uhrin.attila1@gmail.com - A quick and practical example of Hexagonal Architecture in Java

architecture/README.md

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+## Architecture
+
+This module contains articles about software architecture.
+
+### Relevant articles

architecture/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.baeldung.architecture</groupId>
+	<artifactId>architecture</artifactId>
+	<name>architecture</name>
+	<packaging>jar</packaging>
+	<description>Architecture-related articles</description>
+
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-boot-2</artifactId>
+		<version>0.0.1-SNAPSHOT</version>
+		<relativePath>../parent-boot-2</relativePath>
+	</parent>
+
+	<dependencyManagement>
+		<dependencies>
+			<dependency>
+				<groupId>org.junit</groupId>
+				<artifactId>junit-bom</artifactId>
+				<version>${junit-jupiter.version}</version>
+				<type>pom</type>
+				<scope>import</scope>
+			</dependency>
+			<dependency>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-dependencies</artifactId>
+				<version>${spring-boot.version}</version>
+				<type>pom</type>
+				<scope>import</scope>
+			</dependency>
+		</dependencies>
+	</dependencyManagement>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-data-jpa</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+			<scope>runtime</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-devtools</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-core</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<properties>
+	</properties>
+
+</project>

architecture/src/main/java/com/baeldung/hexagonalarchitecture/BookAppConfiguration.java

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+package com.baeldung.hexagonalarchitecture;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import com.baeldung.hexagonalarchitecture.domain.BookService;
+import com.baeldung.hexagonalarchitecture.domain.IBookRepository;
+import com.baeldung.hexagonalarchitecture.domain.IBookService;
+import com.baeldung.hexagonalarchitecture.infrastructure.DatabaseBookRepository;
+import com.baeldung.hexagonalarchitecture.infrastructure.JpaBookRepository;
+
+@Configuration
+public class BookAppConfiguration {
+
+    @Bean
+    IBookRepository bookRepository(JpaBookRepository jpaBookRepository) {
+        return new DatabaseBookRepository(jpaBookRepository);
+    }
+
+    @Bean
+    IBookService bookService(IBookRepository bookRepository) {
+        return new BookService(bookRepository);
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/BookApplication.java

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+package com.baeldung.hexagonalarchitecture;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.PropertySource;
+
+@SpringBootApplication
+@PropertySource(value = { "classpath:hexagonal-architecture.properties" })
+public class BookApplication {
+
+    public static void main(final String[] args) {
+        SpringApplication.run(BookApplication.class, args);
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/application/BookController.java

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+package com.baeldung.hexagonalarchitecture.application;
+
+import java.util.List;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import com.baeldung.hexagonalarchitecture.domain.Book;
+import com.baeldung.hexagonalarchitecture.domain.IBookService;
+
+@RestController
+public class BookController {
+
+    @Autowired
+    private IBookService bookService;
+
+    @GetMapping("/books")
+    ResponseEntity<List<Book>> listAllBooks() {
+        return ResponseEntity.ok(bookService.listAllBooks());
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/domain/Book.java

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+package com.baeldung.hexagonalarchitecture.domain;
+
+public class Book {
+    private String isbn;
+    private String title;
+
+    public Book() {
+
+    }
+
+    public Book(String isbn, String title) {
+        this.isbn = isbn;
+        this.title = title;
+    }
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/domain/BookService.java

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+package com.baeldung.hexagonalarchitecture.domain;
+
+import java.util.List;
+
+public class BookService implements IBookService {
+
+    private IBookRepository bookRepository;
+
+    public BookService(IBookRepository bookRepository) {
+        this.bookRepository = bookRepository;
+    }
+
+    @Override
+    public List<Book> listAllBooks() {
+        return bookRepository.findAllBooks();
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/domain/IBookRepository.java

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+package com.baeldung.hexagonalarchitecture.domain;
+
+import java.util.List;
+
+public interface IBookRepository {
+    List<Book> findAllBooks();
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/domain/IBookService.java

