basic ha example

.gitignore

@@ -0,0 +1,5 @@
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr

build.gradle

@@ -0,0 +1,24 @@
+plugins {
+    id 'org.springframework.boot' version '2.2.2.RELEASE'
+    id 'io.spring.dependency-management' version '1.0.8.RELEASE'
+    id 'java'
+}
+
+group = 'tech.allegro'
+version = '0.0.1-SNAPSHOT'
+sourceCompatibility = '11'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter-web'
+    testImplementation('org.springframework.boot:spring-boot-starter-test') {
+        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
+    }
+}
+
+test {
+    useJUnitPlatform()
+}

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'hexagonal-architecture-by-example'

src/main/java/tech/allegro/hexagon/HexagonalArchitectureExampleApplication.java

@@ -0,0 +1,13 @@
+package tech.allegro.hexagon;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class HexagonalArchitectureExampleApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(HexagonalArchitectureExampleApplication.class, args);
+    }
+
+}

src/main/java/tech/allegro/hexagon/articles/adapters/api/ArticleController.java

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+package tech.allegro.hexagon.articles.adapters.api;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("articles")
+class ArticleController {
+
+    private final Logger log = LoggerFactory.getLogger(ArticleController.class);
+
+    private final ArticleService service;
+
+    ArticleController(final ArticleService service) {
+        this.service = service;
+    }
+
+    @GetMapping("{articleId}")
+    ArticleResponse get(@PathVariable("articleId") final String articleId) {
+        log.info(">>> HTTP GET Request: retrieve an article with id: \"{}\"", articleId);
+        final ArticleResponse articleResponse = service.get(articleId);
+        log.info("<<< HTTP GET Response: article: \"{}\", successfully retrieved", articleResponse.title());
+        return articleResponse;
+    }
+
+    @PostMapping
+    ArticleIdResponse create(@RequestBody final ArticleRequest articleRequest) {
+        log.info(">>> HTTP POST Request: create an article: \"{}\"", articleRequest.title().value());
+        final ArticleIdResponse articleIdResponse = service.create(articleRequest);
+        log.info("<<< HTTP POST Response: article with id: \"{}\", successfully created", articleIdResponse.id());
+        return articleIdResponse;
+    }
+
+
+}

src/main/java/tech/allegro/hexagon/articles/adapters/api/ArticleIdResponse.java

@@ -0,0 +1,22 @@
+package tech.allegro.hexagon.articles.adapters.api;
+
+import tech.allegro.hexagon.articles.domain.model.ArticleId;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+class ArticleIdResponse {
+    private final String id;
+
+    private ArticleIdResponse(final String id) {
+        this.id = id;
+    }
+
+    @JsonProperty("id")
+    public String id() {
+        return id;
+    }
+
+    public static ArticleIdResponse of(final ArticleId articleId) {
+        return new ArticleIdResponse(articleId.value());
+    }
+
+}

src/main/java/tech/allegro/hexagon/articles/adapters/api/ArticleRequest.java

@@ -0,0 +1,32 @@
+package tech.allegro.hexagon.articles.adapters.api;
+
+import tech.allegro.hexagon.articles.domain.model.AuthorId;
+import tech.allegro.hexagon.articles.domain.model.Content;
+import tech.allegro.hexagon.articles.domain.model.Title;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+class ArticleRequest {
+    private final String title;
+    private final String content;
+    private final String authorId;
+
+    ArticleRequest(@JsonProperty("title") final String title, @JsonProperty("content") final String content, @JsonProperty("authorId") final String authorId) {
+        this.title = title;
+        this.content = content;
+        this.authorId = authorId;
+    }
+
+
+    public Title title() {
+        return Title.of(title);
+    }
+
+    public Content content() {
+        return Content.of(content);
+    }
+
+    public AuthorId authorId() {
+        return AuthorId.of(authorId);
+    }
+
+}

src/main/java/tech/allegro/hexagon/articles/adapters/api/ArticleResponse.java

@@ -0,0 +1,45 @@
+package tech.allegro.hexagon.articles.adapters.api;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+class ArticleResponse {
+    private final String id;
+    private final String title;
+    private final String content;
+    private final String authorName;
+
+    private ArticleResponse(final String id, final String title, final String content, final String authorName) {
+        this.id = id;
+        this.title = title;
+        this.content = content;
+        this.authorName = authorName;
+    }
+
+    static ArticleResponse of(final Article article) {
+        return new ArticleResponse(article.id().value(),
+                article.title().value(),
+                article.content().value(),
+                article.author().name().value());
+    }
+
+    @JsonProperty("id")
+    public String id() {
+        return id;
+    }
+
+    @JsonProperty("title")
+    public String title() {
+        return title;
+    }
+
+    @JsonProperty("content")
+    public String content() {
+        return content;
+    }
+
+    @JsonProperty("authorName")
+    public String authorName() {
+        return authorName;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/api/ArticleService.java

