Develop Reference

How to change JDK version from 1.6 to 1.7 in liberty?

I am using websphere 8.5 liberty server to deploy my .EAR application . After running java -version command i can see
Java version "1.6.0_38"
OpenJDK Runtime Environment (IceTea6 1.13.10) (rhe1-1.13.10.0.e17_2-x86_64)
OpenJDK 64-Bit Server VM (build 23.25-bo1, mixed mode)
Now i just want to change the Java version to 1.7 . Should websphere 8.5 liberty server support 1.7 and 1.8 ? How can i change the path ? Please proved any steps .

Websphere Liberty supports 1.6, 1.7 and 1.8 JVM from different vendors (IBM, Oracle). If you want to point it do the specific JVM just create server.env file in the server directory and define JAVA_HOME variable there like this:
JAVA_HOME=C:\wlp\java
Running java -version doesn't tell you anything about JVM used by Liberty, as it just is using default Java from the system. You can see which JVM is used by Liberty in the messages.log e.g.:
Launching defaultServer (WebSphere Application Server 8.5.5.9/wlp-1.0.12.cl50920160227-1523)
on IBM J9 VM, version pwi3280sr1ifx-20150513_01 (SR1+IX90162+IV73188 SR1+IX90162+IV73188) (en_us)
You can also download latest Liberty bundled with Java8 from here https://developer.ibm.com/wasdev/downloads/#asset/runtimes-webprofile7-ibm-java

under WLP directory create a new directory called "etc".
inside the etc directory , create a file called "server.env"
open server.env file for editing and add the following
JAVA_HOME={path_to_java}
This sets the java for all the servers you create under that liberty installation.
if you want to customize at server level , then create the server.env file under the server home location wlp/usr/servers/{server_name} , with the same contents as described abovev

WAS Liberty doesn't bundle a version of Java and can run using any certified Java such as the system Java or any Java that you have defined in your environment. Liberty will use the Java specified in the JAVA_HOME or JRE_HOME environment variables before using a Java that may be found in the PATH. Further information can be found in README.txt that provided in the root directory of your Liberty installation.

What is the path of the JVM inside the JRE?

I am just learning Java and I wanted to know that everywhere its written that JVM present inside JRE. I just wanted to know the complete path where exactly JVM is present inside JRE.

In Windows : inside your JRE, you will have a folder like this : C:\Program Files (x86)\Java\jre7\bin\client --> this directory contains the client JVM jvm.dll.
Under :linux you will find it in /jreInstallation/lib/yourSystemArchtecture(amd64 in my case)/(server/client)/libjvm.so
A VM is nothing but a shared library like dll or so file. Your java exe or other executable file calls the jvm.
Note : You can call your JVM using any language / executable file/ You could write a shell script or a cobol program to execute the JVM

Windows 10, mine:
C:\Users\elb>where java
C:\ProgramData\Oracle\Java\javapath\java.exe
c:\Program Files\Java\jdk1.7.0_07\bin\java.exe

If you intend to use the Invocation API in a native application and access Java APIs installed as part of OpenJDK (Java 10, Java 11, etc.) in ${JAVA_HOME} directory, link against (or dynamically load) jvm.dll found in ${JAVA_HOME}/bin/server/jvm.dll.
Oracle installers (currently up to Java 8) add a Windows Registry key pointing to jvm.dll. For example, when JRE 8 is installed, the following key is added:
HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.8
and it contains a string value RuntimeLib set to absolute path to jvm.dll. Also, information that 1.8 is the CurrentVersion can be found in key:
HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment
As of Java 9, Oracle abbreviated Java Runtime Environment to JRE, so the keys are:
HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\JRE
HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\JRE\9
This is all documented Windows Registry Settings section of the installation guide.

