Setting java.awt.headless=true programmatically

This should work because the call to System.setProperty is before the creation of the toolkit:

public static void main(String[] args)
{
    // Set system property.
    // Call this BEFORE the toolkit has been initialized, that is,
    // before Toolkit.getDefaultToolkit() has been called.
    System.setProperty("java.awt.headless", "true");

    // This triggers creation of the toolkit.
    // Because java.awt.headless property is set to true, this 
    // will be an instance of headless toolkit.
    Toolkit tk = Toolkit.getDefaultToolkit();

    // Check whether the application is
    // running in headless mode.
    GraphicsEnvironment ge = 
        GraphicsEnvironment.getLocalGraphicsEnvironment();
    System.out.println("Headless mode: " + ge.isHeadless());
}

I was working with a main() in a class which statically loads different parts of JFreeChart in Constants (and other static code).

Moving the static loading block to the top of the class solved my problem.

This doesn't work:

  public class Foo() {
    private static final Color COLOR_BACKGROUND = Color.WHITE;

    static { /* too late ! */
      System.setProperty("java.awt.headless", "true");
      System.out.println(java.awt.GraphicsEnvironment.isHeadless());
      /* ---> prints false */
    }

    public static void main() {}
  }

Have java execute the static block as early as possible by moving it to the top of the class!

  public class Foo() {
    static { /* works fine! ! */
      System.setProperty("java.awt.headless", "true");
      System.out.println(java.awt.GraphicsEnvironment.isHeadless());
      /* ---> prints true */
    }

    private static final Color COLOR_BACKGROUND = Color.WHITE;

    public static void main() {}
  }

When thinking about it this makes perfectly sense :). Juhu!