Explaining Entity Beans

i'm a student. i've just stepped into EJB. I find difficult to learn & deploy Entity beans in J2EE server.
Plz help me to learn the functions, deployment procedures & other JDBC related issues to learn for entity bean deployment

I doubt anyone here is able to give you complete entity bean tuition;) The area is big and you must separate it into smaller parts to learn.
But you can start with the easier parts, step by step with the tutorial. Maynbe as a starter with stateless session beans(I find them easier to understand), for example a bean that will answer a "Hallo world" request, then deploy it (initially with the deploytool, later you will learn how the deployment descriptors should look like).
After that you can play with JDBC from standalone application, not EJBs, and after you feel comfortable with those you can go further, join the technologies.

Similar Messages

Can anyone explain the advantage of entity beans

Hi All,
I was wondering if anyone can explain the advantage of entity beans versus session beans. We argue that session beans can perform retrival/storage more efficiently than having an extra layer of entity beans. Basically we can't see any advantage entity beans have to offer except caching a row in a database table. I'd like to see the other side of the argument. So please if someone is an expert in this field, please advise us.
Thanks in advance for any argument
Regards,
Di

-Caching the data is one.
-Seperation of logical layer. Entity beans are used to represent the data layer, while session beans hold the business rules. This is some what nebulous as some business rules are often best implement directly in the database, although they might be replicated at a different level as well.
-Mapping a logical layout to a physical layout. For example 'customer' might have a 'fax' and 'voice' line which is represented as a Customer class with two TN classes hanging off of it. The database might represent this in one of two ways: two tables (customer and TN) or one table (customer with two tn fields).
Both of the above are more readily apparent when dealing with distributed data. If one database holds the customer and another holds the TNs, then caching of data is more relevant and dealing with the actual CRUD stuff is much more complicated. This is likely to lead to a session bean offloading the logic to another class anyways - and it becomes a defacto bean.
And a really excellent example is when the entity bean represents data that isn't accessed via normal database calls. For example the customer record might be on a legacy system which can only be accessed via screen scrapping and batch input. That single customer entity is now the front end for a large sub-system.
All such answers are usually pretty wishy-washy anyways. Why should one use java over C++? Most decisions of this nature are made because developers want to use something rather than because there is any strong technical reason to do so. And even though keeping the data layer seperate for the rules layer seems like a good idea, compromises are always required and adding layers adds complexity.

