2 introduction toentitybeans

Session 2

EJB
Creating First Entity
Bean

Introduction to Entity Bean
1. Entity Bean is something which represents data in persistence store (I
mean any persistence store, like database, files etc). For e.g. row in
database.

2. We can also say that, entity bean is object representation of persistence
store. For e.g. refer below fig.

Customer Table

ID : 42

ID

First_Name

City

First : John

42

John

California

87

Lin

Barcelona

65

Tom

Yugoslavia

Entity Bean

City : California

ID : 87
First : Lin
City : Barcelona

Entity Bean

Introduction to Entity Bean
1. There are 2 different things, say Entity & Entity Bean
2. Entity is real thing that entity bean represents, means entity is the
actual row in database.
3. If you delete the entity (row in database), the entity bean disintegrates.
4. And if entity bean dies on heap, it does delete entity (row in db).

Operations on Entity
1. Create new entity (SQL Insert)

2. Delete a entity (SQL Delete)
3. Update entity set (SQL Update)
4. Search/query on entities (SQL Select)

Creating Entity Bean
1. Lets create a sample entity bean.
2. I assume that you have basic understanding of ejb & you already created
sample Session bean. If not, then go back & refer Session-1 slide. That
will give you proper understanding of this session.
3. Let assume you have Customer table in database with ID, first_name &
city.
4. Where Id is your primary key. (notice ID-Primary Key here it is very
important in entity bean)
Customer Table

ID

First_Name

City

42

John

California

87

Lin

Barcelona

65

Tom

Yugoslavia

Rules for Building a Entity Bean
As you already created session bean (in 1st session), we
follow same steps to create entity bean
• Code to interfaces for bean (component & home)
• Code the bean class with all business method
• Create XML Deployment Descriptor, must be
name it as ejb-jar.xml
• Deploy bean in application server

Creating Component Interface
Component interface rules are simple & same as session bean

1. Component interface must extends EJBObject.
2. The component interface contains declarations of all
business mth which is to be defined by Bean class.
3. Its all mth must throws RemoteException
4. They can also thorws custom application (Checked)
Exception.
5. Its return type must be primitives/Serializable
Objs/Arrays/Collection of primitives or Serializable
Objs/Remote obj (These are called as RMI-IIOP
Complients).
6. In our case lets say we write business method which prints
customer data on console.

Component Interface Customer.java

package com.entity;

import javax.ejb.*;
import java.rmi.*;
public interface Customer extends EJBObject{

}

public void printCustomerData() throws
RemoteException;

Creating the Entity Bean Home Interface
The Home interface rules are Simple
1. Home interface must extends EJBHome

2. You can have multiple overloaded create() mth in home.
3. Your create method must throws CreateException & RemoteException.
4. You are required to put at least one finder mth for an entity bean home.
5. You can have many finder mth in home, but you must have
findByPrimaryKey(String key) mth in every home.
6. Your findByPrimaryKey(String key) mth must throws FinderException
7. The return type must be Component interface (in home interface only).
8. I am not including all entity points here as it may lead to lots of
confusion
9. Lets code the home interface

Home Interface CustomerHome.java
package com.entity;
import javax.ejb.*;
import java.rmi.*;
public interface CustomerHome extends EJBHome {
public Customer create(String astrName,String astrCity)
throws CreateException, RemoteException;
public Customer findByPrimaryKey(String
customerID) throws FinderException,
RemoteException;

}

Creating Bean Class CustomerBean.java
Rules for creating Entity Bean is simple but little different
from Session bean
1. Your bean class (which contains the actual definition of mth
or says business logic) must implements EntityBean
interface according to spec
2. According to java rule you have to implements all
unimplemented mth from interface
3. The printCustomerData() is your actual business mth, which
will be called by client
4. You need to implement create(String astrName,String
astrCity) which is coming from home interface.
5. We create this bean class part by part. Lets create bean
class with above mentioned details

Creating Bean Class CustomerBean.java
public class CustomerBean implements EntityBean{

private String customerId;
private String first_name;
private String city;

public void printCustomerData() {
System.out.println(this.customerId+""+this.first_name+"-"+this.city);
}

Implementing ejbCreate()
1. We have create() mth in home, this mth must be implemented by
bean class as ejbCreate().
2. The return type of ejbCreate() mth (not create() mth) must be
primary key class (we will see more about primary key class in next
few slides).
3. The ejbCreate() mth is responsible for creating the row in
database, that’s why it return type is primary key class.

