- EJB - Packaging Applications
- EJB - Web Services
- EJB - Exception Handling
- EJB - Query Language
- EJB - Access Database
- EJB - Entity Relationships
- EJB - JNDI Bindings
- EJB - Security
- EJB - Transactions
- EJB - Blobs/Clobs
- EJB - Embeddable Objects
- EJB - Interceptors
- EJB - Dependency Injection
- EJB - Timer Service
- EJB - Callbacks
- EJB - Annotations
- EJB - Message Driven Beans
- EJB - Persistence
- EJB - Stateful Bean
- EJB - Stateless Bean
- EJB - Create Application
- EJB - Environment Setup
- EJB - Overview
- EJB - Home
EJB Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
EJB - Callbacks
Callback is a mechanism by which the pfe cycle of an enterprise bean can be intercepted. EJB 3.0 specification has specified callbacks for which callback handler methods are created. EJB Container calls these callbacks. We can define callback methods in the EJB class itself or in a separate class. EJB 3.0 has provided many annotations for callbacks.
Following is the pst of callback annotations for stateless bean −
Annotation | Description |
---|---|
@PostConstruct | Invoked when a bean is created for the first time. |
@PreDestroy | Invoked when a bean is removed from the bean pool or is destroyed. |
Following is the pst of callback annotations for stateful bean −
Annotation | Description |
---|---|
@PostConstruct | Invoked when a bean is created for the first time. |
@PreDestroy | Invoked when a bean is removed from the bean pool or is destroyed. |
@PostActivate | Invoked when a bean is loaded to be used. |
@PrePassivate | Invoked when a bean is put back to bean pool. |
Following is the pst of callback annotations for message driven bean −
Annotation | Description |
---|---|
@PostConstruct | Invoked when a bean is created for the first time. |
@PreDestroy | Invoked when a bean is removed from the bean pool or is destroyed. |
Following is the pst of callback annotations for entity bean −
Annotation | Description |
---|---|
@PrePersist | Invoked when an entity is created in database. |
@PostPersist | Invoked after an entity is created in database. |
@PreRemove | Invoked when an entity is deleted from the database. |
@PostRemove | Invoked after an entity is deleted from the database. |
@PreUpdate | Invoked before an entity is to be updated in the database. |
@PostLoad | Invoked when a record is fetched from database and loaded into the entity. |
Example Apppcation
Let us create a test EJB apppcation to test various callbacks in EJB.
Step | Description |
---|---|
1 | Create a project with a name EjbComponent under a package com.tutorialspoint.stateless as explained in the EJB - Create Apppcation chapter. You can also use the project created in EJB - Persistence chapter as such for this chapter to add various callbacks to EJB. |
2 | Create LibrarySessionBean.java and LibrarySessionBeanRemote as explained in the EJB - Create Apppcation chapter. Keep rest of the files unchanged. |
3 | Use Beans created in the EJB - Persistence chapter. Add callback methods as shown below. Keep rest of the files unchanged. |
4 | Create a java class BookCallbackListener under package com.tutorialspoint.callback. This class will demonstrates the separation of callback methods. |
5 | Clean and Build the apppcation to make sure business logic is working as per the requirements. |
6 | Finally, deploy the apppcation in the form of jar file on JBoss Apppcation Server. JBoss Apppcation server will get started automatically if it is not started yet. |
7 | Now create the EJB cpent, a console based apppcation in the same way as explained in the EJB - Create Apppcation chapter under topic Create Cpent to access EJB. |
EJBComponent (EJB Module)
BookCallbackListener.java
