How to Detect workstation/System Screen Lock/unlock in Linux and Mac OS using java?

Question

I want an event when mac/linux machine goes to sleep and wakeup. Can any one please suggest a solution using java which can detect machine lock and unlock state.

I have tried running some command lines using java which gives a output which shows screen saver status but that process is not reliable because it varies from os versions.

Command that i'm firing for linux is

gnome-screensaver-command -q |  grep -q 'is active'

And for mac is

echo $((`ioreg -n IODisplayWrangler | grep -i IOPowerManagement | perl -pe 's/^.*DevicePowerState\\\"=([0-9]+).*$/\\1/'`))

Answer 1

Ideally, you want Desktop.addAppEventListener. Using that, no native commands are needed:

if (Desktop.isDesktopSupported()) {
    Desktop desktop = Desktop.getDesktop();
    if (desktop.isSupported(Desktop.Action.APP_EVENT_SYSTEM_SLEEP)) {
        desktop.addAppEventListener(new SystemSleepListener() {
            @Override
            public void systemAboutToSleep(SystemSleepEvent event) {
                System.out.println("System is going to sleep.");
            }

            @Override
            public void systemAwoke(SystemSleepEvent event) {
                System.out.println("System is exiting sleep mode.");
            }
        });
    }
}

However, if we look at gtk3_interface.c in the JDK source, and search for ADD_SUPPORTED_ACTION in that file, it appears the only supported desktop actions in Linux and Unix are open, browse, and mail.

In that case, external commands seem like the only option. (I would prefer upower --monitor over gnome-screensaver-command.)

You should not use grep or perl. You don’t need them. You have Java. Java has a full featured regex package which can do everything grep can do and most of the things perl can do:

String os = System.getProperty("os.name");
if (os.contains("Linux")) {
    ProcessBuilder builder = new ProcessBuilder("upower", "--monitor");
    builder.redirectError(ProcessBuilder.Redirect.INHERIT);
    Process upower = builder.start();

    CompletableFuture.runAsync(() -> {
        try (BufferedReader output = upower.inputReader()) {
            String line;
            while ((line = output.readLine()) != null) {
                if (line.contains("sleep") || line.contains("Sleep")) {
                    System.out.println("System is going to sleep.");
                }
                if (line.contains("hibernate") || line.contains("Hibernate")) {
                    System.out.println("System is hibernating.");
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    });
} else if (os.contains("Mac")) {
    ProcessBuilder builder =
        new ProcessBuilder("ioreg", "-n", "IODisplayWrangler");
    builder.redirectError(ProcessBuilder.Redirect.INHERIT);
    Process ioreg = builder.start();

    CompletableFuture.runAsync(() -> {
        try (BufferedReader output = ioreg.inputReader()) {
            Matcher powerStateMatcher =
                Pattern.compile("DevicePowerState\"=([0-9]+)".matcher("");

            String line;
            while ((line = output.readLine()) != null) {
                if (line.contains("IOPowerManagement") &&
                    powerStateMatcher.reset(line).find()) {

                    int newState = Integer.parseInt(
                        powerStateMatcher.group(1));
                    System.out.println("New device state is " + newState);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    });
}