I need to run daily a process in order to do maintenance work on the server (update records).
I have a singleton scope class that runs a timer and an inner class with the injection of the service I need. When I run the programm the timer throws a NullPointerException because the service has not been injected.
#Named("demonService")
#Singleton
public class DemonImpl implements IDemonService
{
private static Logger log = Logger.getLogger(DemonioImpl.class);
#PostConstruct
public void init()
{
log.info("-->Demon");
Calendar today = new GregorianCalendar();//Every day at 2:00am (from now)
today.set(Calendar.HOUR_OF_DAY, 2);
today.set(Calendar.MINUTE, 0);
today.set(Calendar.SECOND, 0);
try
{
Timer timer = new Timer(true);
timer.schedule(new Updater(), today.getTime(), 24*60*60*1000);
}
catch(Exception e)
{
log.fatal(e.getLocalizedMessage());
e.printStackTrace();
}
log.info("--> Demon: exit");
}
private class Updater extends TimerTask
{
private Logger log = Logger.getLogger(Updater.class);
#Inject
#Named("updaterService")
private IUpdaterService updaterService;
#Override
public void run()
{
log.info("Task: update records (start)");
List<Record> list = updaterService.getAll();//<-- This throws the exception
for(Record item : list)
{
updaterService.update(item);
}
log.info("Task: update records (exit)");
}
}
The error is
Exception in thread "Timer-3" java.lang.NullPointerException
at test.service.impl.DemonImpl$Updater.run(DemonImpl.java:66)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
The application works fine except for this class. How can I inject the service when the application is fully working?
Normally you have a NPE when the Class is not a CDI Bean. If you make new Updater() this is not considered by CDI. you have to #Inject the Updater in your Singleton.
CDI won't manage the instance since you instantiate your Updater by calling the constructor of it yourself.
Now there are two ways to fix this:
Inject an instance of the Updater class in DemonImpl and use that one.
Create a new CDI managed instance at runtime by injecting a Provider<Updater> instance in DemonImpl and get a new instance of the Updater class from it.
Related
i am making cron job like loop to do something using new thread.
when module stop, this thread keeps running, so when i deployed updated module, i'm afraid it will make duplicate thread doing similar task
#Component(immediate = true, service = ExportImportLifecycleListener.class)
public class StaticUtils extends Utils{
private StaticUtils() {}
private static class SingletonHelper{
private static final StaticUtils INSTANCE = new StaticUtils();
}
public static StaticUtils getInstance() {
return SingletonHelper.INSTANCE;
}
}
public class Utils extends BaseExportImportLifecycleListener{
public Utils() {
startTask();
}
protected Boolean CRON_START = true;
private void startTask() {
new Thread(new Runnable() {
public void run() {
while (CRON_START) {
System.out.println("test naon bae lah ");
}
}
}).start();
}
#Deactivate
protected void deactivate() {
CRON_START = false;
System.out.println(
"cron stop lah woooooooooooooooooy");
}
}
i'm using liferay 7
I have populated task that i store from db, so this thread is checking is there a task that it must do, then if it exist execute it.
I'm quite new in osgi and liferay. i've try to use scheduler and failed and also exportimportlifecycle listener but dont really get it yet
think again: Do you really need something to run all the time in the background, or do you just need some asynchronous processing in the background, when triggered? It might be better to start a background task as a one-off, that automatically terminates
Liferay provides an internal MessageBus, that you can utilize to listen to events and implement background processing, without the need for a custom thread
You're in the OSGi world, so you can utilize #Activate, #Modified, #Deactivate (from org.osgi.service.component.annotations) or use a org.osgi.framework.BundleActivator.
But, in general, it's preferable if you don't start your own thread
I could not find a definitive answer to whether it is safe to spawn threads within session-scoped JSF managed beans. The thread needs to call methods on the stateless EJB instance (that was dependency-injected to the managed bean).
The background is that we have a report that takes a long time to generate. This caused the HTTP request to time-out due to server settings we can't change. So the idea is to start a new thread and let it generate the report and to temporarily store it. In the meantime the JSF page shows a progress bar, polls the managed bean till the generation is complete and then makes a second request to download the stored report. This seems to work, but I would like to be sure what I'm doing is not a hack.
Check out EJB 3.1 #Asynchronous methods. This is exactly what they are for.
Small example that uses OpenEJB 4.0.0-SNAPSHOTs. Here we have a #Singleton bean with one method marked #Asynchronous. Every time that method is invoked by anyone, in this case your JSF managed bean, it will immediately return regardless of how long the method actually takes.
