I am using a shared process engine on WebSphere and I want to understand how the engine looks up the required resources (custom code shipped with my process application) for a process step invocation. Is a thread context switch applied?
The shared process engine can be used by multiple applications, one of these applications being the Camunda webapplication.
Whenever the process engine "does something" within a process instance, such as executing a service task, it performs a Thread Context Switch. This Thread Context Switch is performed to the application which deployed the BPMN process that the engine is currently executing. This is necessary for the process engine to be able to use resources locally available within that application.
Examples for these kinds of resources:
The application's classloader, in order to instantiate Java Delegates
The application's CDI Bean Manager, in order to be able to invoke CDI Beans.
How does this "Thread Context Switch" work technically?
The process engine executes a callback method on an EJB which has to be included within the application. This is why you include the camunda-ejb-client.jar. Relevant information: the process engine invokes the local business interface of that EJB.
As a result, the Thread Context Switch is performed with EJB local invocation semantics. Whatever Websphere puts in place for an EJB local invocation will work and whatever Websphere does not put in place for an EJB local invocation will not work.
The behavior is exactly the same as it would be if you would put the code from your Java Delegates into an EJB with a local business interface and invoke that from another application.
Related
I have situation where I need to perform certain tasks in case my springboot applications fails to start. Basically I want to release various resources. I tried using #PreDestroy annotation but it did not work as application was not started yet. Is there any way out by which we can perform few actions in case springboot application fails to start
Spring app heavily using threadpool context when start the program , so when the main program fail spring can not manage the standard beans related to spring. you can only start new thread using implements Runnable in main class and no access to spring resources as well , just simple getclassloader().getresourceasstream is available there .
However you can write independence java Agent using -javaagent to do some operation on release resource ,see java.lang.instrument.Instrumentation;
I want to run few tasks asynchronously in a web application. My question is which Spring implementation of task executors i should use in a Container managed environment.
I refereed to this chapter in Spring documentation and found few options.
One option I considered is WorkManagerTaskExecutor. This is very simple and works seamlessly with the IBM Websepher server which I'm currently using but this is very specific to IBM Websphere and Oracle Weblogic servers. I don't want to tie my code specifically to one particular implementation as in some test and local regions we are using Jetty container & this implementation creates problems to run the code in Jetty.
Other options like SimpleThreadPoolTaskExecutor does not seem to be best fit to leverage thread pooling in container managed environment and I don't want to create new thread myself.
Could you pleas suggest how do I go about this. Any pointers to a sample implementation will be great help.
As usual, it depends. If you rely on the container's thread management and want to be able to set thread pools on its admin interface or if you're application is not the only app inside the container or you use specific features like setting thread pool priorities for EJB or JMS you should add support for the WorkManagerTaskExecutor and make it configurable. If not, you can use whatever you want cause in the end threads are just threads. Since Spring is an IOC container you can do it. To use the same app everywhere I wouldn't suggest to change the XML config per app version. Rather
use profiles with configuration to set the executor type and inside your java config return the proper bean type. If you use Jetty you should have a configuration for the thread pool sizes to to be able to tune it.
use spring boot like auto configuration which usually rely on available classes on classpath (#ConditionalOnClass). If your weblogic or websphere specific classes are available or any other container specific thing like env variables you can create the WorkManagerTaskExecutor
With both of these you can deploy the same war everywhere.
I have a scenario in which the results of various students are generated from within one ejb call by looping over the student list. I was thinking of creating threads for processing each student using executorService within a ejb call. Currently i just look up my ejb once.
i think this post should answer your question
EJB's and Threading
in general an EJB should not spawn new threads or do 'handcrafted' asynchronous execution.
In EE 7+ servers, you should just use JSR 236, which let's your application have access to executors/pools that are managed by the application server.
Otherwise, in theory, the EJB spec does not allow EJBs to create their own ExecutorService, which would create/manage its own threads:
The enterprise bean must not attempt to manage threads. The enterprise
bean must not attempt to start, stop, suspend, or resume a thread, or
to change a thread’s priority or name. The enterprise bean must not
attempt to manage thread groups.
