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Entity Bean "Finder" methodsIf you went through the earlier tutorials and exercises, by now you must be familiar with the findByPrimaryKey method. It has a relatively obvious function, of retrieving an EJB given its primary key value.While finding an EJB by its primary key is a useful function, there are other ways to find EJBs also. These are known as its "finder" methods. The findByPrimaryKey will always return only one EJB instance, because EJBs are uniquely identified by their primary keys. But this is not true of other finders. E.g., in the "employee" EJB, a findBySalary finder may match a number of EJBs for a given salary. Therefore, a finder can have two types of signatures. It can return a single EJB, in which case its return type will be the remote interface. Alternatively, it can return a collection of EJBs, all of which matched the search criteria. If the finder found multiple beans but it is declared to return only one, it will return one bean out of the collection it found. If the finder is declared to return multiple beans, you can ask it to return a Collection or an Enumeration. To add a finder to an EJB, you are not supposed to write an implementation. You only need to declare the method in the home interface. As of this writing, the actual details of how the finder is implemented varies from server to server (though in the EJB 2.0 specification which be released later this year, this is more standardized.) To see some finders, regenerate the "props" EJB, but this time, in the Blizzard step 4 , click at the "Generate Finders..." button. Add finders where the "value" field equals a given value. Look at the home interface generated, and you will see the new finder signature. This finder can now be used to find a collection of EJBs where "value" is euqal to the finder argument Exercise:
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