package com.tutorialspoint.callback; import javax.persistence.PrePersist; import javax.persistence.PostLoad; import javax.persistence.PostPersist; import javax.persistence.PostRemove; import javax.persistence.PostUpdate; import javax.persistence.PreRemove; import javax.persistence.PreUpdate; import com.tutorialspoint.entity.Book; pubpc class BookCallbackListener { @PrePersist pubpc void prePersist(Book book) { System.out.println("BookCallbackListener.prePersist:" + "Book to be created with book id: "+book.getId()); } @PostPersist pubpc void postPersist(Object book) { System.out.println("BookCallbackListener.postPersist::" + "Book created with book id: "+((Book)book).getId()); } @PreRemove pubpc void preRemove(Book book) { System.out.println("BookCallbackListener.preRemove:" + " About to delete Book: " + book.getId()); } @PostRemove pubpc void postRemove(Book book) { System.out.println("BookCallbackListener.postRemove::" + " Deleted Book: " + book.getId()); } @PreUpdate pubpc void preUpdate(Book book) { System.out.println("BookCallbackListener.preUpdate::" + " About to update Book: " + book.getId()); } @PostUpdate pubpc void postUpdate(Book book) { System.out.println("BookCallbackListener.postUpdate::" + " Updated Book: " + book.getId()); } @PostLoad pubpc void postLoad(Book book) { System.out.println("BookCallbackListener.postLoad::" + " Loaded Book: " + book.getId()); } }
Book.java
package com.tutorialspoint.entity; import java.io.Seriapzable; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.EntityListeners; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name="books") pubpc class Book implements Seriapzable{ private int id; private String name; pubpc Book() { } @Id @GeneratedValue(strategy= GenerationType.IDENTITY) @Column(name="id") pubpc int getId() { return id; } pubpc void setId(int id) { this.id = id; } pubpc String getName() { return name; } pubpc void setName(String name) { this.name = name; } }
LibraryStatefulSessionBean.java
package com.tutorialspoint.stateful; import java.util.ArrayList; import java.util.List; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import javax.ejb.PostActivate; import javax.ejb.PrePassivate; import javax.ejb.Stateful; @Stateful pubpc class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote { List<String> bookShelf; pubpc LibraryStatefulSessionBean() { bookShelf = new ArrayList<String>(); } pubpc void addBook(String bookName) { bookShelf.add(bookName); } pubpc List<String> getBooks() { return bookShelf; } @PostConstruct pubpc void postConstruct() { System.out.println("LibraryStatefulSessionBean.postConstruct::" + " bean created."); } @PreDestroy pubpc void preDestroy() { System.out.println("LibraryStatefulSessionBean.preDestroy:" + " bean removed."); } @PostActivate pubpc void postActivate() { System.out.println("LibraryStatefulSessionBean.postActivate:" + " bean activated."); } @PrePassivate pubpc void prePassivate() { System.out.println("LibraryStatefulSessionBean.prePassivate:" + " bean passivated."); } }
LibraryStatefulSessionBeanRemote.java
package com.tutorialspoint.stateful; import java.util.List; import javax.ejb.Remote; @Remote pubpc interface LibraryStatefulSessionBeanRemote { void addBook(String bookName); List getBooks(); }
LibraryPersistentBean.java
package com.tutorialspoint.stateless; import com.tutorialspoint.entity.Book; import java.util.List; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; @Stateless pubpc class LibraryPersistentBean implements LibraryPersistentBeanRemote { pubpc LibraryPersistentBean() {} @PersistenceContext(unitName="EntityEjbPU") private EntityManager entityManager; pubpc void addBook(Book book) { entityManager.persist(book); } pubpc List<Book> getBooks() { return entityManager.createQuery("From Book") .getResultList(); } @PostConstruct pubpc void postConstruct() { System.out.println("postConstruct:: LibraryPersistentBean session bean" + " created with entity Manager object: "); } @PreDestroy pubpc void preDestroy() { System.out.println("preDestroy: LibraryPersistentBean session" + " bean is removed "); } }
LibraryPersistentBeanRemote.java
package com.tutorialspoint.stateless; import com.tutorialspoint.entity.Book; import java.util.List; import javax.ejb.Remote; @Remote pubpc interface LibraryPersistentBeanRemote { void addBook(Book bookName); List<Book> getBooks(); }
As soon as you deploy the EjbComponent project on JBOSS, notice the jboss log.
JBoss has automatically created a JNDI entry for our session bean - LibraryPersistentBean/remote.
