SDNotify

SDNotify implements the systemd notification protocol in Java.

The Notify protocol uses datagram unix sockets, which are not accessible via Java; Therefore SDNotify includes a JNA wrapper of the socket API.

SDNotify is available via maven:

<dependency>
    <groupId>info.faljse</groupId>
    <artifactId>SDNotify</artifactId>
    <version>1.3</version>
</dependency>

Basic usage

SDNotify is initialized at the first call to any send* function.

If the systemd environment isn't available, or the initialization fails a warning message is logged. All further calls to SDNotify are ignored.

import info.faljse.SDNotify.SDNotify;
public class SDTest {
    public static void main(String[] args) {
        initMyServer();
        SDNotify.sendNotify(); //notify: ready
    }
}

Status text

systemctl status will print this string

SDNotify.sendStatus("No space left on device");

Watchdog, etc.

If a watchdog is configured systemd will kill the process when SDNotify.sendWatchdog() isn't called every n seconds. isWatchdogEnabled() and getWatchdogFrequency() may be used to determine if and at what interval sendWatchdog() should be called.

Also available: sendReloading(), sendStopping(), sendErrno(), sendBusError() , sendMainPID() - see sd_notify manpage for details.

There is also sendRaw() for unsupported/unknown/future functions.

Sample .service file

systemd service documentation

[Unit]
Description=My Java Server
After=syslog.target

[Service]
Type=notify
NotifyAccess=all
WorkingDirectory=/opt/myserver/
ExecStart=/usr/bin/java -server -jar myserver.jar
# WatchdogSec=30
# Restart=always

[Install]
WantedBy=multi-user.target

Dependencies

• jna
• slf4j