Read environment variable in SpringBoot

问题:

What is the best way to read environment variables in SpringBoot?
In Java I did it using:

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

Is it possible to do it using @Value annotation?

回答1:

Quoting the documentation:

Spring Boot allows you to externalize your configuration so you can work with the same application code in different environments. You can use properties files, YAML files, environment variables and command-line arguments to externalize configuration. Property values can be injected directly into your beans using the @Value annotation, accessed via Spring’s Environment abstraction or bound to structured objects via @ConfigurationProperties.

So, since Spring boot allows you to use environment variables for configuration, and since Spring boot also allows you to use @Value to read a property from the configuration, the answer is yes.

---

This can be tested easily, the following will give the same result:

@Component
public class TestRunner implements CommandLineRunner {
    @Value("${bar}")
    private String bar;
    private final Logger logger = LoggerFactory.getLogger(getClass());
    @Override
    public void run(String... strings) throws Exception {
        logger.info("Foo from @Value: {}", bar);
        logger.info("Foo from System.getenv(): {}", System.getenv("bar")); // Same output as line above
    }
}

回答2:

You can do it with the @Value annotation:

@Value("${bar}")
private String myVariable;

You can also use colon to give a default value if not found:

@Value("${bar:default_value}")
private String myVariable;