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Unable to change the JAVA path to the Oracle JDK

I'm using RHEL8 which has default OpenJDK installed.
which java command points to /usr/bin/java.
java -version gives openjdk version "1.8.0_252"
Installed java in /u01/app/java/ location. Modified the .bashrc like below & sourced it.
export JAVA_HOME=/u01/app/java/jdk1.8.0_241/
PATH="$JAVA_HOME/bin/java:$HOME/.local/bin:$HOME/bin:$PATH"
export PATH
Now JAVA_HOME points to /u01/app/java/jdk1.8.0_241/ But which java or java -version still points to the OpenJDK.
Added the same in .bash_profile file & removed it from the .bashrc : Results are same
Deleted OpenJDK & made changes in .bash_profile. But by doing so ended up with "Command not found" error.
How can i fix it?

It was Path issue.
I have given PATH="$JAVA_HOME/bin/java:$HOME/.local/bin:$HOME/bin:$PATH" for PATH. which should not be the case.
Modified my PATH to below. It worked.
PATH="$JAVA_HOME/bin:$HOME/.local/bin:$HOME/bin:$PATH"
export PATH

That happens because when you invoke java it is actually invoked /usr/bin/java, which, issuing ls -l /usr/bin/java you will probably see is linked to the openjdk installation (probably through a double link: the first one being /usr/bin/java to /etc/alternatives/java and the second one being the link to the "real" java executable). For example, on my debian:
gianluca#asus-debian:~$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 mag 20 2018 /usr/bin/java -> /etc/alternatives/java
gianluca#asus-debian:~$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 43 nov 22 2019 /etc/alternatives/java -> /usr/lib/jvm/java-11-openjdk-amd64/bin/java
You can fix in two ways:
Dirty way, you manually update all the symbolic links in /usr/bin that lead to the unwanted java version and make them point to the desired one
Clean way, you use alternatives that does the job for you.
You can read more about alternatives for RHEL here (mid-page... "The longer version").
Good link

how to set JAVA_HOME on my docker-ubuntu environment?

I'm trying ubuntu inside my mac docker environment for development. javac/gcc works fine, but when I try to use JNI to connect java and c program, I found a problem. I need to find the include file and libjvm.so file on my ubuntu docker image. But unfortunately I found the javac is actually:
root#4968756a1edd:~/mynet/mytest/build/jni# javac -version
javac 1.8.0_191
root#4968756a1edd:~/mynet/mytest/build/jni# ls -lrt `which javac`
lrwxrwxrwx 1 root root 23 Feb 6 07:38 /usr/bin/javac ->
/etc/alternatives/javac
Well, in an ubuntu/centos VM installation, usually there's a directory for a jdk and everything (bin/lib/include) is under this directory. But in docker image, how can I find this jdk installation location and all those headers/libraries?

In bash you can set env variables like this:
sudo -H gedit /etc/environment
JAVA_HOME=/path/to/java/folder

