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Week02

Spring Framework

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https://github.com/eternity-next/score-spring.git

score-client-01

class Lecture Class StandardGrader Class PassFailGrader interface Grader Dependency Use Client Dependency Use Create Dependency inject Dependency

class Lecture Class StandardGrader Class PassFailGrader interface GraderUse Client Use Create inject class ScoreRepositoryUse

class Lecture interface Grader class ScoreRepository Score Server 2) HTTP 1) score 3) JSON 4) score

public class ScoreRepository { private String url; private HttpClient client; public ScoreRepository() { this.url = http://localhost:3000/scores this.client = new HttpClient( new MultiThreadedHttpConnectionManager()); } public int [] getScores() { GetMethod get = new GetMethod(url); try { if (client.executeMethod(get) == HttpStatus.SC_OK) { return new Gson().fromJson(get.getResponseBodyAsString(), int [].class); } else { return new int [0]; } } catch (Exception e) { throw new RuntimeException(e); } finally { get.releaseConnection(); } } } ScoreRepository

public class Lecture { private ScoreRepository scoreRepository; private Grader grader; public Lecture(Grader grader) { this.grader = grader; this.scoreRepository = new ScoreRepository(); } public String grade() { return grader.grade(scoreRepository.getScores()); } } Lecture

Problem Testability

Transitive Dependency

Hidden Dependency

Transitive Dependency

B CA Object A

Object C

Object B

Object A

Object B

depends on

Object C

Object B

depends on

Object A

Object C

depends on

class Lecture interface Grader class ScoreRepository Score Server LectureTest Transitive Dependency

LectureTest

Score Server

depends on

class Lecture interface Grader class ScoreRepository Score Server LectureTest Server Down

LectureTest

Score Server

depends on

public class Lecture { private ScoreRepository scoreRepository; private Grader grader; public Lecture(Grader grader) { this.grader = grader; this.scoreRepository = new ScoreRepository(); } public String grade() { return grader.grade(scoreRepository.getScores()); } } Lecture

Tight Coupling

class Lecture interface Grader class ScoreRepository Score Server LectureTest Test Fail

LectureTest

Score Server

depends on

public class Lecture { private ScoreRepository scoreRepository; private Grader grader; public Lecture(Grader grader) { this.grader = grader; this.scoreRepository = new ScoreRepository(); } public String grade() { return grader.grade(scoreRepository.getScores()); } } Hidden Dependency

Hidden ScoreRepository

@Test public void starndardGrade() { Lecture lecture = new Lecture(new StandardGrader()); String grade = lecture.grade(); assertEquals("A:1 B:1 C:1 D:0 F:2 ", grade); } assertEquals

A:1 B:1 C:1 D:0 F:2 ?

Solution Dependency Injection

class Lecture interface Grader class ScoreRepository Score Server LectureTest Transitive Dependency

LectureTest

Score Server

depends on

class Lecture interface Grader class HttpScore Repository Score Server LectureTest Dependency Breaking

LectureTest

Score Server

depends on

interface ScoreRepository

class Lecture interface Grader class HttpScore Repository Score Server LectureTest Dependency Breaking

LectureTest

Score Server

depends on

class Lecture interface Grader class HttpScore Repository Score Server LectureTest Testable

LectureTest

Score Server

depends on

public class Lecture { private ScoreRepository scoreRepository; private Grader grader; public Lecture(Grader grader) { this.grader = grader; this.scoreRepository = new ScoreRepository(); } public String grade() { return grader.grade(scoreRepository.getScores()); } } Tight Coupling &

Hidden Dependency

public class Lecture { private ScoreRepository scoreRepository; private Grader grader; public Lecture(Grader grader, ScoreRepository scoreRepository) { this.grader = grader; this.scoreRepository = scoreRepository; } Loose Coupling &

Explicit Dependency

{50,20,70,80,90} =>A:1 B:1 C:1 D:0 F:2

@RunWith(MockitoJUnitRunner.class) public class LectureTest { @Mock private ScoreRepository repository; @Test public void starndardGrade() { when(repository.getScores()) .thenReturn(new int [] {50,20,70,80,90}); Lecture lecture = new Lecture(new StandardGrader(), repository); String grade = lecture.grade(); assertEquals("A:1 B:1 C:1 D:0 F:2 ", grade); }

score-client-02

lecture = new Lecture(new StandardGrader(), new HttpScoreRepository()); lecture = new Lecture(new PassFailGrader(), new HttpScoreRepository()); Loose Coupling => Complex Object Graph

Registry

LectureRegistry object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture cache

get Standard Grade Lecture get Pass Fail Grade Lecture Container

public class Score { private static LectureRegistry lectureFactory = new LectureRegistry(); public static void main(String [] args) { Lecture lecture = null; Scanner scanner = new Scanner(System.in); try { System.out.print("grader? "); switch(scanner.next()) { case "st": lecture = lectureFactory.getStandardGradeLecture(); break; case "pf": lecture = lectureFactory.getPassFailGradeLecture(); break; default: return; } System.out.println(lecture.grade()); } finally { scanner.close(); } } } Score class

Complex Object Graph, Simple API

lecture = lectureFactory.getStandardGradeLecture(); lecture = lectureFactory.getPassFailGradeLecture(); Dependency Lookup

score-client-03

Registry?

Dependency Injection?

Spring Registry Spring

Registry = Application Context Dependency Injection Framework IoC Container

class Lecture class Standard Grader class PassFail Grader class HttpScore Repository class Lecture class Lecture class Standard Grader class HttpScore Repository class PassFail Grader Class Configuration Metadata object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture Registry

class Lecture class Standard Grader class PassFail Grader class HttpScore Repository class Lecture class Lecture class Standard Grader class HttpScore Repository class PassFail Grader Class Configuration Metadata object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture Application Context Registry

Refactoring

class Lecture class Standard Grader class PassFail Grader class HttpScore Repository class Lecture Configuration Metadata object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture Application Context XML Spring GenericXml ApplicationContext

class Lecture class Standard Grader class PassFail Grader class HttpScore Repository class Lecture Configuration Metadata XML

Scores.xml

Application Context Application Context

Scores.xml

Application Context Application Context object :HttpScore Repository httpScore Repository

Scores.xml

Application Context Application Context object :Standard Grader object :PassFail Grader object :HttpScore Repository httpScore Repository passFail Grader standard Grader

Scores.xml

Application Context Application Context object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository httpScore Repository passFail Grader standard Grader standard Grade Lecture Dependency Injection

Sores.xml

Application Context Application Context object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture httpScore Repository passFail Grader standard Grader standard Grade Lecture passFail Grade Lecture Dependency Injection

Load Application Context GenericXmlApplicationContext context = new GenericXmlApplicationContext("classpath:scores.xml); Application Context object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture httpScore Repository passFail Grader standard Grader standard Grade Lecture passFail Grade Lecture

Dependency Lookup lecture = context.getBean("passFailGradeLecture", Lecture.class); Application Context object :Lecture object :Standard Grader object :PassFail Grader object :HttpScore Repository object :Lecture httpScore Repository passFail Grader passFail Grade Lecture id class

Dependency Injection

Dependency Lookup

score-client-04

Constructor Injection Discussion public Lecture(Grader grader, ScoreRepository scoreRepository) { this.grader = grader; this.scoreRepository = scoreRepository; }

Setter Injection Discussion public void setGrader(Grader grader) { this.grader = grader; } public void setScoreRepository(ScoreRepository scoreRepository) { this.scoreRepository = scoreRepository; }

Stateful vs Stateless Discussion

Prototype & Singletone Stateful Stateless

Download - [JWAP-2] DI & Spring

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