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

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())
      }
  }

  Output: