An OpenAPI JAX-RS client code generator

Generates Java code to call REST services.

The API classes are intended for use with the MicroProfile client.

The DTO classes can be generated for use with JSON Binding or Jackson FasterXML.

The code generation is configured via 50+ options.

As of version 0.11, this generator requires a Java 21 runtime.

Inspiration

Much of the behavior and templates are lifted more or less directly from openapi-generator.

But the code is implemented from scratch, based on end-to-end tests.

I plan to keep this generator much simpler:

• it will only generate Java code, primarily intended for the MP client.
• it will never have as many features as openapi-generator.
• but its reduced complexity should allow me to acquire the output I desire and retain my sanity.

Examples

A couple of official APIs are kept as examples: azure, bitbucket, and petstore. These should give you an idea of what the generator's output looks like - and they help me evaluate how changes affect the output on larger APIs.

The output from many other test OpenApi documents and configuration settings can be seen in the test folder.

Invocation

Gradle

A Gradle plugin allows easy declaration of OpenApi documents and generator options.

Command Line

Download the cli-jar release of the generator (and verify its signature!).

Then you can run the generator with a Java 21 like this (or see full CLI usage):

$ java -jar ojc-x.y.z-cli.jar --api-package foo.bar.api --dto-package foo.bar.dto -i petstore.yaml -o /tmp/output
[2022-02-26 15:08:47] [INFO] Reads OpenApi document from petstore.yaml 
[2022-02-26 15:08:47] [INFO] Generates files in /tmp/output 
[2022-02-26 15:08:47] [INFO] No configuration file found
...

$ tree /tmp/output/
/tmp/output/
└── foo
    └── bar
        ├── api
        │   └── PetsApi.java
        └── dto
            ├── Error.java
            └── Pet.java

The output looks something like this (petstore).

Roadmap

The current plans for future releases are (note, no time commitments):

0.11.x

• Native generator executables
• More code/package documentation.
• Documentation index with references to the various tests/examples.

1.0.x ideas

• For operations with many query parameters, make builder-like flow-pattern call.
• Handling of extensions (e.g. annotation of in-house @LoggedSecrets operations)
• Options for adding @ClientHeaderParam and/or @RegisterClientHeaders
• Maybe add generation of server-side code

History/Rationale

We generate client code (originally only DTOs) from a lot of different sources at work, and the input OpenApi documents are not all entirely spec-worthy.

So I have spent a lot of hours in the past tweaking openapi-generator to generate code of usable quality. This was not always possible (because of its architecture), and it was always a pain the butt!

To improve my sanity at work, I wrote the bulk of this generator during the Christmas holidays of 2021.

More and more projects at work now use this generator, and many (weird) corner cases have been fixed over time. This has made it possible to deprecated my old generator, so in my book, this is great!

The project has a lot of tests to help ensure I do not (accidentally) break behavior.

While the code generation output is the primary goal of the project, I also use it as a test bed for use of code quality tooling and Gradle build logic organization.

Community Collaboration

I like Open Source just as much as the next guy.

This tool provides infrastructure to whomever uses it, so it should be Open Source. And it is (Apache License).

But (my definition of) stability and quality of the generator's output is more important to me than being able to accept changes from other parties.
It is a tool I rely on to provide a difference for colleagues at work.

So while you are welcome to access and fork the source code, I am not as such interested in contributions.
Unless they just happen to align with my interests, of course.

If you are itching to make some changes, please open an issue first, so we can discuss.
I do not want you to waste your time!

I welcome bug reports if you use the generator and experience problems.

Consultancy

The project is Open Source and I am happy for you to use the generator, report bugs and suggest changes.

But while the source code is free, it does not come bundled with promises or guarantees of free work.

I will try to fix reported bugs, but will commit to no time tables.

However, I am willing to implement feature requests as a paid service (1,200DKK/hour) assuming:

• I agree with the suggested feature
• Approval from my employer to work for you (not expected to be a problem, as the context will be this project)
• I have not reached my limit of hours (40 hours - Danish VAT limit is 50,000DKK/running-12-months)

Please reach out to me via email if you would like to make use of this offer.

If the above requirements are not agreeable, you are more than welcome to fork the project and do your own thing.