[EJB3] - How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
12:14 a.m.
Adheep M [https://community.jboss.org/people/adheep] created the discussion
"How does a @EJB dependency injection work on a Stateless Bean? Will that injected
class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/743539#743539
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Hi guys,
I have this question on the latest version EJB 3.1 has the "@EJB" annotation
which is used for the dependency injection.
I have two stateless session bean and a singleton bean
@Stateless
public class PrimaryStatelessBean {
@EJB
SecodaryStatelessBean secondaryStatelessBean;
@EJB
SimpleSingletonBean simpleSingletonBean;
public String processRequest ( ) {
.....
secondaryStatelessBean.getValue();
simpleSingletonBean.getAnotherValue();
....
}
}
How does the @EJB annotation work, will the injected class behave like an Instance
variable of the PrimaryStatelssBean ? :-/
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2:07 a.m.
New subject: [EJB3] - Re: How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
Viggo Navarsete [https://community.jboss.org/people/viggo.navarsete] created the
discussion
"Re: How does a @EJB dependency injection work on a Stateless Bean? Will that
injected class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/743572#743572
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Yes, you're correct! Whenever a new instance of PrimaryStatelessBean is created by the
EJB container (and since it's a stateless annotated bean, you will get a new one for
each request), then you will get injected a new instance of SecondaryStatelessBean (since
it's most likely also a stateless annotated bean, based on your naming convention),
and you will get access to the *one instance* of SimpleSingletonBean that has been created
by the EJB container (since it's a Singleton annotated bean).
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4:21 a.m.
New subject: [EJB3] - Re: How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
Adheep M [https://community.jboss.org/people/adheep] created the discussion
"Re: How does a @EJB dependency injection work on a Stateless Bean? Will that
injected class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/743609#743609
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@ https://community.jboss.org/people/viggo.navarsete Viggo Navarsete: Thanks for your
reply.
But this brings me an another question, Supose if a method in
"PrimaryStatelessBean" is annotated with REST will it work the same way, because
we will not create a new instance for the PrimaryStatelessBean if it is invoked as a
RESTful webservice.
@Stateless
public class PrimaryStatelessBean {
@EJB
SecodaryStatelessBean secondaryStatelessBean;
@EJB
SimpleSingletonBean simpleSingletonBean;
@POST
@Path("/requestService")
@Consumes("*/*")
@Produces("*/*")
public String processRequest ( ) {
.....
secondaryStatelessBean.getValue(); //(After making a first request) When I
make another request will i get the same value "Testing Value" here
simpleSingletonBean.getAnotherValue();
secondaryStatelessBean.setValue("Testing Value"); // set values for
secondaryStatelessBean in the first request
....
}
}
On the first request to my to "processRequest" service using REST, if i change
the value of a member variable in SecondaryStatelessBean by
secondaryStatelessBean.setValue("Testing Value"); // set values for
secondaryStatelessBean in the first request
and on the next request, will i get the value "Testing Value" here ?
secondaryStatelessBean.getValue(); //(After making a first request) When I make another
request will i get the same value "Testing Value" here
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4:25 a.m.
New subject: [EJB3] - Re: How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
Viggo Navarsete [https://community.jboss.org/people/viggo.navarsete] created the
discussion
"Re: How does a @EJB dependency injection work on a Stateless Bean? Will that
injected class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/743610#743610
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No, the "Testing Value" will not be there on the second request! But, it
shouldn't be too difficult for you to actually test it, or? But I would assume that if
you set a value on the simpleSingletonBean on the first request, then it would still be
there on the second request!
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7:17 a.m.
New subject: [EJB3] - Re: How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
Adheep M [https://community.jboss.org/people/adheep] created the discussion
"Re: How does a @EJB dependency injection work on a Stateless Bean? Will that
injected class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/743664#743664
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Viggo Navarsete wrote:
No, the "Testing Value" will not be there on the second request! But, it
shouldn't be too difficult for you to actually test it, or? But I would assume that if
you set a value on the simpleSingletonBean on the first request, then it would still be
there on the second request!
I did try an example and below are the codes
package com.sample.rest.service;
import javax.ejb.EJB;
import javax.ejb.Stateless;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import com.test.ejb.PrimaryStatelessBean;
import com.test.ejb.SampleSingletonBean;
@Stateless
@Path("/services")
public class PrimaryStatelessBean{
@EJB
PrimaryStatelessBean primaryStatelessBean;
@EJB
SampleSingletonBean sampleSingletonBean;
@GET
@Path("/getValue")
@Produces("text/xml")
public String getValue(){
//To get initial value
System.out.println("Before Setting Value::" +
primaryStatelessBean.getMessage());
//set value for the Bean
primaryStatelessBean.setMessage("Hi Buddy Cool!!");
//After setting value
System.out.println("After Setting Value::" +
primaryStatelessBean.getMessage());
return
"<MESSAGE>"+primaryStatelessBean.getMessage()+"</MESSAGE><REQUEST_COUNT>"+
sampleSingletonBean.getCount() +"</REQUEST_COUNT>";
}
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10:23 a.m.
New subject: [EJB3] - Re: How does a @EJB dependency injection work on a Stateless Bean? Will that injected class behave like an instance variable in that stateless session bean?
Didac Montero Mendez [https://community.jboss.org/people/umbreak] created the discussion
"Re: How does a @EJB dependency injection work on a Stateless Bean? Will that
injected class behave like an instance variable in that stateless session bean?"
To view the discussion, visit: https://community.jboss.org/message/792647#792647
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And in reference to the class SecondaryStatelessBean, this is an example of how a
Stateless class should NOT be used.
From JavaEnterPrise Beans:
The procedure runs from beginning to end, finally returning the result. Once the
invocation completes, nothing about the data that was manipulated or the details of the
request is available. When finished servicing a method invocation, an SLSB instance may be
reused as the target for a new request.
Bypassing conversational state doesn’t mean that a stateless session bean can’t have
instance variables or maintain any kind of internal state. Nothing prevents you from
keeping a variable that tracks the number of times a bean instance has been called or
a variable that saves data for debugging. However, it is important to remember that this
state may never be visible to a client. The caller of an SLSB can’t assume that the same
bean instance will service all of its requests. Instance variables may have different
values in different bean instances, so their state is likely to appear to change randomly
as stateless session beans are swapped from one client to another. Therefore, anything you
reference in instance variables should be generic and not leaked out through the API.
As a summary: SLSB are reusable. The container guarantees concurrency having a pool
of instances, so NEVER two users will consume the same instance at the same time. The
container choose one instance among all the available instances on the pool.
For this reason, in the example, the value retrieved in primaryStatelessBean.getMessage()
is the one set in the previous call. If you perform the test with ab (Apache Benchmark)
with concurrency, you would see that different instances are created and that different
values would be shown.
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5 comments
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participants (3)
-
Adheep M -
Didac Montero Mendez
-
Viggo Navarsete