Error: JAVA_HOME is not defined correctly executing maven

Assuming you use bash shell and installed Java with the Oracle installer, you could add the following to your .bash_profile

export JAVA_HOME=$(/usr/libexec/java_home)
export PATH=$JAVA_HOME/jre/bin:$PATH

This would pick the correct JAVA_HOME as defined by the Oracle installer and will set it first in your $PATH making sure it is found.

Also, you don't need to change it later when updating Java.

EDIT

As per the comments:

Making it persistent after a reboot

Just add those lines in the shell configuration file. (Assuming it's bash)

Ex: .bashrc, .bash_profile or .profile (for ubuntu)

Using a custom Java installation

Set JAVA_HOME to the root folder of the custom Java installation path without the $().

Ex: JAVA_HOME=/opt/java/openjdk

JAVA_HOME should be /usr/lib/jvm/java-7-oracle/jre/.

$JAVA_HOME should be the directory where java was installed, not one of its parts:

export JAVA_HOME=/usr/lib/jvm/java-7-oracle

We open a terminal and look for the location of java:

manuel@zonademanel:~ → whereis java

java: /usr/bin/java /etc/java /usr/bin/X11/java /usr/share/java /usr/share/man/man1/java.1.gz

What we are looking for is /usr/bin/java continue on the command line to find the absolute path , as this is only a symbolic link.

manuel@zonademanel:~ → ls -lah /usr/bin/java

lrwxrwxrwx 1 root root 22 may 19 2015 /usr/bin/java -> /etc/alternatives/java

manuel@zonademanel:~ → ls -lah /etc/alternatives/java

lrwxrwxrwx 1 root root 39 dic 7 11:52 /etc/alternatives/java -> /usr/lib/jvm/java-8-oracle/jre/bin/java

I modified my /etc/environment file with the following values

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/jvm/java-8-oracle/jre/bin" JAVA_HOME="/usr/lib/jvm/java-8-oracle/jre"

If I do not want to relogin I can reload the changes with:

source /etc/environment 

​​And run mvn -version correctly

manuel@zonademanel:~ → mvn -version

Apache Maven 3.0.5
Maven home: /usr/share/maven
Java version: 1.8.0_77, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-8-oracle/jre
Default locale: es_MX, platform encoding: UTF-8
OS name: "linux", version: "3.16.0-70-generic", arch: "amd64", family: "unix"