Cordova/Android not finding JDK on OSX and PATH/JAVA_HOME correct

So cordova requirements is still failing for Android after trying and verifying all paths, versions and suggestions. It's on OSX 10.10.5 and a clean install of Android SDKs/Studio and cordova. Have tried Apple recommended (export JAVA_HOME=/usr/libexec/java_home -v 1.8) and direct paths with same failed result. Have verified both java/javac are in the bin directory of the JDK path.
sh-3.2# cordova requirements
Requirements check results for android:
Java JDK: not installed
Failed to run "java -version", make sure that you have a JDK installed.
You can get it from: http://www.oracle.com/technetwork/java/javase/downloads.
Your JAVA_HOME is invalid: /Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home
Android SDK: installed
Android target: installed android-9,android-10,android-19,android-22,android-23,android-24,Google Inc.:Google APIs:22,Google Inc.:Google APIs:23
Gradle: installed
Error: Some of requirements check failed
sh-3.2# echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/dzhon/bin:/opt/dzhon/sbin:/opt/X11/bin:/usr/local/MacGPG2/bin:/Users/rob/Library/Android/sdk/tools:/Users/rob/Library/Android/sdk/platform-tools:/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/bin:/Users/rob/Documents/software/apache-ant-1.9.7/bin
sh-3.2# echo $JAVA_HOME
/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home
sh-3.2# java -version
java version "1.8.0_102"
Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)
sh-3.2# javac -version
javac 1.8.0_102
sh-3.2# node -v
v5.3.0
sh-3.2# cordova -v
6.2.0
and in ~/.bash_profile:
export ANT_HOME=/Users/rob/Documents/software/apache-ant-1.9.7
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
export ANDROID_HOME=/Users/rob/Library/Android/sdk
export PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools:${JAVA_HOME}/bin:$ANT_HOME/bin
have also checked all the symlinks:
sh-3.2# ls -la /System/Library/Frameworks/JavaVM.framework/Versions/
total 32
drwxr-xr-x 11 root wheel 374 20 Jul 11:54 .
drwxr-xr-x 12 root wheel 408 6 Jan 2016 ..
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.4 -> CurrentJDK
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.4.2 -> CurrentJDK
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.5 -> CurrentJDK
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.5.0 -> CurrentJDK
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.6 -> CurrentJDK
lrwxr-xr-x 1 root wheel 10 26 Mar 2015 1.6.0 -> CurrentJDK
drwxr-xr-x 8 root wheel 272 6 Jan 2016 A
lrwxr-xr-x 1 root wheel 1 26 Mar 2015 Current -> A
lrwxr-xr-x 1 root wheel 59 20 Jul 11:54 CurrentJDK -> /Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents
The only thing in digging through the source for cordova-android on gitHub is in check_reqs.js, the error message is:
Failed to run "javac -version", make sure that you have a JDK installed.
rather than as it currently reports:
Failed to run "java -version", make sure that you have a JDK installed.
Any help greatly appreciated.
Rob

So a number of issues. check_reqs.js is where the platform/environment checks are done (app/platforms/android/cordova/lib/). The call to forgivingWhichSync('javac') on line 98 was returning the non-JDK link (as it was using Current, not CurrentJDK):
/System/Library/Frameworks/JavaVM.framework/Versions/A/Commands/javac
By repointing the Current symlink in /System/Library/Frameworks/JavaVM.framework/Versions/ to CurrentJDK it fixed this first issue:
lrwxr-xr-x 1 root wheel 10 21 Jul 12:03 Current -> CurrentJDK
lrwxr-xr-x 1 root wheel 59 21 Jul 12:06 CurrentJDK -> /Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents
The next issue was a problem with the tryCommand method testing javac. As correctly noted, javac -version returns the information in stderr. The issue (at least on OSX) is that the call to child_process.exec on line 44 also returns information in err:
Error: Command failed: /bin/sh -c javac -version
javac 1.8.0_102
javac: no source files
Usage: javac <options> <source files>
where possible options include:
-g Generate all debugging info
-g:none Generate no debugging info
-g:{lines,vars,source} Generate only some debugging info
-nowarn Generate no warnings
-verbose Output messages about what the compiler is doing
-deprecation Output source locations where deprecated APIs are used
-classpath <path> Specify where to find user class files
-cp <path> Specify where to find user class files
-sourcepath <path> Specify where to find input source files
-bootclasspath <path> Override location of bootstrap class files
-extdirs <dirs> Override location of installed extensions
-endorseddirs <dirs> Override location of endorsed standards path
-d <directory> Specify where to place generated class files
-encoding <encoding> Specify character encoding used by source files
-source <release> Provide source compatibility with specified release
-target <release> Generate class files for specific VM version
-version Version information
-help Print a synopsis of standard options
-X Print a synopsis of nonstandard options
-J<flag> Pass <flag> directly to the runtime system
The handling of the callback to this child_process.exec always triggered an error if err was non null:
if (err) d.reject(new CordovaError(errMsg));
changing this to only trigger this error if the catchStderr flag was not set now correctly handles the test for javac:
if (err && !catchStderr) d.reject(new CordovaError(errMsg));
and now success:
sh-3.2# cordova requirements
Requirements check results for android:
Java JDK: installed .
Android SDK: installed
Android target: installed android-9,android-10,android-16,android-18,android-19,android-22,android-23,android-24,Google Inc.:Google APIs:16,Google Inc.:Google APIs:18,Google Inc.:Google APIs:22,Google Inc.:Google APIs:23
Gradle: installed
Unfortunately need to edit check_reqs.js for each project when you cordova platform add android but at least it's now finding everything.

