A question about entity manager in stateless session bean.

JSR 220 ejbcore, page 47 : stateless session bean: All business object references of the same interface type for the same stateless session bean have the "same object identity", which is assigned by the container.
So, if we have two session beans in client code...
@EJB Cart cart1;
@EJB Cart cart2;
then cart1.equals(cart2)==true
If we declare entity manager in stateless session bean:
@PersistenceContext( unitName="ds" ,type=PersistenceContextType.TRANSACTION)
private EntityManager em;If cart1 and cart2 are the same reference, do we have any problem when using the same reference(maybe the same em? ) to get data from db?

If cart1 and cart2 are the same reference, do we have
any problem when using the same reference(maybe the
same em? ) to get data from db?No. In EJB, there is a distinction between the EJB reference and the bean instance.
Each time you make an invocation on an EJB reference for a stateless session bean,
the container can choose any instance of that bean's bean class to process the
invocation. That's true whether you invoke the same reference multiple times or
two difference references to the same bean.
Each bean instance is guaranteed to be single-threaded.

Similar Messages

Transaction management in stateless session beans.

Hi all,
I am using EJB 1.1.
I have a statless session bean that has two methods- A and B.
which does not involve any database interaction
like inserting/updating/deleting the data in the database.
The process flow is such the client always calls A first followed by the call to B.
I have the Transaction attribute set as TX_REQUIRED at the whole bean level.
Now my question is as follows:
Since it is a stateless bean, ejbCreate() is called for every method's invocation.
So does it mean that a new transaction is started for every method invocation?
Also since a transaction ends by commit/rollback.
The transation associated with the method A/B will never get completed as there is no commit/rollback involved in method implementation.
So how is this transaction ended?
Any more details about the transaction management in stateless session beans is highly appreciated.
Any input at the earliest is highly appreciated.
Thanks in advance.

Since it is a stateless bean, ejbCreate() is called for every method's invocation.For stateless session bean , Create() is not delegated to the instance.
So does it mean that a new transaction is started for every method invocation?This depends opon the Tx attribute and sequence of calls. Since you have given Tx_required then if you call any method and there is no Tx context associated with client,then a new TX will be started by container othere wise it will execute in the same TX context as the calling client. Note that client can be jsp or other ejb method.
Also since a transaction ends by commit/rollback.
The transation associated with the method A/B will never get completed >as there is no commit/rollback involved in method implementation.
So how is this transaction ended?If you are using COntainer managed TX then Transaction handling like starting , ending etc is handled by the container. You need not worry about that.
Any more details about the transaction management in stateless session >beans is highly appreciated.
Any input at the earliest is highly appreciated.Some time back I had read the article on how the Transaction management done by container on IBM Site. I dont have URL , but you can search the site.
HTH
-Ashwani

Where to store stateless session bean reference?

Hi,
I am currently writing my first ejb-jar <-> web app pair of applications. Thanks to EJB3.0 and J2EE5 the ejb part was quite easy to learn. J2EE has become a really cool platform in its recent version.
On the Web Application side I have the following question:
Where should references to stateless session beans generally be stored? Is it OK to store them in the ServletContext? In the HTTP session? Or is it better to do a JNDI lookup on a per request basis?

Application Scope (ServletContext) if many servlets use it, initialised by applicationListener (big advantage is that your webapp will not load if bean lookup fails.
Page scope (instance variable of servlet ), initialised in init() method of servlet if only needed by this page (servlet).
Session scope: makes no sense for stateless session beans, useful for stateful session beans only
Request scope: rarely used for this because JNI lookup overhead.
Hope this helps, R

