Environment variables in configuration in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of environment variables in Spring Boot configuration?

Environment variables allow you to externalize configuration from your Spring Boot application. This means you can change settings like database URLs or API keys without changing the code, making your app flexible and secure.

beginner

How do you reference an environment variable in Spring Boot's application.properties file?

You use the syntax ${ENV_VAR_NAME}. For example, spring.datasource.url=${DB_URL} will use the value of the environment variable DB_URL.

intermediate

What happens if an environment variable used in Spring Boot configuration is not set?

If the environment variable is missing and no default value is provided, Spring Boot will throw an error on startup. You can provide a default like ${ENV_VAR_NAME:defaultValue} to avoid this.

beginner

How can you set environment variables for a Spring Boot app when running it locally?

You can set environment variables in your operating system or use command line before running the app, for example: DB_URL=jdbc:mysql://localhost:3306/mydb ./mvnw spring-boot:run or set them in your IDE run configuration.

beginner

Why is using environment variables for configuration considered a good practice in Spring Boot?

It keeps sensitive data like passwords out of your codebase, allows different settings per environment (dev, test, prod), and makes your app easier to deploy and maintain.

How do you inject an environment variable named 'API_KEY' into Spring Boot's application.properties?

A api.key=$API_KEY

B api.key=API_KEY

C api.key=${API_KEY}

D api.key=ENV[API_KEY]

The correct syntax is ${API_KEY} to reference environment variables in Spring Boot properties.

What will happen if you use ${DB_PASS} in configuration but 'DB_PASS' is not set and no default is given?

A Spring Boot will throw an error and fail to start

B Spring Boot will start normally with an empty value

C Spring Boot will ignore the property

D Spring Boot will prompt for input

Missing environment variables without defaults cause Spring Boot to fail startup to avoid misconfiguration.

Which of these is a good reason to use environment variables in Spring Boot config?

A To make configuration flexible across environments

B To hardcode passwords in code

C To increase app size

D To avoid using properties files

Environment variables help keep configuration flexible and secure across different environments.

How can you provide a default value for an environment variable in Spring Boot properties?

A ${VAR_NAME?defaultValue}

B ${VAR_NAME=defaultValue}

C ${VAR_NAME|defaultValue}

D ${VAR_NAME:defaultValue}

The syntax ${VAR_NAME:defaultValue} sets a default if the environment variable is missing.

Where can environment variables be set for a Spring Boot app running in production?

A Only inside application.properties

B In the operating system or container environment

C Only in the source code

D In the browser

Environment variables are typically set in the OS or container environment where the app runs.

Explain how environment variables improve configuration management in Spring Boot applications.

Think about how changing settings without code changes helps.

Describe the syntax and usage of environment variables in Spring Boot's application.properties file.

Focus on how to write the variable and handle missing values.