Real world use cases for stateful session EJB

We currently have a couple of Stateful EJBs in one of our applications running on production. So I suppose, it can be considered as a real world example.

This EJBs are used to provide large amounts of data to the clients by dividing this data in chunks and sending this chunks on demand. All this works as follows:

• client prepares a request, specifying filters he wants data to be looked up against;
• he submits this request using Stateful EJB method;
• request is processed on a server and result set is prepared;
• as a response to his request client gets a descriptor to the server-side result set;
• having this descriptor he now can fetch chunks of data using Stateful bean methods.

Was a Stateful bean a necessity in solving such a problem? Not at all.

Described functionality could be achieved with a Stateless bean. But in this case we have only two ways of implementing it. Either we are forced to prepare result sets for requests each time a client needs next chunk of data (as we don't have any state), or we use some static storage and take care of security and concurrent access by our own. /By security here I mean preventing situations in which one client can gain access to the result set of another using his descriptor/

The first way is simply slower and less efficient comparing to implementation on Stateful beans. The second way is more complicated and less stable under load due to synchronization.

With Stateful bean we just get what we need in an efficient manner and without extra effort.

Remote Interface

import javax.ejb.Remote;
 
@Remote
public interface LibraryStatefulSessionBeanRemote {
   //add business method declarations
}

Stateful EJB

@Stateful
public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote {
   //implement business method 
}

LibraryStatefulSessionBeanRemote.java

package com.tutorialspoint.stateful;
 
import java.util.List;
import javax.ejb.Remote;
 
@Remote
public interface LibraryStatefulSessionBeanRemote {
   void addBook(String bookName);
   List getBooks();
}

LibraryStatefulSessionBean.java

package com.tutorialspoint.stateful;
 
import java.util.ArrayList;
import java.util.List;
import javax.ejb.Stateful;
 
@Stateful
public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote {
    
   List<String> bookShelf;    
 
   public LibraryStatefulSessionBean() {
      bookShelf = new ArrayList<String>();
   }
 
   public void addBook(String bookName) {
      bookShelf.add(bookName);
   }    
 
   public List<String> getBooks() {
      return bookShelf;
   }
}

JBoss Application Server Log Output

...
16:30:01,401 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
   LibraryStatefulSessionBean/remote - EJB3.x Default Remote Business Interface
   LibraryStatefulSessionBean/remote-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryStatefulSessionBean,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote ejbName: LibraryStatefulSessionBean
16:30:02,731 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
 
   LibraryStatefulSessionBean/remote - EJB3.x Default Remote Business Interface
   LibraryStatefulSessionBean/remote-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote - EJB3.x Remote Business Interface
...

To define a session bean, you first need to define the service interface containing all its business methods. The session bean interface is just plain old Java interface without any annotation. The client uses this interface to retrieve a stub object of the session bean from the EJB 3.0 container

package demo.ejb3;

public interface SessionDemoItf {

   public String doQuery (String param);

}

We’ve also added the @PostConstruct and @PreDestroy notations, which are not compulsory but it’s helpful to understand the lifecycle of the EJB.

package demo.ejb3;

import javax.annotation.PostConstruct;
import javax.ejb.*;

@Stateless
public class SessionDemoBean implements SessionDemoItf {

    public String doQuery(String param) {
        return "Query with param " + param + " executed.";
    }

    @PostConstruct
    public void initialize () {
        // Initialize here objects which will be used
        // by the session bean
        System.out.println("SessionDemoBean initialized.");
    } 


    @PreDestory
    public void destroyBean() {
        // Free here resources acquired by the session bean
        System.out.println("SessionDemoBean initialized.");
    } 
}

In order to compile a project which uses EJBs, it is sufficient to include the jakarta.jakartaee-api dependency in your pom.xml:

<dependencies>
        <dependency>
          <groupId>jakarta.platform</groupId>
          <artifactId>jakarta.jakartaee-api</artifactId>
          <version>${jakartaee.version}</version>
          <scope>provided</scope>
        </dependency>
</dependencies>

<properties>
        <jakartaee.version>8.0.0</jakartaee.version>
</properties>

<properties>
        <jakartaee.version>9.0.0</jakartaee.version>
</properties>