Getting Started with Enterprise Beans. Written in the Java programming language, an enterprise bean is a server-side component that encapsulates the business logic of an application. The business logic is the code that fulfills the purpose of the application.
In an inventory control application, for example, the enterprise beans might implement the business logic in methods called checkInventoryLevel and orderProduct. By invoking these methods, clients can access the inventory services provided by the application. For several reasons, enterprise beans simplify the development of large, distributed applications. First, because the EJB container provides system-level services to enterprise beans, the bean developer can concentrate on solving business problems.
The EJB container, rather than the bean developer, is responsible for system-level services such as transaction management and security authorization. The client developer does not have to code the routines that implement business rules or access databases.
As a result, the clients are thinner, a benefit that is particularly important for clients that run on small devices. Third, because enterprise beans are portable components, the application assembler can build new applications from existing beans.
You should consider using enterprise beans if your application has any of the following requirements:. The application must be scalable. Working with message-driven beans is more involved than using session beans.
In an event-driven environment you'll typically need a message broker like ActiveMQ. While session beans are simpler, and thus more commonly used in EJB, event-driven architectures have become popular, especially with the explosion of microservices.
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. EJBs can be packaged in their own jars, deployed, and invoked from lots of places.
They are common components. True, POJOs can be carefully! 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.
Change Language. Related Articles. Table of Contents. Save Article. Improve Article. Like Article. Previous Count the nodes of a tree whose weighted string does not contain any duplicate characters. Next Count the nodes of a tree whose weighted string is an anagram of the given string. Recommended Articles. Article Contributed By :.
0コメント