Programming WebLogic Enterprise JavaBeans

      

Deployment Guidelines for Enterprise Java Beans

The following sections contain EJB-specific deployment guidelines. For deployment topics that are common to all deployable application units, you will see cross-references to topics in Deploying Applications to WebLogic Server, a comprehensive guide to deploying WebLogic Server applications and modules.

 

Before You Deploy an EJB

Before starting the deployment process you should have:

 

Understanding and Performing Deployment Tasks

Table 8-1 is a guide to WebLogic Server documentation topics that help you make decisions about deployment strategies and provide instructions for performing deployment tasks. For EJB-specific deployment topics, see Deployment Guidelines for EJBs.

Table 8-1 Deployment Tasks and Topics
If You Want To.... See This Topic
Deploy in a development environment Deploying and Packaging from a Split Development Directory in Developing Applications with WebLogic Server.
Select a deployment tool Deployment Tools in Deploying Applications to WebLogic Server
Determine appropriate packaging for a deployment Preparing Applications and Modules for Deployment in Deploying Applications to WebLogic Server.
Organizing EJB components in a split directory structure. EJBs in Developing Applications with WebLogic Server.
Select staging mode Controlling Deployment File Copying with Staging Modes in Deploying Applications and Modules.
Perform specific deployment tasks Overview of the Deployment Process in Deploying Applications to WebLogic Server.

 

Deployment Guidelines for EJBs

The following sections provide guidelines for deploying EJBs.

 

Deploy EJBs as Part of an Enterprise Application

Oracle recommends that you package and deploy your stand-alone EJB applications as part of an Enterprise application. An Enterprise application is a J2EE deployment unit that bundles together Web applications, EJBs, and Resource Adapters into a single deployable unit.

This is a Oracle best practice, which allows for easier application migration, additions, and changes. Also, packaging your applications as part of an Enterprise application allows you to take advantage of the split development directory structure, which provides a number of benefits over the traditional single directory structure. See “Overview of the Split Development Directory Environment” in Developing Applications with WebLogic Server.

 

Deploy EJBs That Call Each Other in the Same Application

When an EJB in one application calls an EJB in another application, WebLogic Server passes method arguments by value, due to classloading requirements. When EJBs are in the same application, WebLogic Server can pass method arguments by reference; this improves the performance of method invocation because parameters are not copied.

For best performance, package components that call each other in the same application, and set enable-call-by-reference in weblogic-ejb-jar.xml to True. (By default, enable-call-by-reference is False.)

 

Deploying EJBs that Use Dependency Injection

When an EJB uses dependency injection, the resource name defined in the class and the superclass must be unique. For example: 

public class ClientServlet extends HttpServlet {

    @EJB(name = 'DateServiceBean', beanInterface = DateService.class)

    private DateService bean; .... } 

public class DerivedClientServlet extends ClientServlet { 

    @EJB(name = MyDateServiceBean', beanInterface = DateService.class)

    private DateService bean; .... }

For more information about dependency injection, see “Using Java EE Annotations and Dependency Injection” in Developing Applications With WebLogic Server.

 

Deploy Homogeneously to a Cluster

If your EJBs will run on a WebLogic Server cluster, Oracle recommends that you deploy them homogeneously—to each Managed Server in the cluster. Alternatively, you can deploy an EJB to only to a single server in the cluster (that is, “pin” a module to a server). This type of deployment is less common, and should be used only in special circumstances where pinned services are required. For more information, “Understanding Cluster Configuration” in Using Clusters.

 

Deploying Pinned EJBs to a Cluster

There is a known issue with deploying or redeploying EJBs to a single server instance in a cluster—referred to as pinned deployment—if the JAR file contains contain uncompiled classes and interfaces.

During deployment, the uncompiled EJB is copied to each server instance in the cluster, but it is compiled only on the server instance to which it has been deployed. As a result, the server instances in the cluster to which the EJB was not targeted lack the classes generated during compilation that are necessary to invoke the EJB. When a client on another server instance tries to invoke the pinned EJB, it fails, and an Assertion error is thrown in the RMI layer.

If you are deploying or redeploying an EJB to a single server instance in a cluster, compile the EJB with appc or ejbc before deploying it, to ensure that the generated classes are copied to all server instances available to all nodes in the cluster.

For more information on pinned deployments, see “Deploying to a Single Server Instance (Pinned Deployment)” in Using Clusters.

 

Redeploying an EJB

When you make changes to a deployed EJB's classes, redeploy the EJB. If you use automatic deployment, deployment occurs automatically when you restart WebLogic Server. Otherwise, explicitly redeploy the EJB.

Redeploying an EJB deployment enables an EJB provider to make changes to a deployed EJB's classes, recompile, and then “refresh” the classes in a running server.

When you redeploy, the classes currently loaded for the EJB are immediately marked as unavailable in the server, and the EJB's classloader and associated classes are removed. At the same time, a new EJB classloader is created, which loads and maintains the revised EJB classes.

When clients next acquire a reference to the EJB, their EJB method calls use the changed EJB classes.

You can redeploy an EJB that is standalone or part of an application, using the weblogic.Deployer tool or the Administration Console. For instructions, see “Updating Applications in a Production Environment” in Deploying Applications to WebLogic Server.

Notes: Production redeployment is not supported for:

Note: For more information on production redeployment limitations, see “Requirements and Restrictions for Production Redeployment” in Deploying Applications to WebLogic Server.

 

Redeploying an Individual EJB Implementation Class

During iterative development of an EJB application, you make many modifications to the EJB implementation class file, typically redeploying an EJB module multiple times during its development.

In this release of WebLogic Server, you can redeploy an individual implementation class. For information about this feature, see “Individual EJB Classloader for Implementation Classes” in Developing Applications with WebLogic Server.

To enable this feature, set the enable-bean-class-redeploy element to True in weblogic-ejb-jar.xml. This feature is not recommended for use in production environments. For considerations and limitations related to deploying an individual implementation class, feature, see enable-bean-class-redeploy.

 

Understanding Warning Messages

To get information about a particular warning, use the weblogic.GetMessage tool. For example:

java weblogic.GetMessage -detail -id BEA-010202.

 

Disabling EJB Deployment Warning Messages

You can disable certain WebLogic Server warning messages that occur during deployment. You may find this useful if the messages provide information of which you are already aware.

For example, if the methods in your EJB makes calls by reference rather than by value, WebLogic Server generates this warning during deployment: "Call-by-reference not enabled."

You can use the disable-warning element in weblogic-ejb-jar.xml to disable certain messages. For a list of messages you can disable, and instructions for disabling the messages, see disable-warning.