Two classes with almost duplicate code inside

问题

At this moment, I have two classes: UserHibernateDao and TicketHibernateDao:

import java.util.List;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import model.dao.Dao;
import model.entity.User;

public class UserDaoHibernate extends HibernateDaoSupport implements Dao<User> {

    public User get(long id) {
        return getHibernateTemplate().get(User.class, id);
    }

    public void save(User user) {
        getHibernateTemplate().save(user);

    }

    public void remove(long id) {
        getHibernateTemplate().delete(
                getHibernateTemplate().get(User.class, id));
    }
}

and second:

import java.util.List;

import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import model.dao.Dao;
import model.entity.Ticket;

public class TicketDaoHibernate extends HibernateDaoSupport implements
        Dao<Ticket> {

    public Ticket get(long id) {

        return getHibernateTemplate().get(Ticket.class, id);

    }

    public void save(Ticket ticket) {
        getHibernateTemplate().save(ticket);
    }

    public void remove(long id) {

        getHibernateTemplate().delete(
                getHibernateTemplate().get(Ticket.class, id));

    }

    public void save(Ticket ticket) {

        getHibernateTemplate().saveOrUpdate(ticket);

    }
}

I see that both classes contain almost equal methods and method implementations.

I think, it is not very good. What do you think? Or it is normal?

回答1:

Something like this should work for you, it's generally called the "Generic DAO Pattern".

public abstract class BaseDaoHibernate<T> extends HibernateDaoSupport implements Dao<T> {

    private final Class<T> entityType;

    protected BaseDaoHibernate(Class<T> entityType) {
        this.entityType = entityType;
    }

    public T get(long id) {
        return getHibernateTemplate().get(entityType, id);
    }

    public void save(T entity) {
        getHibernateTemplate().save(entity);
    }

    public void remove(long id) {
        getHibernateTemplate().delete(get(id));
    }
}

and then:

public class TicketDaoHibernate extends BaseDaoHibernate<Ticket> {
    public TicketDaoHibernate() {
        super(Ticket.class);
    }
}

and

public class UserDaoHibernate extends BaseDaoHibernate<User> {
    public UserDaoHibernate() {
        super(User.class);
    }
}

回答2:

Use Generics and read this document. It's excellent.

回答3:

Add the following useful method to public abstract Dao<T>:

public Class<E> getEntityClass() {
    if (entityClass == null) {
        Type type = getClass().getGenericSuperclass();
        if (type instanceof ParameterizedType) {
            ParameterizedType paramType = (ParameterizedType) type;
            entityClass = (Class<E>) paramType.getActualTypeArguments()[0];
        } else
            throw new IllegalArgumentException("Could not guess entity class");
    }
    return entityClass;
}

Then your get and remove methods can be moved to Dao<T> and rewritten as:

public T get(long id) {
    return getHibernateTemplate().get(getEntityClass(), id);
}

public void remove(long id) {
    getHibernateTemplate().delete(get(id));
}

来源：https://stackoverflow.com/questions/9006288/two-classes-with-almost-duplicate-code-inside

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java

model

dao

persistent