@@ -0,0 +1,24 @@
+package tech.allegro.hexagon.articles.adapters.api;
+
+import tech.allegro.hexagon.articles.domain.ArticleFacade;
+import tech.allegro.hexagon.articles.domain.model.ArticleId;
+import org.springframework.stereotype.Component;
+
+@Component
+class ArticleService {
+
+    private final ArticleFacade articleFacade;
+
+    ArticleService(final ArticleFacade articleFacade) {
+        this.articleFacade = articleFacade;
+    }
+
+    ArticleResponse get(final String articleId) {
+        return ArticleResponse.of(articleFacade.get(ArticleId.of(articleId)));
+    }
+
+    ArticleIdResponse create(final ArticleRequest articleRequest) {
+        final ArticleId articleId = articleFacade.create(articleRequest.authorId(), articleRequest.title(), articleRequest.content());
+        return ArticleIdResponse.of(articleId);
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/authorservice/AuthorExternalModel.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.authorservice;
+
+class AuthorExternalModel {
+    /**
+     * External author service model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/authorservice/ExternalServiceClientAuthorRepository.java

@@ -0,0 +1,27 @@
+package tech.allegro.hexagon.articles.adapters.authorservice;
+
+import tech.allegro.hexagon.articles.domain.model.Author;
+import tech.allegro.hexagon.articles.domain.model.AuthorId;
+import tech.allegro.hexagon.articles.domain.model.PersonName;
+import tech.allegro.hexagon.articles.domain.ports.AuthorRepository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+@Component
+class ExternalServiceClientAuthorRepository implements AuthorRepository {
+    private final Logger log = LoggerFactory.getLogger(ExternalServiceClientAuthorRepository.class);
+
+    @Override
+    public Author get(final AuthorId authorId) {
+        /**
+         * external author service integration implementation comes here
+         */
+        log.info("Author: \"William Shakespeare\" fetched", authorId.value());
+        return Author
+                .author()
+                .withId(authorId)
+                .withName(PersonName.of("William Shakespeare"))
+                .build();
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/config/ArticleConfig.java

@@ -0,0 +1,26 @@
+package tech.allegro.hexagon.articles.adapters.config;
+
+import tech.allegro.hexagon.articles.domain.ArticleFacade;
+import tech.allegro.hexagon.articles.domain.ports.ArticleAuthorNotifier;
+import tech.allegro.hexagon.articles.domain.ports.ArticleEventPublisher;
+import tech.allegro.hexagon.articles.domain.ports.ArticleRepository;
+import tech.allegro.hexagon.articles.domain.ports.AuthorRepository;
+import tech.allegro.hexagon.articles.domain.ports.SocialMediaPublisher;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import java.util.List;
+
+@Configuration
+class ArticleConfig {
+
+    @Bean
+    ArticleFacade articleFacade(final ArticleRepository articleRepository,
+                                final AuthorRepository authorRepository,
+                                final ArticleEventPublisher eventPublisher,
+                                final List<SocialMediaPublisher> socialMediaPublishers,
+                                final List<ArticleAuthorNotifier> articleAuthorNotifiers) {
+        return new ArticleFacade(eventPublisher, articleRepository, authorRepository, socialMediaPublishers, articleAuthorNotifiers);
+    }
+
+}

src/main/java/tech/allegro/hexagon/articles/adapters/events/ArticleCreatedEvent.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.events;
+
+class ArticleCreatedEvent {
+    /**
+     * Message broker model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/events/ArticleRetrievedEvent.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.events;
+
+class ArticleRetrievedEvent {
+    /**
+     * Message broker model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/events/MessageBrokerArticleEventPublisher.java

