How can I get System variable value in Java

Question

How can I get the System Variable value which is present in   MyComputer - gt  Properties - gt  Advanced - gt  Environment Variables - gt  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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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   gt  java exe -DmaxInMemory 100M -DpagingDirectory c  temp -jar myApp jar   These properties can be modified at runtime  barring security policy restrictions

User · Answer

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

User · Answer

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

User · Answer

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       - gt  new CustomException  ENV VAR1 is not set in the environment

User · Answer

Use the System getenv String  method  passing the name of the variable to read

[java] How can I get System variable value in Java?

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