Everything worked perfectly when I did the installation with Cordova version 7 and JDK 1.8u131 on OSX. Nothing had to be changed or configured. Possibly the older versions of Cordova had issues.

java_home not found on osx mavericks

Can anyone help me figure out why every command I execute involving
JAVA_HOME
results in
-bash: /usr/libexec/java_home: No such file or directory
interestingly when i do an ls -al of /usr/libexec/java_home is listed as
lrwxr-xr-x 1 root wheel
79 Apr 10 13:15 java_home -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/java_home
I am unable to run any java based programs because JDK isn't working.

Where is the Java SDK folder in my computer? Ubuntu 12.04

I know it's installed because when I type:
$java -version
I get:
OpenJDK Runtime Environment (IcedTea6 1.12.5) (6b27-1.12.5-0ubuntu0.12.04.1)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)
And when I type:
$locate jdk
I get:
/home/arturo/Documents/2012a/sys/java/jre/glnxa64/jre/lib/servicetag/jdk_header.png
/usr/share/app-install/desktop/openjdk-6-jre:openjdk-6-java.desktop
/usr/share/app-install/desktop/openjdk-7-jre:openjdk-7-java.desktop
/usr/share/app-install/icons/openjdk-6.png
/usr/share/app-install/icons/openjdk-7.png
What worries me about the first item in the list is that the 2012a folder is my MATLAB folder and not a standard 'usr/lib' folder. I'm really confused on where the JDK and JRE got installed, because I need to set the $JAVA_HOME path pointing to the folder. Where am I missing something?

WAY-1 : Updated for the shortest and easy way
Below command will give you the path, But it will only work if java command is working in other words if java path is configured.
readlink -f $(which java)
Read more at Where can I find the Java SDK in Linux?
WAY-2 (Better than WAY-1) : Below answer is still working and try it if above command is not working
for you.
You need to dig into symbolic links. Below is steps to get Java directory
Step 1:
$ whereis java
java: /usr/bin/java /etc/java /usr/share/java
That tells the command java resides in /usr/bin/java.
Dig again:
Step 2:
$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 2009-01-15 18:34 /usr/bin/java -> /etc/alternatives/java
So, now we know that /usr/bin/java is actually a symbolic link to /etc/alternatives/java.
Dig deeper using the same method above:
Step 3:
$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 31 2009-01-15 18:34 /etc/alternatives/java -> /usr/local/jre1.6.0_07/bin/java
So, thats the actual location of java: /usr/local/jre.....
You could still dig deeper to find other symbolic links.
Reference : where is java's home dir?

Please use this command:
readlink -f $(which java)
It works for me with Ubuntu gnome.
On my computer the result is:
/usr/lib/jvm/java-7-oracle/jre/bin/java
Regards.

In generally, java gets installed at /usr/lib/jvm . That is where my sun jdk is installed. check if it is same for open jdk also.

$whereis java
java: /usr/bin/java /usr/bin/X11/java /usr/share/java /usr/share/man/man1/java.1.gz
$cd /usr/bin
$ls -l java
lrwxrwxrwx 1 root root 22 Apr 15 2014 java -> /etc/alternatives/java
$ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 39 Apr 15 2014 /etc/alternatives/java -> /usr/lib/jvm/java-7-oracle/jre/bin/java
So,JDK's real location is /usr/lib/jvm/java-7-oracle/

Location of JRE in Ubuntu:
/usr/lib/jvm/java-7-oracle/jre

$ whereis java
java: /usr/bin/java /usr/lib/java /usr/bin/X11/java /usr/share/java /usr/share/man/man1/java.1.gz

On Ubuntu 14.04, it is in /usr/lib/jvm/default-java.

For me, on Ubuntu, the various versions of JDK were in /usr/lib/jvm.

I found the solution to this with path name:
/usr/lib/jvm/java-8-oracle
I'm on mint 18.1

I am using Ubuntu 18.04.1 LTS. In my case I had to open the file:
/home/[username]/netbeans-8.2/etc/netbeans.conf
And change the jdk location to:
netbeans_jdkhome="/opt/jdk/jdk1.8.0_152"
Then saved the file and re-run Netbeans. It worked for me.

you can simply write the following command in the terminal of your linux system and get the java path :- echo $JAVA_HOME

The easiest way to do so is by typing echo $JAVA_HOME on your terminal.