@@ -0,0 +1,29 @@
+package tech.allegro.hexagon.articles.adapters.events;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.ports.ArticleEventPublisher;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+@Component
+class MessageBrokerArticleEventPublisher implements ArticleEventPublisher {
+
+    private final Logger log = LoggerFactory.getLogger(MessageBrokerArticleEventPublisher.class);
+
+    @Override
+    public void publishArticleCreationEvent(final Article article) {
+        /**
+         * message broker integration implementation using {@link ArticleCreatedEvent} comes here
+         */
+        log.info("Article: \"{}\" creation event published on event bus", article.title().value());
+    }
+
+    @Override
+    public void publishArticleRetrievalEvent(final Article article) {
+        /**
+         * message broker integration implementation using {@link ArticleRetrievedEvent} comes here
+         */
+        log.info("Article: \"{}\" retrieval event published on event bus", article.title().value());
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/notifications/ArticleAuthorMailNotifier.java

@@ -0,0 +1,21 @@
+package tech.allegro.hexagon.articles.adapters.notifications;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.ports.ArticleAuthorNotifier;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+@Component
+class ArticleAuthorMailNotifier implements ArticleAuthorNotifier {
+
+    private final Logger log = LoggerFactory.getLogger(ArticleAuthorMailNotifier.class);
+
+    @Override
+    public void notifyAboutArticleCreation(final Article article) {
+        /**
+         * mail system integration implementation using {@link ArticleMailModel} comes here
+         */
+        log.info("Mail sent to author: \"{}\"", article.author().name());
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/notifications/ArticleAuthorSmsNotifier.java

@@ -0,0 +1,21 @@
+package tech.allegro.hexagon.articles.adapters.notifications;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.ports.ArticleAuthorNotifier;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+@Component
+class ArticleAuthorSmsNotifier implements ArticleAuthorNotifier {
+
+    private final Logger log = LoggerFactory.getLogger(ArticleAuthorSmsNotifier.class);
+
+    @Override
+    public void notifyAboutArticleCreation(final Article article) {
+        /**
+         * sms system integration implementation using {@link ArticleSmsModel}comes here
+         */
+        log.info("SMS sent to author: \"{}\"", article.author().name());
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/notifications/ArticleMailModel.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.notifications;
+
+class ArticleMailModel {
+    /**
+     * Mail model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/notifications/ArticleSmsModel.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.notifications;
+
+class ArticleSmsModel {
+    /**
+     * Sms model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/persistence/ArticleDatabaseModel.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.persistence;
+
+class ArticleDatabaseModel {
+    /**
+     * Database model implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/persistence/DbArticleRepository.java

@@ -0,0 +1,56 @@
+package tech.allegro.hexagon.articles.adapters.persistence;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.model.ArticleId;
+import tech.allegro.hexagon.articles.domain.model.Author;
+import tech.allegro.hexagon.articles.domain.model.AuthorId;
+import tech.allegro.hexagon.articles.domain.model.Content;
+import tech.allegro.hexagon.articles.domain.model.PersonName;
+import tech.allegro.hexagon.articles.domain.model.Title;
+import tech.allegro.hexagon.articles.domain.ports.ArticleRepository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+import java.util.UUID;
+
+@Component
+class DbArticleRepository implements ArticleRepository {
+
+    private final Logger log = LoggerFactory.getLogger(DbArticleRepository.class);
+
+
+    @Override
+    public Article save(final Author author, final Title title, final Content content) {
+        /**
+         * Database integration implementation using {@link ArticleDatabaseModel} comes here
+         */
+        final String articleId = UUID.randomUUID().toString();
+        log.info("Article: \"{}\" persisted", title.value());
+        return Article.article()
+                .withId(ArticleId.of(articleId))
+                .withAuthor(author)
+                .withTitle(title)
+                .withContent(content)
+                .build();
+    }
+
+    @Override
+    public Article get(final ArticleId id) {
+        /**
+         * Database integration implementation using {@link ArticleDatabaseModel} comes here
+         */
+        final Title title = Title.of("Hexagonal Architecture");
+        log.info("Article \"{}\" fetched", title.value());
+        return Article.article()
+                .withId(id)
+                .withAuthor(Author
+                        .author()
+                        .withId(AuthorId.of(UUID.randomUUID().toString()))
+                        .withName(PersonName.of("William Shakespeare"))
+                        .build())
+                .withTitle(title)
+                .withContent(Content.of("Lorem ipsum"))
+                .build();
+    }
+}

src/main/java/tech/allegro/hexagon/articles/adapters/twitter/ArticleTwitterModel.java

@@ -0,0 +1,7 @@
+package tech.allegro.hexagon.articles.adapters.twitter;
+
+class ArticleTwitterModel {
+    /**
+     * twitter implementation comes here
+     */
+}

src/main/java/tech/allegro/hexagon/articles/adapters/twitter/TwitterArticlePublisher.java

