ManagedScheduledExecutorService vs EJB Timer

Over the past years I always used EJB Timer Service to implement scheduled tasks in my Java Enterprise applications. Since Java EE7 the ManagedScheduledExecutorService is a new pattern to implement a scheduler service. The ManagedScheduledExecutorService is part of the SE ScheduledExecutorService and provides methods for submitting delayed or periodic tasks for execution.

Implementing a ManagedScheduledExecutorService is quite simple. See the following example:

public class MyScheduler {
    ManagedScheduledExecutorService scheduler;    

    MyService myService; 

    public void init() {
        this.scheduler.scheduleAtFixedRate(this::run, 500, 500,

    public void run() {

In compare to a EJB Timer it seems to be quite simple to use this pattern. But the ManagedScheduledExecutorService is more a lightweight scheduling framework and it does not support features like transaction support, full lifecycle operations (create, read, cancel timers) which are supported by EJB Timers. In addition EJB Timers can be persisted and so survive server crash and restart. And in fact I personally run into a problem with execution exceptions during a redeployment scenario in Wildfly a few days ago. So is a EJB Timer an outdated technology just because it’s an EJB?

The Advantage and Restrictions of EJB Timers

In the early beginning of my Java EE career I learned that EJB timers are persisted an managed by the ejb container on the application server level. This ensures that the timer is executed correctly without conflicts in scenarios with multiple threads. This means even in a clustered environment, a persistent EJB timer runs only in one cluster member which might not necessarily be the same cluster member it was created in. Since we are today mostly talking about horizontally scalable applications spread across multiple servers, this seems to be a restriction. And this was also my first thought when I switched from EJB Timer to ManagedScheduledExecutorService.

But on the other hand, that’s the common expectation for a timer at a specific point to fire only at one of the nodes in order to avoid duplication. For example, you might probably do not want to send out meeting notices twice from different nodes. So the idea that a persisted EJB Timer runs only in one instance even in a large cluster environment can be an important feature and not a restriction.

Non-Persistent EJB Timers

Since EJB 3.1 specification there is a variant of non-persistent EJB Timers. Non-persistent timers have similar semantics and behaviour as the origin persistent timers, but without the overhead of a data store. This means they have a different life cycle and are easier to use than persistent timers. Non-persistent timers are active only while the application server is active and are not maintained across application server crashes, shutdowns and restarts. But in difference to the ManagedScheduledExecutorService the non-persistent EJB Timer is transactional during the creation and cancellation which can be important for many scenarios. If a timer is created within a transaction and that transaction is later rolled back, the creation of the timer is rolled back as well. Similar rules apply to the cancellation of a timer.

This is an example how a EJB Timer can be implemented:

public class MyTimerService {
    MyService myService;
    @Schedule(second="*/1", minute="*",hour="*", persistent=false)
    public void doWork(){

In a clustered environment a non-persistent timer runs in each cluster member that it was created in. And a automatic non-persistent timers run in each cluster member that contains the EJB. So this means the non-persistent EJB Timer scales horizontal within a clustered environment – e.g. a Kubernetes cluster. More details about the EJB Timer variants can be found here.


So we have seen how ManagedScheduledExecutorService and EJB Timers can be used to implement scheduled tasks in Jakarta EE. In my personal opinion you should use EJB timers if you are running on a Jakarta EE stack. The EJB Timer provides you with more features and is even scalable as the more lightweight ManagedScheduledExecutorService. This is just my personal opinion. Choose the technology that best fits your app.

JSF and Transactioncontext

Today I want to talk about a detail in the JSF Framework, which is on the first view not obviously. In different to Spring, business logic placed in a JSF front-end controller (JSF Backing Beans) did not initializes a separate transaction context. Normally business logic which need to be transaction save should be spread out into EJBs. EJBs are the recommended place for business logic. So in JSF/EJB business logic should be put into stateless session EJBs and controlled the page flow of a web application through the so called front end controllers  – JSF Backing beans. As I mentioned before spring starts a transaction context also in front-end controllers, but jsf does not.

