CODEWITHSUNDEEP
javaenvironment-variables
raja
raja

Reputation: 4193

How can I get System variable value in Java?

How can I get the System Variable value which is present in 

MyComputer -> Properties -> Advanced -> Environment Variables -> System Variables

in Java?

Edit

I have used System.getenv() method.

It is printing value if I give 

System.out.println(System.getenv("JAVA_HOME"));

and it is showing null value if I try the same for system variable created by me 

System.out.println(System.getenv("DBE"));

Upvotes: 239

Views: 356770

Answers (9)

Shila Mosammami
Shila Mosammami

Reputation: 1067

This code gives you a map of Environment variables' names and the corresponding values.

public static void main(String[] args) {
            Map<String, String> map = System.getenv();
            System.out.println(map);
        }

Upvotes: 1

EliuX
EliuX

Reputation: 12625

Actually the variable can be set or not, so, In Java 8 or superior its nullable value should be wrapped into an Optional object, which allows really good features. In the following example we gonna try to obtain the variable ENV_VAR1, if it doesnt exist we may throw some custom Exception to alert about it:

String ENV_VAR1 = Optional.ofNullable(System.getenv("ENV_VAR1")).orElseThrow(
  () -> new CustomException("ENV_VAR1 is not set in the environment"));

Upvotes: 35

keving
keving

Reputation: 31

Are you on a linux system? If so be sure you are exporting your variable.

myVar=testvalue; export myVar

I get null unless I use export to define the value globally.

Upvotes: 3

Rob
Rob

Reputation: 48369

Use the System.getenv(String) method, passing the name of the variable to read.

Upvotes: 274

voidMainReturn
voidMainReturn

Reputation: 3513

As mentioned by sombody above, restarting eclipse worked for me for the user defined environment variable. After I restart eclipse IDE, System.getenv() is picking up my environment variable.

Upvotes: 4

Chris Bunch
Chris Bunch

Reputation: 89823

Google says to check out getenv():

Returns an unmodifiable string map view of the current system environment.

I'm not sure how system variables differ from environment variables, however, so if you could clarify I could help out more.

Upvotes: 6

Elijah
Elijah

Reputation: 13604

To clarify, system variables are the same as environment variables. User environment variables are set per user and are different whenever a different user logs in. System wide environment variables are the same no matter what user logs on.

To access either the current value of a system wide variable or a user variable in Java, see below:

String javaHome = System.getenv("JAVA_HOME");

For more information on environment variables see this wikipedia page.

Also make sure the environment variable you are trying to read is properly set before invoking Java by doing a:

echo %MYENVVAR%

You should see the value of the environment variable. If not, you may need to reopen the shell (DOS) or log off and log back on.

Upvotes: 63

Dilum Ranatunga
Dilum Ranatunga

Reputation: 13374

There are a few details of interest when getting system/environment properties.

First, System.getenv(String) was introduced way-back-when, then deprecated. The deprecation (foolishly, IHMO) continued all the way into JSE 1.4.

It got re-introduced in JSE 5.

Those are set using the Environment Variables panel in Windows. Changes to the variables may not get picked up until your current VM is shutdown, and the CMD.exe instance is exited.

In contrast to the environment properties, Java also has Java system properties, accessible through System.getProperties(). These variables can be initialized when the VM is started using a series -Dname=value command line arguments. For example, the values for the properties maxInMemory and pagingDirectory are set in the command below:

C:\> java.exe -DmaxInMemory=100M -DpagingDirectory=c:\temp -jar myApp.jar

These properties can be modified at runtime, barring security policy restrictions.

Upvotes: 32

trilobite
trilobite

Reputation: 316

Have you tried rebooting since you set the environment variable?

It appears that Windows keeps it's environment variable in some sort of cache, and rebooting is one method to refresh it. I'm not sure but there may be a different method, but if you are not going to be changing your variable value too often this may be good enough.

Upvotes: 6

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