java - How to determine if GraphicsEnvironment exists

Question

I have an application that needs user input for password.

What i want to do is to either read the password from console (if the OS supports one e.g unix) or display a JOptionPane and ask the user to enter his password (if the OS supports graphical interface e.g windows).

Some people may argue that a console will always be available in both the above cases so a console input will be sufficient. But problem is if the Java app starts using javaw.exe then a console is not available. Thus, i need a way to determine if i can do either case.

My problem is how to determine if the environment that the application runs from supports either a console or a graphical interface.

I know that a static method exists GraphicsEnvironment.isHeadless() but from the Java doc i think that this method cannot distinguish if the OS supports graphics, but rather than if the OS can support one of the I/O devices (keyboard, mouse, screen).

Does anyone know more about this? Am i able to retrieve if the OS supports console or graphics environment?

Thanks in advance.

Answer 1

GraphicsEnvironment.isHeadless() will return true in case:

• the system property java.awt.headless has been set to true
• your are running on a Unix/Linux system and there is no DISPLAY environment variable set

Here is the code that is used to retrieve the headless property:

    String nm = System.getProperty("java.awt.headless");

    if (nm == null) {
        /* No need to ask for DISPLAY when run in a browser */
        if (System.getProperty("javaplugin.version") != null) {
            headless = defaultHeadless = Boolean.FALSE;
        } else {
            String osName = System.getProperty("os.name");
            headless = defaultHeadless =
                Boolean.valueOf(("Linux".equals(osName) || "SunOS".equals(osName)) &&
                                (System.getenv("DISPLAY") == null));
        }
    } else if (nm.equals("true")) {
        headless = Boolean.TRUE;
    } else {
        headless = Boolean.FALSE;
    }

If you want to know if there is any screen available, you can invoke GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices() which returns all the available screens.

import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.HeadlessException;

public class TestHeadless {

    private static boolean isReallyHeadless() {
        if (GraphicsEnvironment.isHeadless()) {
            return true;
        }
        try {
            GraphicsDevice[] screenDevices = GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices();
            return screenDevices == null || screenDevices.length == 0;
        } catch (HeadlessException e) {
            e.printStackTrace();
            return true;
        }
    }

}