Client Program accessing J2EE entity Bean

I have trouble find my Course J2EE bean from a client. (The client
runs on the same computer but a different VM from the bean.)
In Glassfish (Sun Application Server Nine), I set up a simple
Container-Managed Entity Bean. I tried to access it from an external
client as described in the glassfish EJB
FAQ https://glassfish.dev.java.net/javaee5/ejb/EJB-FAQ.html
Here is the client program:
package RS;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.xml.parsers.*;
import org.apache.xml.serialize.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import RS.CourseHome;
import RS.CoursePK;
import javax.naming.InitialContext;
import javax.naming.Context;
import javax.naming.NamingException;
import java.rmi.RemoteException;
import javax.rmi.*;
import java.util.Properties;
import Debug.*;
public class Client {
public static void main (String arg[]) throws IOException {
try {
InitialContext jndiContext = new InitialContext ();
Debug.P("jndic ongtext" + jndiContext);
Object o = jndiContext.lookup("RS.CourseHome");
Debug.P("looked up object "+o + "|"+o.getClass().getName());
RS.CourseHome home =
    (RS.CourseHome)PortableRemoteObject.narrow(o,RS.CourseHome.class);
Debug.P("got home "+home);
Course C = home.create(1);
C.setName("blah");
CoursePK PK = new CoursePK();
PK.number=1;
C = home.findByPrimaryKey(PK);
Debug.P(C.getName());
catch (java.rmi.RemoteException re) {Debug.P("Remote Exception" + re.getMessage());}
catch (javax.naming.NamingException ne){Debug.P("Naming Exception"+ne.getMessage());}
catch (javax.ejb.CreateException ce){Debug.P("Create Exception"+ce.getMessage());}
catch (javax.ejb.FinderException fe){Debug.P("Finder Exception"+fe.getMessage());}
}Here is the error message:
Exception in thread "main" java.lang.ClassCastException
at com.sun.corba.ee.impl.javax.rmi.PortableRemoteObject.narrow
                   (PortableRemoteObject.java:294)
at javax.rmi.PortableRemoteObject.narrow(PortableRemoteObject.java:137)
at RS.Client.main(Client.java:26)The debugging indicates that I got the Initial Context
and got the object but the PortableObject.narrow failed:
jndic ongtextjavax.naming.InitialContext@1d85f79
looked up object IOR: (huge number deleted)
com.sun.corba.ee.impl.corba.CORBAObjectImplEarlier, I tried the version below, but based on the suggestion by Mr. Ebbert
in the forum started "Error When running the Client Program" by sree_devi,
I checked
the following. I went to "Jndi Tree Browsing" from the Administrative Console
and I found a "RS.CourseHome" entry under "ejb" I found RS.CourseHome there
but did not see the "Course" tghat I expected to see
Thus, I tried the version above:
package RS;
   --- imports deleted for conciseness
import Debug.*;
public class Client {
public static void main (String arg[]) throws IOException {
try {
InitialContext jndiContext = new InitialContext ();
Object o = jndiContext.lookup("Course");
CourseHome home =
    (CourseHome)PortableRemoteObject.narrow(o,CourseHome.class);
Course C = home.create(1);
C.setName("blah");
CoursePK PK = new CoursePK();
PK.number=1;
C = home.findByPrimaryKey(PK);
Debug.P(C.getName());
catch (java.rmi.RemoteException re) {Debug.P("Remote Exception" + re.getMessage());}
catch (javax.naming.NamingException ne){Debug.P("Naming Exception"+ne.getMessage());}
catch (javax.ejb.CreateException ce){Debug.P("Create Exception"+ce.getMessage());}
catch (javax.ejb.FinderException fe){Debug.P("Finder Exception"+fe.getMessage());}
}When I run it, I get the following Naming Exception: Course not found
I confirmed at the administrative console, that I have "Course" listed
under Enterprise Applications:
As per the ejb FAQ, I set up my $CLASSPATH so it starts as follows:
/opt/j2ee/SUNWappserver/lib/appserv-rt.jar:
/opt/j2ee/SUNWappserver/lib/javaee.jar:I also verifed in my domain.xml that the orb-listener-1, the default
naming service port was at 3700.
Here is the info on the Bean that I have running for both of the tries
at my Client code.
ejb-jar.xml
<?xml version="1.0" encoding="ISO-8859-1"?>
<ejb-jar xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/ejb-jar_2_1.xsd"
version="2.1">
<enterprise-beans>
    <entity>
       <description>Course</description>
       <display-name>CourseBean</display-name>
       <ejb-name>CourseBean</ejb-name>
       <home>RS.CourseHome</home>
       <remote>RS.Course</remote>
       <ejb-class>RS.CourseBean</ejb-class>
       <persistence-type>Container</persistence-type>
       <prim-key-class>RS.CoursePK</prim-key-class>
       <reentrant>false</reentrant>
       <abstract-schema-name>Course</abstract-schema-name>
       <cmp-field><field-name>number</field-name></cmp-field>
       <cmp-field><field-name>name</field-name></cmp-field>
    </entity>
</enterprise-beans>
<assembly-descriptor>
     <security-role>
        <description>Everyone</description>
       <role-name>everyone</role-name>
     </security-role>
     <method-permission>
        <unchecked/>
        <method>
           <ejb-name>CourseBean</ejb-name>
           <method-name>*</method-name>
        </method>
      </method-permission>
     <container-transaction>
        <method>
           <ejb-name>CourseBean</ejb-name>
           <method-name>*</method-name>
        </method>
        <trans-attribute>Required</trans-attribute>
     </container-transaction>
</assembly-descriptor>
</ejb-jar>
Sun-ejb-jar.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sun-ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Application Server 8.1 EJB 2.1//EN"
"http://www.sun.com/software/appserver/dtds/sun-ejb-jar_2_1-1.dtd">
<sun-ejb-jar>
<enterprise-beans>
     <name>CourseBean</name>
     <ejb>
       <ejb-name>CourseBean</ejb-name>
       <jndi-name>Course</jndi-name>
     </ejb>
<cmp-resource>
     <jndi-name>jdbc/__default</jndi-name>
     <create-tables-at-deploy>true</create-tables-at-deploy>
     <drop-tables-at-undeploy>true</drop-tables-at-undeploy>
</cmp-resource>
</enterprise-beans>
</sun-ejb-jar>
Course.java
package RS;
import java.rmi.RemoteException;
public interface Course extends javax.ejb.EJBObject {
public String getName() throws RemoteException;
public void setName (String Str) throws RemoteException;
public int getNumber() throws RemoteException;
public void setNumber (int n) throws RemoteException;
CourseHome.java
package RS;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.FinderException;
public interface CourseHome extends javax.ejb.EJBHome {
public Course create(int id) throws
CreateException,RemoteException;
public Course findByPrimaryKey(CoursePK pk)
throws FinderException,RemoteException;
CourseBean.java
package RS;
import javax.ejb.EntityContext;
public abstract class CourseBean implements javax.ejb.EntityBean {
public CoursePK ejbCreate (int number) throws javax.ejb.CreateException{
this.setNumber(number);
return null;
public void ejbPostCreate (int number) {
public abstract String getName();
public abstract void setName (String str);
public abstract int getNumber ();
public abstract void setNumber (int number);
public void setEntityContext (EntityContext ctx) {}
public void unsetEntityContext() {}
public void ejbActivate () {}
public void ejbPassivate () {}
public void ejbLoad () {}
public void ejbStore () {}
public void ejbRemove() {}
}Laurence L. Leff, Ph.D. Associate Professor of Computer Science
Western Illinois University, 1 University Circle 61455, Pager: 309 367 0787
FAX 309 298 2302

