Spring Boot 4.0 GA: New Features, Performance Boosts, and Migration Guide

Introduction

Spring Boot 4.0 has reached General Availability, marking a shift toward cloud‑native, high‑performance Java backend development. The release requires a minimum of Java 17 (LTS) and recommends JDK 21, while supporting future JDK 25.

1. Baseline Requirements and Modern Java

Minimum JDK: Java 17 (LTS), recommended JDK 21

Build tools: Maven ≥ 3.6.3, Gradle ≥ 7.6.4

Web container: Servlet 6.1 + WebSocket 2.2, requiring Tomcat 11+ or Jetty 12.1+

Legacy components such as XML configuration, javax.* packages, JUnit 4, and Feign client APIs are deprecated in favor of Jakarta EE 10/11, JUnit 5, and the new @HttpExchange client.

2. Performance Revolution

2.1 Virtual Thread Support (JDK 21)

Spring Boot 4.0 seamlessly integrates JDK 21 virtual threads. Enabling them requires a single property:

spring:
  threads:
    virtual:
      enabled: true

Methods annotated with @Async run on lightweight virtual threads, delivering measured improvements:

RPS increased from 12 k to 85 k

CPU usage reduced by 40%

Support for millions of concurrent connections

2.2 GraalVM Native Image Support

GraalVM native images are now first‑class citizens. Cold‑start time drops from 500 ms to 50 ms (‑90%), and memory usage falls from 2 GB to 120 MB (‑80%). The feature integrates with Serverless and Kubernetes burst‑traffic scenarios.

@NativeHint(
  options = {"--enable-http", "--enable-https"},
  resources = @Resource(patterns = ".*\\.properties")
)
public class NativeConfig {}

Using @NativeHint together with the official Maven plugin simplifies native compilation.

3. Developer Experience Enhancements

3.1 API Versioning

Spring Boot 4.0 adds a version attribute to @GetMapping, allowing clean API version control without manual URL concatenation.

@RestController
@RequestMapping("/api/user")
public class UserController {
    @GetMapping(version = "1")
    public User getUserV1() { /* ... */ }

    @GetMapping(version = "2")
    public UserDetail getUserV2() { /* ... */ }
}

Global configuration can route based on path, header, or Accept‑Type:

@Configuration
public class ApiConfig implements WebMvcConfigurer {
    @Override
    public void configureApiVersioning(ApiVersionConfigurer configurer) {
        configurer.usePathSegment(1); // /api/v1/user
    }
}

3.2 Declarative HTTP Client – @HttpExchange

The new @HttpExchange annotation replaces Feign for lightweight, reactive HTTP calls.

@HttpExchange(url = "/api/user", accept = "application/json")
public interface UserService {
    @GetExchange("/{id}")
    User getUserById(@PathVariable Long id);
}

Code size reduced by ~60%

Latency improved from 15 ms to 3 ms

Seamless integration with Spring WebFlux

Developers no longer need the verbose @FeignClient + fallback configuration.

4. Security, Observability, and Operations

Built‑in JWT dynamic validation with OAuth 2.1 integration (setup time reduced by 90%).

Micrometer 2.0 + OpenTelemetry provide unified metrics, logs, and tracing.

Logback‑Cloud‑Watch plugin auto‑injects TraceID, improving cross‑service trace efficiency by 60%.

SSL certificate health check adds an expiringChains field for proactive expiration warnings.

These enhancements make Spring Boot applications “out‑of‑the‑box” observable in Kubernetes, lowering SRE overhead.

5. Breaking Changes to Watch

Jackson 2.x → upgrade to Jackson 3.x

Spring JCL → replace with Apache Commons Logging 1.3+

JUnit 4 → migrate to JUnit 5

XML configuration namespaces → adopt Java Config

javax.annotation → use Jakarta annotations

Migration advice: Do not upgrade production systems directly. First transition to Spring Boot 3.5.0 GA, verify stability, then test 4.0 compatibility on a feature branch.

Conclusion

Spring Boot 4.0 is not merely an incremental release; it propels the Java ecosystem toward higher performance, lower cost, and faster delivery. While the learning curve may feel steep, embracing these changes is essential for staying competitive in the cloud‑native era.