Spring Boot 3.4 Upgrade Guide: Major Changes and Features

Spring Boot 3.4 introduces significant performance improvements, enhanced observability, and better developer experience. This guide outlines the most important changes and provides code examples to help with migration.

1. RestClient and RestTemplate – Automatic configuration now supports multiple HTTP clients (Apache HttpComponents, Jetty, Reactor Netty, JDK HttpClient). The client priority order is listed. Example configuration:

# 1. Use http-components
spring.http.client.factory=http-components

# 2. Use jetty
spring.http.client.factory=jetty

# 3. Disable redirects
spring.http.client.redirects=dont-follow

2. Bean Validation for Configuration Properties – Validation follows the Bean Validation spec and only validates nested properties annotated with @Valid. Example before/after:

@ConfigurationProperties(prefix = "pig")
@Validated
public class GatewayConfigProperties {
    private SwaggerProperties swagger;
}

@ConfigurationProperties(prefix = "pig")
@Validated
public class GatewayConfigProperties {
    @Valid // added
    private SwaggerProperties swagger;
}

3. Graceful Shutdown – All embedded web servers (Jetty, Reactor Netty, Tomcat, Undertow) enable graceful shutdown by default. To disable:

server.shutdown=immediate

4. Structured Logging – Supports ECS, GELF, and Logstash formats. Example ECS JSON:

{
  "@timestamp":"2024-01-01T10:15:00.067462556Z",
  "log.level":"INFO",
  "process.pid":39599,
  "service.name":"simple",
  "message":"No active profile set, falling back to 1 default profile: \"default\"",
  "ecs.version":"8.11"
}

Configuration to enable ECS format for file and console:

# File output uses ECS format
logging.structured.format.file=ecs

# Console output uses ECS format
logging.structured.format.console=ecs

5. Observability Improvements – Application grouping and OTLP tracing settings:

# Set application group
spring.application.group=order-processing

# Include group in logs
logging.include-application.group=true

# Enable gRPC transport for OTLP
management.otlp.tracing.transport=grpc
management.otlp.tracing.endpoint=grpc://otel-collector:4317

6. Dependency Version Upgrades – Core Spring framework components upgraded (Spring Framework 6.2, Spring Data 2024.1, Spring Security 6.4, Spring Batch 5.2) and third‑party libraries (Hibernate 6.6, Jackson 2.18.0, Micrometer 1.14, Reactor 2024.0, Testcontainers 1.20.3).

7. Testing Enhancements – MockMvc now supports AssertJ assertions:

@Autowired
private MockMvcTester mockMvcTester;

@Test
void testEndpoint() throws Exception {
    mockMvcTester.get("/api/data")
        .andExpect(status().isOk())
        .andExpect(jsonPath("$.name").value("Sample Data"));
}

8. Deprecated Features – Example of old management endpoint properties replaced with new access‑based settings.

management.endpoints.enabled-by-default=false
management.endpoint.health.enabled=true

management.endpoints.access.default=none
management.endpoint.health.access=read-only