JDK 21 Features

Just a try. It’s related to this blog post:

• https://blog.soebes.io/posts/2023/06/2023-06-24-how-to-use-jdk21-preview-features-incubator/

State

It’s just a Proof Of Concept

Requirements

JDK21+

POM Details

Compiler Configuration

Some detailed hints about the configuration in the pom.xml for the compiler etc.

If you missed the configuration <arg>-proc:full</arg> as part of the maven-compiler-plugin configuration for JDK21+ you will get the following output during the compilation of the production code (src/main/java) and your test code (src/test/java):

Annotation processing is enabled because one or more processors were found
on the class path. A future release of javac may disable annotation processing
unless at least one processor is specified by name (-processor), or a search
path is specified (--processor-path, --processor-module-path), or annotation
processing is enabled explicitly (-proc:only, -proc:full).
Use -Xlint:-options to suppress this message.
Use -proc:none to disable annotation processing.

That requires the setup of the arg configuration element for the maven-compiler-plugin. More details can be found in this article.

Dynamic Agents

In case you will see the following WARNING while using mockito or alike:

OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
WARNING: A Java agent has been loaded dynamically (/Users/khm/.m2/repository/net/bytebuddy/byte-buddy-agent/1.14.5/byte-buddy-agent-1.14.5.jar)
WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
WARNING: Dynamic loading of agents will be disallowed by default in a future release

this means you are running on at least JDK21+ which means you have to enhance your configuration for maven-surefire-plugin and for maven-failsafe-plugin with the following:

<argLine>-XX:+EnableDynamicAgentLoading</argLine>

That means in the end you have to have the following configuration for your plugins like this:

<plugin>
  <artifactId>maven-surefire-plugin</artifactId>
  <configuration>
    <!--
     ! Needed to suppress WARNINGs related to the usage of dynamic agents (byte-buddy)
     -->
    <argLine>-XX:+EnableDynamicAgentLoading</argLine>
  </configuration>
</plugin>
<plugin>
  <artifactId>maven-failsafe-plugin</artifactId>
  <configuration>
    <!--
     ! Needed to suppress WARNINGs related to the usage of dynamic agents (byte-buddy)
     -->
    <argLine>-XX:+EnableDynamicAgentLoading</argLine>
  </configuration>
</plugin>