Programming WebLogic Enterprise JavaBeans
The sections that follow describe the EJB implementation process, and provide guidance for how to get an EJB up and running in WebLogic Server.
It is assumed that you understand WebLogic Server's value-added EJB features, have selected a design pattern for your application, and have made key design decisions.
For a review of WebLogic Server EJB features, see WebLogic Server Value-Added EJB Features.
For discussion of design options for EJBs, factors to consider during the design process, and recommended design patterns see Designing Enterprise Java Beans.
This section is a brief overview of the EJB development process. It describes the key implementation tasks and associated results.
Figure 4-1 illustrates the process of developing an EJB. The steps in the process, and the results of each are described in Table 4-1. Subsequent sections detail each step in the process.
Figure 4-1 EJB Development Process Overview
Table 4-1 EJB Development Tasks and Result
Create the directory structure for your source files, deployment descriptors, and files that are generated during the implementation process. |
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Create the classes that make up your bean. Insert appropriate tags in your source code to enable automatic generation of deployment descriptor elements later in the implementation process. |
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Write or generate deployment descriptors that configure the runtime behavior and environment for the bean. |
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You may need to edit deployment descriptors to ensure they correctly reflect all desired runtime behaviors for your bean. If your source was thoroughly annotated with markup that specifies the optional features the bean uses, and you used EJBGen to generate the deployment descriptors automatically, edits to your deployment descriptor should be minima. |
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Generate the container classes used to access the deployment unit, including classes for home and remote interfaces. |
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7. Package |
Package compiled files, generated files, and deployment descriptors for deployment. If appropriate, you can leave your files unarchived in an exploded directory. |
|
8. Deploy |
Target the archive or application directory to desired Managed Server, or a WebLogic Server cluster, in accordance with selected staging mode. |
The deployment settings for the bean are written to |
Create a source directory where you will assemble the EJB.
BEA recommends a split development directory structure, which segregates source and output files in parallel directory structures. For instructions on how to set up a split directory structure and package your EJB as an enterprise application archive (EAR), see Overview of the Split Development Directory Environment in Developing Applications with WebLogic Server.
If you prefer to package and deploy your EJB in a JAR file, create a directory for your class files, and within that directory, a subdirectory named META-INF
for deployment descriptor files.
Listing 4-1 Directory Structure for Packaging JAR
myEJB/
META-INF/
ejb-jar.xml
weblogic-ejb-jar.xml
weblogic-cmp-jar.xml
foo.class
fooHome.class
fooBean.class
The classes required depend on the type of EJB you are developing, as described in Table 2-1.
BEA offers productivity tools for developing class and interface files. The EJBGen command line utility automates the process of creating class and interface files, and also generates deployment descriptor files for the EJB. For more information and instructions for using these tools see EJBGen Reference.
The sections that follow provide tips and guidelines for using WebLogic Server-specific EJB features.
For each EJB type, WebLogic Server provides a generic class that contains Java callbacks, or listeners, that are required for most EJBs. The generic classes are in the weblogic.ejb
package:
You can implement a generic bean template in a class of your own by importing the generic class into the class you are writing. This example imports the GenericSessionBean
class into HelloWorldEJB
:
import weblogic.ejb.GenericSessionBean;
...
public class HelloWorldEJB extends GenericSessionBean {
The following sections provide guidelines for programming client access to an EJB.
Local clients obtain initial context using the getInitialContext
method, similar to the following excerpt.
Listing 4-2 Local Client Performing a Lookup
...
Context ctx = getInitialContexLt("t3://localhost:7001", "user1", "user1Password");
...
static Context getInitialContext(String url, String user, String password) {
Properties h = new Properties();
h.put(Context.INITIAL_CONTEXT_FACTORY,
"weblogic.jndi.WLInitialContextFactory");
h.put(Context.PROVIDER_URL, url);
h.put(Context.SECURITY_PRINCIPAL, user);
h.put(Context.SECURITY_CREDENTIALS, password);
return new InitialContext(h);
Remote clients obtain an InitialContext
from the WebLogic Server InitialContext
factory.
