maven minimal pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0">
  <modelVersion>4.0.0</modelVersion>

  <groupId>java-21-test</groupId>
  <artifactId>java-21-test</artifactId>
  <version>0.0.0-SNAPSHOT</version>

  <properties>
    <maven.compiler.release>21</maven.compiler.release>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven-clean-plugin.version>3.3.2</maven-clean-plugin.version>
    <maven-compiler-plugin.version>3.13.0</maven-compiler-plugin.version>
    <maven-enforcer-plugin.version>3.4.1</maven-enforcer-plugin.version>
    <maven-jar-plugin.version>3.3.0</maven-jar-plugin.version>
    <maven-resources-plugin.version>3.3.1</maven-resources-plugin.version>
    <maven-surefire-plugin.version>3.2.5</maven-surefire-plugin.version>
    <maven-toolchains-plugin.version>3.1.0</maven-toolchains-plugin.version>
    <versions-maven-plugin.version>2.16.2</versions-maven-plugin.version>
  </properties>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-enforcer-plugin</artifactId>
        <executions>
          <execution>
            <id>enforce-maven</id>
            <goals>
              <goal>enforce</goal>
            </goals>
            <configuration>
              <rules>
                <requireMavenVersion>
                  <version>3.9.5</version>
                </requireMavenVersion>
              </rules>
            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-toolchains-plugin</artifactId>
        <executions>
          <execution>
            <goals>
              <goal>toolchain</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <toolchains>
            <jdk>
              <version>21</version>
            </jdk>
          </toolchains>
        </configuration>
      </plugin>
    </plugins>

    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-clean-plugin</artifactId>
          <version>${maven-clean-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>${maven-compiler-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-enforcer-plugin</artifactId>
          <version>${maven-enforcer-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-jar-plugin</artifactId>
          <version>${maven-jar-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-resources-plugin</artifactId>
          <version>${maven-resources-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>${maven-surefire-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-toolchains-plugin</artifactId>
          <version>${maven-toolchains-plugin.version}</version>
        </plugin>

        <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>versions-maven-plugin</artifactId>
          <version>${versions-maven-plugin.version}</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

<?xml version="1.0" encoding="UTF-8"?>
<toolchains>
  <toolchain>
    <type>jdk</type>
    <provides>
      <version>1.8</version>
      <vendor>openjdk</vendor>
    </provides>
    <configuration>
      <jdkHome>/opt/jdk-1.8/</jdkHome>
    </configuration>
  </toolchain>

  <toolchain>
    <type>jdk</type>
    <provides>
      <version>11</version>
      <vendor>openjdk</vendor>
    </provides>
    <configuration>
      <jdkHome>/opt/jdk-11/</jdkHome>
    </configuration>
  </toolchain>

  <toolchain>
    <type>jdk</type>
    <provides>
      <version>17</version>
      <vendor>openjdk</vendor>
    </provides>
    <configuration>
      <jdkHome>/opt/jdk-17/</jdkHome>
    </configuration>
  </toolchain>

  <toolchain>
    <type>jdk</type>
    <provides>
      <version>21</version>
      <vendor>openjdk</vendor>
    </provides>
    <configuration>
      <jdkHome>/opt/jdk-21/</jdkHome>
    </configuration>
  </toolchain>
</toolchains>