@Value Annotation in Spring Explained

Direct Answer

@Value can inject an individual property placeholder such as ${server.port}, a default such as ${timeout:30}, or a Spring Expression Language expression such as #{2 * 5} into a Spring-managed bean. Use it for a small number of isolated settings. Use @ConfigurationProperties for a related group that benefits from type-safe binding and validation.

Code Example

@Service
public class PaymentService {
    private final String apiKey;
    private final int timeout;
    private final boolean featureEnabled;
    private final double calculatedRate;

    public PaymentService(
            @Value("${payment.api.key}") String apiKey,  // Property from application.properties
            @Value("${payment.timeout:5000}") int timeout,  // Default 5000 if not set
            @Value("${features.new-checkout:false}") boolean featureEnabled,  // Boolean property
            @Value("#{${payment.base.rate} * 1.15}") double calculatedRate) {  // SpEL expression
        this.apiKey = apiKey;
        this.timeout = timeout;
        this.featureEnabled = featureEnabled;
        this.calculatedRate = calculatedRate;
    }

    public void processPayment(Order order) {
        System.out.println("Using API key: " + apiKey.substring(0, 5) + "...");
        System.out.println("Timeout: " + timeout + "ms");
        if (featureEnabled) {
            System.out.println("New checkout flow with rate: " + calculatedRate);
        }
    }
}

Common Mistakes & Pitfalls

• Confusing ${} and #{}: Freshers often mix up dollar-brace for property placeholders and hash-brace for SpEL. ${server.port} reads a property, #{2 + 2} evaluates an expression. Using ${2 + 2} won't compute anything, it'll look for a property literally named "2 + 2".
• Forgetting defaults for optional properties: If you use @Value("${optional.feature}") without a default and the property is missing, the app crashes at startup. Always provide defaults with colon: ${optional.feature:false}.
• Using @Value on non-Spring beans: If you create a class with new PaymentService(), @Value does nothing. Spring must create the bean for injection to work.
• Hardcoding values instead of externalizing: Freshers sometimes use @Value("localhost") instead of @Value("${database.host}"). The whole point is to read from properties files so you can change config without recompiling.