hi s-mcgowan,
"some other processing" comprises of printing of debug lines and publishing to the message queue using JMS. I added more debug lines so that i could see whats really happening... here is the result
myTableHome.create(...); <----------- no exception was thrown and it returned LocalMyTable object
print out "Insert successful"
print out "publishing message"
... publish message to message queue using JMS...
print out "Publish done"
... after few milliseconds...
java.sql.BatchUpdateException: Data exception -- row already exist in index PK_MYTABLE on table MYTABLE.
From the exception it seems like its doing a batch insert. So that seems to explain why the java.sql.BatchUpdateException is thrown few milliseconds after my call to myTableHome.create(...);
Is it possible to disable batch update / insert? how?
thanks in advance,
leigh

Urgent: Can't lookup entity bean

Dear all,
I define a business process in workflow engine, which invoke a java class to get
DB data through CMP entity bean. The entity bean was packed in to a ear and was
workable/callable within the same ear.
However, when the workflow engine can't invoke the entity bean, the workflow engine
always throw exception as following.
javax.naming.LinkException: . Root exception is javax.naming.NameNotFoundException:
Unable to resolve 'app/ejb/ConsignmentEntityBean.jar#Consignments/local-home'
Resolved: 'app/ejb' Unresolved:'ConsignmentEntityBean.jar#Consignments' ; remaining
name 'ConsignmentEntityBean.jar#Consignments/local-home'
I think the problem may occur in deployment/configuration. Since the problem is
very urgent, anyone can help me? To all developers, How do you package/deploy
Entity Bean in Integration Server?
Thx,
Philip

I solved this.
Since I was testing the action code only, I didn't define a navigation entry corresponding to the action string returned for this button:
<h:commandButton value="Add" style="height:21px; width:51px;font-size:8pt; font-color: black;" action="#{resourceBean.addAction}">
</h:commandButton>After I added a nav definition, it worked. I don't know why at this point. I suspect a key step in the lifecycle was pre-empted...someone else can probably explain why. If I get a chance to research it after I'm done with my project, I'll update this post.
Thanks.
-L

Problems accessing ejb 3.0 entity bean from project

I have written some code using ejb 3.0 and was previously accessing the entity bean without problem when both ejbs and the accessing code were in the same project. However I have moved the accessing code into a different project within the same application and now when the code tries to accessing the entity bean I get the following error:
com.colwilson.web.ingestion.IdentifiedException: java.lang.ClassCastException: __Proxy3
     at com.colwilson.web.ingestion.IngestionHandler.recordArrived(IngestionHandler.java:140)
     at com.colwilson.web.ingestion.IngestionHandler.main(IngestionHandler.java:52)
Caused by: java.lang.ClassCastException: __Proxy3
     at com.evermind.server.ejb.StatelessSessionRemoteInvocationHandler.getFreshObject(StatelessSessionRemoteInvocationHandler.java:21)
     at com.evermind.server.rmi.RecoverableRemoteInvocationHandler.getReplacementObject(RecoverableRemoteInvocationHandler.java:64)
     at com.evermind.server.rmi.RecoverableRemoteInvocationHandler.handleRecovery(RecoverableRemoteInvocationHandler.java:41)
     at com.evermind.server.rmi.RecoverableRemoteInvocationHandler.invoke(RecoverableRemoteInvocationHandler.java:30)
     at com.evermind.server.ejb.StatelessSessionRemoteInvocationHandler.invoke(StatelessSessionRemoteInvocationHandler.java:43)
     at __Proxy1.mergeEntity(Unknown Source)
     at com.colwilson.web.ingestion.IngestionHandler.recordArrived(IngestionHandler.java:137)
     ... 1 more
Now, of course I could move the code back into the same project, but as I understand it that is just the point of ejbs. I'm looking up the entity bean thus:
final Context context = InitialContext();
ingestionSessionEJB =
(IngestionSessionEJB)context.lookup("IngestionSessionEJB");
It may be true that I don't understand the way lookup works, but to be honest I can't find the docs that explain what I've got wrong.
Please help.