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+package com.baeldung.hexagonalarchitecture.domain;
+
+import java.util.List;
+
+public interface IBookService {
+    List<Book> listAllBooks();
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/infrastructure/BasicBookRepository.java

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+package com.baeldung.hexagonalarchitecture.infrastructure;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.baeldung.hexagonalarchitecture.domain.Book;
+import com.baeldung.hexagonalarchitecture.domain.IBookRepository;
+
+public class BasicBookRepository implements IBookRepository {
+    @Override
+    public List<Book> findAllBooks() {
+        List<Book> books = new ArrayList<Book>();
+        books.add(new Book("9780136083238", "Clean Code: A Handbook of Agile Software Craftsmanship"));
+        return books;
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/infrastructure/DatabaseBookRepository.java

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+package com.baeldung.hexagonalarchitecture.infrastructure;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import com.baeldung.hexagonalarchitecture.domain.Book;
+import com.baeldung.hexagonalarchitecture.domain.IBookRepository;
+
+public class DatabaseBookRepository implements IBookRepository {
+
+    private JpaBookRepository jpaBookRepository;
+
+    public DatabaseBookRepository(JpaBookRepository jpaBookRepository) {
+        this.jpaBookRepository = jpaBookRepository;
+    }
+
+    @Override
+    public List<Book> findAllBooks() {
+        return jpaBookRepository.findAll()
+            .stream()
+            .map(bookEntity -> new Book(bookEntity.getIsbn(), bookEntity.getTitle()))
+            .collect(Collectors.toList());
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/infrastructure/JpaBookEntity.java

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+package com.baeldung.hexagonalarchitecture.infrastructure;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class JpaBookEntity {
+    @Id
+    private String isbn;
+    private String title;
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String iSBN) {
+        isbn = iSBN;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+}

architecture/src/main/java/com/baeldung/hexagonalarchitecture/infrastructure/JpaBookRepository.java

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+package com.baeldung.hexagonalarchitecture.infrastructure;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface JpaBookRepository extends JpaRepository<JpaBookEntity, String> {
+}

architecture/src/main/resources/hexagonal-architecture.properties

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+spring.datasource.url=jdbc:h2:mem:db
+spring.datasource.driverClassName=org.h2.Driver
+spring.datasource.username=sa
+spring.datasource.password=
+spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

architecture/src/test/java/com/baeldung/hexagonalarchitecture/BookServiceUnitTest.java

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+package com.baeldung.hexagonalarchitecture;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import com.baeldung.hexagonalarchitecture.domain.Book;
+import com.baeldung.hexagonalarchitecture.domain.BookService;
+import com.baeldung.hexagonalarchitecture.domain.IBookRepository;
+import com.baeldung.hexagonalarchitecture.domain.IBookService;
+
+@DisplayName("Book service")
+@ExtendWith(MockitoExtension.class)
+public class BookServiceUnitTest {
+
+    private IBookService bookService;
+
+    @Mock
+    private IBookRepository bookRepository;
+
+    @BeforeEach
+    void init() {
+        bookService = new BookService(bookRepository);
+    }
+
+    @Test
+    @DisplayName("When listing all books then it should use repository")
+    void whenListingAllBooks_thenItShouldUseRepository() {
+        List<Book> booksFromRepository = new ArrayList<>();
+        booksFromRepository.add(new Book("testIsbn", "testTitle"));
+        when(bookRepository.findAllBooks()).thenReturn(booksFromRepository);
+
+        List<Book> booksFromService = bookService.listAllBooks();
+
+        verify(bookRepository).findAllBooks();
+        assertThat(booksFromService).containsExactlyElementsOf(booksFromRepository);
+    }
+}

pom.xml

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                 <module>apache-tika</module>
                 <module>apache-velocity</module>
 
+                <module>architecture</module>
+
                 <module>asciidoctor</module>
                 <module>asm</module>
 
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                 <module>apache-thrift</module>
                 <module>apache-tika</module>
                 <module>apache-velocity</module>
+
+                <module>architecture</module>
 
                 <module>asciidoctor</module>
                 <module>asm</module>