Enterprise JavaBeans is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component. An EJB web container provides a runtime environment for web related software components, including computer security, Java servlet lifecycle management, transaction processing, other web services; the EJB specification is a subset of the Java EE specification. The EJB specification was developed in 1997 by IBM and adopted by Sun Microsystems in 1999 and enhanced under the Java Community Process as JSR 19, JSR 153, JSR 220, JSR 318 and JSR 345; the EJB specification provides a standard way to implement the server-side'business' software found in enterprise applications. Such software addresses the same types of problem, solutions to these problems are repeatedly re-implemented by programmers. Enterprise JavaBeans is intended to handle such common concerns as persistence, transactional integrity and security in a standard way, leaving programmers free to concentrate on the particular parts of the enterprise software at hand.
The EJB specification details how an application server provides the following responsibilities: Transaction processing Integration with the persistence services offered by the Java Persistence API Concurrency control Event-driven programming using Java Message Service and Java EE Connector Architecture Asynchronous method invocation Job scheduling Naming and directory services Interprocess Communication using RMI-IIOP and Web services Security Deployment of software components in an application serverAdditionally, the Enterprise JavaBean specification defines the roles played by the EJB container and the EJBs as well as how to deploy the EJBs in a container. Note that the current EJB 3.2 specification does not detail how an application server provides persistence, but instead details how business logic can integrate with the persistence services offered by the application server. Businesses found; this is because the original specification allowed only for remote method invocation through CORBA though the large majority of business applications do not require this distributed computing functionality.
The EJB 2.0 specification addressed this concern by adding the concept of local interfaces which could be called directly without performance penalties by applications that were not distributed over multiple servers. The EJB 3.0 specification was a departure from its predecessors, following a new light-weight paradigm. EJB 3.0 shows an influence from Spring in its use of plain Java objects, its support for dependency injection to simplify configuration and integration of heterogeneous systems. Gavin King, the creator of Hibernate, participated in the EJB 3.0 process and is an outspoken advocate of the technology. Many features in Hibernate were incorporated in the Java Persistence API, the replacement for entity beans in EJB 3.0. The EJB 3.0 specification relies on the use of annotations and convention over configuration to enable a much less verbose coding style. Accordingly, in practical terms EJB 3.0 is much more lightweight and nearly a new API, bearing little resemblance to the previous EJB specifications.
The following shows a basic example of what an EJB looks like in code: The above defines a service class for persisting a Customer object. The EJB takes care of managing the persistence context and the addCustomer method is transactional and thread-safe by default; as demonstrated, the EJB focuses only on business logic and persistence and knows nothing about any particular presentation. Such an EJB can be used by a class in e.g. the web layer as follows: The above defines a JavaServer Faces backing bean in which the EJB is injected by means of the @EJB annotation. Its addCustomer method is bound to some UI component, such as a button. Contrary to the EJB, the backing bean does not contain any business logic or persistence code, but delegates such concerns to the EJB; the backing bean does know about a particular presentation. An EJB container holds two major types of beans: Session Beans that can be either "Stateful", "Stateless" or "Singleton" and can be accessed via either a Local or Remote interface or directly without an interface, in which case local semantics apply.
All session beans support asynchronous execution for all views. Message Driven Beans. MDBs support asynchronous execution, but via a messaging paradigm. Stateful Session Beans are business objects having state: that is, they keep track of which calling client they are dealing with throughout a session and thus access to the bean instance is limited to only one client at a time. If concurrent access to a single bean is attempted anyway the container serializes those requests, but via the @AccessTimeout annotation the container can instead throw an exception. Stateful session beans' state may be persisted automatically by the container to free up memory after the client hasn't accessed the bean for some time; the JPA extended persistence context is explicitly supported by Stateful Session Beans. Examples Checking out in a web store might be handled by a stateful session bean that would use its state to keep track of where the customer
The Alliance for Social and Economic Advancement is a political party in Hong Kong. The party is led by Herman Yuen; the party describes itself as part of a "construction camp", preferring to focus on citizen livelihood and public policy rather than politics. The party fielded three candidates in the 2019 Hong Kong local elections. In response to criticism regarding the party only fielding candidates in constituencies held by pro-Beijing district councillors, Yuen said the choice of constituencies was made based on familiarity with each area and a dissatisfaction with livelihood work there. Although the party is part of the pro-Beijing camp, it believes that the government's response to the 2019 Hong Kong protests has been ineffective and that the government should better listen to its people; the party's political positions include modifying the Lantau Tomorrow Vision, land reclamation at the Ngong Shuen Chau Naval Base and at Sandy Bay, an elderly care plan in the Greater Bay Area, the construction of a comprehensive elderly care complex near Guangzhou South railway station
The bearded guan is a species of bird in the family Cracidae, the chachalacas and curassows. It is found in Peru, its natural habitat is tropical moist montane forest. It is threatened by habitat loss; the bearded guan is a small brown bird, about 55 cm large, named for it red dewlap While most of the bird is brown, it has dark grayish-brown upper parts and rear underparts as well as a silver crown and neck feathers. The bird has white feathers edging its neck and breast, red legs, a rufous tail; the bearded guan lives at an altitude of 1200–3000 m in a humid environment located in northwest Peru and southern Ecuador. The greatest threat to the bearded guan is deforestation for mining. No information is known about the dietary habits of the bearded guan, however guans in general eat various fruits and berries and well as leaves and insects. Bearded guan are territorial species that mate at the beginning of the rain season. Most species of Guan reach sexual maturity at two years and can reproduce until they reach the age of twenty.
A pair of guan will produce a clutch of three eggs -- 28 days. BirdLife Species Factsheet. Guans at FAO.org Bearded Guan at Neotropical Birds Bearded Guan videos and photos on the Internet Bird Collection Photo & specifics-High Res.