hi
Double Click on the project which is goin to use the project which contains bean from the Application Navigator window. The project properties window will open. Choose the "Dependencies" item from left panel. click on the radio "User Project Settings" and select another project which contain ejb which you're goin to access...
Best Of Luck
Ravi A. Trivedi

Query about reentrant in ejb-jar.xml file(in case of entity Bean)

Hi all friends,
I am new to EJB I couldn't understand in ejb-jar.xml file in case Entity Bean[<reentrant>False</reentrant>
&<reentrant>true</reentrant>]what is the function of this tag and what is the effect of value true and false of this tag.Can any one please explain it.
Regards
Bikash

Hi,
Re-entrant tag is used in the ejb-jar.xml to notify the container if you would want your bean to call itself through another bean.
Most of the time you would want it to be set to FALSE because you would have to consider the multi-threading issues if you set it TRUE.
Regards
Meka Toka

Compund primary key in entity bean

hi,
can somebody please explain how to use the compound primary key in entity beans? i have got a database table, the key of which consists of three fields, which I assign as PK when setting up the entity bean. In turn I get a compoundPK class, but without get/set-methods - is it necessary to write own get/set-methods within this class?
In the bean class itself I get a compundPK-create() method - but what is the use of it? actually, in my findByPK-method I need the PK already.
Hints appreciated - btw, help.sap.com is not very helpful in this case...
regards, matthias

WebLogic Server supports mapping a cmr field to the primary key.

Strange Session/Entity Bean Cross-Instance Calls in Cluster

In one of our enviroments, we are seeing session entity bean cross-instance
          calls that are hard to explain. The following is our configuration:
          The cluster contains 4 instances on 2 machines (2 on each machine). The same
          beans are deployed to each instance. "jndi.properties" is on the classpath
          for the each instance with jndi provider url = mach1inst1-ip, mach1inst2-ip,
          mach2inst1-ip, mach2inst2-ip:70001. Same servlets are also deployed to each
          instances.
          Requests from the web are load balanced through weblogic's proxy plugin for
          IPlanet and are forwarded to the 4 weblogic cluster instances. The servlet
          processing the requests calls a stateless session bean which uses an entity
          bean. The entity bean is configured with "home-is-clusterable" set to
          "false".
          What we have observed is that when all 4 instances are up, sometimes (even
          when the load is not high) the session bean is accessing entity bean from an
          instance on one machine to an instnace on another machine, while if only one
          machine (with 2 instances) is up, we don't see such calls.
          My theory is that because the jndi provider url is the same for all
          instances, the jndi lookup from each instance goes to the instance bound to
          the first IP specified in the provider url: machine 1 istance 1. If the
          request is from machine 2, because of co-location optimization, even though
          the home stub is from machine 1 instance 1, the session bean returned from
          the home stub actually is from machine 2. However, when the session bean
          does jndi lookup to get an entity bean home, the home stub is from machine 1
          and instance 1. And unfortunately, because the entity bean home is not
          clusterable, the stub can only point back to machine 1, co-location can not
          work. Thus entity bean from machine 1 is referenced by the session bean
          located on machine 2. I do not have a chance to verify this. But it seems to
          make sense to me.
          Unfortunately, I don't feel that I have a theory to explain why we don't see
          cross instance session entity bean calls when only 1 machine is up (with 2
          instances).
          Any ideas or hints would be greatly appreciated.
          Thanks,
          David Chen


rs = stmt.executeQuery() , insert statement is not a query. So use executeUpdate.

