Architecting well-structured Java applications

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ARCHITECTING WELL-STRUCTURED JAVAAPPLICATIONS

Eduards Sizovs

@eduardsi

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MOST APPS BEGIN LIFE SMALL AND NEAT.

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TIME GOES BY...

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HELLO. I AM YOUR ROTTING ENTERPRISE APP.

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- RIGIDITY

- FRAGILITY

- IMMOBILITY

- VISCOSITY

- OPACITY

- NEEDLESS COMPLEXITY

- NEEDLESS REPITITION

SMELLING SYMPTOMS ->

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HIBERNATE CORE V4.3.8.FINAL

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JDK V1.7.0_51

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A JDK CODE BASE IS DEEPLY INTERCONNECTED AT BOTH THE API AND THEIMPLEMENTATION LEVELS, HAVING BEEN BUILT OVER MANY YEARS

PRIMARILY IN THE STYLE OF A MONOLITHIC SOFTWARE SYSTEM. WE’VESPENT CONSIDERABLE EFFORT ELIMINATING OR AT LEAST SIMPLIFYING AS

MANY API AND IMPLEMENTATION DEPENDENCES AS POSSIBLE, SO THATBOTH THE PLATFORM AND ITS IMPLEMENTATIONS CAN BE PRESENTED AS A

COHERENT SET OF INTERDEPENDENT MODULES, BUT SOME PARTICULARLYTHORNY CASES REMAIN.

(C) MARK REINHOLDS, CHIEF ARCHITECT OF THE JAVA PLATFORM

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SPRING V4.1.6

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PRINCIPLES.

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PACKAGE IS THE FIRST-CLASS CITIZEN ANDKEY ELEMENT OF LOGICAL DESIGN.

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TREAT PACKAGES AS A HIERARCHY EVEN IFTHEY’RE REPRESENTED FLAT.

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io.shwitter.userio.shwitter.user.registrationio.shwitter.user.profileio.shwitter.timeline

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io.shwitter.user (part of)io.shwitter.user.registrationio.shwitter.user.profileio.shwitter.timeline

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io.shwitter.userio.shwitter.user.registration (part of)io.shwitter.user.profile io.shwitter.timeline

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io.shwitter.userio.shwitter.user.registrationio.shwitter.user.profile (part of)io.shwitter.timeline

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io.shwitter.userio.shwitter.user.registrationio.shwitter.user.profileio.shwitter.timeline (part of)

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USE PACKAGES TO GROUP FUNCTIONALLY-RELATED ARTIFACTS. DO NOT GROUPARTIFACTS THAT DO THE SAME THING, BUTARE DIFFERENT BY NATURE.

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io.shwitter.controllerio.shwitter.daoio.shwitter.domainio.shwitter.servicesio.shwitter.exceptions

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io.shwitter.controllerio.shwitter.daoio.shwitter.domainio.shwitter.servicesio.shwitter.exceptions

io.shwitter.userio.shwitter.user.registrationio.shwitter.user.profileio.shwitter.timeline

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- ABILITY TO DISTRIBUTE YOUR LAYERS OVER MULTIPLE PHYSICAL TIERS (HA-HA)

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- DECOUPLING / ABSTRACTING FOR EXHANGEABILITY (HA-HA)

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- DECOUPLING / ABSTRACTING FOR INDEPENDENT EVOLUTION (HA-HA)

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- DECOUPLING FOR REUSE (HA-HA)

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- SEPARATION OF CONCERNS (IS PARTICULAR LAYER OUR CONCERN?)

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- RELATED STUFF CO-LOCATION (ARE DAOS REALLY RELATED?)

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- RELATED STUFF CO-LOCATION (ARE DAOS REALLY RELATED?)

- CONSTRAINT ENFORCEMENT (IS THERE A BETTER WAY?)

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APPLY SERVICE-ORIENTED MINDSET TOSOFTWARE STRUCTURE.

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LAYERING IS YOUR SERVICE'S DETAIL AND ISINTERNAL TO THE SERVICE.

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GROUP TIGHTLY COUPLED CLASSESTOGETHER. IF CLASSES THAT CHANGETOGETHER ARE IN THE SAME PACKAGE, THENTHE IMPACT OF CHANGE IS LOCALIZED.

- THE COMMON CLOSURE PRINCIPLE

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MAKE PACKAGES HIGHLY COHESIVE BYFOLLOWING SINGLE RESPONSIBILITYPRINCIPLE.

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io.shwitter.user.registrationio.shwitter.user.notificationsio.shwitter.user.profileio.shwitter.user.profile.blocking

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io.shwitter.user.registrationio.shwitter.user.notificationsio.shwitter.user.profileio.shwitter.user.profile.blocking

io.shwitter.user :(

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KEEP PACKAGES LOOSELY COUPLED, IDEALLY– COMPLETELY INDEPENDENT. REFLECTIONDOESN’T COUNT.

