This topic describes application packaging when you use Enterprise JavaBeans™ (EJB) 3.0 beans.
Packaging applications that use EJB 3.0 beans is similar to the assembly requirements for Java™ 2 Platform, Enterprise Edition (J2EE) 1.4 applications: components are packaged into modules, and modules are packaged into application enterprise archive (EAR) files. The components and modules both have describing metadata provided in an Extensible Markup Language (XML) deployment descriptor. The EJB 3.0 specification supports an additional method to describing metadata and for packaging persistence units.
EJB modules without deployment descriptors
You can package EJB modules without a deployment descriptor if you are using EJB 3.0 beans. To do this, you must create a JAR file with metadata in an annotation which is located in the EJB component. EJB 3.0 beans do not need an entry in the ejb-jar.xml file for metadata that you have defined through annotations.
If you installed the Feature Pack for EJB 3.0, the default was to scan annotations during the installation of an EJB 3.0 module. For WebSphere® Application Server, Version 7.0, the default is not to scan pre-Java EE 5 modules during the application install or at server startup
To preserve backward compatibility with both the Feature Pack for EJB 3.0 and the Feature Pack for Web Services, you have a choice whether or not to scan legacy Web modules for additional metadata. A server level switch is defined for each feature pack scan behavior. If the default is not appropriate, the switch must be set on each server and administrative server that requires a change in the default. The switches are server custom properties com.ibm.websphere.webservices.UseWSFEP61ScanPolicy={true|false} and com.ibm.websphere.ejb.UseEJB61FEPScanPolicy={true|false}. To define these properties in the administrative console click
.EJB modules with deployment descriptors
You can continue to use EJB modules with deployment descriptors. Modules with deployment descriptors can support any EJB specification version level, including EJB 3.0, but generally these descriptors should reflect the implementation requirements of the components in the module.
An EJB module can have an EJB 2.1-, or earlier, style deployment descriptor, or an EJB 3.0-style deployment descriptor.
For EJB 2.1-style deployment descriptors, it is assumed that the deployment descriptor contains the full metadata for the module, and no additional scanning of annotation metadata occurs.
The EJB container annotation scanning is performed on EJB modules that either have no deployment descriptor or have an ejb-jar.xml deployment descriptor at the EJB 3.0 schema level. In other words, the scan finds the annotation and its describing metadata.
Persistence units
Persistence units, including the persistence.xml file and the classes associated with it, can be packaged in the module for which they are required. They can also be packaged in the separate utility JAR file that is packaged in the EAR file with its dependent module.
Application packaging
You can mix EJB 2.x and earlier beans with EJB 3.0 beans in the same application, but you do need to separate EJB 2.x and earlier beans from EJB 3.0 beans so that they are not in the same modules. EJB 3.0 beans are not recognized in modules that contain EJB 2.1-style, or earlier, deployment descriptors.
JPA packaging
It is recommend that persistence units be packaged in separate JAR files to make them more accessible and reusable. These can be tested outside the container, with or without actual database persistence occurring. Persistence units can be included in standalone applications or into EAR files as utility JAR files. Because of the variety of use cases and potential performance issues when scanning large quantities of classes, it is recommended that the persistence unit defines the classes of the persistence units.
Session facades used for persistence scenario
A common pattern is to use session facades for persistence. Using session bean facades to drive JPA is supported. The EntityManager interface is not thread safe, therefore, servlets should never inject @PersistenceContext. Servlets must either use the facade pattern or use an EntityManagerFactory instance to create an EntityManager on each request.
It is recommended that JPA persistence units be defined in a separate JAR file, apart from the session bean facades. Not only is this a best practice that gives greater flexibility in sharing, it also avoids problems mixing JPA and non-JPA annotated classes.
Manifest-Version: 1.0 Class-Path: TradeInfo.jarThe session facade in the EJB3Trade.jar file refers to JPA entity classes and persistence units in the TradeInfo.jar file. The Web application defined in the TradeWeb.war file can do the same to work with the JPA entity objects as Data Transfer Objects flowing between the Web and EJB container tiers.
Cross-tier and cross version session bean reference scenario
There are several ways to define and use references to EJB 3.0 session beans. For EJB 3.0 session to session, the @EJB injection target can be used. For cross-tier, for example, Web application to EJB 3.0 session, or cross-version, for example, EJB 2.1 session to EJB 3.0 session, an XML deployment descriptor reference can be used to define ejb-refs and ejb-local-refs. There are two variations of these, depending on whether an EJB 3.0 business interface is referred to, or a pre-EJB 3.0 component-style interface that also defines an EJBLocalHome is referred to. Web applications and client applications can also utilize the @EJB annotation if the component being referenced can be resolved using autolink.
<ejb-local-ref id="EJBLocalRef_1154112538064"> <description>com.ibm.persistence.ejb3.order.facadecom.ibm.persistence.ejb3.order.facade</description> <ejb-ref-name>ejb/OrderEJB</ejb-ref-name> <ejb-ref-type>Session</ejb-ref-type> <local-home></local-home> <local>com.ibm.persistence.ejb3.order.facade.OrderProcessor</local> </ejb-local-ref>The client code also needs to be adjusted to do the appropriate casting for the object being looked up. In this case, the business interface instead of the home interface:
try { InitialContext ctx = new InitialContext(); orderProcessor = (OrderProcessor)ctx.lookup("java:comp/env/ejb/OrderEJB"); } catch(Exception e) { e.printStackTrace(System.out); throw new ServletException(e); }