A client can look up the entity bean's home interface in one of two ways:
Using EJB links is a BEA best practice and WebLogic Server fully supports EJB links as defined in the EJB 2.1 Specification. You can link an EJB reference that is declared in one application component to an enterprise bean that is declared in the same J2EE application.
In the ejb-jar.xml
file, specify the link to the EJB using the ejb-link
element of the ejb-ref
element of the referencing application component. The value of ejb-link
must match that of the ejb-name
in both ejb-jar.xml
and weblogic-ejb-jar.xml
of the target EJB. The target EJB can be in any EJB JAR file in the same J2EE application as the referencing application component.
Because ejb-name
s are not required to be unique across EJB JAR files, you may need to provide the qualified path for the link. Use the following syntax to provide the path name for the EJBs within the same J2EE application.
<ejb-link>../products/product.jar#ProductEJB</ejb-link>
This reference provides the path name of the EJB JAR file that contains the referenced EJB with the appended ejb-name
of the target bean separated from the path by "#". The path name is relative to the referencing application component JAR file.
To enable an EJB to open an HttpURLConnection
to an external HTTP server using the java.net.URL
resource manager connection factory type, specify the URL, or specify an object bound in the JNDI tree that maps to a URL, using the resource-ref
element in ejb-jar.xml
and the res-ref-name element in weblogic-ejb-jar.xml
.
To specify the URL to which an EJB sends requests:
weblogic-ejb-jar.xml
, specify the URL in the <jndi-name>
element of the resource-description element:To specify an object that is bound in JNDI and maps to a URL, instead of specifying a URL:
ejb-jar.xml
, specify the name by which the URL is bound in JNDI in the <jndi-name>
element of the resource-ref
element.weblogic-ejb-jar.xml
, specify the name by which the URL is bound in JNDI in the <jndi-name>
element of the resource-description element:<resource-description>
<res-ref-name>url/MyURL1</res-ref-name>
<jndi-name>firstName</jndi-name>
</resource-description>
where firstName
is the object bound to the JNDI tree that maps to the URL. This binding could be done in a startup class. When jndi-name
is not a valid URL, WebLogic Server treats it as an object that maps to a URL and is already bound in the JNDI tree, and binds a LinkRef
with that jndi-name
.
Regardless of how you specified an HTTP resource—by its URL or a JNDI name that maps to the URL—you can access it from EJB code in this way:
URL url = (URL) context.lookup("java:comp/env/url/MyURL");
connection = (HttpURLConnection)url.openConnection();
You can control the attributes of the network connection an EJB uses for communications by configuring a custom network channel and assigning it to the EJB. For information about WebLogic Server network channels and associated configuration instructions see Configure Network Resources in Configuring WebLogic Server Environments. After you configure a custom channel, assign it to an EJB using the network-access-point element in weblogic-ejb-jar.xml
.
Transaction design decisions are discussed in Features and Design Patterns. The following sections contain guidelines for programming transactions.
For information using transactions with entity beans, see Understanding ejbLoad() and ejbStore() Behavior.
Container-managed transactions are simpler to program than bean-managed transactions, because they leave the job of demarcation—starting and stopping the transaction—to the EJB container.
You configure the desired transaction behaviors in ejb-jar.xml
and weblogic-ejb-jar.xml
. For related information see Container-Managed Transactions Elements.
Key programming guidelines for container-managed transactions include:
commit
, setAutoCommit
, and rollback
methods of java.sql.Connection
getUserTransaction
method of javax.ejb.EJBContext
javax.transaction.UserTransaction
setRollbackOnly
method of the EJBContext
interface. (If the bean throws an application exception, typically an EJBException
, the rollback is automatic.) weblogic-ejb-jar.xml
set to TransactionSerializable
, exceptions or rollbacks in the EJB client might occur if contention occurs between clients for the same rows. To avoid such exceptions, you can:In this release of WebLogic Server, you can specify that, if a business method that has started a transaction fails because of a transaction rollback, the EJB container will start a new transaction and retry the failed method up to a specified number of times. If the method fails for the specified number of retry attempts, the EJB container throws an exception.
