how to call Java Threads in Web application

Question

I need to create a thread, which everyday checks whether I have to create the tasks for this user or not. I know to create and run java threads by using main(). But how to run it in web application. Seriously I searched a lot and didn't get any answer for running in web application. I have few questions regarding this.

1 How my thread will initially start and from where it will run?

2 Do I need to define my thread in any XML file ?

This is my thread

public class TaskGenerationThread implements Runnable {


@Override
public void run(){
    System.out.println("callled at "+ new Date());
    /*try {
        Thread.sleep(500);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }*/
    /*List<Users> listOfCA = complianceUserService.getAllCA();
    if(listOfCA !=null && !listOfCA.isEmpty()){
        Users ca = complianceUserService.fetchUserByUserId(1).get(0);
        Date currentDate = new Date();
        Calendar calendar = Calendar.getInstance();         
        calendar.add(Calendar.MONTH, 1);
        calendar.set(Calendar.DATE, calendar.getActualMinimum(Calendar.DAY_OF_MONTH)); //getting first day of month
        Date nextMonthFirstDay = calendar.getTime();
        calendar.set(Calendar.DATE, calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); //getting last day of month
        Date nextMonthLastDay = calendar.getTime();
        taskGeneratorService.generateCronJobTaskForCompanyCompliance(nextMonthFirstDay,nextMonthLastDay,ca);
    }*/

}

}

I did this way. Implemented ServletContextListener and passed my Thread object. But didnt work

public class ThreadImplementation implements ServletContextListener{

ScheduledExecutorService  listChecker =null;

@Override
public void contextInitialized(ServletContextEvent sce){


    listChecker = Executors.newScheduledThreadPool(1);
    listChecker.scheduleAtFixedRate(new TaskGenerationThread(), 01, 01, TimeUnit.SECONDS); 

}

@Override
public void contextDestroyed(ServletContextEvent sce) {

        if (listChecker != null) {
            listChecker.shutdownNow();
            try {
                listChecker.awaitTermination(60, TimeUnit.SECONDS);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }   



 }

 }

Any help will be highly appreciated. Thank you

Scary Wombat · Accepted Answer · 2017-04-25 08:44:25Z

1

Write a class that

implements ServletContextListener

override

public void contextInitialized(ServletContextEvent sce)

and kick off some scheduler from here

e.g.

listChecker = Executors.newScheduledThreadPool(1);
listChecker.scheduleAtFixedRate(filechecker, 60, 60, TimeUnit.SECONDS);

note this works for Tomcat

Your contextDestroyed should be something like

@Override
public void contextDestroyed(ServletContextEvent sce) {

    log.info("Scheduler entered contextDestroyed");

    if (listChecker != null) {
        listChecker.shutdownNow();
        log.info("waiting [60 seconds] for collector threads to finsih");
        try {
            listChecker.awaitTermination(60, TimeUnit.SECONDS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }   

    log.info("Scheduler finished contextDestroyed");
}

And of course you need to add it to web.xml

<listener>
    <listener-class>
             myPackage.Scheduler 
        </listener-class>
   </listener>

edited Apr 25, 2017 at 8:44

answered Apr 25, 2017 at 7:20

Scary Wombat

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7 Comments

Scary Wombat Over a year ago

In my example above I am just using an java.util.concurrent.ScheduledExecutorService and passing in a Runnable class filechecker

Scary Wombat Over a year ago

You shouldn't really be extending Thread instead implement Runnable

Muddassir Rahman Over a year ago

changed to Runnable. But not yet working . Am I missing something ? :(

Muddassir Rahman Over a year ago

some thing like this

Muddassir Rahman Over a year ago

<listener-class>com.uforic.compliance.spring.task.Scheduler </listener-class>

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