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In this guide we will discuss about Transactions of EJB

A transaction is a single unit of work items, which follows the ACID properties. ACID stands for Atomic, Consistent, Isolated, and Durable.

• Atomic − If any of the work item fails, the whole unit will be considered failed. Success meant, all items execute successfully.
• Consistent − A transaction must keep the system in consistent state.
• Isolated − Each transaction executes independent of any other transaction.
• Durable − Transaction should survive system failure if it has been executed or committed.

EJB Container/Servers are transaction servers and handles transactions context propagation and distributed transactions. Transactions can be managed by the container or by custom code handling in bean’s code.

• Container Managed Transactions − In this type, the container manages the transaction states.
• Bean Managed Transactions − In this type, the developer manages the life cycle of transaction states.

Container Managed Transactions

EJB 3.0 has specified following attributes of transactions, which EJB containers implement −

• REQUIRED − Indicates that business method has to be executed within transaction, otherwise a new transaction will be started for that method.
• REQUIRES_NEW − Indicates that a new transaction, is to be started for the business method.
• SUPPORTS − Indicates that business method will execute as part of transaction.
• NOT_SUPPORTED − Indicates that business method should not be executed as part of transaction.
• MANDATORY − Indicates that business method will execute as part of transaction, otherwise exception will be thrown.
• NEVER − Indicates if business method executes as part of transaction, then an exception will be thrown.

Example

package in.adglob.txn.required;
 
import javax.ejb.*
 
@Stateless
@TransactionManagement(TransactionManagementType.CONTAINER)
public class UserDetailBean implements UserDetailRemote {
	
   private UserDetail;

   @TransactionAttribute(TransactionAttributeType.REQUIRED)
   public void createUserDetail() {
      //create user details object
   }
}

createUserDetail() business method is made Required using Required annotation.

package in.adglob.txn.required;
 
import javax.ejb.*
 
@Stateless
public class UserSessionBean implements UserRemote {
	
   private User;

   @EJB
   private UserDetailRemote userDetail;

   public void createUser() {
      //create user 
      //...
      //create user details
      userDetail.createUserDetail();
   }
}

createUser() business method is using createUserDetail(). If exception occurred during createUser() call and User object is not created then UserDetail object will also not be created.

Bean Managed Transactions

In Bean Managed Transactions, Transactions can be managed by handling exceptions at application level.

Following are the key points to be considered −

• Start − When to start a transaction in a business method.
• Sucess − Identify success scenario when a transaction is to be committed.
• Failed − Identify failure scenario when a transaction is to be rollback.

Example

package in.adglob.txn.bmt;
 
import javax.annotation.Resource;
import javax.ejb.Stateless;
import javax.ejb.TransactionManagement;
import javax.ejb.TransactionManagementType;
import javax.transaction.UserTransaction;
 
@Stateless
@TransactionManagement(value=TransactionManagementType.BEAN)
public class AccountBean implements AccountBeanLocal {
 
   @Resource
   private UserTransaction userTransaction;

   public void transferFund(Account fromAccount, double fund , 
      Account toAccount) throws Exception{

      try{
         userTransaction.begin();

         confirmAccountDetail(fromAccount);
         withdrawAmount(fromAccount,fund);

         confirmAccountDetail(toAccount);
         depositAmount(toAccount,fund);

         userTransaction.commit();
      }catch (InvalidAccountException exception) {
         userTransaction.rollback();
      }catch (InsufficientFundException exception) {
         userTransaction.rollback();
      }catch (PaymentException exception) {
         userTransaction.rollback();
      }
   }

   private void confirmAccountDetail(Account account) 
      throws InvalidAccountException {
   }

   private void withdrawAmount() throws InsufficientFundException {
   }

   private void depositAmount() throws PaymentException{
   }
}

In this example, we made use of UserTransaction interface to mark the beginning of transaction using userTransaction.begin() method call. We mark the completion of transaction, by using userTransaction.commit() method and if any exception occured during transaction then we rollback the complete transaction using userTransaction.rollback() method call.

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