Java.io in J2ee stateless session bean, general questions about debugging

Doing conventional Java IO (with java.io functions and classes such as
PrintWriter and println) in a Enterprise bean has been discussed before
in this and other forum. We know that the EJB specification says not to do it.
(For example the EJB 2.0 spec, 24.1.2) says that an enterprise
bean must not use the java.io package to attempt to access files and
directories int he file system."
The discussion in various forums including this one is that
a) using java.io in a bean would impact portability, ability to
move the bean for load balancing
b) However, this is not always an an issue and it may be reasonable
to use these functions anyway. e. g. see the response by "maozhoulu"
on Jun 21, 2002.
I tried it in Sun Application Server Nine in my stateless Session Bean:
package RS;
import RS.CourseHome;
import RS.CoursePK;
import java.rmi.RemoteException;
import javax.naming.InitialContext;
import javax.naming.Context;
import javax.rmi.PortableRemoteObject;
import javax.ejb.EJBException;
import java.io.*;
public class AddCourseBean implements javax.ejb.SessionBean {
   public void ejbCreate(){};
   public void CreateCourse (int CourseNumber, String CourseName) {
    try {
     System.out.println("in Create Course");
     PrintWriter F = null;
     try {
      F = new PrintWriter (new FileOutputStream("/tmp/v/af"));
     catch (java.io.FileNotFoundException fe){}
     F.println ("here zero");F.flush();
     InitialContext jndiContext = new InitialContext();
     F.println ("here one");F.flush();
     Object o = jndiContext.lookup("ejb/X");
         ...I got a Null pointer exception on the line:
"F.println("here zero"); Is there anyway one can do simple debugging with print lines in one's beans?
Or is there something obviousthat I am overlooking? (I saw mention of doing
debugging with System.out.println but to where would the bean write?)
I tried using the Jakarta Commons Logging, but I got a
java.lang.NoClassDefFoundError on org/apache/commons/logging/LogFactory
Which logging system does one use in GlassFish, hopefully one with minimal
configuration? I want to do some debugging, not set up logging for a full
enterprise system.
Thanks for your insight and advice.
Dr. Laurence Leff, Associate Professor of Computer Science WIU ST447 61455
Pager 309 367 0787, Fax 309 298 2302

My apology for posting this message twice. I looked for it before and
did not see it. I thought I forget to click the "Post message" button.
Also, I did resolve one problem. System.out.println does go to
the log file, which in my case turned out to be:
/opt/j2ee/SUNWappserver/domains/domain1/logs/server.log
(Obvously, the first part would vary based upon where you installed your
Application Server Nine.)
However, it would be nice if there was some way to use FILE I/O inside of
beans. I am teaching some J2EE in the graduate software engineering course,
and I believe this would be pedagogically sound even if other techniques
would be appropriate for a production environment.
Thanks for your patience with this problem and my duplicate post.

Stateless Session Bean + EJB Question + Jboss

Hello,
If I have a stateless session bean on a linux machine and it works locally what do i need to do to access a method in the session bean from a remote windows machine.
I would like to be able to execute my client jar file on a windows machine and have it access the jboss server on the linux machine. what do i need to do?
i have the session bean working locally on both windows and linux machine. do i need to to have a JSP/Servlet to access the session bean? can the session bean not be accessed directly? what should my classpath look like? do I need to include extra jar files in my client jar file.?
Thanks,
Joyce

Thanks guys for the help but I am still a little lost.
My Client windows machine has the client jar file and all the other jar files. This is my client class
package helloworld.client;
import javax.naming.Context;
import javax.naming.InitialContext;
import java.util.Hashtable;
import java.util.Properties;
import helloworld.interfaces.HelloWorldHome;
import helloworld.interfaces.HelloWorld;
public class HelloClient
     public static void main(String[] args)
          Hashtable prop = new Hashtable();
          prop.put ("java.naming.factory.url.pkgs","org.jboss.naming:org.jnp.interfaces");
          prop.put ("java.naming.provider.url","jnp://172.16.220.160:1099");
          prop.put ("java.naming.factory.initial","org.jnp.interfaces.NamingContextFactory");
          try
               Context ctx = new InitialContext(prop);
               Object obj = ctx.lookup("ejb/helloworld/HelloWorld");
               System.out.println(obj);
               HelloWorldHome home = (HelloWorldHome)javax.rmi.PortableRemoteObject.narrow(obj, HelloWorldHome.class);
               HelloWorld helloWorld = home.create();
               String str = helloWorld.sayHelloEJB("JOYCE is COOL");
               System.out.println(str);
               helloWorld.remove();
          catch(Exception e)
               e.printStackTrace();
I get a NullPointer ie the home object is null. The IP address is the IP of the Linux machine that has Jboss running on.
Questions are:
1. Do I need to have Tomcat running on my client machine if I am to connect via HTTP? Does this alter my client code.?
2. My JNDI lookup is what is causing the problem. Does my jboss.xml and my ejb-jar.jar look okay to you.
jboss.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jboss PUBLIC "-//JBoss//DTD JBOSS//EN" "http://www.jboss.org/j2ee/dtd/jboss.dtd">
<jboss>
<enterprise-beans>
<session>
<ejb-name>helloworld/HelloWorld</ejb-name>
<jndi-name>ejb/helloworld/HelloWorld</jndi-name>
</session>
</enterprise-beans>
<resource-managers>
</resource-managers>
</jboss>
ejb-jar.jar
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">
<ejb-jar >
<description>No Description.</description>
<display-name>Generated by XDoclet</display-name>
<enterprise-beans>

<session >
<description><![CDATA[No Description.]]></description>
<ejb-name>helloworld/HelloWorld</ejb-name>
<home>helloworld.interfaces.HelloWorldHome</home>
<remote>helloworld.interfaces.HelloWorld</remote>
<ejb-class>helloworld.session.HelloWorldBean</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Bean</transaction-type>
</session>





</enterprise-beans>


<assembly-descriptor >



</assembly-descriptor>
</ejb-jar>
Do I need RMI ? Do I need to concern myself with CORBA? All Im looking for is a step by step to understanding what I need to configure? Is their some way I can debug?
Thanks alot,
Joyce

Paradox - Should entity CMP EJB be faster than stateless session bean?