To configure automatic retry of container-managed transactions:
You can configure automatic retry of container-managed transactions for container-managed session and entity beans only. You cannot configure automatic retry of container-managed transactions for message-driven beans because MDBs do not acknowledge receipt of a message they are processing when the transaction that brackets the receipt of the message is rolled back; messages are automatically retried until they are acknowledged. You also cannot configure automatic retry of container-managed transactions for timer beans because, when a timer bean's ejbTimeout method starts and is rolled back, the timeout is always retried.
RequiresNew
. If a method's transaction attribute (trans-attribute
element in ejb-jar.xml
) is RequiresNew
, a new transaction is always started prior to the invocation of the method and, if configured, automatic retry of transactions occurs if the transaction fails.Required
. If a method's transaction attribute (trans-attribute
element in ejb-jar.xml
) is Required
, the method is retried with a new transaction only if the failed transaction was begun on behalf of the method.trans-attribute
element in ejb-jar.xml
, see trans-attribute
in Container-Managed Transaction Elements in ejb-jar.xml and Sun documentation.weblogic-ejb-jar.xml
. The retry-count subelement to retry-methods-on-rollback can also be modified via the Administration Console.
This section contains programming considerations for bean-managed transactions. For a summary of the distinguishing features of bean-level transactions and a discussion of related design considerations, see Bean-Level Transaction Management.
UserTransaction
object and begin a transaction before you obtain a Java Transaction Service (JTS) or JDBC database connection. To obtain the UserTransaction
object, use this command:ctx.lookup("javax.transaction.UserTransaction");
After obtaining the UserTransaction
object, specify transaction boundaries with tx.begin()
, tx.commit()
, tx.rollback()
.
If you start a transaction after obtaining a database connection, the connection has no relationship to the new transaction, and there are no semantics to "enlist" the connection in a subsequent transaction context. If a JTS connection is not associated with a transaction context, it operates similarly to a standard JDBC connection that has autocommit
equal to true
, and updates are automatically committed to the datastore.
Once you create a database connection within a transaction context, that connection is reserved until the transaction commits or rolls back. To optimize performance and throughput, ensure that transactions complete quickly, so that the database connection can be released and made available to other client requests. See Features and Design Patterns for more information.
Note: You can associate only a single database connection with an active transaction context.
See Listing 4-3 for a code sample.
Listing 4-3 Setting Transaction Isolation Level in BMT
import javax.transaction.Transaction;
import java.sql.Connection
import weblogic.transaction.TxHelper:
import weblogic.transaction.Transaction;
import weblogic.transaction.TxConstants;
User Transaction tx = (UserTransaction)
ctx.lookup("javax.transaction.UserTransaction");
//Set transaction isolation level to TransactionReadCommitted
Transaction tx = TxHelper.getTransaction();
tx.setProperty (TxConstants.ISOLATION_LEVEL, new Integer
(Connection.TransactionReadCommitted));
getRollbackOnly
and setRollbackOnly
methods of the EJBContext
interface in bean-managed transactions. These methods should be used only in container-managed transactions. For bean-managed transactions, invoke the getStatus
and rollback methods of the UserTransaction
interface.This section describes two approaches for distributing a transaction across multiple beans, which may reside on multiple server instances.
The code fragment below is from a client application that obtains a UserTransaction
object and uses it to begin and commit a transaction. The client invokes two EJBs within the context of the transaction.
u = (UserTransaction) jndiContext.lookup("javax.transaction.UserTransaction");
u.begin();
account1.withdraw(100);
account2.deposit(100);
u.commit();
...
The updates performed by the account1
and account2
beans occur within the context of a single UserTransaction
. The EJBs commit or roll back together, as a logical unit, whether the beans reside on the same server instance, different server instances, or a WebLogic Server cluster.
