I have a java application which runs on a linux machine many times at a single login. At the beginning of it, I need to set some environment variables for further use. I did that by appending my variables and their values at the end of both ~/.bashrc and ~/.profile files.
In order to make those variables permanent, I should call "source ~/.bashrc" or "source ~/.profile". The problem here is that the source command can not be called through java because of it's scope concerns.
In a single word: How can I set permanent environment variables on my linux machine at the begining of my java application?
Related
iam using the below link to understand environment variables and system properties.
https://docs.oracle.com/javase/tutorial/essential/environment/env.html
The link says environment variables are set by OS and passed to applications.
When i fetch environment variables using System.getenv() it shows me lot of properties which i never set.
So it must be OS (im using macOS) which had set these properties.
Some of the properties in System.getenv() are MAVEN_CMD_LINE_ARGS, JAVA_MAIN_CLASS_1420, JAVA_MAIN_CLASS_1430.
My question is why would OS would like to set the java specific properties in environment variables? Ideally these should be set by JVM (in System.properties()).
P.S.: From whatever i have read on net i understand that environment variables are set by OS and System.properties() are set by JVM
Also if someone can point me to a good link on environment variable and System.properties it will be very helpful. Iam very confused between the two.
Environment variables is an OS concept, and are passed by the program that starts your Java program.
That is usually the OS, e.g. double-click in an explorer window or running command in a command prompt, so you get the OS-managed list of environment variables.
If another program starts your Java program1, e.g. an IDE (Eclipse, IntelliJ, NetBeans, ...) or a build tool (Maven, Groovy, ...), it can modify the list of environment variables, usually by adding more. E.g. the environment variable named MAVEN_CMD_LINE_ARGS would tend to indicate that you might be running your program with Maven.
In a running Java program, the list of environment variables cannot be modified.
System properties is a Java concept. The JVM will automatically assign a lot of
system properties on startup.
You can add/override the values on startup by using the -D command-line argument.
In a running Java program, the list of system properties can be modified by the program itself, though that is generally a bad idea.
1) For reference, if a Java program wants to start another Java program, it will generally use a ProcessBuilder to set that up. The environment variables of the new Java process will by default be the same as the current Java program, but can be modified for the new Java program by calling the environment() method of the builder.
I am writing an application in Java and I need to use environmental variables in AWS EC2 machine (Linux). I am using System.getenv("myvariable") in the application to get the particular environment variable. I need to set the permanent environmental variables and currently I have set the variable in ~/.bashrc , ~/.profile and also ~/.bash_profile.
I am giving export myvariable=xyz in al the 3 files and then I ran source ~/.bashrc , source ~/.profile and source ~/.bash_profile. However I am getting null in the application.
I still don't understand why I am not able to get any environmental variables even though I am exporting the variable in ~/.bash_profile.I have even checked by running echo $myvariable and I can see xyz.
If I set the same environment variable in my local MAC machine in the same way I set above and use the same shell to run the same java code, I can see the variable with the value.
So basically I am getting null every time in my AWS EC2 linux machine.
Is there any other place I need to set the variable? I have even restarted the machine but it didn't help.
It sounds like the problem is how you are setting the env variables. Sudo does not preserve them by default, so you need to use the sudo -E option.
This is explained in more detail in: How to keep Environment Variables when Using SUDO
Everywhere I search, it says you can get an environment variable by using System.getenv(str).
It's not working for me. Here's what I am doing:
OS : Mac OS x 10.7
Java 1.6.x
If I do export abc=/hello/ in my terminal and then echo $abc, it gives me the variable. If I close the terminal, reopen it again and do echo $abc, it's gone. To overcome this, I edited my .bash_profile file and inserted export abc=/hello/. Close the terminal, do echo $abc and it works. So I understood that the env variable is permanent now.
Now if in my java console app, I print System.getenv("abc"), it returns null. What am I missing?
The reason that you needed to put the export in your .bash_profile is that setting environment variables in a shell only persist the variables in that shell, and - since you used export - to children of that shell, or in other words, other programs launched by that shell.