Please bear with me on this.
Just thinking of this scenario: hello world application. It can be implemented both as stateless session bean and entity bean.
There's no persistent. So for the entity bean, it will be container managed, and no code to do anything to the load/remove/create. - comparably the same as stateless bean.
Next, for the stateless session bean, each client call would require a dedicated instance of the EJB on the server (although for a very short amount of time). For the entity bean, it's shared, so only 1 instance is needed. It's also thread safe.
So, for a very high traffic, shouldn't the entity bean do better because of single instance?
What's other overhead?
Does the entity bean cost more connections than the stateless bean?

Feels like a comparison between apples and oranges.
A stateless session bean is like every other instance, so these can be pooled by the EJB container. The container is free to create an instance for each client if necessary. That's different.
A stateless session bean doesn't have to deal with a database that may or may not be located on another machine the way an entity bean does. There could be another network round trip involved. That's different.
Session and entity beans are intended for entirely different purposes. Just because you can write Hello World with both doesn't mean it's representative of what EJBs are used for. I don't think it's a good, meaninful comparison. JMO - MOD

A tough one for EJB experts - Stateless session bean spec question

I am busy learning more about EJBs and came across something confusing regarding the legal operations in the various container callback methods for stateless session beans.
Specifically, the EJB spec states that in the ejbCreate() method, the SessionContext can be used to obtain a reference to the EJB Object. Now this makes perfect sense with stateful session beans, since the ejbCreate() method isn't called until a client is creating a bean and the container has linked that bean to the client's EJB Object. However, it is my understanding that when it comes to stateless session beans, the container creates the beans and adds them to the bean pool at its leisure. It is not until a business method is called by a client that a stateless bean is actually linked to an EJB object. So, how is it that a stateless bean could ever obtain a reference to an EJB Object from within ejbCreate(). Which EJB Object would it be linked to? This operation just doesn't appear to make sense in that context.
Can anyone clarify this for me?

Interesting question. I have such questions all the time! Here's a link to a similar discussion
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=70&t=000905
Also, I tried this using Weblogic 8.1. Tried to access the EJBObject in ejbCreate before any business method was invoked. I did this by specifying a value for initial-beans-in-free-pool and found that the hash code for the EJBObject was the same for all the bean instances that were created on startup.
I then invoked a business method and accessed the EJBObject in that method. Again the hash code for the object was the same as the one created on startup.
Seemed to be that there is a 1:n relation between the EJBObject and bean instances.
This may be container specific. The spec says the user should be able to invoke the getEJBObject() method in ejbCreate(), its upto the container to comply with it.

Transaction Management - App Module in Stateless Session Bean

Hi All,
We are using Application Module in local mode in a Stateless Session Bean. The application module gets the database connection from the datasource of the application server(Oracle 9iAS).
The problem that we are facing is as follows
- When a database update/insert is made using the Application Module and the ViewObject (and the underlying Entity Object), the changes are not being commited.
Please note that we are not using the ApplicationModule.getTransaction.commit() as it does not give us commit/rollback control from another Session Bean/UseCase. We instead are relying on the Container to manager the transaction and commit the database changes. But the container does not seem to refresh the changes to the database.
Q1 - Is there a contract between the container and the application module that needs to be created so that the container managed-transaction and the application module work together ?
Any help in this matter would be greatly appreciated.
-Ankur Sinha

Q1 - Is there a contract between the container and the application module that needs to be created so that the container managed-transaction and the application module work together ?For stateless beans you have to call postChanges in the business method for the changes to be applied to the db. For stateful beans bc4j we do that automatically just before the transaction ends.
Take a look at the following howto
http://otn.oracle.com/products/jdev/howtos/bc4j/ejbstateless_with_bc4j.html
In 9.0.3 you'll be able to create a stateless service bean declaritively.
dhiraj Hi dhiraj,
- I looked at the example but was not able to find the ContainerManagedTxnHandlerImpl class in the BC4J jars. Can you point me to the latest version of BC4J on technet ?. I already have JDeveloper 9.0.2
- Regarding your response, what do you mean by creating stateless service bean declaritively ?
Thanks,
Ankur

