Skip to main content

EJB called from another, specifically Message driven bean with container transaction.

The other day I had a weird defect in the application I worked on, we had a Message driven bean [MDB] calling another EJB inside the message processing code and everything was working fine and passed two different testing periods.

after going live on production something happened, the MDB received a message and invoked the EJB to do some work, that work included calling a web service, this service client thrown time out exception and thrown an exception and the EJB couldn't finish its work because that's what is expected, the weird thing is that the exact same message was reprocessed by the MDB automatically.. we don't have anything in our code that did that.

this didn't happen before with other EJBs called from an MDB..

after thorough investigation I found the following :

1- The MDB uses container transaction [ found configuration in the ejb-jar.xml] (this is used in EJB2)
2-  The EJB method that was invoked also had container transaction configured with transaction attribute as Required
3- When an exception is thrown from the EJB method, it calls : context.setRollBackOnly(); which means the container transaction will roll back

but why was the message reprocessed again? Luckily in production the service didn't time out the second time and the message was processed successfully, but I did a test where the EJB always fails and that led in having the MDB reprocessing the message indefinitely until I shutdown the server.

I tried and changed the EJB transaction attribute in the ejb-jar.xml to 'RequiresNew' instead of 'Required' because at that point I felt that there is a relation between the transaction failing in the EJB and the MDB transaction [Yes MDBs have transactions] and that WORKED.

it's critical to configure the EJBs [ MDB is an EJB ] transactions to match the need of the application, in our case we didn't want the message to be reprocessed everytime it failed, so a new transaction in the EJB did the trick


Comments

Popular posts from this blog

Android RecyclerView - Adding Empty View

So RecyclerView was introduced to replace List view and it's optimized to reuse existing views and so it's faster and more efficient as stated in the documentation:

https://developer.android.com/training/material/lists-cards.html

While using it, I faced the issue of missing a useful functionality that is implemented in ListView.
that feature is setting an empty view in case there was no records.

In ListView it was as simple as this

View emptyView = findViewById(R.id.mylist_empty_view);
ListView  myList = ....
myList.setEmptyView(emptyView);

but this method doesn't exist for recycler view so we need a work around until android team fixes this.


and here are the screen shots of both list view and recycler view fix

List view :

Recycler view :



here is how I fixed it:



here is the content of empty_view, it can be anything.



Enjoy.

Android - Multiple themes for one application

Sometimes you want to have multiple themes for your app
one strong example is having the ability to switch between dark and light themes because during night, a white bright screen can really be annoying for users eyes

Android will do most of the work for you but it may be required to change icons between themes to fit colors
In this blog I'll show a simple app with both dark and light themes and how to change icons without having to do that from code and keep things clean and centralized.
first of all let's create our activity, it will look something like this :


In /rest/values/styles.xml, we inherit Theme.AppCompat
 <!--
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
    -->
    <style name="AppBaseTheme" parent="Theme.AppCompat">
        <!--
            Theme customizations available in newer API levels can go in
            res/values…

Creating your own OAuth2 server and clients using spring security - part 1

In this series of posts, I'll try to put together a simple working example on how to create your own OAuth2 server.

if you want to know more on OAuth2 and when to use it as authentication and authorization protocol then you can search about it on google and i'll put some URLs later.

Now I assume you are familiar with java web applications using Spring and maven.

to get started we need to create the server side with all dependencies required and i'll list them here, i'll use maven 2 to ease downloading dependencies for us.


Steps:

1- Create new maven project with arch type webapp:



2- Add the required depenedencies for spring, spring security, spring-oauth2, hibernate & other libraries (required for this tutorial only you can use other libraries if you like)

https://gist.github.com/anonymous/d33a31ddc3ba84375cf3

3- I used hibernate to automate the creation of the schema required by spring OAuth2 to manage tokens (it's required to have schema created in db if you a…