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 Compiling Sources Using A Different JDK
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 Edwin Punzalan
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 2006-07-05
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Compiling Sources Using A Different JDK

* Using Maven Toolchains

  The preferable way to use a different JDK is to use the toolchains mechanism. During the build of a project, Maven, 
  without toolchains, will use the JDK to perform various steps, like compiling the Java sources, generate the Javadoc,
  run unit tests or sign JARs. Each of those plugins need a tool of the JDK to operate: <<<javac>>>, <<<javadoc>>>,
  <<<jarsigner>>>, etc. A toolchains is a way to specify the path to the JDK to use for all of those plugins in a
  centralized manner, independant from the one running Maven itself.
  
  To set this up, refer to the {{{/guides/mini/guide-using-toolchains.html}Guide to Using Toolchains}}, which makes use
  of the {{{/plugins/maven-toolchains-plugin/}Maven Toolchains Plugin}}.

  With the maven-toolchains-plugin you configure 1 default JDK toolchain for all related maven-plugins. 
  Since maven-compiler-plugin 3.6.0 when using with Maven 3.3.1+ it is also possible to give the plugin its own 
  toolchain, which can be useful in case of different JDK calls per execution block (e.g. the test sources require a 
  different compiler compared to the main sources).  

* Configuring the Compiler Plugin

  Outside of a toolchains, it is still possible to tell the Compiler Plugin the specific JDK to use during compilation.
  Note that such configuration will be specific to this plugin, and will not affect others.
  
  The <<<compilerVersion>>> parameter can be used to specify the version of the
  compiler that the plugin will use. However, you also need to set <<<fork>>>
  to <<<true>>> for this to work. For example:

+-------
<project>
  [...]
  <build>
    [...]
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>${project.version}</version>
        <configuration>
          <verbose>true</verbose>
          <fork>true</fork>
          <executable><!-- path-to-javac --></executable>
          <compilerVersion>1.3</compilerVersion>
        </configuration>
      </plugin>
    </plugins>
    [...]
  </build>
  [...]
</project>
+-------

  To avoid hard-coding a filesystem path for the executable, you can use a
  property.  For example:

+-------
          <executable>${JAVA_1_4_HOME}/bin/javac</executable>
+-------

  Each developer then defines this property in
  {{{http://maven.apache.org/ref/current/maven-settings/settings.html}settings.xml}},
  or sets an environment variable, so that the build remains portable.

+-------
<settings>
  [...]
  <profiles>
    [...]
    <profile>
      <id>compiler</id>
        <properties>
          <JAVA_1_4_HOME>C:\Program Files\Java\j2sdk1.4.2_09</JAVA_1_4_HOME>
        </properties>
    </profile>
  </profiles>
  [...]
  <activeProfiles>
    <activeProfile>compiler</activeProfile>
  </activeProfiles>
</settings>
+-------

  If you build with a different JDK, you may want to
  {{{http://maven.apache.org/plugins/maven-jar-plugin/examples/manifest-customization.html}
  customize}} the jar file manifest.