src/it/multirelease-patterns/singleproject-toolchains/pom.xml

<?xml version="1.0" encoding="UTF-8"?>
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  ~ Licensed to the Apache Software Foundation (ASF) under one
  ~ or more contributor license agreements.  See the NOTICE file
  ~ distributed with this work for additional information
  ~ regarding copyright ownership.  The ASF licenses this file
  ~ to you under the Apache License, Version 2.0 (the
  ~ "License"); you may not use this file except in compliance
  ~ with the License.  You may obtain a copy of the License at
  ~
  ~   http://www.apache.org/licenses/LICENSE-2.0
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  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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<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/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>multirelease</groupId>
  <artifactId>multirelease</artifactId>
  <version>1.0.0-SNAPSHOT</version>

  <name>Single Project :: Toolchains</name>

  <properties>
    <!-- The oldest Java version supported by this tool. -->
    <!-- Will control compilation of the main code and the unit tests. -->
    <base.java.version>1.8</base.java.version>

    <!-- set the property when running from the release plugin -->
    <arguments>-Dmulti_release=true</arguments>
  </properties>

  <build>
    <plugins>

      <!-- Use toolchains to select the compilers -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-toolchains-plugin</artifactId>
        <version>1.1</version>
        <executions>
          <execution>
            <goals>
              <goal>toolchain</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <toolchains>
            <jdk>
              <version>${base.java.version}</version>
            </jdk>
          </toolchains>
        </configuration>
      </plugin>

      <!-- define the possible compilations -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>@project.version@</version>
        <configuration>
          <source>${base.java.version}</source>
          <target>${base.java.version}</target>
        </configuration>
        <executions>
          <!-- for Java 9 -->
          <execution>
            <id>java9</id>
            <phase />
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <release>9</release>
              <jdkToolchain>
                <version>9</version>
              </jdkToolchain>
              <compileSourceRoots>
                <compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot>
              </compileSourceRoots>
              <multiReleaseOutput>true</multiReleaseOutput>
            </configuration>
          </execution>
          <!-- for Java 10 -->
          <execution>
            <id>java10</id>
            <phase />
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <release>10</release>
              <jdkToolchain>
                <version>10</version>
              </jdkToolchain>
              <compileSourceRoots>
                <compileSourceRoot>${project.basedir}/src/main/java10</compileSourceRoot>
              </compileSourceRoots>
              <multiReleaseOutput>true</multiReleaseOutput>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  
  <profiles>

    <!-- enable java9 compilation -->
    <profile>
      <id>compile-java9</id>
      <activation>
        <jdk>[9,)</jdk>
      </activation>
      <build>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <executions>
              <execution>
                <id>java9</id>
                <phase>compile</phase>
              </execution>
            </executions>
          </plugin>
        </plugins>
      </build>
    </profile>

    <!-- enable java10 compilation -->
    <profile>
      <id>compile-java10</id>
      <activation>
        <jdk>[10,)</jdk>
      </activation>
      <build>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <executions>
              <execution>
                <id>java10</id>
                <phase>compile</phase>
              </execution>
            </executions>
          </plugin>
        </plugins>
      </build>
    </profile>

    <profile>
      <id>test-toolchains-bypass</id>
      <activation>
        <property>
          <name>!multi_release</name>
        </property>
      </activation>

      <build>
        <plugins>
          <!-- Run the unit tests with the JVM used to run maven -->
          <plugin>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>2.21.0</version>
            <configuration>
              <jvm>${env.JAVA_HOME}/bin/java</jvm>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </profile>

    <profile>
      <id>multi-jar</id>
      <activation>
        <property>
          <name>multi_release</name>
        </property>
      </activation>

      <build>
        <plugins>
          <!-- enable java9 - java11 compilations -->
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <executions>
              <execution>
                <id>java9</id>
                <phase>compile</phase>
              </execution>
              <execution>
                <id>java10</id>
                <phase>compile</phase>
              </execution>
              <execution>
                <id>java11</id>
                <phase>compile</phase>
              </execution>
            </executions>
          </plugin>

          <!-- add the multi-release:true manifest entry -->
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>
            <version>2.4</version>
            <configuration>
              <archive>
                <manifestEntries>
                  <Multi-Release>true</Multi-Release>
                </manifestEntries>
              </archive>
              <excludes>
                <exclude>**/javac*</exclude>
                <exclude>**/org.codehaus.plexus.compiler.javac.JavacCompiler*arguments</exclude>
              </excludes>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </profile>
  </profiles>
</project>