Network Deployment (Distributed operating systems), v8.0 > Develop and deploying applications > Develop EJB applications
Develop enterprise beans
One of two enterprise bean development scenarios is typically used with the product. The first is command-line using Ant, Make, Maven or similar tools. The second is an IDE-based development and build environment. The steps in this article focus on development without an IDE.
EJB 2.x beans only: Design a J2EE application and the enterprise beans that it needs.
- Before developing entity beans with container-managed persistence
(CMP), read the topic Concurrency control.
EJB 3.x beans only: Design a Java EE application and the enterprise beans that it needs.
- Before developing
entity beans with CMP, read the topic, Concurrency
control. Keep in mind that EJB 3.x modules do not support entity beans.
We must continue to place entity beans in your EJB 2.x-level modules.
The two basic approaches to select tools for developing enterprise beans are as follows:
- We can use one of the available IDE tools that automatically generate significant parts of the enterprise bean code and contain integrated tools for packaging and testing enterprise beans. The Rational Application Developer
product is the recommended IDE.
Add install_root/dev/JavaEE/j2ee.jar to the IDE project build path to resolve compilation dependencies on the new EJB 3.x API classes. Code assist works when this JAR file is added to the project build path. If you define a server (see J2EE Perspective), point the server to the product installation directory. When you create a Java EE related project in Rational Application Developer, the project automatically adds install_root/dev/JavaEE/j2ee.jar. to the project build path.
- If you have decided to develop enterprise beans without an IDE, you need at least an ASCII text editor. We can also use a Java development tool that does not support enterprise bean development. We can then use tools available in the Java Software Development
Kit (SDK) and in this product to assemble, test, and deploy the beans.
Like the assembly tool, a standard Java EE command-line build environment requires some change to use the EJB 3.x modules. As with previous Java EE application development patterns, include the j2ee.jar file located in the install_root/dev/JavaEE directory on the compiler class path. An example of a command-line build environment using Ant is located in the install_root/samples/src/TechSamp directory.
The following steps primarily support the second approach, development without an IDE.
Procedure
- If necessary, 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.
- 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 you implement a local interface, also define a local home interface.
Attention: 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.
- 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. Review the topic Java Persistence API for more information. If you choose to develop entity beans to earlier EJB specifications, follow these steps:
- Create a database schema
for the entity bean persistent data.
- For entity beans with CMP, 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 your CMP beans require complex database mappings, IBM recommends that you use Rational Application Developer to generate code for the database tables. For more information about using the assembly tools, see the assembly tool information center.
- For entity beans with bean-managed persistence (BMP), you can create the database and database table by using the database tools
or use an existing database and database table.
For more information about creating databases and database tables, review your database documentation.
- (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 that contains specialized
finder methods (other than the findByPrimaryKey method).
Logic other than the findByPrimaryKey method is required for each finder method that is 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.
- Create a database schema
for the entity bean persistent data.
Example
This usage scenario and example shows how to write an EJB application that uses a read-only entity bean.
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.
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 in V6.0.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
Assemble the beans in one or more EJB modules. See the topic Assembling EJB modules, or Assembling EJB 3.x modules if you are using EJB 3.x beans.
Related
Configure EJB bindings in SCA applications
Use EJB bindings in SCA applications in a cluster environment
EJB 3.0 specification
EJB 3.x module considerations
EJB metadata annotations
EJB 3.x interceptors
Create stubs command
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
Develop read-only entity beans
Migrate enterprise bean code to the supported specification
WebSphere extensions to the EJB specification
Enterprise bean development best practices
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
Unknown primary-key class
Configure a timer service
Create timers using the EJB timer service for enterprise beans
Define data sources for entity beans
Lightweight local operational mode for entity beans
Apply lightweight local mode to an entity bean
Application exceptions
Enterprise beans
Concurrency control
Task overview: Storing and retrieving persistent data with the JPA API
Develop applications that use JNDI
Assembling EJB 3.x modules
Assembling EJB modules
Use EJB query
Related
http://publib.boulder.ibm.com/infocenter/radhelp/v7r5mbeta/topic/com.ibm.jee5.doc/topics/cejb3.html
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