java-modern

Java Modern Skill

Java 21+ language features and how to use them in Spring Boot applications.

When to Use

• Building new Spring Boot 4.x applications (default to modern features)
• Modernizing/refactoring existing Java code
• User asks about records, sealed classes, pattern matching, virtual threads

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Records (Java 16+)

DTOs

// ✅ Records for request/response DTOs
public record ProductRequest(
    @NotBlank String name,
    @DecimalMin("0.0") BigDecimal price
) {}

public record ProductResponse(
    Long id,
    String name,
    BigDecimal price,
    LocalDateTime createdAt
) {
    public static ProductResponse from(Product entity) {
        return new ProductResponse(
            entity.getId(),
            entity.getName(),
            entity.getPrice(),
            entity.getCreatedAt()
        );
    }
}

Configuration Properties

// ✅ Records for config properties (Spring Boot 4.x)
@ConfigurationProperties(prefix = "app.notification")
public record NotificationProperties(
    boolean enabled,
    String fromEmail,
    Duration timeout,
    Retry retry
) {
    public record Retry(int maxAttempts, Duration delay) {}
}

When NOT to use records

• JPA entities (Hibernate needs mutable objects, no-arg constructor)
• Classes that need inheritance
• Objects with mutable state

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Sealed Classes (Java 17+)

Domain Modeling

// ✅ Restrict payment types at compile time
public sealed interface PaymentResult
    permits PaymentSuccess, PaymentFailure, PaymentPending {
}

public record PaymentSuccess(String transactionId, BigDecimal amount)
    implements PaymentResult {}

public record PaymentFailure(String errorCode, String message)
    implements PaymentResult {}

public record PaymentPending(String referenceId)
    implements PaymentResult {}

// Usage in service
public PaymentResult processPayment(PaymentRequest request) {
    try {
        String txId = gateway.charge(request);
        return new PaymentSuccess(txId, request.amount());
    } catch (InsufficientFundsException e) {
        return new PaymentFailure("INSUFFICIENT_FUNDS", e.getMessage());
    }
}