#Singleton
public class JobProcessor {
#Asynchronous
#Lock(READ)
#AccessTimeout(-1)
public Future<String> addJob(String jobName) {
// Pretend this job takes a while
doSomeHeavyLifting();
// Return our result
return new AsyncResult<String>(jobName);
}
private void doSomeHeavyLifting() {
try {
Thread.sleep(SECONDS.toMillis(10));
} catch (InterruptedException e) {
Thread.interrupted();
throw new IllegalStateException(e);
}
}
}
Here's a little testcase that invokes that #Asynchronous method several times in a row.
Each invocation returns a Future object that essentially starts out empty and will later have its value filled in by the container when the related method call actually completes.
import javax.ejb.embeddable.EJBContainer;
import javax.naming.Context;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
public class JobProcessorTest extends TestCase {
public void test() throws Exception {
final Context context = EJBContainer.createEJBContainer().getContext();
final JobProcessor processor = (JobProcessor) context.lookup("java:global/async-methods/JobProcessor");
final long start = System.nanoTime();
// Queue up a bunch of work
final Future<String> red = processor.addJob("red");
final Future<String> orange = processor.addJob("orange");
final Future<String> yellow = processor.addJob("yellow");
final Future<String> green = processor.addJob("green");
final Future<String> blue = processor.addJob("blue");
final Future<String> violet = processor.addJob("violet");
// Wait for the result -- 1 minute worth of work
assertEquals("blue", blue.get());
assertEquals("orange", orange.get());
assertEquals("green", green.get());
assertEquals("red", red.get());
assertEquals("yellow", yellow.get());
assertEquals("violet", violet.get());
// How long did it take?
final long total = TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - start);
// Execution should be around 9 - 21 seconds
assertTrue("" + total, total > 9);
assertTrue("" + total, total < 21);
}
}
Example source code
Under the covers what makes this work is:
The JobProcessor the caller sees is not actually an instance of JobProcessor. Rather it's a subclass or proxy that has all the methods overridden. Methods that are supposed to be asynchronous are handled differently.
Calls to an asynchronous method simply result in a Runnable being created that wraps the method and parameters you gave. This runnable is given to an Executor which is simply a work queue attached to a thread pool.
After adding the work to the queue, the proxied version of the method returns an implementation of Future that is linked to the Runnable which is now waiting on the queue.
When the Runnable finally executes the method on the real JobProcessor instance, it will take the return value and set it into the Future making it available to the caller.
Important to note that the AsyncResult object the JobProcessor returns is not the same Future object the caller is holding. It would have been neat if the real JobProcessor could just return String and the caller's version of JobProcessor could return Future<String>, but we didn't see any way to do that without adding more complexity. So the AsyncResult is a simple wrapper object. The container will pull the String out, throw the AsyncResult away, then put the String in the real Future that the caller is holding.
To get progress along the way, simply pass a thread-safe object like AtomicInteger to the #Asynchronous method and have the bean code periodically update it with the percent complete.
Introduction
Spawning threads from within a session scoped managed bean is not necessarily a hack as long as it does the job you want. But spawning threads at its own needs to be done with extreme care. The code should not be written that way that a single user can for example spawn an unlimited amount of threads per session and/or that the threads continue running even after the session get destroyed. It would blow up your application sooner or later.
The code needs to be written that way that you can ensure that an user can for example never spawn more than one background thread per session and that the thread is guaranteed to get interrupted whenever the session get destroyed. For multiple tasks within a session you need to queue the tasks.
Also, all those threads should preferably be served by a common thread pool so that you can put a limit on the total amount of spawned threads at application level.
Managing threads is thus a very delicate task. That's why you'd better use the built-in facilities rather than homegrowing your own with new Thread() and friends. The average Java EE application server offers a container managed thread pool which you can utilize via among others EJB's #Asynchronous and #Schedule. To be container independent (read: Tomcat-friendly), you can also use the Java 1.5's Util Concurrent ExecutorService and ScheduledExecutorService for this.
Below examples assume Java EE 6+ with EJB.
Fire and forget a task on form submit
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
#EJB
private SomeService someService;
public void submit() {
someService.asyncTask();
// ... (this code will immediately continue without waiting)
}
}
#Stateless
public class SomeService {
#Asynchronous
public void asyncTask() {
// ...
}
}
Asynchronously fetch the model on page load
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
private Future<List<Entity>> asyncEntities;
#EJB
private EntityService entityService;
#PostConstruct
public void init() {
asyncEntities = entityService.asyncList();
// ... (this code will immediately continue without waiting)
}
public List<Entity> getEntities() {
try {
return asyncEntities.get();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new FacesException(e);
} catch (ExecutionException e) {
throw new FacesException(e);
}
}
}
#Stateless
public class EntityService {
#PersistenceContext
private EntityManager entityManager;
#Asynchronous
public Future<List<Entity>> asyncList() {
List<Entity> entities = entityManager
.createQuery("SELECT e FROM Entity e", Entity.class)
.getResultList();
return new AsyncResult<>(entities);
}
}
In case you're using JSF utility library OmniFaces, this could be done even faster if you annotate the managed bean with #Eager.