So what is the problem here? When you look at the following JSF example, you maybe will not recognize the problem at first:

//jsf bean...
@EJB ejb1;
public String process(businessobject) {

The JSF front-end controller method ‘process(businessobject)’ injects an EJB and calls two ejb methods. This will propaply work without any side effects. But it can produce errors in some cases. The problem in this pattern is that the front-end controller performed two apparently dependent business actions completely separately. If these two methods need to be transaction save but are operating on the same database entities this can result in serious problems. In a high concurrent system indeed this pattern can cause a corrupted DB state even if you thought JPA will solve all the transaction stuff for you.

The reason for the unexpected behavior is the missing wrapping transaction. Each ejb method starts it own transaction with all the transaction control provided by the ejb container. But the hole business method is not transaction save.

To solve this you have two possible solutions:

1) add a UserTranaction context to the front-end controller:

//jsf bean...
@Resource UserTransaction tx;
@EJB ejb1;
public String process(businessobject) {
 try {
 finaly {

In this example now the jsf controller starts itself the UserTransaction. As a result both EJB methods (with default transaction mode ‘mandatory’) run in the same transaction context. Even operations on the database in a high concurrent system will be transaction save.

2) Merge the EJB Methods into one transaction save business method

The second solution merges both ejb methods into a single EJB method call:

// JSF bean calls new ejb method...
public String process(Entity entity) {
 // ...

with the following ejb implementation:

// EJB
public void op1op2(Entity entity) {

Now the new ejb method is transaction save an there is no need to fiddle with UserTransaction in the jsf fornt-end controller.

The second solution is recommended because there is no more risk that the transaction context is split by the front-end. And you can reuse the new ejb method easily with now need to think about the transaction context scenarios.

Maybe this will help you solving some problems with jsf transaction context in the future.

JPA – EclipseLink – MySQL – @OneToMany

Today I was faced with a really strange problem concerning JPA, EclipseLink an MySQL. I have Service EJB (3.1) with some JPA Entity Beans. They are joined with @OneToMany constraints. I am deploying my application typically under GlassFish 3.1 with MySQL Database. Everything works fine so far. But in some really strange cases – long complex transactions with a lot of updates and inserts I got a JPA Exception like this:

[#|2014-09-25T17:21:01.989+0200|WARNING|glassfish3.1.2|org.eclipse.persistence.session.file:/opt/glassfish-3.1.2/glassfish/domains/domain2/applications/office/office-ejb-1.0.0_jar/_org.imixs.workflow.jee.jpa|_ThreadID=160;_ThreadName=Thread-2;|Local Exception Stack: 
Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`mydatabase`.`ENTITY_WRITEACCESS`, CONSTRAINT `FK_ENTITY_WRITEACCESS_writeAccessList_ID` FOREIGN KEY (`writeAccessList_ID`) REFERENCES `WRITEACCESS` (`ID`))
Error Code: 1451
    bind => [1 parameter bound]
Query: DeleteObjectQuery(org.imixs.workflow.jee.jpa.WriteAccess@5aa4670a)

I was confronted with such error messages in the past and solved them by changing the transaction boundaries in my code by encapsulating some of the jpa stuff in separate methods with new transaction context.

But The real reason for this kind of error is an inaccurate mapping of the database schema in MySQL made by EclipseLink. My table ‘ENTITY_WRITEACCESS’ is a crosstable needed for a @OneToMany relationship of my JPA entity beans.  I never looked at the schema in detail, because in my opinion that is stuff of the OR-Mapper.
The problem was that per default no CascadeType is defined for a @OneToMany relationship. But even when you define a CascadeType like CascadeType.DELETE – which is also implied by CascadeType.ALL – to your entity beans this will not necessarily be reflected to the database schema generated from the OR-Mapper. When you look at the generated schema you’ll notice that ON DELETE CASCADE is not added to the constraint. When you alter your schema and Add ON DELETE CASCADE to actual tables this will fix the problem above.

Note that this all depends on the JPA implementors how the constrains are created. So take a look at your generated table schemas.

GlassFish – EJB timer service not available

Today I had a situation where after a hardware crash my GlassFish Server did not work correctly. Specially the timer service did no longer work. The server log shows a lot of errors about

...EJB Timer Service not available

In the easiest case the reason why the timer service did not start are old db.lck files.

You can check this by stopping the server and then look for any lock files in the domain folder


After removing the files


you can restart the server and every thing should work again.

See also the following thread if this did not work for you: