Sample program using ejb

Annotations that can be used by other Java EE 6 components are in more generic packages, such javax. The AccountBean bean file is a plain Java file that implements the Account business interface; it is not required to implement any EJB-specific interface. The class-level Stateful metadata annotation specifies that the EJB is of type stateful session. The class-level Remote annotation specifies the name of the remote interface of the EJB; in this case it is the same as the business interface, Account.

This class typically includes a business method interceptor method, as well as lifecycle callback interceptor methods. See Example of an Interceptor Class for details about this class. The field-level EJB annotation specifies that the annotated variable, service , is injected with the dependent ServiceBean stateless session bean context.

The method-level ExcludeClassInterceptors annotation specifies that the AroundInvoke method specified in the associated interceptor class AuditInterceptor should not be invoked for the sayHelloFromAccountBean method. The method-level PreDestroy annotation specifies that the EJB container should invoke the preDestroy method before the container destroys an instance of the AccountBean. This shows how you can specify interceptor methods for both business methods and lifecycle callbacks in the bean file itself, in addition to using an associated interceptor class.

The method-level AroundInvoke specifies the business method interceptor method. You can use this annotation only once in an interceptor class. The method-level PostActivate and PrePassivate annotations specify the methods that the EJB container should call after reactivating and before passivating the bean, respectively. This example shows how a message-driven bean to implement a listener interface with no methods.

A bean that implements a no-methods interface exposes all non-static public methods of the bean class and of any superclasses, except java. Object , as message listener methods. EJB 3. This example demonstrates the use of the EJB 3. In this example, a Singleton session bean provides a central counter service. The Counter EJB is called from a Java client to demonstrate it is being used, with the count being consistently incremented by "1" as the client is invoked multiple times.

Adding the Asynchronous annotation to an EJB class or specific method will direct the EJB container to return control immediately to the client when the method is invoked. The method may return a Future object to allow the client to check on the status of the method invocation, and then retrieve result values that are asynchronously produced.

In this example, an Stateless bean is annotated at the class level, with Asynchronous indicating its methods are all asynchronous, with each of the methods simulating a long-running calculation. When a message arrives, the container calls the message-driven bean's onMessage method to process the message. The onMessage method normally casts the message to one of the five JMS message types and handles it in accordance with the application's business logic.

The onMessage method can call helper methods or can invoke a session bean to process the information in the message. A message can be delivered to a message-driven bean within a transaction context, so all operations within the onMessage method are part of a single transaction. If message processing is rolled back, the message will be redelivered. As discussed before, MDBs are event-driven, so in this section, we'll talk about how to access and invoke methods of session beans.

To invoke the methods of an EJB locally, the bean can be injected in any managed class running in the container — say a Servlet:. Invoking the method from a remote JVM is trickier and requires a bit more code. As a prerequisite, EJB must implement a remote interface to enable remoting capabilities.

You will need to write an EJB client which will perform a lookup over the network. Now let's write the client which in this case would just be a simple Java SE application with the main method:.

First, we created a Context with properties referring to the remote JVM. Once we get the remote EJB instance, we were able to invoke the method. As it happens, the Maven EJB plugin will generate a client jar file which will only have all the remote interfaces.

You just need to configure the plugin:. In case of Stateful beans, a new instance of the bean is returned every time a client performs a lookup. In case of Stateless beans, any one bean from the pool is returned. With both Stateless and Stateful enterprise beans, methods can be concurrently invoked by multiple clients or by multiple threads from the same client. However, in case of Singleton enterprise beans, the default mode is LockType.

This means that only one thread is allowed to invoke the method at once. That can be changed by adding the annotation over a method and setting to LockType. READ :. This fine-grained concurrency management over method level allows developers to build robust multi-threaded applications without having to deal with actual threads.

Most clients read from the Map but a few do put elements into it. Marking the get method as lock type read and put method as lock type write would make up for a perfect implementation:. A write-lock locks the whole class, so when the map is being updated in the addElement method, all the threads trying to access getElement will also be blocked. Running scheduled jobs in EJB is simplified to the maximum possible level i.

Parameters of this annotation configure when the timer will be executed:. Note here that the EJB is a Singelton. This is important because only singleton beans guarantee that only one instance of the bean will be created and we don't want our scheduler to be fired from multiple instances. By signing up, you agree to our Terms of Use and Privacy Policy. Forgot Password? This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy.

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