Schedule background jobs on application start
#Singleton
public class BackgroundJobManager {
#Schedule(hour="0", minute="0", second="0", persistent=false)
public void someDailyJob() {
// ... (runs every start of day)
}
#Schedule(hour="*/1", minute="0", second="0", persistent=false)
public void someHourlyJob() {
// ... (runs every hour of day)
}
#Schedule(hour="*", minute="*/15", second="0", persistent=false)
public void someQuarterlyJob() {
// ... (runs every 15th minute of hour)
}
#Schedule(hour="*", minute="*", second="*/30", persistent=false)
public void someHalfminutelyJob() {
// ... (runs every 30th second of minute)
}
}
Continuously update application wide model in background
#Named
#RequestScoped // Or #ViewScoped
public class Bean {
#EJB
private SomeTop100Manager someTop100Manager;
public List<Some> getSomeTop100() {
return someTop100Manager.list();
}
}
#Singleton
#ConcurrencyManagement(BEAN)
public class SomeTop100Manager {
#PersistenceContext
private EntityManager entityManager;
private List<Some> top100;
#PostConstruct
#Schedule(hour="*", minute="*/1", second="0", persistent=false)
public void load() {
top100 = entityManager
.createNamedQuery("Some.top100", Some.class)
.getResultList();
}
public List<Some> list() {
return top100;
}
}
See also:
Spawning threads in a JSF managed bean for scheduled tasks using a timer
I tried this and works great from my JSF managed bean
ExecutorService executor = Executors.newFixedThreadPool(1);
#EJB
private IMaterialSvc materialSvc;
private void updateMaterial(Material material, String status, Location position) {
executor.execute(new Runnable() {
public void run() {
synchronized (position) {
// TODO update material in audit? do we need materials in audit?
int index = position.getMaterials().indexOf(material);
Material m = materialSvc.getById(material.getId());
m.setStatus(status);
m = materialSvc.update(m);
if (index != -1) {
position.getMaterials().set(index, m);
}
}
}
});
}
#PreDestroy
public void destory() {
executor.shutdown();
}
In an MVC / WebAPI environment I would use InRequestScope to bind the DbContext.
However, I am now on a Console application / Windows service / Azure worker role (doesn't really matter, just there's no Web request scope), which periodically creates a number of Tasks that run asynchronously. I would like each task to have its own DbContext, and since tasks run on their own thread, I tried binding DbContext using InThreadScope.
Unfortunately, I realize that the DbContext is not disposed when a task is finished. What actually happens is, the thread returns to the Thread Pool and when it is assigned a new task, it already has a DbContext, so DbContexts stay alive forever.
Is there a way InThreadScope can be used here or should I use some other scope? How can ThreadScope be used when threads are returning from ThreadPool every now and then?
If you decide to go on with custom scope, the solution is:
public sealed class CurrentScope : INotifyWhenDisposed
{
[ThreadStatic]
private static CurrentScope currentScope;
private CurrentScope()
{
}
public static CurrentScope Instance => currentScope ?? (currentScope = new CurrentScope());
public bool IsDisposed { get; private set; }
public event EventHandler Disposed;
public void Dispose()
{
this.IsDisposed = true;
currentScope = null;
if (this.Disposed != null)
{
this.Disposed(this, EventArgs.Empty);
}
}
}
Binding:
Bind<DbContext>().To<MyDbContext>().InScope(c => CurrentScope.Instance)
And finally:
using (CurrentScope.Instance)
{
// your request...
// you'll get always the same DbContext inside of this using block
// DbContext will be disposed after going out of scope of this using block
}
I'm trying to create a long running windows service, so I need to run the actual worker class on a separate thread, to avoid the "service did not respond in a timely fashion" error when I right click and select start in Windows Service Manager.
The worker class ("NotificationProcess") has a whole raft of dependencies and I'm using Autofac to satisfy these.
I'm really not sure how to set up Autofac for the worker class. At the moment I'm getting errors telling me that the DbContext has been disposed when I go to use it in the "Execute" method of the worker class.
I guess I'm looking for how to write a windows service and use a new thread for the worker class with dependencies satisfied by autofac.
I've googled and can't find any examples of this.
Any suggestions would be awesome.
Here's what I've got so far...