@@ -0,0 +1,22 @@
+package tech.allegro.hexagon.articles.adapters.twitter;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.ports.SocialMediaPublisher;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+@Component
+class TwitterArticlePublisher implements SocialMediaPublisher {
+
+    private final Logger log = LoggerFactory.getLogger(TwitterArticlePublisher.class);
+
+
+    @Override
+    public void publish(final Article article) {
+        /**
+         * social media integration implementation  using {@link TwitterModel} comes here
+         */
+        log.info("Article: \"{}\" published on twitter", article.title().value());
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/ArticleFacade.java

@@ -0,0 +1,47 @@
+package tech.allegro.hexagon.articles.domain;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.model.ArticleId;
+import tech.allegro.hexagon.articles.domain.model.Author;
+import tech.allegro.hexagon.articles.domain.model.AuthorId;
+import tech.allegro.hexagon.articles.domain.model.Content;
+import tech.allegro.hexagon.articles.domain.model.Title;
+import tech.allegro.hexagon.articles.domain.ports.ArticleAuthorNotifier;
+import tech.allegro.hexagon.articles.domain.ports.ArticleEventPublisher;
+import tech.allegro.hexagon.articles.domain.ports.ArticleRepository;
+import tech.allegro.hexagon.articles.domain.ports.AuthorRepository;
+import tech.allegro.hexagon.articles.domain.ports.SocialMediaPublisher;
+
+import java.util.List;
+
+public class ArticleFacade {
+
+    private final ArticleEventPublisher eventPublisher;
+    private final ArticleRepository articleRepository;
+    private final AuthorRepository authorRepository;
+    private final List<SocialMediaPublisher> socialMediaPublishers;
+    private final List<ArticleAuthorNotifier> articleAuthorNotifiers;
+
+    public ArticleFacade(final ArticleEventPublisher eventPublisher, final ArticleRepository articleRepository, final AuthorRepository authorRepository, final List<SocialMediaPublisher> socialMediaPublishers, final List<ArticleAuthorNotifier> articleAuthorNotifiers) {
+        this.eventPublisher = eventPublisher;
+        this.articleRepository = articleRepository;
+        this.authorRepository = authorRepository;
+        this.socialMediaPublishers = socialMediaPublishers;
+        this.articleAuthorNotifiers = articleAuthorNotifiers;
+    }
+
+    public ArticleId create(final AuthorId authorId, final Title title, final Content content) {
+        final Author author = authorRepository.get(authorId);
+        final Article article = articleRepository.save(author, title, content);
+        eventPublisher.publishArticleCreationEvent(article);
+        socialMediaPublishers.forEach(socialMediaPublisher -> socialMediaPublisher.publish(article));
+        articleAuthorNotifiers.forEach(articleAuthorNotifier -> articleAuthorNotifier.notifyAboutArticleCreation(article));
+        return article.id();
+    }
+
+    public Article get(final ArticleId id) {
+        final Article article = articleRepository.get(id);
+        eventPublisher.publishArticleRetrievalEvent(article);
+        return article;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/Article.java

@@ -0,0 +1,71 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class Article {
+    private final ArticleId id;
+    private final Title title;
+    private final Content content;
+    private final Author author;
+
+
+    private Article(final ArticleId id, final Title title, final Content content, final Author author) {
+        this.id = id;
+        this.title = title;
+        this.content = content;
+        this.author = author;
+    }
+
+    public ArticleId id() {
+        return id;
+    }
+
+    public Title title() {
+        return title;
+    }
+
+    public Content content() {
+        return content;
+    }
+
+    public Author author() {
+        return author;
+    }
+
+    public static ArticleBuilder article() {
+        return new ArticleBuilder();
+    }
+
+
+    public static final class ArticleBuilder {
+        private ArticleId id;
+        private Title title;
+        private Content content;
+        private Author author;
+
+        private ArticleBuilder() {
+        }
+
+        public ArticleBuilder withId(ArticleId id) {
+            this.id = id;
+            return this;
+        }
+
+        public ArticleBuilder withTitle(Title title) {
+            this.title = title;
+            return this;
+        }
+
+        public ArticleBuilder withContent(Content content) {
+            this.content = content;
+            return this;
+        }
+
+        public ArticleBuilder withAuthor(Author author) {
+            this.author = author;
+            return this;
+        }
+
+        public Article build() {
+            return new Article(id, title, content, author);
+        }
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/ArticleId.java

