Spring Boot Environment Variables Docs Generator

The aim of this project is to identify environment variables from a Spring Boot property file, and generate a Markdown template documentation for these environment variables.

• What are Spring Boot environment variables?
• Defining valid environment variables syntax
  • Valid
  • Invalid
• Run
  • Get environment variables from yaml file and generate markdown file
  • Get environment variables from properties file
  • Generate markdown file from edited output.json
  • Get environment variables from yaml file and update json file
• Test
• Enhancements

What are Spring Boot environment variables?

In Spring Boot, configuration can be externalised from Java code using application.yaml or application.properties files found in src/main/resources/.

This is done using the @Value annotation (see docs).

E.g., if we have the following entry in application.yaml:

microservice:
  endpoint: https://localhost:3000

We can access this configuration in code via the following:

@Component
public class ExternalService {
  @Value("${microservice.endpoint}")
  private String microserviceEndpoint;
}

We can further externalise these configurations from the source code into environment variables.

To do so, we now use the ${} syntax inside the configuration file. E.g.

application.yaml/application.yml

microservice:
  endpoint: ${MICROSERVICE_ENDPOINT:https://localhost:3000}

application.properties

microservice.endpoint=${MICROSERVICE_ENDPOINT:https://localhost:3000}

Now we can define an environment variable called MICROSERVICE_ENDPOINT and its value will be used within the program. We can also indicate a default value using the colon (":") as in above, where the default value is https://localhost:3000. See this Baeldung article.

To set an environment variable you can do (Windows) Open command prompt and enter set MICROSERVICE_ENDPOINT=https://api.dev/api/v1/users or (Unix) Open terminal and enter MICROSERVICE_ENDPOINT=https://api.dev/api/v1/users.

Defining valid environment variables syntax

Valid

Standard, with default value

property: ${PROPERTY:property A}

With nested environment variable

property: ${PROPERTY:property ${NAME_OF_PROPERTY:A}}

if PROPERTY was provided through environment variable, NAME_OF_PROPERTY value will never be used

With default empty value

property: ${PROPERTY:}

value of property will just default to an empty string ""

Invalid

Space character after colon

property: ${PROPERTY: property A}

syntatically invalid and yaml checker (if any) will complain as well

however not invalid in properties file and default value will be treated as " property A" (note extra space before)

Without default value

property: ${PROPERTY}

syntatically it is valid, but jar runner will error out if no environment variable is provided, hence for this project's sake we force default value to be indicated

No closing brace

property: ${PROPERTY:property A

Spring Boot will not recognise PROPERTY as an environment variable, and will treat the entire string "${PROPERTY:property A" as the value for property

Run

Install: npm i spring-env-docs

Get environment variables from yaml file and generate markdown file

sedocs pg application.yaml output.json output.md

• parse from application.yaml file
• store environment variables in output.json
• generate markdown file output.md based on output.json

Get environment variables from properties file

sedocs pg application.properties output.json output.md

• same as yaml version

Generate markdown file from edited output.json

sedocs g output.json output.md

• generate markdown file output.md based on output.json

You can add more information (description, type) in the json file before generating the markdown documentation.

Get environment variables from yaml file and update json file

sedocs p application.yaml output.json -u

• parse from application.yaml file
• update environment variables in output.json if exists

Test

Same as Run but do npm run build then replace the command with node dist/index.js.

Debug using nodemon command.

Enhancements

• To not flag file configuration such as ${application.name} with no default value as an error, and exclude such configs from environment variables.
• Update error messages
• Add version info