Develop Reference

Ant is unable to find a javac compiler

I am trying to build some binaries of an application. When i am trying to make the build, I am getting this:
BUILD FAILED
/home/.../ant-build.xml:84: Unable to find a javac compiler;
com.sun.tools.javac.Main is not on the classpath.
Perhaps JAVA_HOME does not point to the JDK.
It is currently set to "/usr/lib/jvm/java-8-openjdk-amd64/jre"
The application requires java 7, and i have it installed but i had it along java 8. The build requires for tools.jar which is located in java 7 only, therefore after several attempts i uninstalled java 8. However, when I am trying make again, i get the same error, even though i don't have java8 installed at all!
I set the JAVA_HOME properly:
$ echo $JAVA_HOME
/usr/lib/jvm/java-7-openjdk-amd64/
I doubt i need the path but i set that one up just in case as well :
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/jvm/java-7-openjdk-amd64/bin
I'm running out of ideas here :P any help would be appreciated.
Also something maybe important, I had to add the repo manually to get java-7 otherwise it wasnt able to locate the package. Thats when i got double jdk-s.

I guess you are calling the JAVAC command from any other source/tool like Jenkins/Bamboo/Teamcity. Make sure you have set the environment variable of that tool. usually it lies in the manage tool option.
I was facing same issue while using Jenkins.If you don't set up an environment variable in tool from which you are making a call it take your
"/usr/lib/jvm/java-8-openjdk-amd64/jre" so go and set the the env variable JAVA_HOME of you tools. attaching screen shot of Jenkins issue. Go to Manage Jenkins -->configure system --> environment variables and set you java_home path.
Cheers

I just encountered the same situation.
That is because JAVA_HOME is not correctly set in sudo environment.
I added export JAVA_HOME=/path/to in /root/.bashrc, and eventually it was built right.

It seems that you are using javac of java8 with JAVA_HOME or CLASS_PATH pointing to java7.
You can use which java to check that.
export JAVA_HOME=/lib/jvm/java-7-openjdk-amd64
export export ${PATH}=${JAVA_HOME}:/bin:${PATH}`

jnetpcap library unable to build on ubuntu 12.04

I am trying to install JNetPcap and followed the instructions given at here. At step 12, I am unable to run the ant command and i see the error
Error: JAVA_HOME is not defined correctly.
We cannot execute /usr/lib/jvm/java-6-sun/bin/java
As I am able to run Java classes from eclipse or from command line I don't think if it's a problem with JAVA_HOME.
echo $PATH shows
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/lib/jvm/java-6-sun/bin
Kindly let me know if am missing something here.
thanks in advance

Neither running java from the command line or running eclipse will require JAVA_HOME to be set. However, the build procedure you are trying to use ant, and ant often does require JAVA_HOME to be set appropriately. (It actually depends on the version of ant that you are using. The use of JAVA_HOME is typically in the wrapper script for ant.)
Just set it.
JAVA_HOME should probably be set to /usr/lib/jvm/java-6-sun ... based on what you gave said PATH to.
However, it is also possible that the problem is that your PATH is incorrect. Or that you have (somehow) managed to get the owner/group/permissions on your Java install incorrect, such that the java command isn't executable.
Check that running java -version displays the installed Java version.
Repeat with /usr/lib/jvm/java-6-sun/bin/java -version.

Cordova Android platform - ant installation not recognized

I keep recieving the following error when attempting to add a platform to a cordova project.
ERROR: executing command 'ant', make sure you have ant installed and added to your path.
I have added my JAVA_HOME, ANT_HOME and ANDROID_HOME (both \tools and \platform-tools) environment variables and can confirm they are all installed correctly be executing 'java', 'ant -version' and 'android' commands in my console and getting responses.
Right now, I have the above mentioned environment variables as both User and System variables, but have also tried just having them configured as System variables.
Ant version: 1.9.2
java: jdk1.8.0_11
I'm quite stumped right now because everything seems to be configured/installed correctly. Is there a specific location I should install/un-zip these components?

You have to show full path to bin folder of ANT. see for the variable name path, edit it. add one of the following to the end of it's value.
Suppose your ant folder is in d drive like this D:\ant then your ANT_HOME value should be D:\ant. Then add this to your path variable
%ANT_HOME%\bin
OR add the full path like
D:\ant\bin

How do I set the Environment variables for Jython?

I have set the variables JYTHON_HOME to the directory where I have installed Jython and JYTHON_PATH to the bin folder, but I still get the following error when I try to run jython:
'jython' is not recognized as an internal or external command,
operable program or batch file.
Why do I get this error? The Java installation has no issues.

I am Windows user & I have installed Jython in C:\jython2.7.0.
What I had before?
I had neither set the JYTHON_HOME environment variable nor added %JYTHON_HOME%\bin to PATH environment variable. I also got the same error as shown in the question.
How I fixed?
I created new environment variable named JYTHON_HOME with value C:\jython2.7.0.
You've to use your own Jython's installation folder.
Then I added %JYTHON_HOME%\bin to PATH environment variable as the below 2 image shows.
Create new PATH environment variable if it is not already there (This is rare case).
Open new Terminal and type jython, it will work. Now you can try executing simple Python statements as the below image shows.
Do not use the already opened Terminal.
That's it.

You still need to add the path to the executable jython.bat to your PATH environment variable. Here as an example I'm providing my ini-jython.bat, which I use before executing my jython project (in this case it's a Django on Jython project, you can safely ignore the Django stuff, or adapt it to your needs):
set JYTHON_HOME=c:\tools\jython2.5.2
set PATH=%JYTHON_HOME%\bin;%PATH%
set CLASSPATH=dep1;dep1/lib/*;_lib/*
set JYTHONPATH=.;..\django-debug-toolbar;..\django-common
set DJANGO_SETTINGS_MODULE=site_projname.settings
set PYTHONPATH=%JYTHONPATH%
set manage=jython c:\tools\jython2.5.2\bin\django-admin.py
set makemessages=django-admin makemessages --extension html,py
set compilemessages=django-admin compilemessages

'javac' cannot be found problem

I have a Java application hosted on a remote tomcat instance that executes a bat file which contains the following line
javac filename.java
I receive the following error :-
'javac' is not recognized as an
internal or external command, operable
program or batch file.
I have set the path in the environmental variables. I tried running the same bat file on the machine, it works(which means there is nothing wrong with the path). But running it through the application gives the error. What might be the problem?

Setting the correct path in your environment does not fix the path in the environment of the running tomcat process. If you changed the path in the system settings, a tomcat restart (or system reboot) probably solves your problem.

Once you add %JAVA_HOME%\bin to the PATH var on the remote machine (assuming you have %JAVA_HOME% set there), you will need to run up a new cmd window for the new PATH to be available.

You should set the classpath for the user who is executing tomcat, not only for your login user.

If you have the JRE installed, and not the JDK, you'd be able to run Tomcat but there wouldn't be a javac.exe. Go to JAVA_HOME/bin and see if there's a javac.exe. If not, you have the JRE installed, and you'll have to go get the JDK.
Just curious - why is your Tomcat app calling javac.exe? Are you creating classes on the fly? If yes, why would you not be generating byte code using ASM instead?