@@ -0,0 +1,17 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class ArticleId {
+    private final String value;
+
+    private ArticleId(final String value) {
+        this.value = value;
+    }
+
+    public static ArticleId of(final String articleId) {
+        return new ArticleId(articleId);
+    }
+
+    public String value() {
+        return value;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/Author.java

@@ -0,0 +1,42 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class Author {
+    private final AuthorId id;
+    private final PersonName name;
+
+
+    public Author(final AuthorId id, final PersonName name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public static AuthorBuilder author() {
+        return new AuthorBuilder();
+    }
+
+    public PersonName name() {
+        return name;
+    }
+
+    public static final class AuthorBuilder {
+        private AuthorId id;
+        private PersonName name;
+
+        private AuthorBuilder() {
+        }
+
+        public AuthorBuilder withId(AuthorId id) {
+            this.id = id;
+            return this;
+        }
+
+        public AuthorBuilder withName(PersonName name) {
+            this.name = name;
+            return this;
+        }
+
+        public Author build() {
+            return new Author(id, name);
+        }
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/AuthorId.java

@@ -0,0 +1,17 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class AuthorId {
+    private final String value;
+
+    private AuthorId(final String value) {
+        this.value = value;
+    }
+
+    public static AuthorId of(final String authorId) {
+        return new AuthorId(authorId);
+    }
+
+    public String value() {
+        return value;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/Content.java

@@ -0,0 +1,17 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class Content {
+    private final String value;
+
+    private Content(final String value) {
+        this.value = value;
+    }
+
+    public static Content of(final String content) {
+        return new Content(content);
+    }
+
+    public String value() {
+        return value;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/PersonName.java

@@ -0,0 +1,17 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class PersonName {
+    private final String value;
+
+    private PersonName(final String value) {
+        this.value = value;
+    }
+
+    public static PersonName of(final String content) {
+        return new PersonName(content);
+    }
+
+    public String value() {
+        return value;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/model/Title.java

@@ -0,0 +1,17 @@
+package tech.allegro.hexagon.articles.domain.model;
+
+public class Title {
+    private final String value;
+
+    private Title(final String value) {
+        this.value = value;
+    }
+
+    public static Title of(final String title) {
+        return new Title(title);
+    }
+
+    public String value() {
+        return value;
+    }
+}

src/main/java/tech/allegro/hexagon/articles/domain/ports/ArticleAuthorNotifier.java

@@ -0,0 +1,9 @@
+package tech.allegro.hexagon.articles.domain.ports;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+
+public interface ArticleAuthorNotifier {
+
+    void notifyAboutArticleCreation(Article article);
+
+}

src/main/java/tech/allegro/hexagon/articles/domain/ports/ArticleEventPublisher.java

@@ -0,0 +1,11 @@
+package tech.allegro.hexagon.articles.domain.ports;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+
+public interface ArticleEventPublisher {
+
+    void publishArticleCreationEvent(Article article);
+
+    void publishArticleRetrievalEvent(Article article);
+
+}

src/main/java/tech/allegro/hexagon/articles/domain/ports/ArticleRepository.java

@@ -0,0 +1,14 @@
+package tech.allegro.hexagon.articles.domain.ports;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+import tech.allegro.hexagon.articles.domain.model.ArticleId;
+import tech.allegro.hexagon.articles.domain.model.Author;
+import tech.allegro.hexagon.articles.domain.model.Content;
+import tech.allegro.hexagon.articles.domain.model.Title;
+
+public interface ArticleRepository {
+
+    Article save(Author author, Title title, Content content);
+
+    Article get(ArticleId id);
+}

src/main/java/tech/allegro/hexagon/articles/domain/ports/AuthorRepository.java

@@ -0,0 +1,9 @@
+package tech.allegro.hexagon.articles.domain.ports;
+
+import tech.allegro.hexagon.articles.domain.model.Author;
+import tech.allegro.hexagon.articles.domain.model.AuthorId;
+
+public interface AuthorRepository {
+
+    Author get(AuthorId authorId);
+}

src/main/java/tech/allegro/hexagon/articles/domain/ports/SocialMediaPublisher.java

@@ -0,0 +1,9 @@
+package tech.allegro.hexagon.articles.domain.ports;
+
+import tech.allegro.hexagon.articles.domain.model.Article;
+
+public interface SocialMediaPublisher {
+
+    void publish(Article article);
+
+}

src/main/resources/application.properties

@@ -0,0 +1 @@
+