Java Layered Architecture Concepts

Service is the business layer

DAO (data access Object) access

1.JAVA Action layer, service layer, modle layer and DAO layer function distinguish? (the service layer described below is biz)
First, this is now the most basic layering method, combining the SSH architecture. The Modle layer is the entity class for the corresponding database table.

The DAO layer uses Hibernate to connect to the database, to manipulate the database (add and revise).

All of the above hibernate,struts need to be injected into spring's configuration file, and spring links these together to become a whole.

other answers:  
action  is part of the business layer, is a manager   (main switch) (the function is to reverse) (take out the foreground interface data, call the Biz method, forward to the next action or page)     
action is a controller  dao mainly doing the interactive work of the database  Modle  is the model   storing your entity class  Biz  doing the corresponding business logic processing    

What is the difference between the DAO layer and the Biz layer in 2.java?
hehe, this question I have also had, remember before just learn programming time, are in service directly call Dao,service inside on new A DAO class object, call, other meaningful thing did not do, also do not understand have this have what use, attend work long after will know , business is the most serious work.  
again there is no understanding of the question, this is the experience, hehe, in fact, you will understand. Just started to write the code is a request, I went to the database fetch, business almost no.   

Other excellent answers:
(1), assume that now you do this function will use the user table and the permission table, then your front page access action,action to call the User module service, User module service to determine whether you are operating the user table or permission table, If you are working with the user table, the service implementation class will call Userdao. If you are manipulating a permission table, invoke the right of the DAO
(2), that is, DAO must be corresponding to each table one by one of the database, and the service is not. You got that? Actually you a project a service and a DAO actually also can operate the database,

It's just that if there's a lot of problems, it's a lot of trouble, and it's too messy.

(3), the advantage is that your entire project is very systematic, and the database table can be consistent, and functional modularity, so that later maintenance or error is easier to change, performance is also higher
As for why you're talking about using service layer encapsulation, I think: In general, some of the business processes of a program need to connect to the database, some do not need to deal with the database and directly is some business processing, so that we need to integrate into the service, This can play a better role in development and maintenance, but also is the embodiment of the model layer function in the MVC design pattern

What is the action in 3.java and what is DAO?
action class   is a class that [obtains form form data and processes logic]  
DAO (data access object)   is an interface implementation [through Sessionfactory access to the operation of the database session, and the implementation of some basic delete   Add   modify data, in the servlet more practical business operations] 
 
4.  What is the Pojo class?  
simple Java object (plain  Old java objects) is actually the general Javabeans, The Pojo name is used to avoid confusion with EJBs,  and for short, .  some of these properties and their getter setter methods, sometimes as Value object or DTOs (Data  transform object) to use. Of course, if you have a simple arithmetic attribute is also possible, but do not allow business methods, and can not carry a method such as connection.  

What are the 5.pojo classes and VO classes respectively?
VO has two kinds of statements, one is ViewObject, the other is valueobject.

Take the former for example, it is only responsible for encapsulating the data passed over the page, which is somewhat different from the PO.

Take Struts1 For example, Actionform is a typical viewobject. And Valueobject is the object that holds the value when the page is passed between pages ....

In general, the PO is the thing that eventually passes to Bo and Bo to pass a DAO, and in many cases it corresponds to our real database table.

And ViewObject is the data submitted on a page, not necessarily the same as the PO properties ....

the difference between Pojo and DTOs

Ational the abbreviation for Mapping (Object Relational mapping).Java's (Po,vo,to,bo,dao,pojo) explanation
 
PO (Persistant object) Persistent object
The concept that occurs at the O/R mapping, without the O/R mapping, does not exist. Usually the corresponding data model (database), itself also has some business logic processing. Can be seen as a Java object mapped to a table in the database. The simplest PO is a record in a table in the corresponding database, and 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 PO, which contains only data. 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. Personally feel the same DTO (data transfer object) that is passed on the web.

to (Transfer object), data transfer object
Objects that are transferred between different tie (relationships) in the application

BO (business object) service object
From the business model perspective, see the domain objects in the UML component Domain model. A Java object that encapsulates the business logic, by invoking the DAO method and combining Po,vo for business operations.

POJO (Plain ordinary Java object) simple, rule-free Java objects
Java objects that are purely traditional in meaning. In some object/relation mapping tools, the Persisent object that maintains database table records is a pure Java object that conforms to the Java Bean Specification and does not add other properties and methods. My understanding is the most basic Java Bean, only attribute fields and setter and getter Method!.

