What is "<release>" element on "<configuration>" for the "maven-compiler-plugin" in a JavaFX app

Question

I used the org.openjfx:javafx-archetype-simple Maven archetype to start my first JavaFX project.

The resulting POM:

<project xmlns = "http://maven.apache.org/POM/4.0.0"
         xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example.invoicing</groupId>
    <artifactId>Invoicer</artifactId>
    <version>1.0-SNAPSHOT</version>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>14</maven.compiler.source>
        <maven.compiler.target>14</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-controls</artifactId>
            <version>14</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <release>14</release>  🡄 ???
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.openjfx</groupId>
                <artifactId>javafx-maven-plugin</artifactId>
                <version>0.0.4</version>
                <configuration>
                    <mainClass>com.example.invoicing.App</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

➥ What is the purpose of the <release>14</release> line in <configuration> for the plugin <artifactId>maven-compiler-plugin</artifactId>?

I found this documentation for the Maven Compiler Plugin, Compiling Your Java Sources. But it only mentions <!-- put your configurations here -->. So I do not know anything about specific configuration options here.

Is <release>14</release> the version of Java being used to compile? Is it the version of OpenJFX? Something else?

I tried using 28 arbitrarily. Doing a Maven > install threw this error with an unhelpful error message with no clue as to a release of what product:

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project Invoicer: Fatal error compiling

Answer 1

The release flag is equivalent to specifying the source and target of the same value for the compiler plugin. It supports the -release argument for the Java compiler since Java-9.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.1</version>
    <configuration>
        <source>14</source>
        <target>14</target>
    </configuration>
</plugin>

Note: For the same reason, you can get rid of the redundant properties declared as

<maven.compiler.source>14</maven.compiler.source>
<maven.compiler.target>14</maven.compiler.target>

Further: What is the --release flag in the Java 9 compiler? | The -release flag in javac was introduced to Compile for Older Platform Versions.

---

To complete the answer over the part where you've tried the version value as 28. While using Maven version -

Apache Maven 3.6.1 (d66c9c0b3152b2e69ee9bac180bb8fcc8e6af555; 2019-04-05T00:30:29+05:30)

The error message reads very clearly what it should (if you could share the complete logs in the question)

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project forty-bits-of-java: 
Fatal error compiling: error: release version 28 not supported