Transactions in EJB

This material is from the book JBuilder Developer's Guide , written by Saleem Siddiqui, Michael Landy, and Jeff Swisher, published by Sams Publishing.

© Copyright Sams Publishing. All rights reserved.

Transactions play an important role in most application development projects. This is not different when developing an EJB-based solution. Transactions can be complex features to implement, but EJB-based systems require that the vendors implement transaction processing within the container. This does not mean, however, that you do not have to be concerned about transactions.

Simply put, a transaction is a grouping of work that represents a single unit or task. This single unit may contain something as simple as one step or many complex steps to be treated as one. Many times, people ask "Why do I need transactions?" Transactions help to alleviate the complexity of coordinating data or resource access across many clients.

Whenever you use transactions, you need to understand the four main characters: Atomicity, Consistency, Isolation, and Durability, commonly referred to as ACID. These four properties and the basic requirements fulfilled through the use of transactions are shown in Table 1.

Table 1 Properties of a Successful Transaction

Transaction Attributes

With declarative demarcation you specify to the container which methods are going to be included within transactional processing. Each method is given a transactional context that it uses to participate within the given transaction. Enterprise JavaBeans define seven different types of transaction attributes, each having a slightly different implementation, as shown in Table 2.

Table 2 Transaction Attributes Available for EJB Transactional Implementation

Transaction Usage

Transaction usage within the container is specified within the deployment descriptor. JBuilder's EJB Designer provides an easy-to-use interface that gives access to the transactional attributes. This interface makes it simple to define a transactional context that will ultimately be contained within the deployment descriptor. For example, let's look at our Employee entity bean again. The following process is used to define the transactional context for the entity bean:

1. Select a bean to define a transaction attribute.

2. Underneath the Employee entity you will see a child node entitled Container Transaction.

3. Double-click on the Container Transaction; this loads the Container Transaction editor, shown in Figure 1.


Figure 1
Define a transaction attribute using the Container Transaction editor.

4. Using the drop-down combo boxes, select the interface—either Home, Remote, LocalHome, or Local. After you select an interface, you are then allowed to either select all the methods (*) or specify a method.

5. Finally, select the appropriate transactional attribute.

The results of this process are placed in the deployment descriptor, as shown in Listing 1.

Listing 1 Portion of the Deployment Descriptor Containing the Transaction Attributes

<container-transaction>
  <method>
    <description />
    <ejb-name>Employee</ejb-name>
    <method-intf>LocalHome</method-intf>
    <method-name>create</method-name>
    <method-params>
      <method-param>java.lang.Short</method-param>
    </method-params>
  </method>
  <trans-attribute>Required</trans-attribute>
</container-transaction>
<container-transaction>
  <method>
    <description />
    <ejb-name>Employee</ejb-name>
    <method-intf>LocalHome</method-intf>
    <method-name>findAll</method-name>
    <method-params />
  </method>
  <trans-attribute>Supports</trans-attribute>
</container-transaction>

About the Authors

Saleem Siddiqui is a technical architect and trainer with Dunn Solutions Group. He is also a Sun Certified Developer and a Borland Certified JBuilder Instructor. At Dunn, he provides consulting services and business application development.

Michael Landy is Director of Business Applications for Dunn Solutions Group directing the strategic solutions for clients.

Jeff Swisher is a technical manager for the Dunn Solutions Group business applications. He works as a programmer, trainer, architect, and instructional designer. He is a Sun Certified Java Developer and a Borland Certified Instructor in JBuilder.

Source of this material

This material is from Chapter 23: Developing Entity Beans from the book JBuilder Developer's Guide (ISBN: 0-672-32427-X) written by Saleem Siddiqui, Michael Landy, and Jeff Swisher, published by Sams Publishing. © Copyright Sams Publishing. All rights reserved.

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