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You can import the OpenAPI document into SwaggerHub and generate a client from there. SwaggerHub is simple to use but does not support all the languages, libraries and options that Codegen supports, so you might want to look into it next.

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Swagger Codegen

Swagger Codegen is a Java based code generator. You can run it from the command line as a CLI application, or through Maven. It supports a large amount of languages and has a large amount of customisation options.

java -jar swagger-codegen-cli.jar generate \
  -i openapi.json \
  -o apiclient \
  -l java

OpenAPI Generator

OpenAPI Generator is similar to Swagger Codegen. Most of the options are identical. It supports a slightly different set of languages and libraries, and generates slightly different style of code.

• Github documentation

• openapi-generator.tech

java -jar openapi-generator-cli.jar generate \
  -i openapi.json \
  -o apiclient \
  -g java \
  --skip-validate-spec