Observer

Program to abstraction Program to abstraction

Strategy

DP

Client-server architecture

• 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

– Who is on the server and who is on the client?

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Client Server

View

Controller Model

POSA

Methods won’t be like methods

• 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

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Client Server

View

Controller Model

Model Proxy Observer Proxy

DP

Observer Stub Model Stub

Connectionless client server

• Web application – one of the most popular connectionless client-server architecture

– Decode the URLs

– Call the correct methods

– Keep the model state

– Object creation

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Client (Browser)

Server

View

(AJAX Controller)

Model

Front Controller (Container)

Command (Struts 2 Action)

Session (Container)

PEAA

DP

Persistence

• 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

• Extract the persistence logic from the domain model

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PEAA

Data mapper example

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+initialize()+exit()+getNavigator() : NavigationModel+getDisplayModel() : ImageDisplayModel+getMotionController() : MotionController+getLanguageManager() : LanguageManager+getPreferences() : Preferences+getViewHistory() : ViewHistory+getReaderManager() : ComicBookSuiteReaderManager+getParallelTaskQueue() : BlockingQueue<Runnable>

<<interface>>core::ComicSurferModel

+initialize(in path : string)+loadLanguage(in name : String) : bool+getLocalizedText(in key : string) : string+getCurrentLanguage() : string+setCurrentLanguage(in name : string) : string+getAvailableLanguages() : Set<string>+addLanguageChangeListener(in listener : LanguageChangeListener)+removeLanguageChangeListener(in listener : LanguageChangeListener)

<<interface>>core::LanguageManager

+setPreference(in key : string, in value : string)+getPreference(in key : string) : string+getPreferenceKeys() : string[]+addPreferencesListener(in listener : PreferencesListener)+removePreferencesListener(in listener : PreferencesListener)

<<interface>>core::Preferences

+getRecordCount() : int+getMaximumRecordCapacity() : int+getLastRecord() : ViewRecord+getRecord(in index : int) : ViewRecord+getRecord(in name : string) : ViewRecord+getRecords() : Iterator<ViewRecord>+setLastViewRecord(in name : string, in uri : URI, in volume : int, in page : int)+setMaximumRecordCapacity() : int+addViewHistoryListener()

<<interface>>core::ViewHistory

+saveHistory(in history : ViewHistory)+loadHistory(in history : ViewHistory)

<<interface>>core::ViewHistoryManager

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1

1

1

1

1

1

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+loadPreferences(in preferences : Preferences)+savePreferences(in preferences : Preferences)

<<interface>>core::PreferencesManager

Comic Surfer readers

• Comic surfer supports many formats

– How about ISO, RAR, or comic books on the web?

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Plug-in architecture pattern

• Plug-in pattern can be seen is many software and platforms

– 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

– Strategy for utilizing plug-ins

– Command for invoking functions

– Mediator for plug-in communication

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PEAA

DP

DP

DP

DP

3rd-party readers management

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Plug-in

+open()+close()+getPageCount() : int+getPage(in index : int) : Page

<<interface>>core::ComicBook

11..*

+getContent() : InputStream+close()

<<interface>>core::Page

+getComicBookCount() : int+getComicBook(in index : int) : ComicBook+getSuitePath() : string+getSuitePath() : URI+close()+open()

<<interface>>core::ComicBookSuite

11..*

+getDescription() : string+getExtension(in file : File) : string+getSupportedSchemes() : string[]+isFolderReader() : bool+canRead(in uri : URI) : bool+read(in uri : URI) : ComicBookSuite

<<interface>>core::ComicBookSuiteReader

+addReader(in reader : ComicBookSuiteReader)+addReaders(in readers : ComicBookSuiteReader[])+loadThirdPartyReaders(in path : string)+read(in uri : URI) : ComicBookSuite+getBestFitReader(in uri : URI) : ComicBookSuiteReader

<<interface>>core::ComicBookSuiteReaderManager

1*

+createReaders() : ComicBookSuiteReader[]

<<interface>>core::ComicBookSuiteReaderFactory

Strategy

Factory method

Compatibility issue

• 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?

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How to adapt the changes?

• This method is NOT silver bullet

– Change interfaces and adapt changes on the abstract classes

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core::AbstractComicBookSuite core::AbstractComicBook core::AbstractPage

+open()+close()+getPageCount() : int+getPage(in index : int) : Page

<<interface>>core::ComicBook

+getContent() : InputStream+close()

<<interface>>core::Page

1 1..*

+getComicBookCount() : int+getComicBook(in index : int) : ComicBook+getSuitePath() : string+getSuitePath() : URI+close()

<<interface>>core::ComicBookSuite

1 1..*

ThirdPartyComicBookSuite ThirdPartyComicBook ThirdPartyPage

Layer architecture pattern

• When the model becomes more complicated

– The components in the model can be organized in different logical layers

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http://docs.oracle.com/javase/7/docs/

POSA

Visibility in layer

• 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)

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Layer 4

Layer 3

Layer 2

Layer 1 Layer 1

Layer 2

Layer 3

Layer 4

Ideal case Real case

DP

Dependency in layers

• 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)

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Dependency inversion principle

• Decouple the dependency between layers

– Extract interface

• Two façade, one for the upper client and another for the lower service provider

• Factory or dependency injection (Spring framework)

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Layer N + 1

Façade for the upper client

Interfaces for the lower service provider

Adapter to the upper layer

Layer N

Façade for the upper client

Interfaces for the lower service provider

Adapter to the upper layer

RF

Dependency inversion example

• The reader layer and streaming layer

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+run()+stop()+pause()+isRunning() : bool+setSleepTime(in time : unsigned int)

-DEFAULT_IO_SLEEP_TIME : unsigned int-_sleepTime : unsigned int-_stream : TransportStream*

nsc::MediaReader

#synchronize()+readPacket() : TransportPacket

nsc::TransportStream +close()+open() : bool+read() : char+read(in buffer : char*, in length : int) : int+isAvaliable() : bool+isOpened() : bool

<<interface>>nsc::InputStream

* 1

-_dataSocket : Socket*

nsc::NetworkTransportStream nsc::FileInputStream

+connect(in host : string, in port : int)+read(in data : void*, in length : int) : int+write(in data, in length : int) : int+close()

<<interface>>network::Socket

network::BluetoothTCPSocket network::BluetoothUDPSocket network::EthernetSocket

From layers to tiers

• Layers vs. tiers

– A tier is a physical deployment unit

– Web services

– Dependency inversion principle

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Layer 1

Layer 2

Layer 3

Layer 4 Model Service tier

Presentation tier

Layer 1

Layer 2

Layer 3

Layer 4

Model state

• Which machine should keep the model state?

– May the client cookie or server session help you?

– Duplicate states?

• Database state

• Disposable model objects

– Reduce network overhead

• Data transfer objects

– Transaction

• Unit of work

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Model Service tier

Presentation tier

Layer 1

Layer 2

Layer 3

Layer 4

PEAA

PEAA

PEAA

Scale up

• Concurrency vs. transaction

– Martin Fowler’s first law of distributed object design: don’t distribute your objects!

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Model Service tier

Presentation tier

Layer 1

Layer 2

Layer 3

Layer 4

Load Balancer

Load Balancer

Cloud dream

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http://tedxtaipei.com/talks/2012-simon-chang/

Think different

• 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

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http://zh.wikipedia.org/wiki/Think_Different

Keep on the correct direction

• Evolutional software architecture (refactoring) is an endless story and harmless, not like...

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