Develop Reference

Maven on WSL2 can't see JAVA_HOME

I have JDK 11 and Maven 3.8.1 installed on my Windows 10 machine. Took care that install paths don't have spaces.
Made the value of JAVA_HOME visible inside the Ubuntu shell following the advice here. Then I restarted the Ubuntu shell.
Here are the outputs from inside an Ubuntu shell on Windows Terminal:
user#computer:/path$ java -version
openjdk version "11.0.10" 2021-01-19
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.10+9)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.10+9, mixed mode)
user#computer:/path$ env | grep JAVA
JAVA_HOME=/mnt/c/AdoptOpenJDK/jdk-11-hotspot
user#computer:/path$ mvn -v
The JAVA_HOME environment variable is not defined correctly
This environment variable is needed to run this program
NB: JAVA_HOME should point to a JDK not a JRE
So although the value of JAVA_HOME is visible inside the Ubuntu shell, somehow mvn can't see it. How do I fix this?
Maven run from cmd gives this output:
C:\path>mvn -v
Apache Maven 3.8.1 (05c21c65bdfed0f71a2f2ada8b84da59348c4c5d)
Maven home: C:\Maven\bin\..
Java version: 11.0.10, vendor: AdoptOpenJDK, runtime: C:\AdoptOpenJDK\jdk-11-hotspot
Default locale: en_IN, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"
Versions:
Windows 10 version 2004 (OS Build 19041.1110)
Java 11.0.10
Maven 3.8.1
WSL2
Ubuntu 20.04.2 LTS (via WSL2)

I gave up and simply installed JDK 11 & Maven 3.8.1 inside WSL2 using SDKMAN.
Not an ideal solution, but didn't feel like spending more time on this issue.

I don't disagree with your solution to use the Linux versions of Java and Maven inside WSL, but I do think I see why your example in the original question was failing.
The problem appears to be that you are using the Windows versions of Java/Maven, BUT your JAVA_HOME from inside WSL is using the "Linux form" of the path (/mnt/c/AdoptOpenJDK/jdk-11-hotspot).
Maven is complaining, because since it is running under Windows, it doesn't understand that path. It needs to see C:\AdoptOpenJDK\jdk-11-hotspot.
I believe this is because the answer you linked to said to use setx WSLENV "JAVA_HOME/p". The /p is forcing the translation from the Windows path to the WSL/Linux mapping, which you don't want in this case.
Also, be sure to restart the Terminal from which you launch WSL so that it can pick up the new environment variables.

Maven: Fatal error compiling: invalid target release: 1.8

We just upgraded the project from jdk 1.6 to jdk 1.8. While building the project in my machine, i'm getting following error.
[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-compiler-plugin:3.3:compile
(default-compile) on project exception: Fatal error compiling: invalid
target release: 1.8 -> [Help 1]
Here is the maven compiler plugin which is been used
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
I looked at the many post and most of them were related with not having the correct version configured for java_home. I verified all of these aspects and couldn't find any of them alarming.
Java version -
qadeersmsiphone:main pdubey$ java -version
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)
Maven Version -
qadeersmsiphone:main pdubey$ mvn -version
Apache Maven 3.1.1 (0728685237757ffbf44136acec0402957f723d9a; 2013-09-17 08:22:22-0700)
Maven home: /usr/share/maven
Java version: 1.8.0_51, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_51.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.8.5", arch: "x86_64", family: "mac"
and I checked that while building the project maven uses jdk 1.8
qadeersmsiphone:main pdubey$ mvn install -debug
Apache Maven 3.1.1 (0728685237757ffbf44136acec0402957f723d9a; 2013-09-17 08:22:22-0700)
Maven home: /usr/share/maven
Java version: 1.8.0_51, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_51.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.8.5", arch: "x86_64", family: "mac"
[INFO] Error stacktraces are turned on.
[DEBUG] Reading global settings from /usr/share/maven/conf/settings.xml
[DEBUG] Reading user settings from /Users/pdubey/.m2/settings.xml
[DEBUG] Using local repository at /Users/pdubey/.m2/repository
[DEBUG] Using manager EnhancedLocalRepositoryManager with priority 10.0 for /Users/pdubey/.m2/repository
[INFO] Scanning for projects...
UPDATE: I could get it working by removing the
maven-compiler-plugin in pom file (Ideally, i don't want to do this). And i also observed that even if i
remove this plugin, maven by default downloads the 3.3 version of
compiler plugin in my local repo. I'm not sure what's wrong in this
plugin although source and target appears to be correct.

