| Q: |
What
are the methods of Entity Bean?
|
| A: |
An entity bean consists of 4 groups of methods:
1. create methods:
To create a new instance of a CMP entity
bean, and therefore insert data into the
database, the create() method on the bean's
home interface must be invoked. They look
like this: EntityBeanClass ejbCreateXXX(parameters),
where EntityBeanClass is an Entity Bean
you are trying to instantiate, ejbCreateXXX(parameters)
methods are used for creating Entity Bean
instances according to the parameters specified
and to some programmer-defined conditions.
A bean's home interface may declare zero
or more create() methods, each of which
must have corresponding ejbCreate() and
ejbPostCreate() methods in the bean class.
These creation methods are linked at run
time, so that when a create() method is
invoked on the home interface, the container
delegates the invocation to the corresponding
ejbCreate() and ejbPostCreate() methods
on the bean class.
2. finder methods:
The methods in the home interface that begin
with "find" are called the find
methods. These are used to query the EJB
server for specific entity beans, based
on the name of the method and arguments
passed. Unfortunately, there is no standard
query language defined for find methods,
so each vendor will implement the find method
differently. In CMP entity beans, the find
methods are not implemented with matching
methods in the bean class; containers implement
them when the bean is deployed in a vendor
specific manner. The deployer will use vendor
specific tools to tell the container how
a particular find method should behave.
Some vendors will use object-relational
mapping tools to define the behavior of
a find method while others will simply require
the deployer to enter the appropriate SQL
command.
There are two basic kinds of find methods:
single-entity and multi-entity. Single-entity
find methods return a remote reference to
the one specific entity bean that matches
the find request. If no entity beans are
found, the method throws an ObjectNotFoundException
. Every entity bean must define the single-entity
find method with the method name findByPrimaryKey(),
which takes the bean's primary key type
as an argument.
The multi-entity find methods return a collection
( Enumeration or Collection type) of entities
that match the find request. If no entities
are found, the multi-entity find returns
an empty collection.
3. remove methods:
These methods (you may have up to 2 remove
methods, or don't have them at all) allow
the client to physically remove Entity beans
by specifying either Handle or a Primary
Key for the Entity Bean.
4. home methods:
These methods are designed and implemented
by a developer, and EJB specification doesn't
have any requirements for them except the
need to throw a RemoteException is each
home method. |
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