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About Ilias Tsagklis

Ilias Tsagklis
Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

Reference EJB in another EJB of different applications

This is an example of how to create a reference of an EJB in another EJB of different applications. Enterprise beans are Java EE components that implement Enterprise JavaBeans (EJB) technology. Enterprise beans run in the EJB container, a runtime environment within the Application Server (see Container Types). Although transparent to the application developer, the EJB container provides system-level services such as transactions and security to its enterprise beans. These services enable you to quickly build and deploy enterprise beans, which form the core of transactional Java EE applications.

Here, we have created two EJB implementations, the CalculatorService and the EmployeeService that has a reference of CalculatorService that belongs to a different application, as described below:

The CalculatorService EJB implementation class

The CalculatorService is an EJB implementation class that is a stateless session bean that implements four methods. It is annotated with the javax.ejb.Stateless annotation. The class must have a default public constructor. The CalculatorService has a local interface that defines the bean’s business and life cycle methods, decorated with the @Local annotation. It also has a remote interface decorated with the @Remote annotation, that can run on a different machine and a different Java virtual machine (JVM) than the CalculatorService.

The CalculatorService EJB implementation class:

package com.javacodegeeks.snippets.enterprise;

import javax.ejb.Stateless;

@Stateless
public class CalculatorService implements CalculatorServiceLocal, CalculatorServiceRemote {

    public CalculatorService() {
    }

    @Override
    public long add(long i, long j) {

  return (i + j);
    }

    @Override
    public double divide(long i, long j) {

  return ((double)i / j);
    }

    @Override
    public long multiply(long i, long j) {

  return (i * j);
    }

    @Override
    public long subtract(long i, long j) {

  return (i - j);
    }
    
}

The Calculator service EJB local interface (suitable for in VM communication):

package com.javacodegeeks.snippets.enterprise;

import javax.ejb.Local;

@Local
public interface CalculatorServiceLocal {

    public long add(long i, long j);
    public long subtract(long i, long j);
    public long multiply(long i, long j);
    public double divide(long i, long j);
    
}

The Calculator service EJB remote interface (suitable for intra VM communication):

package com.javacodegeeks.snippets.enterprise;

import javax.ejb.Remote;

@Remote
public interface CalculatorServiceRemote {

    public long add(long i, long j);
    public long subtract(long i, long j);
    public long multiply(long i, long j);
    public double divide(long i, long j);
    
}

The application.xml file describing the modules in the Calculator application .ear archive:

<?xml version="1.0" encoding="UTF-8"?>
<application 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/application_1_4.xsd"


 version="1.4">
  <display-name>Calculator Application</display-name>

  <module>
     <ejb>calculatorServiceEJB3.jar</ejb>
  </module>

</application>

The structure of the .ear archive:

calculatorApp.ear
 |
 |_calculatorServiceEJB3.jar
 |   |_com
 |   |  |_javacodegeeks
 |   |     |_snippets
 |   |
  |_enterprise
 |   |
     |_CalculatorService.class
 |   |
     |_CalculatorServiceLocal.class
 |   |
     |_CalculatorServiceRemote.class
 |   |_META-INF
 |
 |_META-INF
    |_application.xml

The Data Transfer (Domain) object

Class Employee is an entity, that is a lightweight persistence domain object. Typically an entity represents a table in a relational database, and each entity instance corresponds to a row in that table. The persistent state of an entity is represented either through persistent fields or persistent properties. These fields or properties use object/relational mapping annotations to map the entities and entity relationships to the relational data in the underlying data store. The class is annotated with the javax.persistence.Entity annotation, it has a public or protected, no-argument constructor and it implements the Serializable interface.

package com.javacodegeeks.snippets.enterprise;

import java.io.Serializable;
import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Employee implements Serializable {
    