All EJBs called from a single transaction context must support the client transaction—each beans' trans-attribute
element in ejb-jar.xml
must be set to Required
, Supports
, or Mandatory
.
You can use a "wrapper" EJB that encapsulates a transaction. The client calls the wrapper EJB to perform an action such as a bank transfer, and the wrapper starts a new transaction and invokes one or more EJBs to do the work of the transaction.
The wrapper EJB can explicitly obtain a transaction context before invoking other EJBs, or WebLogic Server can automatically create a new transaction context, if the wrapper's trans-attribute
element in ejb-jar.xml
is set to Required
or RequiresNew
.
All EJBs invoked by the wrapper EJB must support the wrapper EJB's transaction context— their trans-attribute
elements must be set to Required
, Supports
, or Mandatory
.
This release of WebLogic Server supports the EJB timer service defined in the EJB 2.1 Specification. The EJB timer service is an EJB-container provided service that allows you to create timers that schedule callbacks to occur when a timer object expires. Timer objects can be created for entity beans, message-driven beans, and stateless session beans. Timer objects expire at a specified time, after an elapsed period of time, or at specified intervals. For instance, you can use the timer service to send out notification when an EJB remains in a certain state for an elapsed period of time.
The WebLogic EJB timer service is intended to be used as a coarse-grained timer service. Rather than having a large number of timer objects performing the same task on a unique set of data, BEA recommends using a small number of timers that perform bulk tasks on the data. For example, assume you have an EJB that represents an employee's expense report. Each expense report must be approved by a manager before it can be processed. You could use one EJB timer to periodically inspect all pending expense reports and send an email to the corresponding manager to remind them to either approve or reject the reports that are waiting for their approval.
This section summarizes the Java programming interfaces defined in the EJB 2.1 Specification that you can use to program timers. For detailed information on these interfaces, refer to the EJB 2.1 Specification. This section also provides details about the WebLogic Server-specific timer-related interfaces.
EJB 2.1 interfaces you can use to program timers are:
javax.ejb.TimedObject
interface, which must be implemented by the enterprise bean class of a bean that will be registered with the timer service for timer callbacks. This interface has a single method, ejbTimeout
.EJBContext
interface, which has a getTimerService
method, through which the timer service is accessed.javax.ejb.TimerService
interface which allows you to create new EJB timers or access existing EJB timers for the EJB.javax.ejb.Timer
interface which contains information about a particular EJB timer.javax.ejb.TimerHandle
interface which allows WebLogic Server to obtain a serializable timer handle that can be persisted. Since timers are local objects, a TimerHandle
must not be passed through a bean's remote interface or Web service interface.For more information on EJB 2.1 timer-related programming interfaces, see the EJB 2.1 Specification.
This section describes WebLogic Server-specific interfaces you can use to program timers.
