How to Access System Properties in Java?

--
This code example shows how to list all system properties, get/set the value of a system property:

import java.util.Enumeration;
import java.util.Properties;

public class ListingAllSystemProperties {

  public static void main(String[] args) {

    //List All System Properties
    Properties props = System.getProperties();
    Enumeration enumeration = props.keys();
    while (enumeration.hasMoreElements()) {
      String propName = (String) enumeration.nextElement();
      String propValue = (String)props.get(propName);
      System.out.println(propName + " = " + propValue); 
    }
      

    // Set a system property
    String previousValue = System.setProperty("myjava.version", "5.0");
    //Get a system property
    String version = System.getProperty("myjava.version");
    System.out.println("myjava.version=" + version);  
      
  }
}

Here is an example to get the working directory (which is the location in the file system from where the java command was invoked):

String curDir = System.getProperty("user.dir");

A system property can be set or overridden by specifying the -D option to the java command when running your program.

java -Dmyjava.version="5.0" MyApplication