Check the java and Javac version - My Java version was 1.8.0_51
$ java -version
java version "1.8.0_51"
But javac version was pointing to old jdk 1.7.0_67
$ javac -version
javac 1.7.0_67
There are couple of thing which we should try -
Ensure that symbolic link is pointing to correct jdk. If not, remove existing link and create new one for your jdk
cd /System/Library/Frameworks/JavaVM.framework/Versions/
rm CurrentJDK
ln -s /Library/Java/JavaVirtualMachines/<jdk version>.jdk/Contents/ CurrentJDK
In /Library/Java/Extension, i had a tools.jar. I believe, this was from old jdk.
cd /Library/Java/Extensions
-rw-r--r-- 1 root admin 15286304 Jan 14 2015 tools.jar
Remove this
sudo rm -rf /Library/Java/Extensions
point 2 did the trick for me :)

Sometimes this problem is related to a JAVA_HOME used by maven.
In my particular case I tried to start an install target and had an exact the subj message.
Then I just tried an mvn -version command and I realized that it uses jdk7
Then I run in a console set JAVA_HOME=C:\Java\jdk8 (my jdk path, so your own could be different)
Then typed mvn clean install test and it worked just fine at last
Good luck!

Same issue here, but I was using run configurations inside Eclipse when maven kept throwing this error. Fixed by setting the right JDK version here:

I had the same issue:
> java -version
java version "1.8.0_111"
>javac -version
javac 1.7.0.6
I checked the Path in System variables, and the jdk was not updated to jdk 8.
After I updated the path with the right jdk it worked.

In cent os we can use alternatives to switch the version.
alternatives --config javac
alternatives --config java
But MAVEN uses JAVA_HOME.
And this JAVA_HOME can be possible to a link.
Either we have to point the JAVA_HOME manually to new jdk folder, OR manually remove/delete the link and create a new same link again from above answers.
From alternatives we can get the path of jdk

First of all, it is definitely versions issue.
In my situation:
java -version showed the result
java version "1.8.0_172"
and javac -version was showing
javac 1.8.0_172
BUT: Maven uses JAVA_HOME environment variable to get your JDK version to build a project and run it's a plugin. So the way how we have to check it is
echo %JAVA_HOME%
Which in my situation was
jdk1.7.0_172
So simply change the path to the variable will solve the issue.
Hope it will save time to someone.

Setting M2_HOME

I use Intellij Idea. Now I'm trying to set up new system and have came up with the next issue:
I've downloaded java, installed it, set JAVA_HOME(C:\Progra~2\Java\jdk1.7.0_51), added to PATH (C:\Progra~2\Java\jdk1.7.0_51\bin), checked from console java -version and %JAVA_HOME% - everything works fine (java version "1.7.0_51"Java(TM) SE Runtime Environment (build 1.7.0_51-b13) Java HotSpot(TM) Client VM (build 24.51-b03, mixed mode, sharing)).
I've downloaded maven, installed it, set M2_HOME(C:\Progra~2\Java\maven), added to PATH(C:\Progra~2\Java\maven\bin), checked from console mvn -version(Apache Maven 3.3.3 2015-04-22T14:57:37+03:00) Maven home: C:\Progra~2\Java\maven Java version: 1.7.0_51, vendor: Oracle Corporation Java home: C:\Progra~2\Java\jdk1.7.0_51\jre Default locale: ru_RU, platform encoding: Cp1251 OS name: "windows 7", version: "6.1", arch: "x86", family: "windows") and enter cd %M2_HOME% - it goes there normally.
But when I try to do mvn -clean or -install or any other action from Intellij, it says:
-Dmaven.multiModuleProjectDirectory system propery is not set. Check $M2_HOME environment variable and mvn script match.
Process finished with exit code 1

If you use the newest Maven 3.3.3 you have to take care of the new calling design. It changed from bat to cmd files. Your IDE probably isn't right now compatible to this new design. Try to take an older version of maven.
Maybe you have a look here too: `-Dmaven.multiModuleProjectDirectory not set` issue with Maven and IntelliJ