WebLogic Server-specific timer-related programming interfaces are:
weblogic.management.runtime.EJBTimerRuntimeMBean
, which provides runtime information and administrative functionality for timers from a particular EJBHome
. The weblogic.management.runtime.EJBTimerRuntimeMBean
interface is shown in Listing 4-4.Listing 4-4 weblogic.management.runtime.EJBTimerRuntimeMBean
Interface
public interface weblogic.management.runtime.EJBTimerRuntimeMBean {
public int getTimeoutCount(); // get the number of successful timeout notifications that have been made
public int getActiveTimerCount(); // get the number of active timers for this EJBHome
public int getCancelledTimerCount(); // get the number of timers that have been cancelled for this EJBHome
public int getDisabledTimerCount(); // get the number of timers temporarily disabled for this EJBHome
public void activateDisabledTimers(); // activate any temporarily disabled timers
}
weblogic.ejb.WLTimerService
interface which extends the javax.ejb.TimerService
interface to allow users to specify WebLogic Server-specific configuration information for a timer. The weblogic.ejb.WLTimerService
interface is shown in Listing 4-5; for information on the javax.ejb.TimerService
, see the EJB 2.1 Specification.Listing 4-5 weblogic.ejb.WLTimerService
Interface
public interface WLTimerService extends TimerService {
public Timer createTimer(Date initial, long duration, Serializable info,
WLTimerInfo wlTimerInfo)
throws IllegalArgumentException, IllegalStateException, EJBException;
public Timer createTimer(Date expiration, Serializable info,
WLTimerInfo wlTimerInfo)
throws IllegalArgumentException, IllegalStateException, EJBException;
public Timer createTimer(long initial, long duration, Serializable info
WLTimerInfo wlTimerInfo)
throws IllegalArgumentException, IllegalStateException, EJBException;
public Timer createTimer(long duration, Serializable info,
WLTimerInfo wlTimerInfo)
throws IllegalArgumentException, IllegalStateException, EJBException;
}
weblogic.ejb.WLTimerInfo
interface which is used in the weblogic.ejb.WLTimerService
interface to pass WebLogic Server-specific configuration information for a timer. The weblogic.ejb.WLTimerInfo
method is shown in Listing 4-6Listing 4-6 weblogic.ejb.WLTimerInfo
Interface
public final interface WLTimerInfo {
public static int REMOVE_TIMER_ACTION = 1;
public static int DISABLE_TIMER_ACTION = 2;
public static int SKIP_TIMEOUT_ACTION = 3;
/**
* Sets the maximum number of retry attempts that will be
* performed for this timer. If all retry attempts
* are unsuccesful, the timeout failure action will
* be executed.
*/
public void setMaxRetryAttempts(int retries);
public int getMaxRetryAttempts();
/**
* Sets the number of milliseconds that should elapse
* before any retry attempts are made.
*/
public void setRetryDelay(long millis);
public long getRetryDelay();
/**
* Sets the maximum number of timeouts that can occur
* for this timer. After the specified number of
* timeouts have occurred successfully, the timer
* will be removed.
*/
public void setMaxTimeouts(int max);
public int getMaxTimeouts();
/**
* Sets the action the container will take when ejbTimeout
* and all retry attempts fail. The REMOVE_TIMER_ACTION,
* DISABLE_TIMER_ACTION, and SKIP_TIMEOUT_ACTION fields
* of this interface define the possible values.
*/
public void setTimeoutFailureAction(int action);
public int getTimeoutFailureAction();
}
weblogic.ejb.WLTimer
interface which extends the javax.ejb.Timer
interface to provide additional information about the current state of the timer. The weblogic.ejb.WLTimer
interface is shown in Listing 4-7.Listing 4-7 weblogic.ejb.WLTimer
Interface
public interface WLTimer extends Timer {
public int getRetryAttemptCount();
public int getMaximumRetryAttempts();
public int getCompletedTimeoutCount();
}
The following deployment descriptor elements pertain to timers:
For more information on these elements, see weblogic-ejb-jar.xml Deployment Descriptor Reference.
You cannot migrate a timer object from one server to another; timer objects can only be migrated as part of an entire server. If a server that contains EJB timers goes down for any reason, you must restart the server or migrate the entire server in order for the timers to execute.
This release of WebLogic Server complies with the EJB 2.1 requirements related to declaring and accessing external Web Services. Web Service references, declared in an EJB's deployment descriptor, maps a logical name for a Web Service to an actual Web Service interface, which allows you to refer to the Web Service using a logical name. The bean code then performs a JNDI lookup using the Web Service reference name.
For more information, see Programming Web Services for WebLogic Server.
To see which tools support the compilation process, see Table 4-12.
For information on the compilation process, see Compiling Java Code in Developing Applications with WebLogic Server.
If you annotate your Bean class file with JDK 1.5 annotations, you can use EJBGen to generate the Remote and Home classes and the deployment descriptor files for an EJB application.
BEA reccommends that you use EJBGen to generate deployment descriptors. For more information, see EJBGen Reference.