Two questions about Risk Management 2.0

hi experts,
Please find below two questions about Risk Management:
-In SPRO, Risk Management>Create top node: after completing information and executing I have this error:
Error in the ABAP Application Program
The current ABAP program "/ORM/ORM_CREATE_TOP_NODES" had to be terminated
because it has
come across a statement that unfortunately cannot be executed.
The following syntax error occurred in program "/ORM/SAPLORM_API_SERVICES " in
include "/ORM/LORM_API_SERVICESU10 " in
line 97:
"Bei PERFORM bzw. CALL FUNCTION "GET_ORGUNIT_THRESHOLDS" ist der Aktual"
"parameter "I_ORGUNIT_ID" zum Formalparameter "IV_ORGUNIT_ID" inkompati"
"bel."
The include has been created and last changed by:
Created by: "SAP "
Last changed by: "SAP "
Error in the ABAP Application Program
The current ABAP program "/ORM/ORM_CREATE_TOP_NODES" had to be terminated
because it has
come across a statement that unfortunately cannot be executed.
Do you know where it could come from?
-On the Portal>Risk Management
when I click in a link under the risk management menu(activities and risks, risk report, document risk,...) i alway have an internal server error:
While processing the current request, an exception occured which could not be handled by the application or the framework.
If the information contained on this page doesn't help you to find and correct the cause of the problem, please contact your system administrator. To facilitate analysis of the problem, keep a copy of this error page. Hint: Most browsers allow to select all content, copy it and then paste it into an empty document (e.g. email or simple text file).
Do we have to set up some customizing points before accessing these links?
Thank you !
Regards,
Julien

Hi Julien ,
I have the same error what u described as :-
-On the Portal>Risk Management
when I click in a link under the risk management menu(activities and risks, risk report, document risk,...) i alway have an internal server error:
While processing the current request, an exception occured which could not be handled by the application or the framework.
If the information contained on this page doesn't help you to find and correct the cause of the problem, please contact your system administrator. To facilitate analysis of the problem, keep a copy of this error page. Hint: Most browsers allow to select all content, copy it and then paste it into an empty document (e.g. email or simple text file).
Do we have to set up some customizing points before accessing these links? "
Are you able to solve this. Please let me know how to resolve this???
Thanks
Regards,
Atul

EJB: Stateless Session Bean create() Question.

Lets say I have a stateless session bean that fetches data from my database. The point of the bean is to just do large SQL searches and funnel data back to the client. The prolem I have is that I am somehow fighting memory leaks. Despite having checked the code a number of times, the memory usage on my appserver continues to climb no matter what I do. I have theorized that the problem might be in the way Im using ma DataFetchBean (DFB).
When I start the client, he obtains a user session. This is a stateful session bean that he uses for almost all communication with the server. Then I call "getDataFetchBean" in the user session which calls DataFetchBeanHome.create(). Then the client holds onto the returned reference, using it for the live of his connection. As he disconnects, he calls remove on the bean.
Question is this:
1) Is it better for me to call create() prior to each call to the stateless session bean ?
2) Do you have any theories on why im loosing memory with this setup?
TIA
-- Rob

1. But I thought you were using a 'stateful session bean'?
2. For stateless session beans, there is no direct link between a remote reference and an instance of the bean. It is safe to hang on to the remote reference as long as you would like, of course it may go stale if the server dies. You will also find that the create() method does not actually contact the server, so doing it each usage costs very little. So, either way you should be fine.
3. As for memory leaks, make sure that you are closing all statements, result sets, etc. promptly. These are commonly the problem. Also, use hprof or some other profile tool to determine what types of data you are allocating and (with better tools) what types of data you may be holding on to references to.
Chuck

Can Entity Bean with Home Business Method replace Stateless Session Bean?

Since Entity Bean can have business methods in the Home Interface, can we use Entity Bean with Home Business Methods to replace Stateless Session Bean?
I am assuming we can get better performance by doing this since the overhead of creating Component Object can be avoided as compared to stateless session beans.

Requires-new makes the container start a new transaction. Only use that flag
          at the point that you are certain that a NEW transaction should BEGIN. I
          suggest you use Required as your default for all methods in the application,
          and only change that to anything else when you are certain that you should.
          Peace,
          Cameron Purdy
          Tangosol Inc.
          << Tangosol Server: How Weblogic applications are customized >>
          << Download now from http://www.tangosol.com/download.jsp >>
          "A.J,LEE" <[email protected]> wrote in message
          news:3ba5adb2$[email protected]..
          >
          > I find it result in "dead lock"
          > when I call RequiresNew attributed CMP method in session Bean.
          > Then, Is it possible to use CMP which is set with "RequiresNew"
          transaction attribute?
          >
          > I Wonder why.
          >
          > Thanx in advance.