IntelliJ ships with a bundled Maven thus your settings and maven installation will not be picked up unless you explicitly specify Intellij to use your maven installation and not the bundled one.
You can verify it under: Maven Settings (use CTRL+SHIFT+A to find it if you can't locate it)

${java.home} changes when running Maven on a OS X

This appears to be a problem I do not see on linux or Windows machines. I have my environment setup with a JAVA_HOME derived from /usr/libexec/java_home. This is in my .bashrc file:
export JAVA_HOME=$(/usr/libexec/java_home -version 1.7)
which results in:
~/dev/Endeavor/endeavor-sdk$ echo $JAVA_HOME
/Library/Java/JavaVirtualMachines/jdk1.7.0_17.jdk/Contents/Home
However when I run Maven on my project, I get an error from the native2ascii plugin:
[ERROR] Failed to execute goal org.codehaus.mojo:native2ascii-maven-plugin:1.0-alpha-2-SNAPSHOT:native2ascii (default) on project dataAccessServices: Error starting Sun's native2ascii: -> [Help 1]
My investigation points to that I am using a JRE instead of a JDK. That's odd since I am clearly pointing to the JDK in my JAVA_HOME variable. However, here is the output of mvn -version:
~/dev/Endeavor/endeavor-sdk$ mvn -version
Apache Maven 3.0.4 (r1232337; 2012-01-17 03:44:56-0500)
Maven home: /usr/share/maven
Java version: 1.7.0_17, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.7.0_17.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.7.5", arch: "x86_64", family: "mac"
Notice the "Java home:" line indicates that the ${java.home} variable has been moved to the JRE instead of the JDK that the JAVA_HOME environment variable points to.
I have tried setting the JAVA_HOME in numerous places but I can't seem to find a way to get maven to use the JDK as the home and not the JRE.
UPDATE:
I found this that appears to indicate that this is expected behavior: Java_home in Maven
But that does not explain why the native2ascii plugin cannot find the JDK tool it needs.
I have removed the use of native2ascii since it was largely unnecessary. So, I am avoiding the problem at this point. However, if anyone has an idea as to why this behaves differently on different systems, please let me know.

Have you tried running mvm help:system that should print all environment variable values that are relevant to maven?

There has been lots of discussions on this matter and here Java_home in Maven you can find a real good answer.
In a nutshell: your configuration it's just right, it is just a matter of semantics. You can read further here: http://javahowto.blogspot.com/2006/05/javahome-vs-javahome.html

After Installing Java JDK 7 For Mac OS X - mvn -version still shows java version 1.6.0_31

Oracle released Java JDK 7 on April 26 for Mac OS X. I followed the install instructions and when I do java -version in a terminal window I get:
java version "1.7.0_04"
Java(TM) SE Runtime Environment (build 1.7.0_04-b21)
Java HotSpot(TM) 64-Bit Server VM (build 23.0-b21, mixed mode)
However when I do mvn -version in the terminal window I get:
Apache Maven 3.0.2 (r1056850; 2011-01-08 18:58:10-0600)
Java version: 1.6.0_31, vendor: Apple Inc.
Java home: /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
Default locale: en_US, platform encoding: MacRoman
OS name: "mac os x", version: "10.7.3", arch: "x86_64", family: "mac"
How can I get Maven to use the Java JDK 1.7.0_04?
Thanks for the help.

Finally found the answer here:
http://www.adam-bien.com/roller/abien/entry/java_se_development_kit_7
You should use JAVA_HOME=$(/usr/libexec/java_home) instead on a Mac and then set the current jdk via "Java Preferences.app".
Set JAVA_HOME in ~/.profile

The problem is that the symbolic link "CurrentJDK" inside the versions of JavaVm.framework points to the old jdk, so when i used the following commands to set the CurrentJDK to the latest one (1.7.0_45) it works
cd /System/Library/Frameworks/JavaVM.framework/Versions
sudo rm CurrentJDK
sudo ln -s /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents CurrentJDK
reference: http://java.dzone.com/articles/installing-jdk-7-mac-os-x