These functions are reserved for the EJB container. Allowing the
enterprise bean to manage threads would decrease the container's
ability to properly manage the runtime environment.
In practice, it might work if you have complete control over the server running your application (you know which other applications are running and how many threads/pools they're creating in order to avoid overloading the system), and you limit the actions taken in those threads (for example, java:comp lookups won't work, transactional behavior might be limited, etc.).
As per Oracle docs here
Local Clients A local client has these characteristics.
It must run in the same application as the enterprise bean it
accesses.
It can be a web component or another enterprise bean.
To the local client, the location of the enterprise bean it accesses
is not transparent.
As for :It must run in the same application as the enterprise bean it
accesses.
When it says 'same application, it means the EJb client and the EJB bean must be part of the same jar file? Or same EAR file? If it is part of the same jar file, why even use an EJB in the first place? We can just import the EJB bean in the client and use it like a utility class.
It means the same EAR.
Regardless, the only reason to ever use EJB is because you want to delegate responsibility to the container (transactions, security, interceptors, resource injection, asynchronous methods, timers, etc.). There's nothing to stop you from implementing all the qualities of service yourself (e.g., Spring did it), but by using EJB, you don't have to worry about getting all the details right, and (in theory) you make it easier for many people to develop an application because they share a common understanding.
We are using cucumber-jvm to write an integration test layer in our application. One of the challenges we are finding is managing the database between the tests and the web application.
A typical scenario is that we want to persist some entities in a Given step of a scenario, then perform some actions on the user interface that may, in turn, persoist more entities. At the end, we want to clean the database. Because the cucumber-jvm tests are in one jvm and the web application is running in another jvm we cannot share a transaction (at least in a way of which I am aware) so the database must be cleaned manually.
My initial thought was to use an Embedded Tomcat server running off of an embedded in-memory database (HSQLDB) in the same JVM as the cucumber-jvm test. This way we might be able to share a single spring container, and by extension a single transaction, from which all objects could be retrieved.
During my initial tests it looks like Spring gets loaded and configured twice: once when the test starts and the cucumber.xml is read, and a second time when the embedded tomcat starts and the web application reads its applicationContext.xml. These appear to be in two completely separate containers because if I try to resolve an object in one container that is specified in the other container then it doesn't resolve. If I duplicate my configuration then I get errors about duplicate beans with the same id.
Is there a way that I can tell Spring to use the same container for both my test application and the embedded tomcat?
I'm using Spring 3.2.2.GA and Embedded Tomcat 7.0.39 (latest versions of both libraries).
Am I crazy? Do I need to provide more technical details? Apologies if I use some incorrect terminology.
Thanks
p.s. If my problem seems familiar to you and you can suggest an alternative solution to the one I am trying, please let me know!
Jeff,
It is normal that spring is loaded twice. There are two places where two spring contexts are created:
In the servlet container listener org.springframework.web.context.ContextLoaderListener that is configured in web.xml. This one reads its configuration from the file set by the context-param contextConfigLocation.
In the implementation of ObjectFactory provided by cucumber-spring plugin cucumber.runtime.java.spring.SpringFactory. This one reads its configuration from cucumber.xml.
The two spring contexts are totally different and their instances are kept in two different places. As a servlet context attribute for the former and kept by the JavaBackend for the latter.
When starting the embedded tomcat, it is possible to get access to the servlet context and thus set ourself the spring context used bt tomcat with the one from cucumber. But, spring has a special class called WebApplicationContext for context used in a servlet container. The cucumber SpringFactory on other hand creates its context through ClassPathXmlApplicationContext. So unless there is a way to specify the type of application context from the xml config, we will have to provide an ObjectFactory that shoots a WebApplicationContext.
What we can do is to have two web.xml. One for the normal and one for the test. For the test, we use our version of the ContexLoader listener.