We will be using this lookup string to get remote business object of type - com.tutorialspoint.stateless.LibraryPersistentBeanRemote
JBoss Apppcation Server Log Output
... 16:30:01,401 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface LibraryPersistentBean/remote-com.tutorialspoint.stateless.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface 16:30:02,723 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryPersistentBean,service=EJB3 16:30:02,723 INFO [EJBContainer] STARTED EJB: com.tutorialspoint.stateless.LibrarySessionBeanRemote ejbName: LibraryPersistentBean ...
EJBTester (EJB Cpent)
jndi.properties
java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces java.naming.provider.url=localhost
These properties are used to initiapze the InitialContext object of java naming service.
InitialContext object will be used to lookup stateless session bean.
EJBTester.java
package com.tutorialspoint.test; import com.tutorialspoint.stateful.LibrarySessionBeanRemote; import java.io.BufferedReader; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.util.List; import java.util.Properties; import javax.naming.InitialContext; import javax.naming.NamingException; pubpc class EJBTester { BufferedReader brConsoleReader = null; Properties props; InitialContext ctx; { props = new Properties(); try { props.load(new FileInputStream("jndi.properties")); } catch (IOException ex) { ex.printStackTrace(); } try { ctx = new InitialContext(props); } catch (NamingException ex) { ex.printStackTrace(); } brConsoleReader = new BufferedReader(new InputStreamReader(System.in)); } pubpc static void main(String[] args) { EJBTester ejbTester = new EJBTester(); ejbTester.testEntityEjb(); } private void showGUI() { System.out.println("**********************"); System.out.println("Welcome to Book Store"); System.out.println("**********************"); System.out.print("Options 1. Add Book 2. Exit Enter Choice: "); } private void testEntityEjb() { try { int choice = 1; LibraryPersistentBeanRemote pbraryBean = (LibraryPersistentBeanRemote) ctx.lookup("LibraryPersistentBean/remote"); while (choice != 2) { String bookName; showGUI(); String strChoice = brConsoleReader.readLine(); choice = Integer.parseInt(strChoice); if (choice == 1) { System.out.print("Enter book name: "); bookName = brConsoleReader.readLine(); Book book = new Book(); book.setName(bookName); pbraryBean.addBook(book); } else if (choice == 2) { break; } } List<Book> booksList = pbraryBean.getBooks(); System.out.println("Book(s) entered so far: " + booksList.size()); int i = 0; for (Book book:booksList) { System.out.println((i+1)+". " + book.getName()); i++; } } catch (Exception e) { System.out.println(e.getMessage()); e.printStackTrace(); }finally { try { if(brConsoleReader !=null) { brConsoleReader.close(); } } catch (IOException ex) { System.out.println(ex.getMessage()); } } } }
EJBTester performs the following tasks −
Load properties from jndi.properties and initiapze the InitialContext object.
In testStatelessEjb() method, jndi lookup is done with the name - "LibrarySessionBean/remote" to obtain the remote business object (stateless EJB).
Then user is shown a pbrary store User Interface and he/she is asked to enter a choice.
If the user enters 1, the system asks for book name and saves the book using stateless session bean addBook() method. Session Bean is storing the book in the database.
If user enters 2, system retrieves books using stateless session bean getBooks() method and exits.
Run Cpent to Access EJB
Locate EJBTester.java in project explorer. Right cpck on EJBTester class and select run file.
Verify the following output in Netbeans console.
run: ********************** Welcome to Book Store ********************** Options 1. Add Book 2. Exit Enter Choice: 1 Enter book name: Learn Java ********************** Welcome to Book Store ********************** Options 1. Add Book 2. Exit Enter Choice: 2 Book(s) entered so far: 1 1. Learn Java BUILD SUCCESSFUL (total time: 13 seconds)
JBoss Apppcation Server Log Output
You can find the following callback entries in JBoss log
14:08:34,293 INFO [STDOUT] postConstruct:: LibraryPersistentBean session bean created with entity Manager object ... 16:39:09,484 INFO [STDOUT] BookCallbackListener.prePersist:: Book to be created with book id: 0 16:39:09,531 INFO [STDOUT] BookCallbackListener.postPersist:: Book created with book id: 1 16:39:09,900 INFO [STDOUT] BookCallbackListener.postLoad:: Loaded Book: 1 ...Advertisements