Tuesday, April 4, 2017

OpenAPI Specification : Swagger

The OpenAPI Specification (originally known as the Swagger Specification) is a specification for machine-readable interface files for describing, producing, consuming, and visualizing RESTful Web services. A variety of tools can generate code, documentation and test cases given an interface file. Development of the OpenAPI Specification (OAS) is overseen by the Open API Initiative, an open source collaborative project of the Linux Foundation.
Swagger is a project used to describe and document RESTful APIs. The Swagger specification defines a set of files required to describe such an API. These files can then be used by the Swagger-UI project to display the API and Swagger-Codegen to generate clients in various languages. Additional utilities can also take advantage of the resulting files, such as testing tools.
Applications implemented based on OpenAPI interface files can automatically generate documentation of methods, parameters and models. This helps keep the documentation, client libraries, and source code in sync.
  • The OpenAPI Specification is language-agnostic. It is also extensible into new technologies and protocols beyond HTTP.
  • With Swagger's declarative resource specification, clients can understand and consume services without knowledge of server implementation or access to the server code.
  • The Swagger UI framework allows both developers and non-developers to interact with the API in a sandbox UI that gives clear insight into how the API responds to parameters and options. Swagger may utilize both JSON and XML.
  • Swagger-Codegen contains a template-driven engine to generate documentation, API clients and server stubs in different languages by parsing the OpenAPI/Swagger definition.
How to start:
If you're an API provider and want to use Swagger to describe your APIs - there are several approaches available:
  • A top-down approach where you would use the Swagger Editor to create your Swagger definition and then use the integrated Swagger Codegen tools to generate server implementation.
  • A bottom-up approach where you have an existing REST API for which you want to create a Swagger definition. Either you create the definition manually (using the same Swagger Editor mentioned above), or if you are using one of the supported frameworks (JAX-RS, node.js, etc), you can get the Swagger definition generated automatically for you. If you're doing JAX-RS have a look at the example at https://github.com/swagger-api/swagger-core/wiki/Swagger-Core-JAX-RS-Project-Setup-1.5.X.
If on the other hand you're an API Consumer who wants to integrate with an API that has a Swagger definition you can use the online version of the Swagger UI to explore the API (given that you have a URL to the APIs Swagger definition) - and then use Swagger Codegen to generate the client library of your choice.

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