Refactoring of Large Software Systems revised

Copyright Canoo Engineering AG, www.canoo.com 2

Sibylle Peter Sven Ehrke

> Introduction

> The Case Study: Advisory Tool for Investment Bankers

> The Refactoring

> The Way We Work

> Lessons Learned

Introduction

Definit ion (Mart in Fowler, Refactoring, pg. 53):

Refactoring (noun): a change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior.

Refactor (verb): To restructure software by applying a series of refactorings without changing it ‘s observable behavior

The Case Study

> Productive and successful since 2004

> Continuously expanded/ enlarged since then

> 320 JSP, 1800 classes

> Homegrown MVC framework, similar to Struts

> ca. 70 functional tests

> Few unit tests

> Little documentation

> High employee turnover

> High maintenance costs

> Change requests cannot be implemented

– complex ity

– Side effects

Dependencies

Original Situation

Action

Java Beans

ServiceInvoker

Service

Worker

Controller Helper

Mapper

Container

HttpServlet

BusinessObject

HttpServlet

Action

Java Beans

Container

HttpServlet

BusinessObject

Facade TransferObject

HttpServlet

Masterplan

Service Mapper

Java Beans

Service Mapper

Validator

Facade TransferObject

Action

JSPHttpServlet

Masterplan

Formatter

AggregatingFacade

Standard GUIStandard GUITechnologyTechnology

(TBD)(TBD)

The RefactoringPart I – new service layer

Service Layer Architecture

Presentation Layer

ServiceLayer

aggregation

Facade 1 Facade 2 Facade 3 Facade 4

WS DB Host

Facade 2Facade 1

Step 1: Structuring through Facades

Step 2: Introducing Transfer Objects

PresentationLayer

transfer objects

JSP Java Bean Action HttpRequest

BusinessObjectConverter

TransferObject

Facade

Service

ServiceLayer

Facade Interface

PresentationLayerJSP Java Bean Action HttpRequest

BusinessObject Converter

TransferObject ServiceLayer

ServiceObject

EJB Proxy

simple

complex

1:n Mapper

PresentationLayerJSP Java Bean Action HttpRequest

BusinessObject Converter

TransferObject ServiceLayer

ServiceObject

EJB Proxy

simple

complex

1:1 Mapper

Step 3: New Service Layer

inTO outTO

Service

Service Interface

Step 3: New Service Layer

inTO outTO

Service

outSOinSO

EJB Method

Mapper Mapper

AbstractService

inTO outTO

Services

inTO A outTO A

Service A

Service

inTO B outTO B

Service B

Step 4: Introducing Basetypes

Facade Interface

The Way We Work

Daily Work

Coordination

Daily standup meeting

Regular workshops with the customer‘s lead engineer

retrospective after each

refactoring step

Lightweigth, but intensive

testing process with test team

Monthly meeting with

the project manager of the

customer

Weekly reporting with

the lead engineer and

team lead of the customer

Without changing it’s observable behavior

Functional tests

> 50% code coverage

Continuous integration

> No build server - > installed teamcity on a spare machine

> Nightly build incl. Webtests

Testing

> Functional tests require host services stubs will be created in part 2> Complete test of the application takes 3 weeks Tester integrated in our team for testing phase. > Nightly deployment on test server> Tester created videos (for us and to create more automated tests)

Lessons Learned

Copyright Canoo Engineering AG, www.canoo.com 42Le

> Knowledge transfer to the core team as early as possible

> Continous integration is a must

> Investment in automated test suite

> Dependencies to other systems

> Automated quality assurance

> Testing phase much longer than anticipated

> Focus on technical refactoring can be lifesaving

> Refactoring of a large software system is a new project

> KISS: Simplicity is needed

Copyright Canoo Engineering AG, www.canoo.com 43A

> Costs per feature reduced

> Service oriented architecture

> Side effects removed

> Separation between layers and modules

> Automated quality assurance

> Long required new functionality which served as key differentiator has been implemented

Refactoring Benefits

Refactoring of Large Software Systems is

Refactoring of Large Software Systems needs

• Martin Fowler, Refactoring: Improving the Design of Existing Code

• Stephan Ducasse, Oscar Nierstrasz, Object Oriented Reengineering Patterns PDF: http:/ / www.win.ua.ac.be/ ~sdemey/

Joshua Kerievsky, Refactoring to Patterns•

Martin Lippert, Stefan Rook, Refactoring in Large Software Projects

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