Using a CMP Entity Bean local stub as a field of another CMP Entity Bean

Hello,
Is it possible to implement a field of a CMP Entity bean as another CMP Entity bean and how is it done?
I've seen a pseudo code for this in Ed Roman's Mastering EJBs, second edition, but I can't seem to get it to work (pages: 330 - 1:1 using CMP and 339 - fake M:N using CMP).
I'm using SUN ONE Application Sever 7. Is this server capable of this?
I'm trying to implement a fake M:N relationship using 3 beans: 2 for each side of the relationship and one as the "bridge" table.
For example, the two beans on each side of the relationship are SubscriberBean, SubscriptionBean and the "bridge: bean is SubscriberSubscriptionBean. The SubscriberSubscriptionBean has two fields: SubscriberLocal stub and SubscriptionLocal stub.
Please let me know if you need more information to answer this question.
Thanks.
Nikola

Im sorry but i dont know about the example you are talking about. I kinda learn
all those techniques from forums, articles and tutorials because book often suffer from
not having the information im mostly looking for.
As far as i understand you, you want to implement a bridge been, which is representing a row in a join table. So that if one side of the relation is deleted the join-table entry (your bridge-CMP-Bean) is cascaded. Right?
First of all the simple part: (My approach)
- The joint table is foreign keys only - without a relation description. -
In this case you dont have to implement a bridge bean. Because it just wouldnt represent anything of sense.
Lets think of an entity/table USER whith the columns name (PRIMARY KEY), and prename.
Our second entity/table is ADDRESS with the columns road (PRIMARY KEY) and housenr.
The join table is simply: USER_ADDRESS with fk_name (FOREIGN KEY) and fk_road (FOREIGN KEY) both on CASCADE DELETE. So if the address is deleted the mapping entry is deleted, too same for the user part:
USER -> USER_ADDRESS <- ADDRESS.
Our entity Beans are called User and Address in class-names JNDI-names and names.
Now we want to create the CMR mapping so we can access the addresses of a user from the user bean directly. The methods on the user side are:
public abstract Collection getAddresses();
and
public abstract void setAddresses(Collection new_addresses);
the xdoclet comments on the User side are (for the getter only)
* @ejb.interface-method
* @ejb.relation
*                name = "User-has-Addresses"
*                role-name = "User-Addresses"
*                target-ejb = "Address"
*                target-multiple = "true"
* @sunone.relation
*                column="USER_ADDRESS.fk_name"
*                target="USER_ADDRESS.fk_road"
public abstract Collection getAddresses();
for the other side of the relation we define in the Address-Entity
public abstract Collection getUsers();
and
public void setUsers(Collection users);
the xdoclet comments on the Address side are (for the getter only)
* @ejb.interface-method
* @ejb.relation
*                name = "User-has-Addresses"
*                role-name = "Address-User"
*                target-ejb = "User"
*                target-multiple = "true"
* @sunone.relation
*                target="USER_ADDRESS.fk_road"
*                column="USER_ADDRESS.fk_name"
As we dont want the user or address to be deleted if the other side of the relation is deleted we dont specify cascade-delete="yes" in the ejb.relation namespace.
The sun-cmp-mappings.xml should now look like this:
(For the User - side)

<cmr-field-mapping>
<cmr-field-name>addresses</cmr-field-name>
<column-pair>
<column-name>USER_ADDRESS.fk_name</column-name>
<column-name>USER_ADDRESS.fk_road</column-name>
</column-pair>
</cmr-field-mapping>
and similar on the Address-Side:
<cmr-field-mapping>
<cmr-field-name>users</cmr-field-name>
<column-pair>
<column-name>USER_ADDRESS.fk_road</column-name>
<column-name>USER_ADDRESS.fk_name>/column-name>
</column-pair>
</cmr-field-mapping>
Dont forget that all elements in the Collection must be of the right Interface-type.
First of all the harder part:
Now what you might want is when the relation has some information specified like user live at address and is tenant or facility manager.
The, in the first step you will have to implement the UserAddressRelation entity which will have to CMR fields of the 1:N type.(Just as you wish)
Lets think of the example above extended by the relation type. Our relation bean is named UserAddressRelation.
Now User has the methods as above but the classes in the Collection must now be of the UserAddressRelationLocal/Remote interface and not AddressLocal/Remote-interface.
You will have to change the xdoclet comment to:
* @ejb.interface-method
* @ejb.relation
*                name = "User-has-Addresses"
*                role-name = "User-Address"
*                target-ejb = "UserAddressRelation"
*                target-multiple = "true"
* @sunone.relation
*                target="USER_ADDRESS.fk_name"
*                column="USER.name"
So we now dont reference the other side bean directly. We reference the relation EntityBean. Do the similar changes on the other side.
In particular you will have to specify 4 CMR mappings now:
1. User to UserAddressRelation 1:N
2. UserAddressRelation N:1
3. Address to UserAddressRelation 1:N
4. UserAddressRelation N:1
Which i dont want to explain in detail now because its kinda all the same as above.
Now you cann access the Addresses of a user in the way.
UserLocal.getAddresses(); <- !you get the mappings!
UserLocal.getAddresses().item(0).getAddress() <- you get the address (this is dirty coding just for understanding)
UserLocal.getAddresses().item(0).getUserRole() <. you get the role of the user at this address.
Hope this helped you. You are welcome to ask any detailed question.