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String name;
    private String surname;
    private String title;
    private Double salary;
    private Date created;
    
    public Long getId() {

  return id;
    }
    public void setId(Long id) {

  this.id = id;
    }
    
    public String getName() {

  return name;
    }
    public void setName(String name) {

  this.name = name;
    }
    
    public String getSurname() {

  return surname;
    }
    public void setSurname(String surname) {

  this.surname = surname;
    }
    
    public String getTitle() {

  return title;
    }
    public void setTitle(String title) {

  this.title = title;
    }
    
    public Double getSalary() {

  return salary;
    }
    public void setSalary(Double salary) {

  this.salary = salary;
    }
    public Date getCreated() {

  return created;
    }
    public void setCreated(Date created) {

  this.created = created;
    }
    
    @Override
    public String toString() {

  return "Employee [id=" + id + ", name=" + name + ", surname=" + surname


    + ", title=" + title + ", salary="+salary+ ", created=" + created+"]";
    }

}

The EmployeeService EJB implementation class

The EmployeeService EJB implementation class is also an EJB implementation class that is a stateless session bean and has a reference of the CalculatorService EJB. It uses the javax.persistence.EntityManager interface, that creates and removes persistent entity instances, finds entities by the entity’s primary key, and allows queries to be run on entities. The EntityManager is annotated with the javax.persistence.PersistenceContext annotation to express a dependency on the container-managed EntityManager and its associated persistence context, using the name of the persistence unit as defined in the persistence.xml file. The SessionContext interface provides access to the runtime session context that the container provides for a session bean instance. It is annotated with the @Resource annotation, so that the container will inject an instance of the requested resource into the SessionContext when the SessionContext is initialized. The EmployeeService also has a local and a remote interface.

Using the lookup(Name name) API method of Context the EJB retrieves the CalculatorService, using its local interface. Then, its methods are used in the EmployeeService, so that an Employee object is created. Through the EntityManager API the Employee objects are written to and retrieved from the database.

package com.javacodegeeks.snippets.enterprise;

import java.util.Collection;
import java.util.Date;

import javax.annotation.Resource;
import javax.ejb.SessionContext;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

@Stateless
public class EmployeeService implements EmployeeServiceLocal, EmployeeServiceRemote {

    @PersistenceContext(unitName = "TutorialPU")
    EntityManager entityManager;
    
    @Resource
    SessionContext context;

    public EmployeeService() {
    }

    public Employee createEmployee(String name, String surname, String title, double salary) {

  // We inject a reference of an EJB declared at another application

  CalculatorServiceLocal calculatorService = (CalculatorServiceLocal) context.lookup("calculatorApp/CalculatorService/local");

  long tax = 100;

  double finalSalary = calculatorService.subtract((long)salary, tax);

  Employee employee = new Employee();

  employee.setName(name);

  employee.setSurname(surname);

  employee.setTitle(title);

  employee.setSalary(finalSalary);

  employee.setCreated(new Date());


  entityManager.persist(employee);


  return employee;
    }

    public void removeEmployee(long id) {

  Employee employee = findEmployee(id);

  if (employee != null) {


entityManager.remove(employee);

  }
    }

    public Employee promoteEmployee(long id, String newTitle, double newSalary) {

  Employee employee = entityManager.find(Employee.class, id);

  if (employee != null) {


// We inject a reference of an EJB declared at another application


CalculatorServiceLocal calculatorService = (CalculatorServiceLocal) context.lookup("calculatorApp/CalculatorService/local");


long tax = 100;


double finalSalary = calculatorService.subtract((long)newSalary, tax);


employee.setTitle(newTitle);


employee.setSalary(finalSalary);

  }

  return employee;
    }

    public Employee findEmployee(long id) {

  return entityManager.find(Employee.class, id);
    }

    public Collection<Employee> findAllEmployees() {

  Query query = entityManager.createQuery("SELECT e FROM Employee e");

  return (Collection<Employee>) query.getResultList();
    }

}

The Employee service EJB local interface (suitable for in VM communication)

package com.javacodegeeks.snippets.enterprise;

import java.util.Collection;

import javax.ejb.Local;

@Local
public interface EmployeeServiceLocal {

    public Employee createEmployee(String name, String surname, String title, double salary);
    public void removeEmployee(long id);
    public Employee promoteEmployee(long id, String newTitle, double newSalary);
    public Employee findEmployee(long id);
    public Collection<Employee> findAllEmployees();
    
}

The Employee service EJB remote interface (suitable for intra VM communication)

package com.javacodegeeks.snippets.enterprise;

import java.util.Collection;

import javax.ejb.Remote;

