How to get the value of System Property and Environment Variable in Java?

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How to get the value of Environment variables?

The System class in Java provides a method named System.getenv() which can be used to get the value of an environment variable set in the current system.

Syntax:

public static String getenv(String key);

where key is the Environment variable
whose values we want

Below example illustrates how to use System.getenv() to get the System environment variable:

Example 1: To get the value of a specific environment variable

// Java program to get the value
// of a specific environment variable
// using System.getenv() method
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Get the value of
        // the TEMP environment variable
        System.out.println(System.getenv("TEMP"));
  
        // Get the value of
        // the OS environment variable
        System.out.println(System.getenv("OS"));
  
        // Get the value of
        // the JAVA_HOME environment variable
        System.out.println(System.getenv("JAVA_HOME"));
    }
}

Output:

Example 2: To get the value of all environment variables at once

// Java program to get the value
// of all environment variables at once
// using System.getenv() method
  
import java.util.Map;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Get the value of
        // all environment variables at once
        // and store it in Map
        Map<String, String> env
            = System.getenv();
  
        for (String envName : env.keySet()) {
            System.out.format("%s=%s%n",
                              envName,
                              env.get(envName));
        }
    }
}

Output:

Note: The output will depend on the system on which you run the above code. A sample output is given above

How to get the value of System Property?

The System class in Java has two methods used to read system properties:

java.lang.System.getProperty(String key): fetches only those properties – values that you will specify using the key(associated to that particular value that you want).

Example:

// Java Program illustrating the working
// of getProperty(String key) method
  
import java.lang.*;
import java.util.Properties;
  
public class NewClass {
    public static void main(String[] args)
    {
        // Printing Name of the system property
        System.out.println("user.dir: "
                           + System.getProperty(
                                 "user.dir"));
  
        // Fetches the property set with 'home' key
        System.out.println("home: "
                           + System.getProperty(
                                 "home"));
        // Resulting in Null as no property is present
  
        // Printing 'name of Operating System'
        System.out.println("os.name: "
                           + System.getProperty(
                                 "os.name"));
  
        // Printing 'JAVA Runtime version'
        System.out.println("version: "
                           + System.getProperty(
                                 "java.runtime.version"));
  
        // Printing 'name' property
        System.out.println("name: "
                           + System.getProperty(
                                 "name"));
        // Resulting in Null as no property is present
    }
}

Output:

user.dir: /tmp/hsperfdata_bot
home: null
os.name: Linux
version: 1.8.0_101-b13
name: null

java.lang.System.getProperty(String key, String definition): helps you to create your own key-value sets that you want.

Example:

// Java Program illustrating the working of
// getProperty(String key, String definition) method
  
import java.lang.*;
import java.util.Properties;
  
public class NewClass {
    public static void main(String[] args)
    {
  
        // Here key = "Hello" and
        // System Property = "Geeks"
        System.out.println("Hello property : "
                           + System.getProperty(
                                 "Hello", "Geeks"));
  
        // Here key = "Geek" and
        // System Property = "For Geeks"
        System.out.println("System-property :"
                           + System.getProperty(
                                 "System", "For Geeks"));
  
        // Here key = "Property" and
        // System Property = null
        System.out.println("Property-property :"
                           + System.getProperty(
                                 "Property"));
    }
}

Output:

Hello key property : Geeks
System key property :For Geeks
Property key property :null

java.lang.System.getProperties(): fetches all the properties – values that the JVM on your System gets from the Operating System.

Example:

// Java Program illustrating the working of
// getProperties() method
  
public class GFG {
    public static void main(String[] args)
    {
  
        System.out.println(System.getProperties())
    }
}