Elements in ejb-jar.xml,
weblogic-ejb-jar.xml
, and for container-managed persistence entity beans, weblogic-cmp-jar.xml
, control the run-time characteristics of your application.
If you need to modify a descriptor element, you can edit the descriptor file with any plain text editor. However, to avoid introducing errors, use a tool designed for XML editing. Descriptor elements that you can edit with the WebLogic Server Administration Console are listed in Table 4-11.
The following sections are a quick reference to WebLogic Server-specific deployment elements. Each section contains the elements related to a type of feature or behavior. The table in each section defines relevant elements in terms of the behavior it controls, the bean type it relates to (if bean type-specific), the parent element in weblogic-ejb-jar.xml
that contains the element, and the behavior you can expect if you do not explicitly specify the element in weblogic-ejb-jar.xml
.
For comprehensive documentation of the elements in each descriptor file, definitions, and sample usage, refer to:
ejb-jar.xml.
This table lists the elements in weblogic-ejb-jar.xml
related to security.
Table 4-2 Security Elements in weblogic-ejb-jar.xml
This table lists the elements in weblogic-ejb-jar.xml
that map the names of beans or resources used in source code to their JNDI names in the deployment environment.
Table 4-3 Resource Mapping Elements in weblogic-ejb-jar.xml
JNDI name of a resource or reference available in WebLogic Server. Note: Assigning a JNDI name to a bean is not recommended. Global JNDI names generate heavy multicast traffic during clustered server startup. See Using EJB Links for the better practice. |
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JNDI name for a bean's local home. If a bean has both a remote and a local home, then it must have two JNDI names; one for each home. |
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JNDI name of the JMS connection factory that the bean uses to create queues and topics. |
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JNDI name that associates a message-driven bean with a queue or topic in the JNDI tree. |
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Initial context factory that the EJB container uses to create connection factories. |
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Client ID for the message-driven bean associated with a durable subscriber topic. |
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Maps a message destination reference in the |
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Specifies the URL provider to be used by the |
This table lists elements in weblogic-ejb-jar.xml
that specify how the state of a bean is persisted.
Table 4-4 Persistence Elements in weblogic-ejb-jar.xml
This table lists the elements in weblogic-ejb-jar.xml
related to clustering. These elements control failover and load balancing behaviors for clustered beans in a WebLogic Server cluster.
Table 4-5 Clustering Elements in weblogic-ejb-jar.xml
This table lists the elements in weblogic-ejb-jar.xml
related to the consistency of the bean instance data and the database. These elements control behaviors such as how and when the database is updated to reflect the values in the bean instance is done.
Note: For elements related to container-managed persistence, see Managing Entity Bean Pooling and Caching.
Table 4-6 Data Consistency Elements in weblogic-ejb-jar.xml
Table 4-7 lists the elements in ejb-jar.xml
related to container-managed transactions.
Table 4-7 Container-Managed Transaction Elements in ejb-jar.xml
Specifies how the container manages the transaction boundaries when delegating a method invocation to an enterprise bean's business method. Allowable values are:
Note: In previous releases of WebLogic Server, the EJB container would start a new transaction when no transaction existed and the value of Because clients do not provide a transaction context for calls to an MDB, MDBs that use container-managed transactions must have |
If not specified, the EJB container issues a warning, and uses |
|
This optional element specifies whether an enterprise bean requires distributed transactions for its methods or whether the local transaction optimization may be used. |
If not specified, the container assumes that distributed transactions must be used. |
Table 4-8 lists the elements in weblogic-ejb-jar.xml
related to container-managed transactions.
Table 4-8 Container-Managed Transaction Elements in weblogic-ejb-jar.xml
This table lists the elements in weblogic-ejb-jar.xml
related to performance.