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package io.shwitter.user

@Entity class User { // name, password etc. }

package io.shwitter.timeline

@Entity class Timeline { @OneToOne User user; }

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package io.shwitter.user

@Embeddable class UserId { Long value; }

package io.shwitter.timeline

@Entity class Timeline { @Embedded UserId userId; }

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PROVIDE SLIM PACKAGE INTERFACE AND HIDEIMPLEMENTATION DETAILS.

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AVOID DEPENDENCY MAGNETS. SOMETIMESDUPLICATION IS NOT THAT EVIL.

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MANAGE RELATIONSHIPS. EVERYDEPENDENCY ARROW HAS A REASON.

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FINDBUGS V1.0 - A GREAT START

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FINDBUGS V1.1 – IMPERFECTION CREEPS IN

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FINDBUGS V1.2 – IMPERFECTION TAKES HOLD

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FINDBUGS V1.3 – CHAOS BEGINS

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FINDBUGS V1.4 – EXPLOSION

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THE DEPENDENCIES BETWEEN PACKAGESMUST NOT FORM CYCLES. BURN BI-DIRECTIONAL DEPENDENCES IN FIRE.

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HOW?

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MERGING

package io.shwitter.userclass User { void register(RegistrationNotifier notifier) {}}

package io.shwitter.user.notifyclass RegistrationNotifier { void notify(User user) {}}

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MERGING - REPACKAGING


class RegistrationNotifier { void notify(User user) {}}

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DEPENDENCY INVERSION


package io.shwitter.user.notifyclass RegistrationNotifier { void notify(User user) {}}

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DEPENDENCY INVERSION - REFACTORING STEP 1


package io.shwitter.user.notifyclass RegistrationNotifier implements UserNotifier { void notify(User user) {}}interface UserNotifier { void notify(User user) {} }

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package io.shwitter.userclass User { void register(UserNotifier notifier) {}}

package io.shwitter.user.notifyclass RegistrationNotifier implements UserNotifier { void notify(User user) {}}interface UserNotifier { void notify(User user) {} }

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package io.shwitter.userclass User { void register(UserNotifier notifier) {}}interface UserNotifier { void notify(User user) {} }

package io.shwitter.user.notifyclass RegistrationNotifier implements UserNotifier { void notify(User user) {}}

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ESCALATION

package io.shwitter.userclass User { void register(Notifier n) { n.notify(this); }}

package io.shwitter.user.notifyclass Notifier { void notify(User user) { sendEmailTo(user.email()); }}

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ESCALATION - REFACTORING STEP 1



package io.shwitter.user.registration

class Registrator { void register(User user, Notifier n) {}}

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package io.shwitter.userclass User { void register() { }}



class Registrator { void register(User user, Notifier n) { n.notify(user); }}

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package io.shwitter.userclass User { void register() { }}

package io.shwitter.user.notifyclass Notifier { void notify(String emailAddress) { sendEmailTo(emailAddress); }}


class Registrator { void register(User user, Notifier n) { n.notify(user.email()); }}

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DEMOTION



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DEMOTION - REFACTORING STEP 1

package io.shwitter.userclass User implements EmailHolder { void register(Notifier n) { n.notify(this); }}


package io.shwitter.emailer

interface EmailHolder { String email();}

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DEMOTION - REFACTORING STEP 2

package io.shwitter.userclass User implements EmailHolder { void register(Notifier n) { n.notify(this); }}

package io.shwitter.user.notifyclass Notifier { void notify(EmailHolder emailHolder) { sendEmailTo(emailHolder.email()); }}

package io.shwitter.emailer

interface EmailHolder { String email();}

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TOOLS

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OO Design Principles & Metrics, Jason Gorman http://goo.gl/RTW9GTThe Economics of Software Design, J.B. Rainsberger http://goo.gl/ra7Q8QSOLID Principles, Eduards Sizovs http://goo.gl/RpxavdDesigning Object-Oriented Software, Jouni Smed http://goo.gl/iyE1R2Grand Unified Theory Of Software Design, Jim Weirich http://goo.gl/ASqyAsFun With Modules, Kirk Knoernschild http://goo.gl/i8jx8YPatterns of Modular Architecture http://goo.gl/yFqmZOLet’s turn packages into a module system! http://goo.gl/Mzco8F

MORE

http://goo.gl/i8jx8Y

http://goo.gl/Mzco8F

http://goo.gl/ASqyAs

http://goo.gl/ra7Q8Q

http://goo.gl/RTW9GT

http://goo.gl/iyE1R2

http://goo.gl/yFqmZO

http://goo.gl/Rpxavd

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EITHER YOU WORK TO CREATE ASOFTWARE STRUCTURE OR YOU DON'T.EITHER WAY A STRUCTURE WILL EMERGE.

@EDUARDSI

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THANK YOU

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