Java -version prints a wrong version

I have multiple versions of Java installed in the environment(I know it is bad). I've set the JAVA_HOME to jdk 1_4 directory. This is not installed, but extracted from zip and placed it somewhere. We have java 1.8 JRE also installed in the system. I never set the path to this installed directory. Now i'm trying to run some ant script that depends on jdk 1_4. I get some exception saying that it is not able to find tools.jar in java1.8... .
My question is that when the path and java_home are set to jdk 14 why does the ant look for 1.8 version of java? I'm confused.
Update: I have looked up the duplicate issue.
Additional details: Java -version prints 1.8 with jdk 14 in the path and java_home. I uninstalled 1.8. reopened cmd tried java -version, now it errors out saying that it is not able to find java1.8 instead of trying to find the next java available in the path or java_home.
Error shown:
C:\Users\usrpao>java
Error: could not open `C:\Program Files\Java\jre8\lib\amd64\jvm.cfg'

I have multiple versions of Java installed in the environment(I know it is bad). I've set the JAVA_HOME to jdk 1_4 directory.
Not wrong at all. I have a similar setup because I have to switch between Java version.
First, install Java JDKs in the root of your drive. No spaces in the directory names. For example, C:\Java\Java-1.6-21 and C:\Java\Java-1.7-5.
In your Environment Variables section in your System Control Panel (under Advance), create an environment variable to point to each one of these Java Home directories. For example, JAVA_HOME_17 = C:\Java\Java-1.7.5 and JAVA_HOME_16 = C:\Java\Java-1.6-21. This should be a System Environment variable.
Create a JAVA_HOME environment variable that points to the Java version you want: JAVA_HOME = %JAVA_HOME_17%.
Now in the System PATH, prefix the PATH (the very first entry) with %JAVA_HOME%\bin.
When you open a console window, your default java and javac commands will be the correct Java version.
If you need to change a version, change the JAVA_HOME environment variable to point to the correct environment variable and open a new console window. Now that new Java will be in your path.
NOTE: It is vitally important that %JAVA_HOME%\bin is in the first part of your PATH before C:\Windows\System32. You don't want the java.exe that exists in that directory to be your default java.

You haven't specified the operating system, so:
on windows, java installs a java.exe in C:\Windows\system32, which is probably on the path before java_home, and so gets picked up
on Linux, various distributions that support multiple installed java versions will also have some symlink earlier on the path. Run 'which java' to determine where that symlink is

Multiple java versions in the system is the problem, I uninstalled all the java versions first. Restarted my machine. Path and java home points to the jdk 1.4. java -version now points to the version specified in the path. Thanks all.

How I can use Xuggler with Play! Framework

I was trying to use Xuggler ( http://www.xuggle.com/ ) with play! framework. I'm using Mac OSX and also created the ~/.MacOSX/environment.plist file with xuggler path. I also set these in my ~/.bashrc
export XUGGLE_HOME=/usr/local/xuggler
export LD_LIBRARY_PATH=$XUGGLE_HOME/lib
I put all the jars in the /lib folder of my play! application and updated the dependencies.yml like the following -
require:
- play
- provided -> xuggle-xuggler
repositories:
- provided:
type: local
artifact: "${application.path}/lib/xuggle-xuggler.jar"
contains:
- provided -> *
BTW, I also ran play dependencies and it is still giving this error -
UnsatisfiedLinkError occured : no xuggle-xuggler in java.library.path
How can I fix this?

This error points to a problem with linking to a DLL file, so I checked the Xuggler docs for installation, and it had a section specifically to deal with this type of error.
http://wiki.xuggle.com/Frequently_Asked_Questions#Installation_Questions
It has the following, as a set of instructions you should follow to solve the error.
What's up with java.lang.UnsatisfiedLinkError?
It means that Java can't find the Xuggler native library. Check the
following:
Did you install the Xuggler?
Is the environment variable XUGGLE_HOME defined and
pointing to your Xuggler install directory (usually C:\Program
Files\Xuggle on Windows or /usr/local on Linux/Mac)?
If you installed
on Windows, did you reboot after you installed?
Does your PATH
environment variable include %XUGGLE_HOME%\bin on Windows or
$XUGGLE_HOME/bin on Linux/Mac?
Does your PATH environment variable
include %XUGGLE_HOME%\lib on Windows?
Does your LD_LIBRARY_PATH
environment variable include $XUGGLE_HOME/lib on Linux?
Does your
DYLD_LIBRARY_PATH environmentvariable include $XUGGLE_HOME/lib on Mac
OS-X?
Are you using a 32-bit Java JVM, but a 64-bit version of
Xuggler? Or a 64-bit version of the Java JVM but a 32-bit version of
Xuggler? Unfortunately that won't work. You need to make sure that you
match the "bitness" of each release. Sorry.

