How to Read Environment Variables in Spring Boot Using @Value Annotation?

What is the best approach to read environment variables in Spring Boot?

String foo = System.getenv("bar");

In Spring Boot, you can read environment variables in multiple ways, including using the @Value annotation and the System.getenv() method. The @Value annotation is often preferred for its integration with Spring's dependency injection, allowing you to easily manage configuration values in your application.

@Value("${bar}")
private String foo; // Bar is the name of the environment variable.

Causes

• Environmental variables are key-value pairs available to applications at runtime, used for configuration and to pass sensitive information like API keys or database URLs.

Solutions

• **Using @Value Annotation**: You can directly inject environment variables using the @Value annotation by specifying the variable name within '${}' syntax. For example: `@Value('${MY_ENV_VAR}') String myEnvVar;` This approach ensures that Spring resolves the environment variable when your application context is initialized.
• **Using Environment Object**: Another approach is to use Spring's Environment abstraction, which allows you to access properties and environment variables. Example: `@Autowired private Environment env; String myEnvVar = env.getProperty("MY_ENV_VAR");`
• **Using System.getenv Method**: As shown in your example, this method is also valid but does not leverage Spring's configuration management. Use it directly when Spring features are not necessary.

Mistake: Not including the variable name in the application.properties file.

Solution: Ensure the environment variable is set and accessible to the application. You can also place default values using the syntax: @Value("${MY_ENV_VAR:default_value}")

Mistake: Using incorrect variable names or casing.

Solution: Verify that the name used in @Value matches the actual environment variable name, considering case sensitivity.