Hexagonal architecture, also known as the Ports and Adapters architecture, is a software design pattern that follows the principles of Inversion of Control (IoC) and Dependency Inversion Principle (DIP). It is designed to provide loose coupling between application core logic and peripherals. Hexagonal architecture has been gaining traction as more developers move away from monolithic applications and towards microservices.

What is Hexagonal Architecture?

Hexagonal architecture, also known as Ports and Adapters, provides a mechanism for developers to decouple application core logic from external factors, such as databases or user interfaces. By utilizing ports and adapters the application’s core logic is better encapsulated, leading to a more maintainable and extensible codebase. Instead of directly connecting to an external factor, an application will interact only with an adapter. This adapter provides an abstraction layer that can easily be modified or replaced without affecting the core logic.

The hexagonal architecture revolves around four main components. They are: ports, adapters, application core and peripherals. Ports are the ports at the boundary of the application core component that provide the ability for external components to interact with the core logic. Adapters are the components that connect external components, such as databases and user interfaces, to ports. Application core is the component that contains the business logic of the application. Finally, peripherals are the external components that interact with the application core via an adapter.

The hexagonal architecture is a great way to ensure that the application core is well-encapsulated and can be easily extended. By separating the core logic from external components, developers can easily modify or replace adapters without affecting the core logic. This makes the application more maintainable and extensible, allowing for faster development cycles and better scalability.

Benefits of Hexagonal Architecture

Hexagonal architecture provides developers with multiple advantages. Firstly, it helps to create a cleaner separation of concerns and improves code maintainability. By leveraging ports, adapters and inversion of control, developers have more granular control over the different facets of their applications. Secondly, hexagonal architecture facilitates better management and testability of the application by providing a central point for dependency injection.

Lastly, it enables developers to easily extend their application with less effort. Since most of the application logic is centralized within the application core component and all external entities interact with the core via adapters, it is relatively easy to scale an application or change its functionalities without affecting the existing codebase.

Hexagonal architecture also helps to reduce the complexity of the application by providing a clear separation between the application core and external entities. This makes it easier to debug and troubleshoot any issues that may arise. Additionally, it allows developers to easily switch between different technologies and frameworks without having to rewrite the entire application.

Creating a Hexagonal Architecture in Java

Creating a Java application using the hexagonal architecture follows a few basic steps: creating the application core, setting up ports and adapters, writing port adapters, connecting to the database and testing the final product.

The application core is the heart of the hexagonal architecture. It contains the business logic and is independent of any external systems. The ports and adapters are the interfaces between the application core and the external systems. The port adapters are the code that implements the ports and adapters. Finally, the database is connected to the application core via the port adapters, and the final product is tested to ensure that it is functioning correctly.

Implementing Dependency Inversion Principle

When implementing hexagonal architecture, Dependency Inversion Principle (DIP) comes in handy. DIP states that high-level layers of an application should not depend on lower-level layers (i.e. code should not depend on concrete classes), but instead use abstractions. This means that when writing code for a port adapter, for example, it should not be concerned with which underlying low-level dependency is being used (e.g. a database or user interface).

The Dependency Inversion Principle helps to ensure that the code is more loosely coupled and easier to maintain. It also makes it easier to switch out low-level dependencies without having to rewrite the code. This makes it easier to test the code, as it can be tested in isolation without having to worry about the underlying dependencies.

Setting Up the Hexagonal Architecture Structure

When setting up a hexagonal architecture structure, the first step is to define the ports and their associated adapters. It is possible to have multiple ports connected to each adapter, but it is better practice to have only one port associated with each adapter in order to reduce coupling.

In addition to this, classes for ports and adapters must be created. These classes should consist of both an interface and an implementing class, allowing for adapters to be easily replaced without affecting existing code. The interfaces should specify which methods must be implemented by each adapter.

It is also important to ensure that the ports and adapters are loosely coupled. This can be done by using dependency injection to inject the ports and adapters into the application. This will allow for the application to be more flexible and easier to maintain.

Creating the Application Core

Once the structure of ports and adapters has been created, the next step is to create the application core. This comprises of all of the application’s business logic and classes that are agnostic to external components.

It is important to note that all dependencies of this component should be abstracted using interfaces. This allows for easy unit testing and dependency injection into the application later down the line.

The application core should be designed to be as flexible as possible, so that it can be easily adapted to changing requirements. This can be achieved by using design patterns such as the Model-View-Controller pattern, which separates the application into distinct components.

Writing the Port Adapters

Once the application core has been created, along with its associated ports, it is necessary to write port adapters for each port. These classes will implement the previously created interface and provide a bridge between the peripherals and application core.

The purpose of these classes is to convert external data to a format that can be used by the application core and vice-versa. To achieve this, port adapters will usually contain methods for serializing and deserializing data.

Connecting to the Database

When connecting an application’s ports and adapters to a database, developers must use a combination of JDBC (Java Database Connectivity) and SQL statements. JDBC allows Java applications to connect directly to databases using connection string, credentials and SQL statements.

Once connected, port adapters can execute SQL statements on behalf of the application core in order to fetch data from or send data to the database. Examples of this include SELECT statement for fetching data or INSERT statement for sending data.

Testing the Hexagonal Architecture Application

The final step in creating a Java application using hexagonal architecture is testing it. To do so developers must write unit tests for each port adapter as well as integration tests for ensuring that data is correctly flowing between application core and peripherals.

Conclusion

The hexagonal architecture is a design pattern that makes it easier for developers to decouple their applications from external components in order to make them more maintainable. By leveraging ports and adapters they can create extensible applications than can easily be tested and scaled. Additionally, by utilizing dependency inversion principle they can ensure that all of their code is properly decoupled.