Spring Boot 2.3.0 M4 Release Notes

For changes in earlier milestones, please refer to:

Upgrading from Spring Boot 2.2

In addition to the below, please see the instructions in the 2.3.0.M1, 2.3.0.M2, and 2.3.0.M3 release notes for upgrading from Spring Boot 2.2.

Building layered jars

Default layers

The layers that are created by default have been changed from those in M3. Application classes and resources are now written into a single layer named application. A new layer, spring-boot-loader, that contains the fat jar launcher classes has been introduced.

Customizing layers with Maven

The XML schema for customizing layers jars with Maven has been renamed and improved. The schema is now located at https://www.springframework.org/schema/boot/layers/layers-2.3.xsd. Please refer to the updated reference documentation for details.

Couchbase 3

Spring Boot upgraded to the Couchbase SDK v3 which brings a number of breaking changes:

To connect to a cluster, you should now use spring.couchbase.connection-string instead of the former bootstrap-hosts.
Role-based access controls have now been generalized.
Spring Boot no longer auto-configures a Bucket but you can easily do so using the Cluster API.
Endpoints IO configuration has been harmonized in spring.couchbase.env.io.
If you were extending CouchbaseConfiguration to customize the environment, please use ClusterEnvironmentBuilderCustomizer to do so in a more idiomatic fashion.

A bucket name needs to be provided if you’re using Couchbase with Spring Data.

Embedded Servlet web server threading configuration

The configuration properties for configuring the threads used by embedded Servlet web servers (Jetty, Tomcat, and Undertow) have moved to dedicated threads groups. The properties can now be found in server.jetty.threads, server.tomcat.threads, and server.undertow.threads. The old properties remain in a deprecated form to ease migration.

Disk space health indicator

The auto-configured disk space health indicator no longer requires the path that is monitored to exist when the application starts. A non-existent path will be detected as having zero usable space resulting in a down response from the indicator.

Supported versions of Gradle

If you are using Gradle 6, Gradle 6.3 or later is now required. Gradle 5.6.x is also supported in a deprecated form.

Upgrading from Spring Boot 2.3.0.M3

New and noteworthy

Tip	Check the configuration changelog for a complete overview of the changes in configuration.

Liveness and Readiness probes

Spring Boot now has in-built knowledge of the availability of your application, tracking whether it is alive and whether it is ready to handle traffic. The health endpoint can be configured to expose the liveness (/actuator/health/liveness) and readiness (/actuator/health/readiness) of you application with the management.health.probes.enabled=true configuration property. When running on Kubernetes this is done automatically. To learn more about this feature, please check out this blog post and the reference documentation to which it links.

Building OCI images

DOCKER_* environment variables are now used to locate the Docker daemon when building OCI images with Maven or Gradle.

The name of the image and the builder that is used to build it can now be controlled via a command-line property. When using Maven the properties are spring-boot.build-image.imageName and spring-boot.build-image.builder respectively. The equivalent properties for Gradle are --imageName and --builder.

Building layered jars

Custom layers with Gradle

Support for customizing layers when using Gradle has been added to the bootJar DSL. Please refer to the updated reference documentation for details.

Configurable base path for WebFlux applications

The base path of all web handlers a WebFlux application can now be configured. Use the spring.webflux.base-path property to do so.

Contributing additional tags to Web MVC and WebFlux metrics

Tags that are used in addition to those provided by default for MVC and WebFlux can now be contributed. Contributions can be made using a WebMvcTagsContributor @Bean for MVC and a WebFluxTagsContributor @Bean for WebFlux.

Dependency Upgrades

Spring Boot 2.3 M4 upgrades to the latest milestone of several Spring projects:

Spring Data Neumann-RC1
Spring HATEOAS 1.1.0.M3
Spring Integration 5.3.0.M4
Spring Session Dragonfruit-RC2

Numerous third-party dependencies have been upgraded, some of the more noteworthy of which are the following:

Couchbase Client 3.0
MariaDB 2.6
QueryDSL 4.3

Miscellaneous

Apart from the changes listed above, there have also been lots of minor tweaks and improvements including:

Auto-detection of the cloud platform can be overridden using spring.main.cloud-platform.
Caching of responses from Acuator’s HTTP endpoints is now supported when the request has a principal.
Maven support for creating a fat jar now honors the project.build.outputTimestamp property, allowing its output to be reproducible.
The Javadoc of the Maven plugin is now published.