Entity Beans and Session beans to represet Business lOgic

How cam we implement Entity Beans and Session beans to represent Business Logic.
Can anyone explain how can we do this.
Regards...

I have session beans calling method in entity beans and any client
doesn't have access to entity beans, only via session beans.
If i define security policy and method permissions for session beans
only, do entity beans use that permissions when calling their methods
from sessions beans OR should i define the security policy for entity
beans separately?If you want to set the permission on individual
methods of entity bean ( with different roles)
you have to do it separately.
If you want to delegate the Authenticated user along with
the method call to the Entity Bean you can use
run-as-identity-principal.
For more detail please check out the EJB2.0 Spec.
-utpal

Urgent!Poor performance in Entity beans

we're using Weblogic 5.1, Oracle 8i.(both installed in Solaris 5.8) We
found that the performance of our entity beans is poor, the reason we
guess is because when we issue a select statement, the jdbc, at the same
time, issue a update statement, that's why the response time is slow.
(By the way,we use oracle thin driver to connect.)
I know we can set autocommit to false but our beans are cmp,so we can't
set properties in connection pool.What can we do then?Can we set any
transaction attributes in our ejb,so we can solve our problem?
Thx!
Pete

A few issues with the linked article:
" 1. Where ever possible, using Entity bean with CMP over Entity bean with BMP, will ensure increase in performance... Tuned CMP entity beans offer better performance than BMP entity beans."
Bull. Every time I have seen some statement like the above it has never contained any associated proof nor explaination of how a container vendor's code can interact with a DB any better than mine.
The only means by which a container vendor can generically improve the performance of DB interactivity is to not do it, namely by caching the data and monitoring modification. This is rarely used due to mitigating factors such as any case where the container does not have sole access and omniscience over the DB.
"Moving towards the CMP based approach provides database independence since it does not contain any database storage APIs within it."
Ahh yes, lets trade in EJB container independence for database independence. It's interesting that the biggest proponents of CMP (and the ones who pushed it into the spec) are the biggest container vendors. Database storage APIs??? Perhaps JDBC and "select * from USER where..." are somehow viewed as database specific.

Passivation in entity bean

statement
In an entity bean, passivation includes releasing resources as well as pushing back the data it is
holding to the underlying database prior to the passivation process.
Hi, when i read stateful session bean the author mentioned about passivation because the stateful bean must have to store the conversational states of many clients. so the bean pushes the data to the secondary stoarge (disk) for future use, if at some time any client needs them the bean could use those states.... thats passivation.
but in Entity bean, i see author also talking about passivation. though author did not explain much. the entity bean is already using a permanent storage . why they need any secondary storage which is meant for passivation ?
because here activation means grabbing data from underlying DB. How does passivation helps here ?

Just a guess - I have no idea about EJBs:
Could it be that passivaion in this case simply means "performing the stuff that's needed for an entity bean to be persistent"? An entity bean IIRC represents a persistent set of data, which means that at one point in time, the data must be stored (written to DB) to be accessible later. That'd mean "passivation" is simply a name for an entity bean's normal behavior.

