Spring Boot - Application Properties

Spring Boot uses application.properties (or application.yml) as the central place for externalized configuration. You can inject property values into beans using @Value for simple cases, or @ConfigurationProperties for groups of related settings.

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application.properties

Place application.properties under src/main/resources. Spring Boot picks it up automatically: no extra configuration needed.

Properties
# Server
server.port=8080

# DataSource
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=appuser
spring.datasource.password=secret

# Custom app properties
app.name=My Application
app.max-retries=3
app.timeout-seconds=30

Injecting values with @Value

@Value injects a single property from the environment. A default value can be supplied after the colon.

Java
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

@Service
public class RetryService {

    @Value("${app.max-retries:3}")       // defaults to 3 if not set
    private int maxRetries;

    @Value("${app.timeout-seconds:30}")
    private int timeoutSeconds;

    @Value("${app.name}")
    private String appName;

    public void performWithRetry(Runnable task) {
        for (int i = 0; i < maxRetries; i++) {
            try {
                task.run();
                return;
            } catch (RuntimeException e) {
                System.err.println("Retry " + (i + 1) + " of " + maxRetries);
            }
        }
        throw new RuntimeException("Max retries exceeded");
    }
}

Typed config with @ConfigurationProperties

@ConfigurationProperties maps a group of related properties to a strongly-typed POJO. This is more maintainable than multiple @Value annotations and supports Bean Validation via @Validated.

Java
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties(prefix = "app")
public class AppProperties {

    private String name;
    private int maxRetries;
    private int timeoutSeconds;

    // Spring binds: app.name -> name, app.max-retries -> maxRetries, etc.
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public int getMaxRetries() { return maxRetries; }
    public void setMaxRetries(int v) { this.maxRetries = v; }

    public int getTimeoutSeconds() { return timeoutSeconds; }
    public void setTimeoutSeconds(int v) { this.timeoutSeconds = v; }
}

Inject the properties class wherever needed:

Java
@Service
public class NotificationService {

    private final AppProperties props;

    public NotificationService(AppProperties props) {
        this.props = props;
    }

    public void notify(String msg) {
        System.out.println("[" + props.getName() + "] " + msg);
    }
}

Using application.yml

YAML is supported natively and is often preferred for nested configuration thanks to its cleaner hierarchical syntax.

YAML
server:
  port: 8080

spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/mydb
    username: appuser
    password: secret

app:
  name: My Application
  max-retries: 3
  timeout-seconds: 30

Both application.properties and application.yml work interchangeably with @Value and @ConfigurationProperties.