Master Spring Boot 3.4: Key Changes, New Features, and Migration Guide

1. Introduction

Spring Boot 3.4 brings significant performance improvements, enhanced observability, and a better development experience. This guide highlights the most important changes and provides code examples to help you migrate smoothly.

2. Major Changes and Enhancements

2.1 RestClient and RestTemplate

2.1.1 New Features

Automatic configuration support for multiple HTTP clients, including Apache HTTP Components, Jetty Client, Reactor Netty HttpClient, and JDK HttpClient.

2.1.2 Client Priority Order

Apache HTTP Components (HttpComponentsClientHttpRequestFactory)

Jetty Client (JettyClientHttpRequestFactory)

Reactor Netty HttpClient (ReactorClientHttpRequestFactory)

JDK HttpClient (JdkClientHttpRequestFactory)

Simple JDK HttpURLConnection (SimpleClientHttpRequestFactory)

2.1.3 Configuration Example

<code># 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</code>

2.1.4 Custom Client Example

2.2 Bean Validation for Configuration Properties

2.2.1 Main Changes

Validation now strictly follows the Bean Validation specification.

Nested properties are validated only when the field is annotated with

@Valid

.

2.2.2 Refactoring Example

Before:

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

After:

<code>@ConfigurationProperties(prefix = "pig")
@Validated
public class GatewayConfigProperties {
    @Valid  // add this annotation
    private SwaggerProperties swagger;
}</code>

2.3 Graceful Shutdown

2.3.1 Default Feature

All embedded web servers (Jetty, Reactor Netty, Tomcat, Undertow) now enable graceful shutdown by default.

2.3.2 Configuration

Disable graceful shutdown:

<code>server.shutdown=immediate</code>

2.4 Structured Logging

2.4.1 Supported Formats

Elastic Common Schema (ECS)

<code>{"@timestamp":"2024-01-01T10:15:00.067462556Z","log.level":"INFO","process.pid":39599,"process.thread.name":"main","service.name":"simple","log.logger":"org.example.Application","message":"No active profile set, falling back to 1 default profile: \"default\"","ecs.version":"8.11"}</code>

Graylog Extended Log Format (GELF)

<code>{"version":"1.1","short_message":"No active profile set, falling back to 1 default profile: \"default\"","timestamp":1725958035.857,"level":6,"_level_name":"INFO","_process_pid":47649,"_process_thread_name":"main","_log_logger":"org.example.Application"}</code>

Logstash

<code>{"@timestamp":"2024-01-01T10:15:00.111037681+02:00","@version":"1","message":"No active profile set, falling back to 1 default profile: \"default\"","logger_name":"org.example.Application","thread_name":"main","level":"INFO","level_value":20000}</code>

2.4.2 Configuration

Enable ECS format:

<code># File output using ECS format
logging.structured.format.file=ecs

# Console output using ECS format
logging.structured.format.console=ecs</code>

2.5 Observability Improvements

2.5.1 Application Grouping

<code># Set application group
spring.application.group=order-processing

# Include group information in logs
logging.include-application.group=true</code>

2.5.2 OTLP Tracing Enhancements

<code># Enable gRPC transport
management.otlp.tracing.transport=grpc

# Set endpoint
management.otlp.tracing.endpoint=grpc://otel-collector:4317</code>

3. Dependency Version Upgrades

3.1 Spring Core Framework

Spring Framework → 6.2

Spring Data → 2024.1

Spring Security → 6.4

Spring Batch → 5.2

3.2 Third‑Party Libraries

Hibernate → 6.6

Jackson → 2.18.0

Micrometer → 1.14

Reactor → 2024.0

Testcontainers → 1.20.3

3.3 Maven Configuration Example

<code>&lt;parent&gt;
    &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
    &lt;artifactId&gt;spring-boot-starter-parent&lt;/artifactId&gt;
    &lt;version&gt;3.4.0&lt;/version&gt;
    &lt;relativePath/&gt;
&lt;/parent&gt;</code>

4. Testing Enhancements

4.1 MockMvc AssertJ Support

<code>@Autowired
private MockMvcTester mockMvcTester;

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

5. Deprecated Feature Handling

5.1 Deprecated Configurations

Before:

<code>management.endpoints.enabled-by-default=false
management.endpoint.health.enabled=true</code>

After:

<code>management.endpoints.access.default=none
management.endpoint.health.access=read-only</code>