DAO (data Access object) Access objects
is a sun's standard Java EE design pattern, which has an interface that is DAO, which has negative persistence layer operations. 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. Through its method, combine the PO to carry on the related operation to the database. Sandwiched between business logic and database resources. With VO, provide database crud operations ...

O/R Mapper object/relationship Mapping
After defining all the mapping, this O/R mapper can help us do a lot of work. With these mappings, this O/R mapper can generate all the SQL statements about the object save, Delete, read, and we no longer need to write so many lines of DAL code.

Entity model (solid mode)
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

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PO: Full name is
Persistant Object Persistent Objects
The most vivid understanding is that a PO is a record in the database.
The advantage is that a record can be processed as an object and can be easily converted to other objects.

BO: The full name is
Business object: Operational objects
The main role is to encapsulate the business logic as an object. This object can include one or more other objects.
such as a resume, education experience, work experience, social relations and so on.
We can have an education experience corresponding to a PO, work experience corresponding to a PO, social relations corresponding to a PO.
Create a CV-based Bo object to process resumes, each BO containing these po.
When we handle business logic like this, we can deal with Bo.

VO:
Value Object Value objects
ViewObject Presentation Layer Objects
The data object that the main interface displays. For a Web page, or an interface for SWT and swing, use a Vo object to correspond to the value of the entire interface.

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.

Pojo:
Plain ordinary Java object simple Java objects
Personal feeling Pojo is the most common and changeable object, is an intermediate object, is also our most often dealing with objects.

A Pojo is a PO after persistence
It is the DTO that passes and passes directly through it.
Directly used to correspond to the presentation layer is VO

DAO:
Data Access Object Information
This everyone is most familiar with, and the above several o the biggest difference, basic without the possibility and necessity of mutual transformation.
Primarily used to encapsulate access to a database. It can be pojo to the PO, with PO assembled VO, DTO

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The Po:persistant object is persisted as a Java object that is mapped to a table in the database. The simplest PO is a record in a table in the corresponding database, and multiple records can be used with a collection of PO. The PO should not contain any operations on the database.
 
The Vo:value object value. Typically used for data transfer between business tiers, as is the case with PO, which contains only data. 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. Personally feel the same DTO (data transfer object) that is passed on the web.

Dao:data Access object that is used to access the database. Usually used in conjunction with PO, DAO contains various methods of operation of the database. Through its method, combine the PO to carry on the related operation to the database.

Bo:business object, which encapsulates the Java object of the business logic, invokes the DAO method and combines po,vo for business operations;

Pojo:plain ordinary Java object Simple, non-regular Java objects, I personally think it and other not a level of things, Vo and Po should belong to it.

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VO: Value object, view object
PO: Persistent Object
QO: Querying objects
DAO: Data Access Object
DTO: Data Transfer Object
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The actionform in struts is a VO;
The entity Bean in Hibernate is a PO, also called Pojo;
The criteria in hibernate is equivalent to a qo;
When using hibernate, we define some methods of querying, which are written in the interface and can have different implementation classes. And this interface can be said to be a DAO.
Personally think Qo and DTOs are similar.
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Po or bo, the closest layer to the database, is an ORM O, basically a database field corresponding to a property in Bo, for synchronization and security considerations, it is best to give DAO or service calls, rather than using Packcode,backingbean, or Bo tune.
DAO, the data access layer, the object in the Vo,backingbean can be put into ....
DTOs, seldom used, are basically put into DAO, but play a role in transition.
QO, is to put some with persistent query operations with the statement into the.
The basic elements and methods used in the VO,V layer are placed therein. If you want to call Bo, do the Bo conversion vo,vo convert Bo operation. Vo's advantage is that its page element attributes more than Bo, can play a very good role ....
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It's not right upstairs, PO is a persistent object. Bo=business object-business object.
The PO can be strictly corresponding to the database table, and a single PO is mapped to a table.
Bo is the business logic processing object, my understanding is that it is filled with business logic processing, in the business logic of complex applications to be useful.
Vo:value Object value objects, view object views
PO: Persistent Object
QO: Querying objects
DAO: Data Access Object--also DAO mode
DTO: Data Transfer Object-also DTO mode

Java Layered Architecture Concepts