Program.cs:
static class Program
{
static void Main()
{
using (var container = ServiceStarter.CreateAutoFacContainer())
{
var service = container.Resolve<NotificationService>();
if (Environment.UserInteractive)
{
service.Debug();
}
else
{
ServiceBase.Run(container.Resolve<NotificationService>());
}
}
The Service class:
public partial class NotificationService : ServiceBase
{
private NotificationProcess _app;
readonly ILifetimeScope _lifetimeScope;
public NotificationService(ILifetimeScope lifetimeScope)
{
_lifetimeScope = lifetimeScope;
InitializeComponent();
}
protected override void OnStart(string[] args)
{
_app = _lifetimeScope.Resolve<NotificationProcess>();
_app.Start();
}
The worker class:
public class NotificationProcess
{
private Thread _thread;
private readonly IBankService _bankService;
private readonly IRateService _rateService;
private readonly IEmailService _emailService;
private readonly IRateChangeSubscriberService _rateChangeSubscriberService;
private readonly IRateChangeNotificationService _rateChangeNotificationService;
private readonly ILogManager _logManager;
public NotificationProcess(IBankService bankService, ILogManager logManager, IRateService rateService, IEmailService emailService,
IRateChangeSubscriberService rateChangeSubscriberService, IRateChangeNotificationService rateChangeNotificationService)
{
_bankService = bankService;
_rateService = rateService;
_emailService = emailService;
_rateChangeSubscriberService = rateChangeSubscriberService;
_rateChangeNotificationService = rateChangeNotificationService;
_logManager = logManager;
}
public void Start()
{
_thread = new Thread(new ThreadStart(Execute));
_thread.Start();
}
public void Execute()
{
try
{
var rateChangeToNotify = _rateService.GetRateChangesForNotification();
foreach (var rateChange in rateChangeToNotify)
{
//do whatever business logic.....
}
}
}
The answer is actually simple: use scoping! You should do the following:
Register all services (such as DbContext) that should live for the duration of a request or action with the LifetimeScope lifestyle. You'll usually have a timer in your windows service. Each 'pulse' can be considered a request.
On the beginning of each request begin a lifetime scope.
Within that scope, resolve the root object from the object graph and call its method.
Dispose the scope.
In your case that means you need to change your design, since NotificationService is resolved once and its dependencies are reused on another thread. This is a no-no in dependency injection land.
Here's an alternative design:
// This method is called on a background thread
// (possibly in a timely manner)
public void Run()
{
try
{
using (var scope = container.BeginLifetimeScope())
{
var service = scope.Resolve<NotificationService>();
service.Execute();
}
}
catch (Exception ex)
{
// IMPORTANT: log exception.
// Not logging an exception will leave us in the dark.
// Not catching the exception will kill our service
// because we run in a background thread.
}
}
Using a lifetime scope allows you to get a fresh DbContext for every request and it would even allow you to run requests in parallel (with each request its own DbContext).
I am attempting to create functionality in a JSF1.2/ADF web app that will periodically & dynamically generate a sitemap for a website that will have hundreds of pages whose content will change daily. The catch is that I need to read some config from the application to use as the basis of the sitemap and to do so, I need FacesContext.
Here is what I have attempted to do: I created a class that implements a ServletContextListener and instantiates an application scoped bean. This bean does the heavy lifting to create sitemap.xml using FacesContext. I created a class that extends TimerTask that accesses the bean from application scope, calls the sitemap method and schedules future occurrences. When I run the application, the class that implements ServletContextListener fires and the bean appears to be created, but the class that extends TimerTask is never fired. Any help would be appreciated. If I can answer any questions or if I left anything out, please let me know.
Here are my code samples:
public class WebhomesApplicationContextListener implements ServletContextListener {
private static final String attribute = "SiteMapGenerator";
public void contextInitialized(ServletContextEvent event) {
SiteMapGenerator myObject = new SiteMapGenerator();
event.getServletContext().setAttribute(attribute, myObject);
}
public void contextDestroyed(ServletContextEvent event) {
SiteMapGenerator myObject = (SiteMapGenerator) event.getServletContext().getAttribute(attribute);
event.getServletContext().removeAttribute(attribute);
}
}
public class SiteMapGenerator {
public void generateSitemap() {
// code to generate map...
}
}
public class Scheduler extends TimerTask {
public void run() {
SiteMapGenerator sitemap = (SiteMapGenerator)FacesContext.getCurrentInstance().getExternalContext().getApplicationMap().get("SiteMapGenerator");
sitemap.generateSitemap();
}
}
class MainApplication {
public static void main(String[] args) {
Timer timer = new Timer();
timer.schedule(
new Scheduler(),
1000 * 60);
}
}
No, you can't. The FacesContext is only available in the thread associated with the HTTP servlet request whose URL matched the URL pattern of the FacesServlet and has invoked it. Instead, just pass the SiteMapGenerator to the Scheduler on its construction.
public class Scheduler {
private SiteMapGenerator sitemap;
public Scheduler(SiteMapGenerator sitemap) {
this.sitemap = sitemap;
}
// ...
}
The SiteMapGenerator is surely available at the point you're constructing the Scheduler.
Unrelated to the concrete problem, It's strongly discouraged to use TimerTask in a Java EE application. See also Spawning threads in a JSF managed bean for scheduled tasks using a timer.