Table 4-9 Performance Elements in weblogic-ejb-jar.xml
Whether multiple clients can simultaneously access a bean without triggering a The server throws a |
|||
Causes the container to cache the persistent data of an entity bean between transactions. |
|||
Order in which stateful session beans are removed from the cache. |
|||
Indicates that all clients of the bean are collocated with the bean on the same server instance. This element is only used if the EJB has a global JNDI name; setting it to A value of |
|||
If However, the container still flushes updates to the database before executing an EJB finder or select query if the include-updates element (in the Applicable to both container-managed persistence and bean-managed persistence beans. |
|||
Specifies the thread pool used to handle requests to the bean. |
|||
Improves performance of method invocation for methods called within the same application, by allowing parameters to be passed by reference. Note: Method parameters are always passed by value when an EJB is called remotely. |
|||
The application-level entity cache, which can cache instances of multiple entity beans that are part of the same application. Note: Application level caches are declared in the |
|||
Estimated average size, in bytes, of an entity bean instance. |
|||
Causes beans returned by a Note: Applicable to container-managed persistence beans only. |
|||
Number of seconds of inactivity after which a bean is passivated. |
|||
Number of seconds of inactivity after which a bean is passivated. |
|||
Number of instances of an EJB instantiated by the container at startup. |
|||
The method that changes the state of bean. Specifying this method causes WebLogic server to persist the bean state when the method completes. Note: Applies to bean-managed persistence or EJB 1.1 container-managed persistence beans. |
If not specified, bean state is persisted after each method completes. |
||
The number of seconds between attempts by the EJB container to reconnect to a JMS destination that has become unavailable. |
|||
The number of seconds between |
This table lists the elements in weblogic-ejb-jar.xml
related to network communications.
Table 4-10 Communications Elements in weblogic-ejb-jar.xml
Container classes include the internal representation of the EJB that WebLogic Server uses and the implementation of the external interfaces (home, local, and/or remote) that clients use. You can use WebLogic Workshop or appc
to generate container classes.
Container classes are generated in according to the descriptor elements in weblogic-ejb-jar.xml
. For example, if you specify clustering elements, appc
creates cluster-aware classes that will be used for deployment. You can use appc
directly from the command line by supplying the required options and arguments. See appc for more information.
The following figure shows the container classes added to the deployment unit when the EAR or JAR file is generated.
Figure 4-2 Generating EJB Container Classes
Although infrequent, when you generate classes with appc
, you may encounter a generated class name collision which could result in a ClassCastException
and other undesirable behavior. This is because the names of the generated classes are based on three keys: the bean class name, the bean class package, and the ejb-name
for the bean. This problem occurs when you use an EAR file that contains multiple JAR files and at least two of the JAR files contain an EJB with both the same bean class, package, or classname, and both of those EJBs have the same ejb-name
in their respective JAR files. If you experience this problem, change the ejb-name
of one of the beans to make it unique.
Because the ejb-name
is one of the keys on which the file name is based and the ejb-name
must be unique within a JAR file, this problem never occurs with two EJBs in the same JAR file. Also, because each EAR file has its own classloader, this problem never occurs with two EJBs in different EAR files.
BEA recommends that you package EJBs as part of an enterprise application. For more information, see Deploying and Packaging from a Split Development Directory in Developing Applications with WebLogic Server.
WebLogic Server supports the use of ejb-client.jar
files for packaging the EJB classes that a programmatic client in a different application requires to access the EJB.
Specify the name of the client JAR in the ejb-client-jar
element of the bean's ejb-jar.xml
file. When you run the appc
compiler, a JAR file with the classes required to access the EJB is generated.
Make the client JAR available to the remote client. For Web applications, put the ejb-client.jar
in the /lib
directory. For non-Web clients, include ejb-client.jar
in the client's classpath.
Note: WebLogic Server classloading behavior varies, depending on whether the client is stand-alone. Stand-alone clients with access to the ejb-client.jar
can load the necessary classes over the network. However, for security reasons, programmatic clients running in a server instance cannot load classes over the network.
Deploying an EJB enables WebLogic Server to serve the components of an EJB to clients. You can deploy an EJB using one of several procedures, depending on your environment and whether or not your EJB is in production.