Using oracle db sequence for auto generating of PKs for CMP entity beans

Hi,
I have read quite a number of threads about (auto) generation of keys for primary keys for the CMP entity beans.
My requirement is I am migrating an application deployed on Weblogic to oc4j. The application is using cmp entity beans with auto key generation using a sequence in the Oracle db. This is specified in weblogic-cmp-rdbms-jar.xml file like below:
<automatic-key-generation>
<generator-type>Oracle</generator-type>
<generator-name>REPUSER.DEPT_REPORT_SEQ</generator-name>
<key-cache-size>1</key-cache-size>
</automatic-key-generation>
In the ejb-jar.xml, it is specified as:
<prim-key-class>java.lang.Integer</prim-key-class>
<primkey-field>id</primkey-field>
Now, I need to migrate this to oc4j. Can somebody suggest me options and clarify my questions kindly?
1) I have read articles that say that in the ejb-jar.xml, we need to specify <prim-key-class>java.lang.Object</prim-key-class> and this will create a column called 'autoid' in the respective entity table in the Oracle db.
- How can I use this to assign the value to my primary field, say, id?
2) Now, with the latest oc4j, can I use Oracle database sequence as the key generator for the values of the PKs just by specifying in the xml descriptor ejb-jar.xml?
2.a) If yes, is there any article that explains with the code?
2.b) If no, what are the alternatives I have?
I have read many discussions that say that we can create a stateless session bean that can lookup the database sequence using simple JDBC call to return the nextval of the sequence. The SSB should be called in the ejbCreate() of the entity bean.
My related question is, what is recommended for oc4j? What are limitations of the various options for the latest oc4j available?
How should I go about deploying this kind of ejbs in oc4j?
Any help and pointers are welcome. Please help.
Thanks a lot.
Vadi

Hello ,
Instead of exposing a get/set method for each arribute of your bean (corresponding to database table) expose only one object.
For example
public class CustomerBean implements javax.ejb.EntityBean{
private CustomerVO objCustomer;
private String customerName;
private String customerMail;
private String customerType;
public CustomerVO getCustomer(){
return this.objCustomer;
public void setCustomer(CustomerVO objCustomer){
this.objCustomer = objCustomer;
public void ejbStore(){
customerName = objCustomer.getName();
customerMail = objCustomer.getMail();
customerType = objCustomer.getType();
HTH
VJ

Basic difference between stateful and entity beans???

Could anyone please explain the basic diff between stateful bean and an entity bean.as per my understanding,stateful beans are extensions to clients.they perform a job of a client and they r not persistent.also their state goes off when the server crashes or the machine is reeboted.while in contrast,an entity bean can retain its session coz' they represent a persistent field in the DB.What i have seen in few books(O'reilly,etc)where a session bean can insert some values into the DB,which means it also represents a persistent object in the DB,which contradicts the statement that "stateful session beans dont represent any persistent object in the DB".Could anyone please elaborate on this.Thanks in advance.
Jameel

Thank u very much crackers for ur valuable
suggestions.I'll throw a different one in here for free: clarity of writing is a highly-valued and useful skill in a software professional. This is especially true these days when concepts need to be clearly explained to a variety of technical peoples from all over the world. And then there's the other side of the coin: Management.
You have to get your thoughts across in a very precise manner and, unfortunately for those who have to learn it as a second lanugage, English seems to be the overall preferred medium. Which makes it even more important to use "correct" English in written communications. If you don't, your credibility diminishes and you appear to be (horrors!) unprofessional It's not that much harder to type "you" than it is to use a single letter. Besides, most people that "pay by the byte" appreciate the clarity, as well (as I've seen on Usenet, by way of covering my ass).
Now, back to our regularly scheduled post...
Is this wat u were trying to say if i
understood u correctly.Yes, the EntityBean is directly related to the data being persisted: in this case, a database table. So, using your example from below, the DB table would have two fields: a VARCHAR 'Name' and an INT 'Age.' The EntityBean would have corresponding fields/properties/variables, String name and int age.
"WHICH BEAN (Entity
or Sateful Session) SHOULD I GO 4???"No easy answer. The best one is: it depends. On what? It depends upon what you're trying to do with the data, how it's presented/manipulated, load requirements, environmental requirements, caching strategies, and about another dozen or so other high-level requirements.
My personal preference is if I need caching and the number of EntityBeans actually in existence is pretty "low" (another nebulous and arbitrary value, depending), I'll use a StatelessSessionBean as a Facade (search for "patterns" here in the forum), with the persistence in CMP EntityBeans. Which is influenced by the fact that I like playing with CMP. ;D

