Devoxx Belgium 2025 — UUID v7 on the JVM

Devoxx Belgium 2025 was held in Antwerp from October 6–10, 2025. One of Europe’s largest developer conferences, Devoxx draws thousands of JVM ecosystem developers across Java, Kotlin, and Scala communities.

UUID v7 Comes to the JVM Standard Library

The most anticipated session on UUID topics previewed a JEP (JDK Enhancement Proposal) targeting a future Java LTS release to add UUID.randomUUID7() to java.util.UUID. While not yet merged, the proposal has formal champion status and active discussion on the OpenJDK mailing list.

Until the JEP lands, Devoxx sessions recommeded java-uuid-generator (JUG) as the production-ready bridge:

import com.fasterxml.uuid.Generators;
import java.util.UUID;

UUID id = Generators.timeBasedEpochGenerator().generate(); // UUID v7

JUG is maintained by the author of the Jackson JSON library, widely deployed in Spring Boot applications, and conforms to RFC 9562’s monotonic counter recommendation.

Hibernate 6.5 and Spring Boot

A detailed talk walked through Hibernate 6.5+‘s native UUID v7 support in a Spring Boot 3.3+ application:

@Entity
@Table(name = "orders")
public class Order {

    @Id
    @GeneratedValue
    @UuidGenerator(style = UuidGenerator.Style.TIME)
    private UUID id;

    @Column(nullable = false)
    private String customerId;

    @CreationTimestamp
    private Instant createdAt;
}

UuidGenerator.Style.TIME in Hibernate 6.5 maps to RFC 9562 UUID v7, not the older time-based UUID v1. Speakers confirmed that switching from Style.RANDOM (v4) to Style.TIME (v7) requires no schema migration — the database uuid column type stores both versions identically.

Kotlin Data Classes

For Kotlin-first projects using Spring Data JPA:

@Entity
@Table(name = "products")
data class Product(
    @Id
    @GeneratedValue
    @UuidGenerator(style = UuidGenerator.Style.TIME)
    val id: UUID = UUID(0L, 0L), // placeholder; Hibernate overwrites before persist

    @Column(nullable = false)
    val name: String,
)

The UUID(0L, 0L) default satisfies Kotlin’s non-null requirement while Hibernate replaces it with a v7 UUID before the insert hits the database.

Quarkus and Panache

Quarkus sessions covered UUID v7 in both JPA and Panache active record patterns:

// Panache entity
@Entity
public class Invoice extends PanacheEntityBase {

    @Id
    @GeneratedValue
    @UuidGenerator(style = UuidGenerator.Style.TIME)
    public UUID id;

    public BigDecimal amount;
}

// Usage
Invoice invoice = new Invoice();
invoice.amount = new BigDecimal("99.00");
invoice.persist(); // id is assigned a UUID v7 value by Hibernate before insert

JVM Performance Benchmarks

A benchmarking talk using JMH (Java Microbenchmark Harness) measured UUID generation throughput:

Generation throughput is not the bottleneck in any real application — database insert time dominates. The index performance advantage of UUID v7 over v4 at the database layer far outweighs the negligible generation cost difference.

Related JVM Resources

• Hibernate 6.5 UUID Generator documentation
• java-uuid-generator (JUG) — UUID v7 for all JVM versions
• Quarkus Hibernate ORM with Panache guide
• Spring Data JPA
• RFC 9562 — UUID v7 specification