For general instructions on deploying WebLogic Server applications and modules, including EJBs, see Deploying Applications to WebLogic Server. For EJB-specific deployment issues and procedures, see Deployment Guidelines for Enterprise Java Beans, in this book—Programming WebLogic Enterprise JavaBeans.
The following sections describe WebLogic Server features that are useful for checking out and debugging deployed EJBs.
If you compile your EJBs with appc
, you can use the appc -lineNumbers
command option to add line numbers to generated class files to aid in debugging. For information, see appc Reference.
WebLogic Server collects a variety of data about the run-time operation of a deployed EJB. This data, which you can view in the Deployments node of the Administration Console, can be useful in determining if an EJB has completed desired processing steps. To access EJB run-time statistics, expand the Deployment node in the Administration Console, navigate to the JAR EAR that contains the bean, and select the Monitoring tab.
For information about the data available, see these pages in Administration Console Online Help:
For instructions on how to create messages in your application to help you troubleshoot and solve bugs and problems, see Using WebLogic Logging Services.
This section describes BEA tools that support the EJB development process. For a comparison of the features available in each tool, see Table 4-12.
In the Administration Console, you can view, modify, and persist to the descriptor file within the EJB a number of deployment descriptor elements. Descriptors are modified in the Administration Server copy of the EJB as well as in any deployed copies of the EJB (after deployment). When you modify descriptors, changes are made to your (the user's) original copy of the EJB (prior to deployment).
However, updating these descriptor elements takes place dynamically at runtime without requiring that the EJB be redeployed. The descriptor element that you can change in the Administration Console are limited to only those that may be dynamically changed at runtime, as summarized in Table 4-11.
The javac
compiler provided with the Sun Java J2SE SDK provides java compilation capabilities. For information on javac
, see http://java.sun.com/docs/.
EJBGen is an EJB 2.x code generator. You can annotate your bean class file with javadoc tags and then use EJBGen to generate the remote and home interface classes and the deployment descriptor files for an EJB application, reducing to one the number of EJB files you need to edit and maintain.
BEA recommends that you use EJBGen
to generate deployment descriptors; this is a BEA best practice which allows for easier and simpler maintenance of EJBs. When you use EJBGen
, you have to write and annotate only one bean class file, which simplifies writing, debugging, and maintenance. If you use WebLogic Workshop as a development environment, WebLogic Workshop automatically inserts EJBGen tags for you.
For information on EJBGen, see EJBGen Reference.
The weblogic.Deployer
command-line tool is a Java-based deployment tool that provides a command line interface to the WebLogic Server deployment API. This tool was developed for administrators and developers who need to initiate deployment from the command line, a shell script, or any automated environment other than Java.
See weblogic.Deployer Command-Line Reference in Deploying Applications to WebLogic Server.
The appc
compiler generates and compiles the classes needed to deploy EJBs and JSPs to WebLogic Server. It validates the deployment descriptors for compliance with the current specifications at both the individual module level and the application level. The application-level checks include checks between the application-level deployment descriptors and the individual modules as well as validation checks across the modules.
Note: appc replaces the deprecated ejbc
utility. BEA recommends that you use appc
instead ejbc
.
See appc Reference
DDConverter
is a command line tool that upgrades deployment descriptors from earlier versions of WebLogic Server. BEA recommends that you always upgrade your deployment descriptors in order to take advantage of the features in the current J2EE specification and release of WebLogic Server.
You can use weblogic.DDConverter to upgrade your deployment descriptors. For information on using weblogic.DDConverter, see Developing Applications with WebLogic Server.
Note: With this release of WebLogic Server, the EJB-specific DDConverter, weblogic.ejb20.utils.DDConverter
, is deprecated. Instead, use the new application-level DDConverter, weblogic.DDConverter
, to convert your application's deployment descriptors, including the EJB-specific deployment descriptors.
The following table lists BEA tools for EJB development, and the features provided by each.
.