Use the System.getenv(String) method, passing the name of the variable to read.
Use the System.getenv(String) method, passing the name of the variable to read.
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.
Can we read the OS environment variables in Java? - Stack Overflow
How do you use env files or deal with environment variables in Spring Boot?
trying to fetch .env variables
Do you execute your .env file in your shell before executing the Java application? Java won't automatically read .env files.
Either execute the .env so the variables are set in the shell where you run your Java application or use a library like Dotenv to read them.
More on reddit.comDotenv for Java/Kotlin: Load environment variables from .env
The usefulness of dotenv is its ability configure environment variables by storing configuration information via a .env file that is separate from code. It does this in a framework and language agnostic manner.
The statement about the ability to change an env at runtime may be the point of confusion. Java does not provide a System.setenv, hence you cannot load the environment from an external source. dotenv solves this (indirectly). The environment should be fixed and immutable once set. It should not change after app start. java-dotenv ensures that this is the case. It loads the env on init and does not provide apis to subsequently change the env.
The Spring framework solves this in a similar manner, it just happens to use property files instead.
An advantage to using a .env is that this same configuration mechanism has been ported to many languages. Thus, all services can all be configured using the same mechanism. This becomes important, particularly when deploying many services e.g. in a microservice environment
Bit of history: dotenv grew out of the ruby community and has quickly caught on amongst node, go, python, and more. The aim of this this library to extend this paradigm to Java and JVM users.
More on reddit.comVideos
You should use System.getenv(), for example:
import java.util.Map;
public class EnvMap {
public static void main (String[] args) {
Map<String, String> env = System.getenv();
for (String envName : env.keySet()) {
System.out.format("%s=%s%n",
envName,
env.get(envName));
}
}
}
When running from an IDE you can define additional environment variable which will be passed to your Java application. For example in IntelliJ IDEA you can add environment variables in the "Environment variables" field of the run configuration.
Notice (as mentioned in the comment by @vikingsteve) that the JVM, like any other Windows executable, system-level changes to the environment variables are only propagated to the process when it is restarted.
For more information take a look at the "Environment Variables" section of the Java tutorial.
System.getProperty(String name) is intended for getting Java system properties which are not environment variables.
In case anyone is coming here and wondering how to get a specific environment variable without looping through all of your system variables you can use getenv(String name). It returns "the string value of the variable, or null if the variable is not defined in the system environment".
String myEnv = System.getenv("env_name");