The Hexagon Toolkit provides several libraries to build server applications. These libraries provide single standalone features and are referred to as "Ports".
The main ports are:
- The HTTP server: supports HTTPS, HTTP/2, WebSockets, mutual TLS, static files (serve and upload), forms processing, cookies, CORS and more.
- The HTTP client: which supports mutual TLS, HTTP/2, WebSockets, cookies, form fields and files among other features.
- Serialization: provides a common way of using different data formats. Data formats are pluggable and are handled in the same way regardless of their library.
- Template Processing: allows template processing from URLs (local files, resources or HTTP content) binding name patterns to different engines.
Each of these features or ports may have different implementations called "Adapters".
Hexagon is designed to fit in applications that conform to the Hexagonal Architecture (also called Clean Architecture, Onion Architecture or Ports and Adapters Architecture). Its design principles also fit into this architecture.
Simple Hello World HTTP example.
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Hexagon's goals and design principles:
Put you in Charge: There is no code generation, no runtime annotation processing, no classpath based logic, and no implicit behaviour. You control your tools, not the other way around.
Modular: Each feature (Port) or adapter is isolated in its own module. Use only the modules you need without carrying unneeded dependencies.
Pluggable Adapters: Every Port may have many implementations (Adapters) using different technologies. You can swap adapters without changing the application code.
Batteries Included: It contains all the required pieces to make production-grade applications: logging utilities, serialization, resource handling and build helpers.
Kotlin First: Take full advantage of Kotlin instead of just calling Java code from Kotlin. The library is coded in Kotlin for coding with Kotlin. No strings attached to Java (as a Language).
Properly Tested: The project's coverage is checked in every Pull Request. It is also stress-tested at TechEmpower Frameworks Benchmark.
Not in Scope¶
- Kotlin Native: because of the added complexity of Kotlin Native, focus will be set on the JVM platform, native binaries' generation will rely on GraalVM.
It is an interface for a task. The toolkit ports are designed to work on their own. For example: you can use the http_server module without importing the templates one, and the other way around (taking only the dependencies you need for your application).
Each Port may have different implementations (Adapters).
Ports cannot be used by themselves and in their place, an adapter implementing them should be added to the list of dependencies.
They are implementations of a functionality (Port) for a given product/technology. Clients should only use ports' code (not Adapters specific code), this makes them easy to switch among different adapters with minimum impact.
Adapters are independent of each other, and you can use several adapters for the same port in a single application. For example, you could use many Template adapters to support several template engines.
These modules provide functionality on top of a set of ports combining them, but without relying on any specific adapters. An example would be the Web module that uses http_server and template Ports, but leaves clients the decision of picking the adapters they want.
Singleton object to manage a cross toolkit aspect. I.e., Serialization, Logging or Templates.
The libraries inside the
hexagon_extra repository provide extra features. They may be useful to
develop applications, but not strictly required. Some of these modules are:
- Schedulers: Provides repeated tasks execution based on Cron expressions.
- Models: Contain classes that model common data objects.
- Args: Command line arguments definition and parsing.
How Hexagon fits in your architecture in a picture.
Using this toolkit won't make your application compliant with Hexagonal Architecture (by its nature, no tool can do that), you have to provide a layer of abstraction by yourself.
Ports with their provided implementations (Adapters).
|HTTP Server||Netty, Netty Epoll, Jetty, Servlet, Helidon|
|Templates||Pebble, FreeMarker, Rocker, jte|
|Serialization Formats||JSON, YAML, CSV, XML, TOML|
Module dependencies (including extra modules):
graph TD http_handlers -->|uses| http http_handlers -->|uses| handlers http_server -->|uses| http_handlers http_client -->|uses| http_handlers web -->|uses| http_server web -->|uses| templates rest -->|uses| http_server rest -->|uses| serialization rest_tools -->|uses| rest