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

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// 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"));
    }
}

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Output:

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

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// 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));
        }
    }
}

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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:

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    // 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
        }
    }

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    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:

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    // 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"));
        }
    }

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    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:

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

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    Output:



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