Java Generator

This repository contains the source for the Fern generators that produce Java artifacts:

• fernapi/fern-java-sdk
• fernapi/fern-java-model
• fernapi/fern-java-spring

The generator is written in Java and produces idiomatic code that feels hand-written and is friendly to read.

Fern handles transforming an API definition -- either an OpenAPI or Fern specification -- into Fern intermediate representation. IR is a normalized, Fern-specific definition of an API containing its endpoints, models, errors, authentication scheme, version, and more. Then the Java generator takes over and turns the IR into production-ready code.

Fern is an open source toolkit for designing, building, and consuming REST APIs. With Fern, you can generate client libraries, API documentation, and boilerplate for your backend server.

Head over to the official Fern website for more information, or head over to our Documentation to dive straight in and find out what Fern can do for you!

This generator is used via the Fern CLI, by defining one of the aforementioned Java artifacts as a generator:

- name: fernapi/fern-java-sdk
  version: 0.3.7
  output:
    location: local-file-system
    path: ../../generated/java

By default, Fern runs the generators in the cloud. To run a generator on your local machine, use the --local flag for fern generate. This will run the generator locally in a Docker container, allowing you to inspect its logs and output. Read more.

You can customize the behavior of generators in generators.yml:

default-group: local
groups:
  local:
    generators:
      - name: fernapi/fern-java-sdk
        version: 0.4.9
        output:
          location: local-file-system
          path: ../../generated/java

The Java SDK generator supports the following options:

Type: boolean

Default: false

When enabled, unknown types are defined as Optional<Object> rather than plain Object.

Type: boolean

Default: false

When enabled, generates wrapper types for each alias to increase type-safety. For example if you have an alias ResourceId: string then if this is true, the generator will generate a ResourceId.java file. If false, it will just treat it as java.util.String.

The Java Spring generator supports the following options:

Type: boolean

Default: false

When enabled, generates wrapper types for each alias to increase type-safety. For example, if true and you have an alias ResourceId: string the generator will generate a ResourceId.java file. If false, it will just treat it as java.util.String.

Type: boolean

Default: false

When enabled, generates public constructors for model types.

Type: string

Default: <Organization>ApiClient

Type: string

custom-dependencies: 
  - "implementation com.foo:bar:0.0.0"
  - "testImplementation com.foo:bar:0.0.0"
  - "api com.foo:bar:0.0.0"

The provided string will be used as the client class name.

All generator releases are published in the Releases section of the GitHub repository. You can directly use these version numbers in your generator configuration files.

For instance, if you want to use version 0.3.7 of the Java generator:

default-group: local
groups:
  local:
    generators:
      - name: fernapi/fern-java-sdk
        version: 0.4.9
        output:
          location: local-file-system
          path: ../../generated/java

Fern will handle the rest automatically.

We greatly value community contributions. All the work on Fern generators happens right here on GitHub, both Fern developers and community contributors work together through submitting code via Pull Requests. See the contribution guidelines in CONTRIBUTING on how you can contribute to Fern!