Questions about entity bean caching/pooling

We have a large J2ee app running on weblogic6.1 sp4. We are using entity beans
with cmp/cmr. We have about 200 EntityBeans and accessed quite heavily. We are
struggling with what is the right setting of max-beans-in-cache and idle-time-out.
The current max heap setting is 2GB. With the current setting (default setting
of max-beans-in-cache to 1000, with a few exceptions to take care of cachefullexceptions)
we run into extended gc happening after about 4 hours. The memory freed gradually
reduces with time and lurks around the 30% mark after about 4 hours of run at
the expected load. In relation to this we had the following questions
1. What does caching mean?
a. If a bean with primary key 100 exists in the cache, and the following
is done what is expected
i. findByPrimaryKey(100)
ii. findBySomeOtherKey(xyz)
which results in loading up bean with primary key 100
iii. cmr access to bean with
primary key 100
Is the instance in the cache reused at all between transactions?
If there is minimal reuse of the beans in cache, Is it fair to assume that caching
can only help loading of beans within a transaction. If this is the case, is there
any driver to increase the max-beans-in-cache other than to avoid CacheFullException?
In other words, is it wrong to say that max-beans-in-cache should be set to the
minimum value so as to avoid CacheFullExceptions.
2. Again what is the driver of setting idle-time-out to a value? ( We currently
have it at 30 secs) Partly the answer to this question would again go back to
what amount of reuse is done from cache? Is it right to say that it should be
set to a very low value? (Why is the default 10 min?)
3. Can you provide us any documentation that explains how all this works
in more detail, particularly in relevance to entity beans. We have already read
the documentation from weblogic as is. Anything to give more explicit detail?
Any tools that can be of use.
4. What is the right parameter (from among the things that weblogic console
throws up) to look at for optimizing?
Thanks in advance for your help
Cheers
Arun

The behaviour changes according to these descriptor settings: concurrency-strategy,
db-is-shared and include-updates.
1. If concurrency-strategy is Database, then the database is used to provide locking
and db-is-shared is ignored. A bean's ejbLoad() is called once per transaction,
and the 'cache' is really a per-transaction pool. A findByPrimaryKey() always
initially hits the db, but can use the cache if called again in the same txn (although
you'd simply just pass a reference around). A findByAnythingElse() always hits
the db.
2. If concurrency-strategy is ReadOnly then the cache is longer-term: ejbLoad()
is only called when the bean is activated; thereafter, the number of times ejbLoad()
is called is influenced by the setting of read-timeout-seconds. A findByPrimaryKey()
can use the cache. A findByAnythingElse() can't.
3. If concurrency-strategy is Exclusive then db-is-shared influences how many
times ejbLoad() is called. If db-is-shared is false (i.e. the container has exclusive
use of the underlying table), then the ejbLoad() behaviour is more like ReadOnly
(2. above), and the cache is longer-term. If db-is-shared is true, then the ejbLoad()
behaviour is like Database (1. above).
Exclusive concurrency reduces ejbLoads(), increases the effectiveness of the cache,
but can reduce app concurrency as only one instance of an entity bean can exist
inside the server, and access to it is serialised at the txn level.
You can't use db-is-shared = false in a cluster. So Exclusive mode is less useful.
That's when you think long and hard about Tangosol Coherence (http://www.tangosol.com)
4. If include-updates is true, then the cache is flushed to the db before every
non-findByPrimaryKey() finder call so the finder (which always hits the db) will
get the latest bean values. This overrides a true setting of delay-updates-until-end-of-tx.
The max-beans-in-cache setting refers to the maximum number of active beans (really
beans that have been returned by a finder in a txn that hasn't committed). This
wasn't checked in SP2 (we have an app that accidently loads 30,000 beans in a
txn with a max-beans-in-cache of 3,000. Slow, but it works, showing 3,000 active
beans, and 27,000 passivated ones...).
This setting is checked in SP5, but I don't know about SP4. So you do need to
size appropriately.
In summary:
- The cache isn't nearly as useful as you'd like. You get far more db activity
with entity beans than you'd like (too many ejbLoads()). This is disappointing.
- findByPrimaryKey() finders can use the cache. How long the cache is kept around
depends on concurrency-strategy.
- findByAnythingElse() finders always hit the db.
WebLogic 8 tidies all this up a bit with a cache-between-transactions setting
and optimistic locking. But I believe findByAnythingElse() finders still have
to hit the db - ejbql is never run against the cache, but is always converted
to SQL and run against the db.
Hope this is of some help - feel free to email me at simon-dot-spruzen-at-rbos-dot-com
(you get the idea!)
simon.

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