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Spring Boot 4 Microservices & REST APIs · Lesson

Type-Safe Configuration with @ConfigurationProperties

Bind properties to typed config classes.

Type-Safe Configuration with @ConfigurationProperties is a free Spring Boot 4 Microservices & REST APIs lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Microservices & REST APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Beyond @Value

Scattering dozens of @Value annotations across a feature is brittle and hard to validate. @ConfigurationProperties binds a whole group of related keys to a single strongly typed object.

You get IDE auto-completion, type safety, validation, and a clear contract for what the feature reads.

Binding a Prefix to a Class

Declare a class with a prefix; Spring maps each key under that prefix to a matching field. Relaxed binding lets max-retries in YAML map to maxRetries in Java.

@ConfigurationProperties(prefix = "app.mail")
public class MailProperties {
    private String host;
    private int port;
    private int maxRetries;
    // getters and setters
}

Registering the Properties Bean

A @ConfigurationProperties class must become a bean. The cleanest way is @EnableConfigurationProperties on a configuration class, or @ConfigurationPropertiesScan on the main app.

@SpringBootApplication
@ConfigurationPropertiesScan
public class Application { }

// or explicitly:
@Configuration
@EnableConfigurationProperties(MailProperties.class)
class MailConfig { }

The Backing YAML

With the prefix app.mail, these YAML keys bind to the fields. Relaxed binding accepts kebab-case keys for camelCase fields.

app:
  mail:
    host: smtp.example.com
    port: 587
    max-retries: 3

Injecting the Properties

Inject the typed object anywhere like any other bean. The feature code reads structured config instead of loose strings.

@Service
public class MailService {
    private final MailProperties props;
    public MailService(MailProperties props) {
        this.props = props;
    }
    void send() {
        connect(props.getHost(), props.getPort());
    }
}

Immutable Binding with Records

Spring Boot supports constructor binding, perfect for immutable config. A Java record works directly with @ConfigurationProperties, no setters needed.

@ConfigurationProperties(prefix = "app.mail")
public record MailProperties(
        String host,
        int port,
        int maxRetries) {
}

Default Values

With records you can give defaults in a compact constructor; with classic classes you initialize the field. Defaults apply when the key is absent from the Environment.

@ConfigurationProperties(prefix = "app.mail")
public record MailProperties(String host, Integer port, Integer maxRetries) {
    public MailProperties {
        if (port == null) port = 587;
        if (maxRetries == null) maxRetries = 3;
    }
}

Nested Objects

Configuration trees map to nested types. A field of a custom type binds keys one level deeper, keeping complex config organized.

@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private final Security security = new Security();
    public Security getSecurity() { return security; }
    public static class Security {
        private boolean enabled;
        private String issuer;
        // getters/setters
    }
}

Lists and Maps

Collection-typed fields bind to YAML sequences and maps automatically, which is far cleaner than parsing comma-separated strings by hand.

@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private List<String> allowedOrigins;
    private Map<String, Integer> rateLimits;
    // getters/setters
}
// app.allowed-origins: [a, b]
// app.rate-limits: { read: 100, write: 20 }

Validating Bound Values

Add @Validated to the properties class and JSR-380 constraints to fields. Spring validates at startup and fails fast if config is invalid, instead of erroring deep in production.

@Validated
@ConfigurationProperties(prefix = "app.mail")
public class MailProperties {
    @NotBlank private String host;
    @Min(1) @Max(65535) private int port;
    // getters/setters
}

Metadata and the Processor

Add spring-boot-configuration-processor as an annotation processor to generate metadata. Your IDE then offers auto-complete and docs for your custom keys in application.yml.

<!-- pom.xml -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-configuration-processor</artifactId>
  <optional>true</optional>
</dependency>

Quick Check

Test your understanding of relaxed binding.

Recap

@ConfigurationProperties gives type-safe, grouped configuration.

  • Bind a prefix to a class or record
  • Register via @ConfigurationPropertiesScan or @EnableConfigurationProperties
  • Records enable immutable constructor binding
  • Nested types, lists, and maps bind naturally
  • @Validated makes invalid config fail fast at startup

Frequently asked questions

Is the “Type-Safe Configuration with @ConfigurationProperties” lesson free?

Yes — the full text of “Type-Safe Configuration with @ConfigurationProperties” is free to read here on the web, and the Spring Boot 4 Microservices & REST APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Microservices & REST APIs course, upgrade to CoddyKit PRO.

What will I learn in “Type-Safe Configuration with @ConfigurationProperties”?

Bind properties to typed config classes. You practise Spring Boot 4 Microservices & REST APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Boot 4 Microservices & REST APIs?

No prior experience is required. Spring Boot 4 Microservices & REST APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Type-Safe Configuration with @ConfigurationProperties” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Boot 4 Microservices & REST APIs lesson?

Yes. Every Spring Boot 4 Microservices & REST APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. application.properties and YAML
  2. Profiles for Environments
  3. Type-Safe Configuration with @ConfigurationProperties
  4. Externalized and Override Configuration
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