If you're running your java code from Eclipse, and you launch Eclipse from a shell with your environment variables set, then your program should see the added environment variables. To launch Eclipse from the shell, you'll need to use the OS X open command:
$ open /Applications/eclipse/Eclipse.app
Alternately, you can set the environment variables within your Eclipse project, and you'll need to do this if you're not launching Eclipse from a shell with the proper environment. In the Run Configurations dialog, look for a tab named Environment. Here you'll find a table for adding environment variables that will be passed to your program.
It's better to add the environment variables to the Run Configuration since that way they'll always be available to your project. Your code doesn't actually care where the environment variables are coming from, and adding them to the project is simpler, and will work the same way on different platforms.
Of course, when you run your program outside Eclipse, you'll need to make sure that the same environment variables exist in the shell where you e.g. run java.
Eclipse does not use the system's env variables unless launched directly from the shell (which is how it is generally launched, by clicking its icon). In that case you will have to explicitly set the required env variables in the environment tab of the run configuration of the program.
I too faced The same issue , I resolved it this way.
Open Terminal
cd to the folder where eclipse.app is located E.g cd /Users/Shared/eclipse/jee-2020-09
Type open Eclipse.app/
Eclipse will now open and will be able to access the system environment variables as well.
Check it using the code:
System.getenv().forEach((k, v) -> {
System.out.println("ENV : " + k + ":" + v);
});
echo $MY_FILE prints "/path/to/some/file"
System.out.println(System.getenv("MY_FILE")); prints null
Additionally, when i print JAVA_HOME (from Eclipse), i too get null. From the shell it echoes /Library/Java/Home
Not sure whether this is relevant, but system i am running is a mac
Any hints?
You likely have not exported the environment variable. In most shells, variables declared in the shell are not exported into the environment of subprocesses unless you do so explicitly, either like this:
export MY_HOME=/somewhere/over/the/rainbow
Or when invoking the program:
MY_HOME=/somewhere/over/the/rainbow java com.example.MyApplication
Also keep in mind that the environment is not global, so changes you make to the environment only affect that process and its subprocesses. If you want to affect the environment of all processes on your system, this has to be configured specially. In most cases, exporting in the shell is what you want.
First try to access a system variable not created by you say
System.out.println(System.getenv("JAVA_HOME"));
If the above work, try rebooting your VM
It appears that environment variable are in some sort of cache, and rebooting is one method to refresh it.
The way to access an environment variable is precisely the way you're aware of. That code works just fine, and the results you receive accurately tell you about the execution environment of the JVM that you're asking the questions of. So,
Environment variables are not 'system variables': they don't have system-scope; changing them in a new terminal will not change them in the process that launches terminals, etc.
They are held by an OS process, and are copied to children of that process. So, children also do not change the environment variables of their parents, when they change their own.
If you launch Eclipse, and then set environment variables in .profile or whatever, and then JVMs launched from Eclipse do not reflect these settings, then you know that Eclipse does not launch a shell that reads your .profile before launching the JVM; it may invoke the shell so that it doesn't read .profile, it may invoke another shell altogether, it may launch the JVM directly, without involving a shell.
If you launch Eclipse after setting those variables, and see the same behavior, then you've learned the same of the process that launches Eclipse.
If you reboot after setting those variables, and see the same behavior, then you've learned the same about your windowing environment.
You can't learn that you're "doing it wrong" when you ask for the values of environment variables in Java, as you're actually doing it right.
You can explore your environment with System.getenv()
I want to write java program which adds environment variables and when I open environment tab from MyComputer,then I should be able to see that...
This is what I have tried,but it gives java.lang.unsupportedexception
Map env = System.getenv();
env.put("abc", "pqr");
And One more try is below,it is not giving any error...But I can not see any value added when I open environment variables tablenter code here from My Computer.But When i sysout "env" variable it gives me all paths including myone also...But I need same thing to be shwon in environment variables tab...
ProcessBuilder processBuilder = new ProcessBuilder("cmd.exe","/c","set");
Map env = processBuilder.environment();
env.put("abc", "pqr");
Please help me guys...Thanks in Advance...
There are two ways. The first one is to call the Windows API to change/set the environment variable. You must look for the right Windows API function and call it from Java. However calling any Windows API from Java is a topic on its own.
The second way is to call the setx.exe program with the correct arguments to set environment variables. Check the manual of the setx.exe program how to use it (and when it is installed) to set your environment variables.
In both ways you obviously restrict your Java program to run on Windows systems only.