Develop enterprise beans

One of two enterprise bean development scenarios is typically used with the product.

The steps in this article focus on development without an IDE.

Before starting, review Concurrency control.

EJB 3.x modules do not support entity beans. Place entity beans in EJB 2.x-level modules.

For developing enterprise beans...

Develop without an IDE...

  1. Migrate any pre-existing code to the required version of the EJB specification.

    Applications written to the EJB specification versions 1.1, 2.0, and 2.1 can run unchanged in the EJB 3.x container. See the topic Migrating enterprise bean code to the supported specification.

  2. Write and compile the components of the enterprise bean.

    • At a minimum, a session bean developed with the EJB 3.x specifications requires a bean class.

    • At a minimum, an EJB 1.1 session bean requires a bean class, a home interface, and a remote interface. An EJB 1.1 entity bean requires a bean class, a primary-key class, a home interface, and a remote interface.

    • At a minimum, an EJB 2.x session bean requires a bean class, a home or local home interface, and a remote or local interface. An EJB 2.x entity bean requires a bean class, a primary-key class, a remote home or local home interface, and a remote or local interface. The types of interfaces go together: If we implement a local interface, you must also define a local home interface.

      The primary-key class can be unknown. See the topic Unknown primary-key class for more information.

    • A message-driven bean requires only a bean class.

  3. For each entity bean, complete work to handle persistence operations.

    For EJB 3.x modules, consider using the Java Persistence API (JPA) specification to develop plain old Java Object (POJO) persistent entities.

    If we choose to develop entity beans to earlier EJB specifications:

    • Create a database schema for the entity bean persistent data.

      • For entity beans with CMP, you must store the bean persistent data in one of the supported databases. The assembly tool automatically generates SQL code for creating database tables for CMP entity beans. If the CMP beans require complex database mappings, IBM recommends that you use Rational Application Developer to generate code for the database tables.

      • For entity beans with bean-managed persistence (BMP), we can create the database and database table using the database tools or use an existing database and database table.

    • (CMP entity beans for EJB 2.x only)

      Define finder queries with EJB Query Language (EJB QL).

      With EJB QL, you define finders in terms of CMP fields and container-managed relationships, as follows:

      • Public finders are visible in the bean home interface. Implemented in the bean class, they return only remote interfaces and collection types.

      • Private finders, expressed as SELECT statements, are used only within the bean class. They can return both local and remote interfaces, dependent values, other CMP field types, and collection types.

    • (CMP entity beans for EJB 1.1 only: an IBM extension)

      Create a finder helper interface for each CMP entity bean containing specialized finder methods (other than the findByPrimaryKey method). Logic other than the findByPrimaryKey method is required for each finder method contained in the home interface of an entity bean with CMP:

      • The logic must be defined in a public interface named NameBeanFinderHelper, where Name is the name of the enterprise bean, for example, AccountBeanFinderHelper.

      • The logic must be contained in a String constant named findMethodName WhereClause, where findMethodName is the name of the finder method. The String constant can contain zero or more question marks (?) that are replaced from left to right with the value of the finder method arguments when that method is called.


Example: Use a read-only entity bean

This usage scenario and example shows how to write an EJB application that uses a read-only entity bean.

Usage scenario

A customer has a database of catalog pricing and shipping rate information that is updated daily no later than 10:00 PM local time (22:00 in 24-hour format). They want to write an EJB application that has read-only access to this data. That is, this application never updates the pricing database. Updating is done through some other application.

Example

The customer's entity bean local interface might be:

 
public interface ItemCatalogData extends EJBLocalObject 
{
   public int getItemPrice(); 
   public int getShippingCost(int destinationCode);
 }

The code in the stateless SessionBean method (assume it is a TxRequired) that invokes this EntityBean to figure out the total cost including shipping, would look like:

 .....
 // Some transactional steps occur prior to this point, such as removing the item from 
  // inventory, etc.
  // Now obtain the price of this item and start to calculate the total cost to the purchaser
 
  ItemCatalogData theItemData = 
     (ItemCatalogData) ItemCatalogDataHome.findByPrimaryKey(theCatalogNumber);
 
 int totalcost = theItemData.getItemPrice();
  
 // ... some other processing, etc. in the interim
 // ...
 // ...
  
 // Add the shipping costs
 totalcost = totalcost + theItemData.getShippingCost(theDestinationPostalCode);

At application assembly time, the customer sets the EJB caching parameters for this bean as follows:

  • ActivateAt = ONCE
  • LoadAt = DAILY
  • ReloadInterval = 2200

Deprecated feature: The reloadInterval and reloadingEnabled attributes of the IBM deployment descriptor extensions, including both the WAR file extension (WEB-INF/ibm-web-ext.xmi) and the application extension (META-INF/ibm-application-ext.xmi) were deprecated.depfeat

On the first call to the getItemPrice() method after 22:00 each night, the EJB container reloads the pricing information from the database. If the clock strikes 22:00 between the call to getItemPrice() and getShippingCost(), the getShippingCost() method still returns the value it had before any changes to the database that might have occurred at 22:00, since the first method invocation in this transaction occurred before 22:00. Thus, the item price and shipping cost used remain in sync with each other.


What to do next

  1. Assemble EJB modules
  2. Assemble EJB 3.x modules


Subtopics


Related concepts:

  • Application exceptions
  • EJB 3.0 and EJB 3.1 application bindings overview
  • EJB 3.x module packaging overview
  • EJB 3.0 and EJB 3.1 deployment overview
  • Enterprise beans
  • Concurrency control
  • Lightweight local operational mode for entity beans
    (dist)(zos) Configure EJB bindings in SCA applications
    (dist)(zos) Use EJB bindings in SCA applications in a cluster environment
  • Task overview: Storing and retrieving persistent data with the JPA API
  • Develop read-only entity beans
  • Migrate enterprise bean code to the supported specification
  • Develop applications that use JNDI
  • Set the run time for batched commands with JVM arguments
  • Set the run time for deferred create with JVM arguments
  • Set partial update for container-managed persistent beans
  • Set persistence manager cache invalidation
  • Set the system property to enable remote EJB clients to receive nested or root-cause exceptions
  • Configure a timer service
  • Create timers using the EJB timer service for enterprise beans
  • Define data sources for entity beans
  • Apply lightweight local mode to an entity bean
  • Assembling EJB 3.x modules
  • Assembling EJB modules
  • Use EJB query


    http://pic.dhe.ibm.com/infocenter/radhelp/v9/index.jsp?topic=%2Fcom.ibm.javaee.doc%2Ftopics%2Fcejb3.html

  • EJB 3.0 specification
  • EJB 3.x module considerations
  • EJB metadata annotations
  • EJB 3.x interceptors
  • Create stubs command
  • WebSphere extensions to the Enterprise JavaBeans specification
  • Enterprise bean development best practices
  • Unknown primary-key class
    Dali JPA Tools