April 22, 2015

Grails Goodness: Save Application PID in File

Since Grails 3 we can borrow a lot of the Spring Boot features in our applications. If we look in our Application.groovy file that is created when we create a new Grails application we see the class GrailsApp. This class extends SpringApplication so we can use all the methods and properties of SpringApplication in our Grails application. Spring Boot and Grails comes with the class ApplicationPidFileWriter in the package org.springframework.boot.actuate.system. This class saves the application PID (Process ID) in a file application.pid when the application starts.

In the following example Application.groovy we create an instance of ApplicationPidFileWriter and register it with the GrailsApp:

package mrhaki.grails.sample

import grails.boot.GrailsApp
import grails.boot.config.GrailsAutoConfiguration
import org.springframework.boot.actuate.system.ApplicationPidFileWriter

class Application extends GrailsAutoConfiguration {

    static void main(String[] args) {
        final GrailsApp app = new GrailsApp(Application)

        // Register PID file writer.
        app.addListeners(new ApplicationPidFileWriter())



So when we run our application a new file application.pid is created in the current directory and contains the PID:

$ grails run-app

From another console we read the contents of the file with the PID:

$ cat application.pid

The default file name is application.pid, but we can use another name if we want to. We can use another constructor for the ApplicationPidFileWriter where we specify the file name. Or we can use a system property or environment variable with the name PIDFILE. But we can also set it with the configuration property spring.pidfile. We use the latest option in our Grails application. In the next example application.yml we set this property:

    pidfile: sample-app.pid

When we start our Grails application we get the file sample-app.pid with the application PID as contents.

Written with Grails 3.0.1.