Java Terminology (PO/POJO/VO/BO/DAO/DTO)

PO (Persistant object) Persistent object
In the case of the O/R mapping, there is no such concept if there is no O/R mapping. Usually the corresponding data model (database), itself also has some business logic processing. It can be seen as a Java object mapped to a table in a database. The simplest PO is a record in a table in the corresponding database , multiple records can be used with a collection of PO. The PO should not contain any operations on the database.

VO (Value object) value objects
　　Typically used for data transfer between business tiers, as is the case with the PO. But it should be abstracted out of the business object that can correspond to the table or not, depending on the needs of the business. Personal feel with DTO (data transfer object), passed on the web.

This is used in front-end, to bind controls and the like.
This is the DTO obtained from the server and then converted to VO to bind the control.
You can also remove the dependency on the DTO.
It means that each layer has its own object. Objects that do not depend on other layers. This allows the layer to be testable, portable.
Of course, each layer will have an object transformation, which is the entity obtained from the lower layer, converted to the entity used by itself.
If the underlying changes the entity, this layer only needs to modify the mapping, the internal logic does not have to be modified. If you use the underlying entity directly, you will be walking around with modifications. It's also a place to focus on the changes.

BO (business object) service object
From the business model perspective, see the domain objects in the UML component Domain model. The Java object that encapsulates the business logic, by invoking the DAO method, in conjunction with PO,VO for business operations.

POJO (Plain ordinary Java object) simple, rule-free Java objects
Pure traditional Java object. That is, in some object/relation mapping tools, the ability to maintain database table records Persisent object is a pure Java object that conforms to the Java Bean specification. No additional properties and methods are added. My understanding is the most basic Java Bean, only attribute fields and setter and Getter methods!.

DAO (data Access object) Access objects
is one of Sun's standard Java EE design patterns, one of which is DAO, which is responsible for the operation of the persistence layer. Provides interfaces for the business layer. This object is used to access the database. Usually used in conjunction with PO, DAO contains various methods of operation of the database. Combine PO to perform related operations on the database. Sandwiched between business logic and database resources. With VO, provide database crud operations ...

DTO (Data Transfer object) data transfer objects
It is mainly used for remote calls, etc. where large quantities of objects need to be transferred.
For example, if we have 100 fields in a table, then the corresponding PO has 100 attributes.
But we just show 10 fields on the interface,
The client uses the Web service to get the data, and there is no need to pass the entire PO object to the client.
At this point we can pass the result to the client with a DTO with only these 10 attributes, and this will not expose the service-side table structure. After the client is reached, if the interface is displayed with this object, then its identity will be converted to VO.

DAL (data access Layer)
Idal (interface layer)
Dalfactory (class factory)
BLL (business logic Layer)
BOF business Object Framework service objects Frame
SOA Service Orient Architecture Services-oriented design
EMF Eclipse Model Framework Eclipse Modeling Framework

Java Terminology (PO/POJO/VO/BO/DAO/DTO)