What do you understand by ejb

Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide. Load Comments. What's New. Most popular in Java. More related articles in Java. We use cookies to ensure you have the best browsing experience on our website. In this release of WebLogic Server, you can use logical message destinations to map a logical message destination, defined in ejb-jar.

If a message destination reference cannot be resolved during deployment, a warning is issued but the deployment will succeed. MDBs linked to unavailable message destinations periodically attempt to connect to the message destination.

Until the message destination is available, attempts to look up message-destination-references declared in ejb-jar. When the message destination becomes available, the MDBs will connect to it and service messages from it. This section describes key WebLogic Server features that ease the process of EJB development, and enhance the performance, reliability, and availability of EJB applications. WebLogic Server supports pooling, caching, and other features that improve the response time and performance of EJBs.

In a production environment, these features can reduce the time it takes for a client to obtain an EJB instance and access and maintain persistent data. WebLogic Server maintains a free pool of ready-to-use EJB instances for stateless session beans, message-driven beans, and entity beans.

The EJB container creates a configurable number of bean instances at startup, so that a new instance does not have to be created for every request. When a client is done with an EJB instance, the container returns it to the pool for reuse. For more information see:.

WebLogic Server supports caching for stateful session beans and entity beans. An inactive cached bean instance can be passivated—removed from the cache and written to disk—and restored to memory later as necessary. Passivating bean instances optimizes use of system resources. You can configure the size of the cache, and related behaviors such as rules for removing beans from the cache. Caching is supported for entity EJBs, whether they use container-managed or bean-managed persistence. Additional caching features are available for EJBs that use container-managed persistence, as described in the following section.

WebLogic Server provides these caching capabilities for entity beans that use container managed persistence:.

A group specifies a set of persistent attributes of an entity bean. A field-group represents a subset of the container-managed persistence CMP and container-managed relation CMR fields of a bean.

You can put related fields in a bean into groups that are faulted into memory together as a unit. You can associate a group with a query or relationship, so that when a bean is loaded as the result of executing a query or following a relationship, only the fields mentioned in the group are loaded.

For more information, see Specifying Field Groups. You can configure the behavior of the ejbLoad and ejbStore methods to enhance performance, by avoiding unnecessary calls to ejbStore. As appropriate, you can ensure that WebLogic Server calls ejbStore after each method call, rather than at the conclusion of the transaction.

For more information, see Understanding ejbLoad and ejbStore Behavior. This allows you to avoid the bottlenecks that might otherwise occur when multiple entity instances are affected by a single transaction. For more information, see Ordering and Batching Operations.

This optimization improves performance, especially in applications with a high volume of database updates. If you use the read-mostly pattern, you can use multicast invalidation to maintain data consistency—an efficient mechanism for invalidating read-only cached data after updates.

Use of the invalidate method after the transaction update has completed invalidates the local cache and results in a multicast message sent to the other servers in the cluster to invalidate their cached copies. For more information, see Using the Read-Mostly Pattern. WebLogic Server provides a variety of value-added database access features for entity beans that use container-managed persistence:. For more information, see Automatically Generating Primary Keys.

You can configure the EJB container to automatically change the underlying table schema as entity beans change, ensuring that tables always reflect the most recent object-relationship mapping. This allows you to create and execute new queries without having to update and deploy an EJB. It also reduces the size and complexity of the EJB deployment descriptors.

Defining and consuming enterprise beans was a sticking point for many developers until EJB 3. Annotations make it very easy to configure enterprise beans for a wide range of functionality found in Java EE. Keep reading to get started with EJB annotations. In order to designate a class as a stateless session bean, you use the javax. Stateless annotation, as shown in Listing 1. This stateless bean contains a simple signature that takes no arguments and returns a string.

Don't let simplicity fool you, though: this bean can do anything you need it to, including interacting with other beans, services, or your application's data layer. Here, we inject the stateless bean into a servlet, and then it's available for use. Notice how the bean is identified under the EJB annotation. The "stateless" designation tells us this bean will not track the client.

Because it's stateless, we also know this bean is subject to threading if it does any work outside the invoked method. In this case, it's up to you to define and implement the interface, as shown in Listing 3.

The remote interface is sent to the client to invoke. Calls to it will then be fulfilled by the EJB's server-side implementation. The MyStatelessBean example in Listing 4 implements the remote interface. A remote interface is implemented just like a normal class implementing an interface. As the consumer of a remote EJB, the client application must be able to access the class definition for the remote interface.

They are very useful for creating SOA services. When used for local access they are POJOs with free container services added. This means that if the number of incoming requests per second is greater than the server can handle, we degrade gracefully - there are always some requests being processed efficiently and the excess requests are made to wait.

EJBs can be deployed on separate tier that can be clustered - this gives reliability via failover from one server to another, plus hardware can be added to scale linearly. Concurrency Management. The container ensures that EJB instances are automatically accessed safely serially by multiple clients. The container manages the EJB pool, the thread pool, the invocation queue, and automatically carries out method-level write locking default or read locking through Lock READ.

This protects data from corruption through concurrent write-write clashes, and helps data to be read consistently by preventing read-write clashes. This is mainly useful for Singleton session beans, where the bean is manipulating and sharing common state across client callers. This can be easily over-ridden to manually configure or programmatically control advanced scenarios for concurrent code execution and data access.

Automated transaction handling. Smart interaction with JPA. By default, the EntityManager injected as above uses a transaction-scoped persistence context. This is perfect for stateless session beans. But if other stateless EJBs are called by the method, the container propagates and shares the same PC to them, so same entities are automatically shared in a consistent way through the PC in the same transaction. Life-Cycle Management.

The lifecycle of EJBs is container managed. It also captures all exceptions, logs them, rolls back transactions as required, and throws new EJB exceptions or ApplicationExceptions as required.

Security Management. The server automatically passes the authenticated user details along with each call as security context the calling principal and role. It ensures that all RBAC rules are automatically enforced so that methods cannot be illegally called by the wrong role. It allows plugging in extra security processing or even IAM tools to the container in a standard way. EJB implementations conform to Java EE standards and coding conventions, promoting quality and ease of understanding and maintenance.

It also promotes portability of code to new vendor app servers, by ensuring they all support the same standard features and behaviors, and by discouraging developers from accidentally adopting proprietary non-portable vendor features.

The Real Kicker: Simplicity. All of the above can be done with very streamlined code - either using default settings for EJBs within Java EE 6, or adding a few annotations.

Once you start coding with EJBs, they are rather easy to develop and give a great set of "free ride" benefits. Most web projects did not actually use them. But this has changed significantly with 10 years of tweaking, overhauling, functional enhancement and development stream-lining. In Java EE 6 they provide maximum level industrial strength and simplicity of use.

An EJB is a Java component, containing business logic, that you deploy in a container, and that benefits from technical services provided by the container, usually in a declarative way, thanks to annotations:. Hope this from Oracle doc will help someone like me to understand the topic of EJB in a simple way.

What Is an Enterprise Bean?