DAO and Service Layer with hibernate

问题

im in trouble with implemenetation of a service layer, i think i did not understand this concept very well.

In a DAO implementation i can write all CRUD logic for a specific technology and entity (for example hibernate and User table), and in a service layer we use a DAO for all data operation for the entity in DAO (like getUser, loginUser, etc..) is this ok?

If this is ok i have a simple question, can i handle database connection (or in case of hibernate, session and transaction) within service layer, DAO implementation or neither?

Example, i have a simple GUI with one Button(load all User), and a table will contains all User. Pressing the Button will load the table with all users.

I have a HibernateDAO for User entity (UserHibernateDAO) containing all CRUD operation and a service layer, UserService, for some specific data operation with user.

ServiceLayer:

public class UserService extends AbstractServiceLayer{

    private AbstractDAO dao;

    public UserService(AbstractDAO dao){
     this.dao=dao;
    }

    public List<User> loadAllUsers(){
     return dao.findAll();
    }

}

In actionperformed of Button:

private void buttonActionPerformed(ActionEvent evt) {
    Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
    List<User> users=userService.loadAllUsers();
    loadTableWithUsers(users);
    transaction.commit();
}

Is this implementation ok? Session and transaction handle is in the right position or i have to put it into service layer? ..or perhaps into dao?

EDIT1:

If i have an interface UserDAO and a UserHibernateDAO that implements UserDAO, service layer has no reason to exists, isn't true? Becouse i can have all method to manage an "USER" inside my UserDAO and UserHibernateDAO implements all this methods for hibernate technology... then i could have a UserJdbcDAO, UserMysqlDAO etc... mmm...

EDIT2:

private void buttonActionPerformed(ActionEvent evt) {
    myBusinessMethod();
}

private void myBusinessMethod(){
    Transaction transaction=HibernateUtil.getSessionFactory().getCurrentSession().beginTransaction();
    List<User> users=userService.loadAllUsers();
    loadTableWithUsers(users);
    //some other useful operation before close session
    transaction.commit();
}

im not sure, a business method is a method like this?

Thanks all.

回答1:

1. You are handling the transaction inside your actionPerformed() method. Its clearly defeating the purpose of DAO/Service layer
2. Your UserService is accepting AbstractDAO, which means some other code may pass wrong DAO implementation to your UserService that will screw things up

Now, few suggestions.

1. You can look into GenericDAO concept for this. That might suit your need
2. Most of the time we ain't need all these layers like Service, DAO and BusinessDelegate. So, question yourself are any of these really answering some of your questions. If not, get rid of them. YAGNI
3. Get rid of DAO completely, and treat your Hibernate API as your DAO. Handle database transaction in your business methods. You may like to read this question

[Edited]

After your edit my 3rd suggestion doesn't carry much weight. By the way, you name your DAOs as follows; UserJdbcDAO, UserMysqlDAO etc. Your 2nd name is not making much sense, as we use ORMs just to avoid DB vendor specific DAOs/queries. It might start making some sense if your UserMysqlDAO extends UserJdbcDAO.

来源：https://stackoverflow.com/questions/4031433/dao-and-service-layer-with-hibernate