4. The ejbCreate() mth must throws CreateException.
5. The return & argument type must be RMI-IIOP complient.
6. You also need to implement ejbPostCreate() which is same as
ejbCreate(). This mth invoke after ejbCreate so that you can get
chance to do any other stuff after database row creation.
7. For now I am providing empty definition of this mth.

public String ejbCreate(String astrName,String astrCity) throws CreateException{
this.first_name = astrName;
this.city = astrCity;
this.customerId = this.getPK();
String insertQry = "insert into customer (customer_id,first_name,city) values (?,?,?)";
try{

Connection conn = getDBConnection();
PreparedStatement ps = conn.prepareStatement(insertQry);
ps.setString(1,this.customerId);
ps.setString(2,this.first_name);
ps.setString(3,this.city);
int i = ps.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw new CreateException(e.getMessage());
}
return customerId;
}

public void ejbPostCreate(String first,String city)throws CreateException{
}

private String dbName = "jdbc.test.entity";
public Connection getDBConnection(){
Connection conn = null;
try{
InitialContext ic = new InitialContext();
DataSource ds = (DataSource) ic.lookup(this.dbName);
conn = ds.getConnection();
}
return conn;
}
public String getPK(){
return ""+(int)(Math.random()*32);
}

Implementing EntityBean mth
1.

You also need to implements below EntityBean interface mths
ejbActivate()
ejbLoad()
ejbPassivate()
ejbRemove()
ejbStore()
setEntityContext(EntityContext ctx)
unsetEntityContext()

2.

Three mth are very important for entity bean point of view, they are
ejbLoad(), ejbStore() & setEntityContext().

3. setEntityContext() is called when you create the bean, it is best chance to to
save your context object.
4. This EntityContext object is responsible for giving you primaryKey.
5. You use this object in ejbStore() & ejbLoad() (we will see this in next few
slides).
6. The other methods are also important but I not able cover all of them.

private EntityContext ctx;
public void setEntityContext(EntityContext ctx) throws EJBException,
RemoteException {
this.ctx = ctx;
}
public void unsetEntityContext() throws EJBException,
RemoteException {}
public void ejbActivate() throws EJBException, RemoteException {}

public void ejbPassivate() throws EJBException, RemoteException {}
public void ejbRemove() throws RemoveException, EJBException,
RemoteException {}

1.

ejbLoad() is called before calling any business mth, so that bean get chance
to synchronize its state with database.

2. So what do you think what should be in ejbLoad()???
3. Yes, ejbLoad() mth should contain the select data statement from database.
4. But how you get the particular row from database, if you don’t have primary
key?
5.

Remember we already set EntityContext object in setEntityContext() mth.

6.

Confuse!!! Check the next slide.

public void ejbLoad() throws EJBException, RemoteException {
String cust_id = (String)this.ctx.getPrimaryKey();
ResultSet rs = null;
String selectQry = "Select customer_id,first_name,city from Customer
where customer_id=?";
try{
PreparedStatement ps = conn.prepareStatement(selectQry);
ps.setString(1,cust_id);
rs = ps.executeQuery();
if(rs.next()){
this.customerId = rs.getString(1);
this.first_name = rs.getString(2);
this.city = rs.getString(3);
}
}
}

1.

As ejbLoad() is called before calling any business mth, the same way
ejbStore() is called after calling business mth.

2. The reason is same to stay sync with database.
3. So what do you think what should be in ejbStore()???
4. Yes ejbStore() mth should contain the update data statement for database.

5. You might confuse why ejbStore() call after business mth.
6. The answer is simple, when client call any business mth, there is high
probability that business mth will change the state of bean.
7.

Confuse!!! next slide will give you a clear picture.

