Polygonal 🧱 Architecture

Plug-in which helps you implement clean architecture in your application.

1. Create your polygon definition
2. Share it between projects
3. Keep clean-architecture between multiple micro-services 👌

https://polygonal.io

Getting started | gradle

Because you are here I suppose that you would like to keep clean codebase architecture, wouldn't you? I'm here to help you!
To make the magic happen, you need following gradle configuration:

plugins {
  id 'io.polygonal' version 'X.Y.Z'
}

Next step is to create polygon.yml file, and that's it.

Getting started | maven

The maven configuration looks as standard maven plugin configuration. Currently, the plugin is available only via bintray repository.

<build>
    <plugins>
        <plugin>
            <groupId>io.polygonal</groupId>
            <artifactId>polygonal-architecture-maven-plugin</artifactId>
            <version>X.Y.Z</version>
            <configuration>
                <basePackage>org.example</basePackage>
            </configuration>
        </plugin>
    </plugins>
</build>

What does polygonal mean?

Let assume that every application is built with blocks. From architecture perspective the very basic block/brick in Java app is a package, right? Now imagine that you are going to build a wall from bricks, the only way that bricks will match with each other is that they have the same shape, and the same amount of match side edges. What if the same rule can be applied to the software? Haven't you seen the projects where packaging looks more like delicious spaghetti than a good peace of software? This kind of freaky packages structure projects are really common. Everybody was there, yep? Let stop this! I'd like to show you easy way to keep your architecture clean as a baby ass.

.
├── 📂 accounts  ⬅ this is a domain (polygon)
│   └── ...
|   📂 customers ⬅ this is a domain (polygon)  
│   └── ...
|   📂 api       ⬅ this is a domain (polygon)
│   └── ...
└── 📄 SpringBootApp.java

Maybe you heard about "hexagonal architecture" , "ports&adapters". Polygon architecture it's almost the same, but with additional rules. Your modules need to match with each other. So what is the "polygon" 🤔? To build something using polygons, every peace should match. Whatever polygons you choose -> they can be triangles, quarters, hexagons, doesn't meter, but they need to match with other polygons. In software development language it means that each domain package (polygon) should have the same kind of shape as other domain packages, and the same amount of entrance/communication points (edges).

Plug-in configuration

Let assume that we have following project structure:

.
├── 📂 users
|   ├── 📂 models
|   |   ├── 📄 User.java
|   |   📂 ports
|   |   ├── 📄 UserFinder.java
│   └── RepositoryUserFinder.java
|   📂 posts
|   ├── 📂 models
|   |   ├── 📄 Post.java
|   |   📂 ports
|   |   ├── 📄 PostPublisher.java
│   └── 📄 RSSPostPublisher.java
└── 📄 AppBootstrap.java

We decided to provide clean architecture here. What rules can be applied?

• the root domain level may contains only package-private classes

• the ports domain package should contain only public interfaces

• the models domain package is allowed to contain only public DTO objects

To make that works you need to define gradle DSL configuration or yml one.

YML configuration

You'd like to keep configurations in YML files? no problem. Polygon definition can be kept in yaml file. Default location is src/main/resources/polygon.yml:

// polygon.yml
polygon:
  public: 0
  packagePrivate: -1
  types: ['interface', 'class', 'enum']
  packages:
    models:
      required: true 
      public: -1
      packagePrivate: 0
      types: ['class']
    ports:
      public: -1
      packagePrivate: -1
      types: ['interface']

Yaml elements

Element	Description
polygon	The root element. Required
polygon.public	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed
polygon.packagePrivate	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed
polygon.protected	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed
polygon.internal	Kotlin only. How many internal scope object are allowed. -1 unlimited, 0 not allowed, n n allowed
polygon.types	What types are allowed. Available values are ['interface', 'class', 'enum', 'abstract class', 'data class', 'open class']
polygon.packages	All packages definitions goes here.

Gradle DSL

You can define your architecture also via gradle dsl:

// build.gradle 
polygonalArchitecture {
  sourcesDir = file('src/main/java')
  basePackage = 'org.example'
  
  polygon {
    packageDef {
      publicScope = 0
      packagePrivateScope = -1
      types = ['interface', 'class', 'enum']
    }
    
    packageDef {
      name = 'models'
      required = true
      publicScope = -1
      types = ['class']
    }
    
    packageDef {
      name = 'ports'
      publicScope = -1
      types = ['interface']
    }
  }
} 

Attributes

DSL atribute	Description	Default
sourcesDir	Relative path to the sources. Required	file('src/main/java') or file('src/main/kotlin')
basePackage	The level0 / package where polygons are stored. Your polygonal architecture starts here. Required	``
strictMode	If true, only defined packages are allowed.	false
polygonTemplate	Template file -> if you'd like to keep polygon definition in .yml file. Required if polygon dsl is not defined	null
polygon	Polygon gradle dsl configuration. Required if polygonTemplate is not defined	null
polygon.packageDef	The polygon package rules definition.
polygon.packageDef.name	The name of the package. The nested packages like abc.defg are allowed.	'', it's root level definition
polygon.packageDef.required	If true, definied packages is required inside polygon.	false
polygon.packageDef.publicScope	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed	0
polygon.packageDef.packagePrivateScope	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed	0 (-1 for root level)
polygon.packageDef.protectedScope	How many public scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed	0
polygon.packageDef.internalScope	How many internal scope objects are allowed. -1 unlimited, 0 not allowed, n n allowed	0
polygon.packageDef.types	What types are allowed. Available values are ['interface', 'class', 'enum', 'abstract class', 'data class', 'open class']	['interface', 'class', 'enum', 'abstract class']

YML+Gradle mix

Mixing of gradle DSL, and yaml configuration is allowed. The one rules here is that gradle DSL has higher precedence than yaml, so you can define the base polygon schema in yaml, and then overwrite some rules by gradle configuration.

More examples

Are you looking for more polygon examples? Here you go: polygons gallery

Usage

If you'd like to check your polygons explicitly you should use the following task:

$ ./gradlew verifyPolygons

or maven:

$ ./mvnw polygonal:verifyPolygons

In case of any problems plugin will tell you, where is the problem. Example output:

> Task :kotlin-e2e:verifyPolygons

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':verifyPolygons'.
> 0 public scope objects are allowed in 'models' package

What's next?

• package definition inheritance
• groovy language support
• improve multi-threaded processing for maven

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.