What is JAVA_HOME? How does the JVM find the javac path stored in JAVA_HOME?

I would like to know what JAVA_HOME is. Where do I set the path of javac.exe and java.exe. It is in environment variables? When I compile a Java program from command prompt, how does the JVM find javac.exe?

JVM does not find java.exe. It doesn't even call it. java.exe is called by the operating system (Windows in this case).
JAVA_HOME is just a convention, usually used by Tomcat, other Java EE app servers and build tools such as Gradle to find where Java lives.
The important thing from your point of view is that the Java /bin directory be on your PATH so Windows can find the .exe tools that ship with the JDK: javac.exe, java.exe, jar.exe, etc.

JAVA_HOME and JRE_HOME are not used by Java itself. Some third-party programs (for example Apache Tomcat) expect one of these environment variables to be set to the installation directory of the JDK or JRE. If you are not using software that requires them, you do not need to set JAVA_HOME and JRE_HOME.
PATH is an environment variable used by the operating system (Windows, Mac OS X, Linux) where it will look for native executable programs to run. You should add the bin subdirectory of your JDK installation directory to the PATH, so that you can use the javac and java commands and other JDK tools in a command prompt window. Courtesy: coderanch

set environment variable
JAVA_HOME=C:\Program Files\Java\jdk1.6.0_24
classpath=C:\Program Files\Java\jdk1.6.0_24\lib\tools.jar
path=C:\Program Files\Java\jdk1.6.0_24\bin

The command prompt wouldn't use JAVA_HOME to find javac.exe, it would use PATH.

JAVA_HOME is a environment variable (in Unix terminologies), or a PATH variable (in Windows terminology). A lot of well behaving Java applications (which need the JDK/JRE) to run, looks up the JAVA_HOME variable for the location where the Java compiler/interpreter may be found.

JAVA HOME is used for setting up the environment variable for JAVA. It means that you are providing a path for compiling a JAVA program and also running the same. So, if you do not set the JAVA HOME( PATH ) and try to run a java or any dependent program in the command prompt.
You will deal with an error as
javac : not recognized as internal or external command.
Now to set this, Just open your Java jdk then open bin folder then copy the PATH of that bin folder.
Now, go to My computer right click on it----> select properties-----> select Advanced system settings----->Click on Environment Variables------>select New----->give a name in the text box Variable Name and then paste the path in Value.
That's All!!

JAVA_HOME is an environment variable which is read by some development tools like Apache Tomcat, Apache Maven, Gradle, Jenkins etc. Usually, JAVA_HOME is set to point to JDK instead of JRE because these development tools need to use tools like compiler, debugger, document generator etc. which are only available in JDK since JDK is a development kit. JRE is only meant for running java applications. JDK = JRE + Development tools
Consumer facing Java applications don't read JAVA_HOME variable and they just need to know where the JVM is located and that's why JVM location (directory) needs to be added to the PATH variable. This is automatically done for you when you install Java software. Whenever you try to run a Java application by either double clicking on the app or through command line, your operating system reads PATH variable to locate and run JVM and it doesn't look for JAVA_HOME variable.

use this command /usr/libexec/java_home to check the JAVA_HOME

JAVA_HOME is an Environment Variable set to the location of the Java directory on your computer.
PATH is an internal DOS command that finds the /bin directory of the version of Java that you are using. Usually they are the same, except that the PATH entry ends with /bin

Basically JAVA_HOME is use to set path of the java . it is use in windows. it's used for set path of the multiple software like as java EE , ANT and Maven.
this is the steps to solve your problem:
only for core java to set path :
path :"C:\Program Files\Java\jre1.8.0_77\bin"
but when you are use multi built like as ANT , core java then you are used JAVE_HOME in environment .
follow the steps :
JAVA_HOME:"C:\Program Files\Java\jre1.8.0_77\bin"
ANT_HOME:"C:\ant\apache-ant-1.9.6"
Path: JAVA_HOME, ANT_HOME;
it is the systematic way to set the environment variable..