Code Samples: shutdown-hook

Saturday, June 23, 2018

When do I need to call this method Runtime.getRuntime().addShutdownHook() > Java.lang.Runtime.addShutdownHook(Thread hook) Method > Java Shutdown hook – Runtime.addShutdownHook() > Grails on Groovy: Add a ShutdownHook > Runtime: addShutdownHook(Thread hook)

The java.lang.Runtime.addShutdownHook(Thread hook) method registers a new virtual-machine shutdown hook.The Java virtual machine shuts down in response to two kinds of events


> The program exits normally, when the last non-daemon thread exits or when the exit (equivalently, System.exit) method is invoked


> The virtual machine is terminated in response to a user interrupt, such as typing ^C, or a system-wide event, such as user logoff or system shutdown



Below is a example of how shutdown hook can be used:

package com.pkm;

public class RegisterShutDownHook {
    public static void main(String[] args) {
        System.out.println("PROGRAM STARTED");

        Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() {
                System.out.println("SHUTDOWN HOOK FIRED");
            }
        });

        System.out.println("PROGRAM RUNNING");
    }
}


Output of the above code snippet would be like below:

PROGRAM STARTED
PROGRAM RUNNING
SHUTDOWN HOOK FIRED


When you are using Grails application, you can do that various process. Either registering shutdown hook or implementing DisposableBean




Below is the process using shutdown hook

class BootStrap {
    def init = { servletContext ->
        addShutdownHook {
            println("Running Shutdown Hook");
        }
    }

    def destroy = {

    }
}


Or as below, create another class and registering that from resources.groovy like below:

package com.pkm

import org.springframework.context.ApplicationContextAware
import org.springframework.context.ApplicationContext

class ShutdownHook implements ApplicationContextAware {
    void setApplicationContext(ApplicationContext applicationContext) {
        Runtime.runtime.addShutdownHook {
            println("Application context shutting down...")
            applicationContext.close()
            println("Application context shutdown.")
        }
    }
}

// Adding the following block in grails-app/conf/spring/resources.groovy
// Place your Spring DSL code here
beans = {
    myShutdownHook(com.pkm.ShutdownHook)
}


And my last known process is using DisposableBean

package com.pkm

import grails.transaction.Transactional
import org.springframework.beans.factory.DisposableBean

@Transactional
class HomeService implements DisposableBean {
    @Override
    void destroy() throws Exception {
        println("APPLICATION DESTROYED")
    }
}

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Saturday, June 23, 2018

When do I need to call this method Runtime.getRuntime().addShutdownHook() > Java.lang.Runtime.addShutdownHook(Thread hook) Method > Java Shutdown hook – Runtime.addShutdownHook() > Grails on Groovy: Add a ShutdownHook > Runtime: addShutdownHook(Thread hook)