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Sometimes you want to change the behavior of your code without recompiling or deploying. One way to do this is by defining environment variables that you can change at any time. A typical use case is for database connection properties (username, password, port, etc).

In your Tomcat home create this file $TOMCAT_HOME/bin/setenv.sh and define variables like this:

      
export VAR1=my_var1_value
export VAR2=my_var2_value
   
    

Grant execution permission

      
chmod 755 setenv.sh
   
    

In Windows define variables like this:

      
set VAR1=my_var_value
   
    

After saving the file you must reboot Tomcat.

In your code you get the environment variable this way:

      
//value will be null if VAR1 does not exist
String value = System.getenv("VAR1");