Code for Hexagonal Architecture article.

hexagonal/pom.xml

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+<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.baeldung</groupId>
+  <artifactId>hexagonal</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  <name>Hexagonal</name>
+  <description>Hexagonal Architecture</description>
+</project>

hexagonal/src/main/java/com/baeldung/hexagonal/Hexagonal.java

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+package com.baeldung.hexagonal;
+
+import com.baeldung.hexagonal.bo.BusinessLogic;
+
+public class Hexagonal {
+
+    public static void main(String[] args) {
+        BusinessLogic logic = new BusinessLogic();
+        logic.processUsers();
+    }
+}

hexagonal/src/main/java/com/baeldung/hexagonal/bo/BusinessLogic.java

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+package com.baeldung.hexagonal.bo;
+
+import java.util.List;
+
+import com.baeldung.hexagonal.dto.User;
+import com.baeldung.hexagonal.factory.RepositoryFactory;
+import com.baeldung.hexagonal.repository.UserRepository;
+
+public class BusinessLogic {
+    public void processUsers() {
+        // Use factory to get an adapter for reading users
+        UserRepository repo = RepositoryFactory.getUserRepository();
+        // Get Users 
+        List<User> userList = repo.getUsers();
+        // Perform business logic
+        userList.forEach(user -> {
+            System.out.println(user.getLastName()+", "+user.getFirstName());
+        });
+    }
+}

hexagonal/src/main/java/com/baeldung/hexagonal/dto/User.java

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+package com.baeldung.hexagonal.dto;
+
+public class User {
+    public int id;
+    public String firstName;
+    public String lastName;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+}

hexagonal/src/main/java/com/baeldung/hexagonal/factory/RepositoryFactory.java

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+package com.baeldung.hexagonal.factory;
+
+import com.baeldung.hexagonal.repository.FileBasedUserRepository;
+import com.baeldung.hexagonal.repository.UserRepository;
+
+public class RepositoryFactory {
+    public static UserRepository getUserRepository() {
+        // Here we would implement the logic to determine the type of 
+        // UserRepository to return, presumably based on some configuration 
+        // or environmental setting.
+        return new FileBasedUserRepository();
+    }
+}

hexagonal/src/main/java/com/baeldung/hexagonal/repository/FileBasedUserRepository.java

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+package com.baeldung.hexagonal.repository;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import com.baeldung.hexagonal.dto.User;
+
+public class FileBasedUserRepository implements UserRepository {
+
+    @Override
+    public List<User> getUsers() {
+        String line = "";  
+        List<User> userList = new ArrayList<>();
+        try   
+        {  
+            //parsing a CSV file into BufferedReader class constructor  
+            BufferedReader br = new BufferedReader(new FileReader("users.csv"));  
+            while ((line = br.readLine()) != null)   //returns a Boolean value  
+            {  
+                String[] userComponents = line.split(",");    // use comma as separator  
+                User user = new User();
+                user.setId(Integer.valueOf(userComponents[0]));
+                user.setFirstName(userComponents[1]);
+                user.setLastName(userComponents[2]);
+                userList.add(user);
+            }  
+            br.close();
+            return userList;
+        } catch (IOException e) {  
+            e.printStackTrace();  
+        }
+        return null;
+    }
+}

hexagonal/src/main/java/com/baeldung/hexagonal/repository/UserRepository.java

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+package com.baeldung.hexagonal.repository;
+
+import java.util.List;
+
+import com.baeldung.hexagonal.dto.User;
+
+public interface UserRepository {
+    public List<User> getUsers();
+}

hexagonal/src/test/java/com/baeldung/hexagonal/factory/RepositoryFactoryTest.java

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+package com.baeldung.hexagonal.factory;
+
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.hexagonal.repository.UserRepository;
+
+class RepositoryFactoryTest {
+
+    @Test
+    void test() {
+        UserRepository repo = RepositoryFactory.getUserRepository();
+        assert(repo != null);
+    }
+
+}

hexagonal/src/test/java/com/baeldung/hexagonal/repository/FileBasedUserRepositoryTest.java

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+package com.baeldung.hexagonal.repository;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.hexagonal.dto.User;
+
+class FileBasedUserRepositoryTest {
+
+    @Test
+    void test() {
+        UserRepository repo = new FileBasedUserRepository();
+        List<User> userList = repo.getUsers();
+        assert(userList != null && userList.size() > 0);
+    }
+}

hexagonal/users.csv

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+1,Rachel,Grey
+2,Laura,Jenkins
+3,Craig,Booker
+4,Mary,Smith