Refactoring: Legacy

Who am I?

Victor Polischuk A man with a terrible character. Java architect, team leader and coach. 8+ years of software development experience. 6+ years of Java experience. Have participated in 6+ legacy projects. Have seen numbers of them. Employed in Luxoft

What is...

Short Name DescriptionThe Highlander Old, mature projects, had been written ages

ago. Paragon.

Die Hard Nobody knows why it is still alive.

Fashion Victims Nobody wants this sh%t anymore.

Problem Child Nobody loves it.

Sentenced Customer tired of supporting it, everything is up to you.

Apathetic Nobody cares.

Rewrite or refactor?

What do we need...

1.A legacy project

2.A team of developers eager to refactor it.

3.A customer convinced enough to pay for it.

4.Smart tools (IDE, RegEx, File Manager etc.)

5.Open mind

Customer vs Developer

Be Honest

Be a Friend

Do Care

Trust

Silly equals

Budget + Time Code + Time=Ignorance Risks=

Business Needs Tech Needs=

#1. Build procedure

Target Oriented Model

Each build script is unique

Low-level build instructions

No use of project information

Build flow or process issues

Project Oriented Model

Every script looks like others

High-level goals

Reuse of project information

Predefined build flow

#2. Inversion of control

Reasons

Reduce coupling.

Increase testability.

Makes further integration easier.

Everybody use it.

Attach IoC library

It is FREE!

XSLT

RegEx

Shell

Java

C#

Python

Etc

Etc

Etc

XSLT: Source

<struts-config>…<action-mappings>…<action path="/logon" type="example.LogonAction"> <forward ... /> <exception ... /></action>

<action type="example.LogoutAction" path="/logout"/>…</action-mappings>…</struts-config>

XSLT: Template

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/"> <beans> <xsl:apply-templates select="struts-config/action-mappings/*"/> </beans></xsl:template><xsl:template match="action"> <bean id="{@path}" class="{@type}"/></xsl:template>

</xsl:stylesheet>

XSLT: Result

<beans>

...

<bean id="/logon" class="example.LogonAction"/>

<bean id="/logout" class="example.LogoutAction"/>

...

</beans>

New code

#3. Fortify defence line

Wall Old code

RegEx: Source

public class UserQuery {...public static User getUser(String userName) {…}

/** JavaDoc */private static void doSomething(Object obj) {…}

/** JavaDoc */public static void saveUser(User user) throws MagicError {…}...}

RegEx: Interface introduction

(?ms)(public\s+static\s+([^{]+).*?)(?=\s+public\s+|\}\s+\z)

public class UserQuery {...User getUser(String userName);

void saveUser(User user) throws MagicError;...}

RegEx: Delegate methods 1

void\s+(\w+)\s*\(((?:(\w+)\s+(\w+),?\s*)+)\)\s*;

void $1($2) {UserQuery.$1(<...>);}

public class UserDaoImpl implements UserDao {...User getUser(String userName);

void saveUser(User user) {UserQuery.saveUser(user);}...}

RegEx: Delegate methods 2

(\w+)\s+(\w+)\s*\(((?:(\w+)\s+(\w+),?\s*)+)\)\s*;

$1 $2($3) {return UserQuery.$2(<...>);}

public class UserDaoImpl implements UserDao {...User getUser(String userName) { return UserQuery.getUser(userName);}

void saveUser(User user) {UserQuery.saveUser(user);}...}

Integration Steps

Attach IoC container.

Convert a couple of similar classes.

Develop a concept.

Share it with the team.

#4. Transaction management

Programmatic

Full control

Low scalability

Noise in code

High mistakes probability

Declarative

Limited control

High scalability

Clean code

Rare mistakes

TransactionManager

Shall be only one ruler

rollbackcommitbegin

Programmatic TM Declarative TM

rollback

commit

begin Data Access Tier

Service Tier

UI Controller Tier

Programmatic TM Declarative TM

rollback

commit

begin get

Programmatic TM

Still Working?

Epilogue

Developer + Customer = Trust

Do you really want it?

Just DO it

Small steps

Problems only