@Remote
public interface EmployeeServiceRemote {
    
    public Employee createEmployee(String name, String surname, String title, double salary);
    public void removeEmployee(long id);
    public Employee promoteEmployee(long id, String newTitle, double newSalary);
    public Employee findEmployee(long id);
    public Collection<Employee> findAllEmployees();
    
}

The persistence.xml file driving the JPA framework for the Employee application

<persistence xmlns="http://java.sun.com/xml/ns/persistence"


 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"


 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
  <persistence-unit name="TutorialPU" >

  <jta-data-source>java:/DefaultDS</jta-data-source>

  <properties>

   <property name="hibernate.hbm2ddl.auto" value="create-drop"/>

  </properties>
<!--
    <properties>

<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>

<property name="hibernate.hbm2ddl.auto" value="update"/>

<property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>

<property name="hibernate.connection.username" value="sa"/>

<property name="hibernate.connection.password" value=""/>

<property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
-->    
  </persistence-unit>
</persistence>

The application.xml file describing the modules in the Employee application .ear archive

<?xml version="1.0" encoding="UTF-8"?>
<application 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/application_1_4.xsd"


 version="1.4">
  <display-name>ExampleEJB3</display-name>

  <module>
     <java>exampleEJB3-persistence.jar</java>
  </module>

  <module>
     <ejb>exampleEJB3.jar</ejb>
  </module>

</application>

The structure of the Employee application .ear archive

exampleEJB3.ear
 |
 |_exampleEJB3-persistence.jar 
 |  |_com
 |  |  |_javacodegeeks
 |  |     |_snippets
 |  |
  |_enterprise
 |  |
     |_Employee.class
 |  |_META-INF
 |     |_persistence.xml
 |
 |_exampleEJB3.jar
 |   |_com
 |   |  |_javacodegeeks
 |   |     |_snippets
 |   |
  |_enterprise
 |   |
     |_EmployeeService.class
 |   |
     |_EmployeeServiceLocal.class
 |   |
     |_EmployeeServiceRemote.class
 |   |_META-INF
 |
 |_META-INF
    |_application.xml

A simple client example

In EmployeeServiceClient we connect to JBoss naming service running on local host and on default port 1099. We use the Context to set the configuration for the JBoss server, such as Context.INITIAL_CONTEXT_FACTORY, Context.PROVIDER_URL and Context.URL_PKG_PREFIXES. We get the EmployeeService EJB using the lookup(Name name) method of Context to invoke its methods.

package com.javacodegeeks.snippets.enterprise;

import java.util.Hashtable;

import javax.naming.Context;
import javax.naming.InitialContext;


public class EmployeeServiceClient {

    public static void main(String[] a) throws Exception {


  /*

   * Connecting to JBoss naming service running on local host and on

   * default port 1099 the environment that should be created is like the

   * one shown below :

   */

  Hashtable env = new Hashtable();

  env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");

  env.put(Context.PROVIDER_URL, "jnp://localhost:1099");

  env.put(Context.URL_PKG_PREFIXES, "org.jboss.naming:org.jnp.interfaces");

  

  Context ctx = new InitialContext(env);

  

  // We get a reference of the remote EJB interface to invoke its business methods

  EmployeeServiceRemote employeeService = (EmployeeServiceRemote) ctx.lookup("exampleEJB3/EmployeeService/remote");

  

  Employee employee = employeeService.createEmployee("Byron", "Kiourtzoglou", "Master Software Engineer", 2000d);

  

  long employeeId = employee.getId();

  

  System.out.println(employeeService.findEmployee(employeeId));

  

  employeeService.promoteEmployee(employeeId, "Principal Software Engineer", 3000d);

  

  System.out.println(employeeService.findEmployee(employeeId));

    }

}

Output:

Employee [id=1, name=Byron, surname=Kiourtzoglou, title=Master Software Engineer, salary=1900.0, created=2011-12-05 12:52:56.033]
Employee [id=1, name=Byron, surname=Kiourtzoglou, title=Principal Software Engineer, salary=2900.0, created=2011-12-05 12:52:56.033]

 
This was an example of how to create a reference of an EJB in another EJB of different applications.

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