To find the path from Java Preferences, try
/usr/libexec/java_home -X
My Java7 entry looks like this:
<dict>
<key>JVMArch</key>
<string>x86_64</string>
<key>JVMBundleID</key>
<string>com.oracle.java.7u04.jdk</string>
<key>JVMEnabled</key>
<true/>
<key>JVMHomePath</key>
<string>/Library/Java/JavaVirtualMachines/1.7.0.jdk/Contents/Home</string>
<key>JVMIsBuiltIn</key>
<false/>
<key>JVMName</key>
<string>Java SE 7</string>
<key>JVMPlatformVersion</key>
<string>1.7</string>
<key>JVMVendor</key>
<string>Oracle Corporation</string>
<key>JVMVersion</key>
<string>1.7.0_04</string>
</dict>

You need to change the JAVA_HOME environment variable to the new JDK 1.7 location.
Look at this question for possible locations where JAVA_HOME might be defined. In a terminal, type which java to find the path of your Java installation, and then update JAVA_HOME to point to that path (but exclude the trailing bin folder).

In case anyone is installing Maven on a 64-bit Mac running Mac OSX 'Mavericks' save yourself some time and some hair pulling trying to get Maven installed. I was trying to follow this (which failed because the location of the java_home has changed on Mavericks:
http://maven.apache.org/download.cgi
I was pulling my hair out until I found this website, which recommends you Install homebrew and follow the instructions on this page: http://techspunky.blogspot.in/2013/10/how-to-install-maven-on-mac-osx-109.html
once complete don't panic when $ maven -version doesn't work, instead use $mvn --version as maven.apache.org/download.cgi recommended.
It worked, but then I noticed the Java SDK Maven was using was Java version: 1.6.0_65, which is not the latest SDK I installed on the system.
Once I set the JAVA_HOME=/usr/libexec/java_home
It was using the correct SDK:
Maven home: /usr/local/Cellar/maven/3.1.1/libexec
Java version: 1.7.0_45, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.9", arch: "x86_64", family: "mac"
Success!
but wait...
next time I opened the terminal and ran mvn -v it went back to java version 1.6. WTH!
its some sort of supposed bug from what I read use:
echo JAVA_HOME=/usr/libexec/java_home -v 1.7 | sudo tee -a /etc/mavenrc
and now:
Maven home: /usr/local/Cellar/maven/3.1.1/libexec
Java version: 1.7.0_45, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.9", arch: "x86_64", family: "mac"

The reason Maven is still using Java 6 is that the /usr/bin/mvn script that launches it does not use the correct OS/X method for resolving the current Java version as specified in Java Preferences. See this Maven issue for details:
http://jira.codehaus.org/browse/MNG-4226
Voting it up might get it fixed; in the meantime, if you alter the /usr/bin/mvn script as shown in the comments & patch on that issue you will get the desired result.

Ok on my machine. Yes, the Oracle installer didn't exactly do its job, and it confused me to no end after 1.6 was still running.
java run time was updated
java -version
java version "1.7.0_25"
Java(TM) SE Runtime Environment (build 1.7.0_25-b15)
Java HotSpot(TM) 64-Bit Server VM (build 23.25-b01, mixed mode)
but the SDK HOME is actually a sim link still pointing to 1.6
/Library/Java/Home in finder GetInfo points to /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
in Terminal
./Home -> /System/Library/Frameworks/JavaVM.framework/Home
Go figure.
I found 1.7 here and I'm using that to build with: /Library/Java/JavaVirtualMachines/jdk1.7.0_25.jdk/Contents/Home

I think the problem lies partly with the java launch mechanism. I have been able to get Eclipse to run my code under Java7, but I think eclipse itself is still running under Java6. Also, I have a java program that was last compiled a year ago, and built using jarbundler-2.1.0.jar (with option jvmversion="1.6+"). When I double click the .app file it runs Java6, but when I double click the .jar file inside the .app it runs Java7.
Also, I do not use JAVA_HOME, but I still get the correct java version "1.7.0_04" shown in the question. JAVA_HOME seems to be a red herring. Maybe Maven needs it, but Eclipse doesn't seem to use it, and neither does launching jar files.
And after setting Java7 in the Java Preferences tool, it does not seem to affect launching .app java files. However it does make 'java -version' from the terminal work nicely. I tried unchecking everything but the Java7 option, and then Eclipse wouldn't run at all.

If your JAVA_HOME is located at the local user's bash, mvn will pick the system's current java version no matter what JAVA_HOME you've set.
Hence first run the command 'which mvn' and check which executable mvn you are using. After that edit that mvn file and change the JAVA_HOME variable to your prefered java home.