Client call buss mth
ejbLoad()

updateCustData()

ID : 42
First : John
City : California

updateCustData()
ID : 42
Select Data
from DB

First : John Dhere
City : California

ejbStore()
DB

ID : 42
Update Data

First : John Dhere

City : California

public void ejbStore() throws EJBException, RemoteException {

String udpateQry = "update Customer set first_name=?,city=?
where customer_id=?";
try{

}

PreparedStatement ps = conn.prepareStatement(udpateQry);
ps.setString(1,this.first_name);
ps.setString(2,this.city);
ps.setString(3,this.customerId);
ps.executeUpdate();
}

Implementing ejbFindByPrimaryKey() mth
1.

ejbFindByPrimaryKey() mth use to find the existing entity bean.

2. There are simple rules for ejbFindByPrimaryKey() mth
3.

You can have multiple overloaded mth in home & same implementation in bean
class.

4.

This mth usually take & return the primary key as argument & return type,
which is specified in ejb-jar.xml (we will see this in next few slides)

5.

This mth contains the select statement for bean which must return only one
row, i.e. this mth is single entity finder.

6. For multi entity finder there are other finder methods.

7. Now lets implement ejbFindByPrimaryKey() mth

Implementing ejbFindByPrimaryKey() mth
public String ejbFindByPrimaryKey(String custId){
String selectQry = "Select customer_id,first_name,city from
Customer where customer_id=?";
try{
PreparedStatement ps = conn.prepareStatement(selectQry);
ps.setString(1,custId);
ResultSet rs = ps.executeQuery();
if(rs.next()){
this.customerId = rs.getString(1);
this.first_name = rs.getString(2);
this.city = rs.getString(3);
}
}
return custId;
}

Binding all in ejb-jar.xml
1. Now lets bind all stuff together in ejb-jar.xml
2. As this is entity bean we use entity tag, for session bean we
use session tag.
3. We added three new tag i.e. <reentrant>,<prim-key-class> &
<persistence-type>

4. As we know we are returning primary key of database from
ejbCreate & ejbFindByPrimaryKey mths we must define
<prim-key-class> in DD (deployment descriptor) so that
container can understand this is primary key.
5. You can also create your custom primary key class & declare
in DD (in <prim-key-class> tag).

Sample ejb-jar.xml
<?xml version="1.0" encoding="UTF-8"?>
<ejb-jar xmlns="http://java.sun.com/xml/ns/j2ee" version="2.1"
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">
<enterprise-beans>
<entity>
<ejb-name>DemoCustomer</ejb-name>
<home>com.entity.CustomerHome</home>
<remote>com.entity.Customer</remote>
<ejb-class>com.entity.CustomerBean</ejb-class>
<persistence-type>Bean</persistence-type>
<prim-key-class>java.lang.String</prim-key-class>
<reentrant>false</reentrant>
</entity>
</enterprise-beans>
</ejb-jar>

Sample App Structure
•

Now you have to create the jar of all compiled class with
below structure, which is same as session bean example.
DemoCustomer-Entity.jar
com
entity
Customer.class
CustomerHome.class
META-INF

CustomerBean.class
ejb-jar.xml
glassfish-ejb-jar.xml

Deploying & Calling the Bean mth
•
•
•
•

You also need to create vendor specific DD, as I m using
glassfish server for app deployment so I have glassfish-ejbjar.xml
We will see the deployments of ejb & web application (part)
in later.
Now I am writing the plane jsp to call the Bean mth.
You need to deploy this jsp(war) file in glassfish & run the
jsp.

Client CustomerClient.jsp
<html>
<body>
<%
try{

InitialContext ic = new InitialContext();
Object obj = ic.lookup("DemoCustomerEntity");
Customer customer = home.create("John","California");
System.out.println("Customer Id : "+customer.getPrimaryKey());
customer.printCustomerData();

Customer customer = home.findByPrimaryKey("31");
System.out.println("Customer Id : "+customer.getPrimaryKey());
customer.printCustomerData();
}
%>
</body>
</html>

Thank you
• If you have any doubts in tutorial, please feel free to
contact me on ashishkirpan@gmail.com
• Sorry for spelling & grammar mistakes :)

Have a fun with EJB

2 introduction toentitybeans

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