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The Enterprise JavaBeans specification defines a standard
architecture for implementing the business logic of
multi-tier applications as reusable components. In addition
to Enterprise JavaBeans components, the architecture defines
three other entities: servers, containers, and clients. This
architecture incorporates several design goals:
Enterprise JavaBeans servers are designed to wrap around
legacy systems to provide fundamental services for
containers and the components they contain.
Enterprise JavaBeans containers are designed to handle
details of component life-cycle, transaction, and security
management. By interceding between clients and components at
the method call level, containers can manage transactions
that propagate across calls and components, and even across
containers running on different servers and different
machines. This mechanism simplifies development of both
component and clients.
Component developers are free to focus on business logic,
since containers provide services automatically by
interceding in component method calls. A simple set of
callback interfaces are all that a developer needs to
implement to participate in container provided services.
A client?s view of an Enterprise JavaBean remains the same
regardless of the container it is deployed in. Any container
in which an Enterprise JavaBean is deployed presents the
same interfaces to the client. This extends to containers
from different vendors, running against different servers
and different databases, on diverse systems on a network.
This client transparency ensures wide scalability for
multi-tier applications.
Along with container managed transactions, the Enterprise
JavaBeans architecture enables component- and client-managed
transactions. Containers can participate in component or
client initiated transactions to enforce transaction rules
across method call and component boundaries. Components can
also specify transaction types by method, enabling them to
mix transaction types within a single object.
A variety of Enterprise JavaBean attributes, including the
default component transaction type, can be specified at
either development or deployment time, and enforced through
mechanisms built into the container architecture.
The Enterprise JavaBeans architecture is based on the Java
programming language, so enterprise Beans take full
advantage of the ?write once, run anywhereTM? standard.
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