Spring Boot中带@Value的可选环境变量

Question

Using @Value for non-existing environment variable will cause an IllegalArgumentException: Could not resolve placeholder 'ENV_VAR' in string value "${ENV_VAR}".

For example:

@Autowired
public SomeClass(@Value("{ENV_VAR}") final String value) { }

How can I make this value optional?

Answer 1

Use a default value, and the Optional class (in JDK8).

@Autowired
public SomeClass(@Value("{ENV_VAR:#{null}}") final Optional<String> value) {
    value.ifPresent(/* do something */);
}