Bean-managed stateless session bean can't roll back using JTA

I use weblogic6.1sp2 + jdk131
a stateless session bean must do 2 things:
insert a record to A table and delete another record in A table
this bean has the same structure as the example in
j2eetutorial/examples/src/ejb/teller
I use TxDataSource in weblogic
if delete fail, the roll back is run,but in database,
the insert record is STILL in A table.
any idea?

make sure that your deployment descriptor says "transaction required".
Also, If the insert and delete are two different methods, the client must call these two methods in the same transaction scope.

How to integrate hibernate with Stateless Session bean in weblogic10.0

Hi,
I need to invoke hibernate(3.x) DAO from EJB Stateless Session bean(EJB2.x). I am using mysql database. Can somebody please post the configuration.
Thanks in advance,
Rushi.

Hi Deepak,
Thanks for your reply.
Actually, our stand alone java application already using spring-hibernate feature. Now we are planning divide our application into modules and deploy each module as ejb beans. As it is already integrated with spring-hibernate we are not using entity beans as of now. My understanding is container uses some default transcation management .so, my question is what are all the configurations needs to be done to let weblogic 10.0 server uses org.springframework.orm.hibernate3.HibernateTransactionManager. I mean, is there are any .xml file in weblogic to configure all these? please reply deepak I am struck here..
Regards,
Rushi.

EJB 3.1new instance of stateless session bean not created on new invocation

I am using Netbeans 6.8 bundle that comes with JAVA EE 6. I have created a web application then created restful web services and then created few stateless session beans (with local interfaces) that are invoked from restful web services. From the browser, when I call the url with get method, restful web services are being invoked and they in turn calls stateless session beans and does the appropriate business logic. While testing, I observed that for every new url call from the browser, the same bean is being invoked. I tested this by adding a instance variable vector and adding one item ('test") to the vector in bean's method. My understanding is that on every bean's method invocation the vector should have only one item. However, the vector is growing with many "test" items. I am literally confused, not sure this is the way it is supposed to work. I tried to invoke bean's method from restful web service by using both dependency injection and jndi look up, both instances the vector is growing with many "test" items.
I would really appreciate if some body gives me more insight.

I appreciate your answers. There is a strong reason for posting this question. Basically, I am using JPA and using stateless session beans to invoke database calls. In the bean I am using the following code for entity manager.
@PersistenceContext(unitName = "AsgProtocolServerPU")
private EntityManager em;
I have noticed very strange scenario while getting records. From the application, I have obtained few records of a table. Then, I manually deleted few records from the table. Very strangely, I have obtained the deleted records during my next call to bean. After 2 hours, I tested the same and did not get those records. This is not consistent.
I am totally confused. I am just wondering this is happening because I made beans local (not remote) and placed them in the web application (Java EE6 allows this). I am not sure whether this is JPA related issue or beans issue.

TX isolation level with stateless session bean in oc4j

Hi All,
I have a stateless session bean with container managed transaction method. This method is called in a Servlet. This method retrieves data from database using 'ejb-location'connection pool and closes the connection inside. Max-connection setting for connection pool is 50
I am facing a problem running servlet multiple times.
When i have the tx_attribute as Supports, it works fine. I can run the servlet hundreds of times
But when i have the tx_attribute as Required, i am able to run servlet only 50 times and further it says 'Max connection limit exceed..unable to get the connection'.
I assume that with 'Required' attribute, it starts a transaction. Why is the transaction not getting completed at end of method? Is transaction hanging somewhere?
I assume that i am closing the connection properly as it is working fine with supports attribute.
When i monitor database, there are only 20 connections.
Why am i seeing this behaviour?
Thanks
srinath

Hi Deepak,
Thanks for your reply.
Actually, our stand alone java application already using spring-hibernate feature. Now we are planning divide our application into modules and deploy each module as ejb beans. As it is already integrated with spring-hibernate we are not using entity beans as of now. My understanding is container uses some default transcation management .so, my question is what are all the configurations needs to be done to let weblogic 10.0 server uses org.springframework.orm.hibernate3.HibernateTransactionManager. I mean, is there are any .xml file in weblogic to configure all these? please reply deepak I am struck here..
Regards,
Rushi.

A question about entity manager in stateless session bean.

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