Type-safe configuration in Java/Spring Boot requires several key elements:
Core Requirements
- Strong Typing
-
- Use specific data types (String, int, boolean, List) instead of generic Object or String for everything
-
- Define proper Java classes with typed fields
-
- Avoid raw types and use generics where applicable
2. Configuration Properties Class
@ConfigurationProperties("app.config")
public class TypeSafeConfig {private String name;private int port;private List<String> roles;// getters/setters or constructor
}
3. Registration Mechanism
You need one of these approaches:
- @ConfigurationPropertiesScan (as in your main class)
- @EnableConfigurationProperties(YourClass.class)
- @Component on the properties class
4. Validation Support
@ConfigurationProperties("app")
@Validated
public class ValidatedConfig {@NotNull@Size(min = 1)private String name;@Min(1024)@Max(65535)private int port;}
Additional Type Safety Features
Constructor Binding (as in your AppProperties):
- Immutable objects with @ConstructorBinding
- Final fields prevent modification
- Constructor parameter validation
Nested Properties:
- Type-safe nested objects
- Proper encapsulation of related configuration
Default Values:
- @DefaultValue for constructor parameters
- Field-level defaults in regular properties
Conversion Support:
- Automatic type conversion (String to int, Duration, etc.)
- Custom converters for complex types
Benefits of Type Safety
- Compile-time checking: Catch configuration errors early
- IDE support: Auto-completion and refactoring
- Runtime validation: Fail fast on startup with invalid config
- Documentation: Self-documenting through types and validation annotations
- Refactoring safety: Changes propagate through the codebase
The setup with @ConfigurationPropertiesScan and the AppProperties class with @ConstructorBinding will provide strong type safety for configuration properties.