[maven-2] Specify JDK for Maven to use

I am trying to build a Hudson plugin I've modified and it requires jdk1.6. This is fine, but I don't see how I can tell maven where the different jdk is. I've found few mentions on the internet but they don't seem to apply to me. Some suggest adding some config to .m2/settings.xml but I don't have a settings.xml. Plus, I don't want to use 1.6 for all maven builds.

One kink is I am using mvn in cygwin, if that matters at all. It appears I should be able to make the specification in the project pom file, but the existing pom is pretty bare.

So bottom line is, is there a way to specify a jdk for a single invocation of maven?

If you have installed Java through brew in Mac then chances are you will find your Java Home Directory here:

/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home

The next step now would be to find which Java Home directory maven is pointing to. To find it type in the command:
mvn -version

The fields we are interested in here is: Java version and runtime.

Maven is currently pointing to Java 13. Also, you can see the Java Home path under the key runtime, which is:
/usr/local/Cellar/openjdk/13.0.2+8_2/libexec/openjdk.jdk/Contents/Home

To change the Java version of the maven, we need to add the Java 8 home path to the JAVA_HOME env variable.

To do that we need to run the command:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home in the terminal.

Now if we check the maven version, we can see that it is pointing to Java 8 now.

The problem with this is if you check the maven version again in the new terminal, you will find that it is pointing to the Java 13. To avoid this I would suggest adding the JAVA_HOME variable in the ~/.profile file.

This way whenever your terminal is loading it will take up the value you defined in the JAVA_HOME by default. This is the line you need to add in the ~/.profile file:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home

You can open up a new terminal and check the Maven version, (mvn -version) and you will find it is pointing to the Java 8 this time.

Yet another alternative to manage multiple jdk versions is jEnv

After installation, you can simply change java version "locally" i.e. for a specific project directory by:

jenv local 1.6

This will also make mvn use that version locally, when you enable the mvn plugin:

jenv enable-plugin maven

Maven uses variable $JAVACMD as the final java command, set it to where the java executable is will switch maven to different JDK.

You could also set the JDK for Maven in a file in your home directory ~/.mavenrc:

JAVA_HOME='/Library/Java/JavaVirtualMachines/jdk-11.0.5.jdk/Contents/Home'

This environment variable will be checked by the mvn script and used when present:

  if [ -f "$HOME/.mavenrc" ] ; then
    . "$HOME/.mavenrc"
  fi

https://github.com/CodeFX-org/mvn-java-9/tree/master/mavenrc

I say you setup the JAVA_HOME environment variable like Pascal is saying: In Cygwin if you use bash as your shell should be:

export JAVA_HOME=/cygdrive/c/pathtothejdk

It never harms to also prepend the java bin directory path to the PATH environment variable with:

export PATH=${JAVA_HOME}/bin:${PATH}

Also add maven-enforce-plugin to make sure the right JDK is used. This is a good practice for your pom.

<build>
 <plugins>
   <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-enforcer-plugin</artifactId>
      <executions>
        <execution>
          <id>enforce-versions</id>
          <goals>
            <goal>enforce</goal>
          </goals>
          <configuration>
            <rules>
              <requireJavaVersion>
                <version>1.6</version>
              </requireJavaVersion>
            </rules>
          </configuration>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

Please, see Maven Enforcer plugin – Usage.

Using this command below also worked for me, using it right after installation of Java 8 from here https://www.oracle.com/java/technologies/javase-downloads.html

export JAVA_HOME=$(/usr/libexec/java_home)

I had build problem with maven within Eclipse on Windows 7.

Though I observed mvn build was running just fine from command line.

mvn -T 5 -B -e -X -U -P test clean install -Dmaven.surefire.debug  --settings ..\..\infra-scripts\maven-conf\settings.xml   > output.log

Eclipse was considering as default JVM a JRE installation instead of JDK so it was failing on compilation.

I added to eclipse.ini following line:

-vm
C:\Program Files (x86)\Java\jdk1.8.0_25\bin

Also when starting from eclipse I used in "Goals" section following list:

-T 5 -B -e -X -U -P test clean install -Dmaven.surefire.debug  --settings ..\..\infra-scripts\maven-conf\settings.xml

Compilation error got solved.

As u said "Plus, I don't want to use 1.6 for all maven builds."....So better I will say modify your pom file and specify which jdk version to use.

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.7.0</version>
            <configuration>
                <source>1.9</source>
                <target>1.9</target>
            </configuration>
        </plugin>
    </plugins>
</build>

It will ensure that your particular project uses that version of jdk.

Seems that maven now gives a solution here : Compiling Sources Using A Different JDK

Let's say your JAVA_HOME points to JDK7 (which will run maven processes)

Your pom.xml could be :

<build>
    <plugins>
        <!-- we want JDK 1.6 source and binary compatiblility -->
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.6</source>
                <target>1.6</target>
            </configuration>
        </plugin>
        <!-- ... -->
        <!-- we want sources to be processed by a specific 1.6 javac -->
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <configuration>
              <verbose>true</verbose>
              <fork>true</fork>
              <executable>${JAVA_1_6_HOME}/bin/javac</executable>
              <compilerVersion>1.3</compilerVersion>
            </configuration>
        </plugin>
    </plugins>
</build>

If your developpers just add (and customize) the following lines in their settings.xml, your pom will be platform independant :

<settings>
  [...]
  <profiles>
    [...]
    <profile>
      <id>compiler</id>
        <properties>
          <JAVA_1_4_HOME>C:\Program Files\Java\j2sdk1.4.2_09</JAVA_1_4_HOME>
          <JAVA_1_6_HOME>C:\Program Files\Java\j2sdk1.6.0_18</JAVA_1_6_HOME>
        </properties>
    </profile>
  </profiles>
  [...]
  <activeProfiles>
    <activeProfile>compiler</activeProfile>
  </activeProfiles>
</settings>

For Java 9 :

<build>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.7.0</version>
            <configuration>
                <source>9</source>
                <target>9</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Hudson also allows you to define several Java runtimes, and let you invoke Maven with one of these. Have a closer look on the configuration page.

I know its an old thread. But I was having some issues with something similar to this in Maven for Java 8 compiler source. I figured this out with a quick fix mentioned in this article thought I can put it here and maybe can help others:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

compile:compile has a user property that allows you to specify a path to the javac.

Note that this user property only works when fork is true which is false by default.

$ mvn -Dmaven.compiler.fork=true -Dmaven.compiler.executable=/path/to/the/javac compile

You might have to double quote the value if it contains spaces.

> mvn -Dmaven.compiler.fork=true -Dmaven.compiler.executable="C:\...\javac" compile

See also Maven custom properties precedence.