Support for Apache HttpClient 4 with RestTemplate was removed in Spring Framework 6, in favor of Apache HttpClient 5. Spring Boot 3.0 includes dependency management for both HttpClient 4 and 5. Applications that continue to use HttpClient 4 can experience errors when using RestTemplate that are difficult to diagnose.

Spring Boot 3.1 removes dependency management for HttpClient 4 to encourage users to move to HttpClient 5 instead.

The ServletRegistrationBean and FilterRegistrationBean classes will now fail with an IllegalStateException rather than logging a warning if registration fails. If you need the old behavior, you should call setIgnoreRegistrationFailure(true) on your registration bean.

None.

If you’re using Logback or Log4j2, there’s now the option to have different log levels for console logs and file logs. This can be set using the configuration properties logging.threshold.console and logging.threshold.file.

You can now limit the maximum HTTP response header size if you are using Tomcat or Jetty. For Tomcat you can use the server.tomcat.max-http-response-header-size property and for Jetty you can use server.jetty.max-http-response-header-size. By default, response headers are limited to 8kb.

Spring Boot 3.1.0-M1 moves to new versions of several Spring projects:

• Spring Data 2023.0.0-M2

• Spring Integration 6.1.0-M1

• Spring Security 6.1.0-M1

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

• Kafka 3.4.0

• Kotlin 1.8.10

• Liquibase 4.19.0

• Micrometer 1.11.0-M1

• Micrometer Tracing 1.1.0-M1

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

• Spring Kafka ContainerCustomizer beans are now applied to the auto-configured KafkaListenerContainerFactory.

• A management.otlp.metrics.export.headers property has been added to support sending headers to an OTLP registry.

• JoranConfigurators beans can now be used in AOT processing.

• Additional close-timeout, operation-timeout, auto-startup and auto-create properties have been added to spring.kafka.admin

• BatchInterceptor beans are now applied to the auto-configured ConcurrentKafkaListenerContainerFactory.

• Nomad has been added to the list of recognized CloudPlaform values.

• You can now specify a registration-policy property for spring.jmx.