【Hibernate】【泛型DAO接口+泛型DAO实现类】

背景

1.每个Impl接口都要写get,delete,save,update,list,query的方法
2.每个DAO类都要去实现impl的方法.
结果:造成大量接口和类的代码重复—>违背dry原则

泛型DAO接口

1.声明T需要继承于BaseDomain.
2.声明6个接口方法

public interface IgenericDAO<T extends BaseDomain> {

    public void delete(T o);
    public T get(Long id);
    public void save(T o);
    public void update(T o);
    public List<T> list();
    public Page<List<T>> getPage(IQuery q);
}

此后的所有DAO接口的写法,只需要继承泛型DAO接口

public interface IEmployeeDAO extends IgenericDAO<Employee>{}

泛型DAO实现类

1.实现类中需要将泛型T实体化

• TClass:传入的类的Class对象
• TSimpleName:传入的类的简单名

2 . 实现类要继承于IgenericDAO<T>

@SuppressWarnings("unchecked")
public abstract class  genericDAOImpl<T extends BaseDomain> implements IgenericDAO<T>{

    //将泛型T具体化,通过构造器
    private Class<?> TClass;
    private String TSimpleName;
    public  genericDAOImpl() {
        this.TClass = (Class<T>) ((ParameterizedType)getClass().getGenericSuperclass()).getActualTypeArguments()[0];
        this.TSimpleName=TClass.getSimpleName();
    }

    //Spring注入session工厂
    @Autowired
    private SessionFactory sessionFactory;

    //delete
    public void delete(T o) {
        Session session = sessionFactory.getCurrentSession();
        session.delete(o);
    }

    //get  需要用到TClass
    public T get(Long id) {
        Session session = sessionFactory.getCurrentSession();

        return (T)session.get(TClass, id);
    }

    //save
    public void save(T o) {
        Session session = sessionFactory.getCurrentSession();
        session.save(o);
    }

    //update
    public void update(T o) {
        Session session = sessionFactory.getCurrentSession();
        session.update(o);
    }

    //list 需要用到TSimpleName
    public List<T> list() {
        Session session = sessionFactory.getCurrentSession();
        String HQL="select o from "+this.TSimpleName+" o "+" order by o.id asc";

        List<T> list = session.createQuery(HQL).list();
        return list;
    }

    //高级查询  只要将两个HQL主体改一下类名, ps 以后的XXXObjct要以o为对象了
    public Page<List<T>> query(IQuery q) {
        Session session = sessionFactory.getCurrentSession();
        //获取totalCount
        String countHQL ="select count(o) from "+this.TSimpleName+" o "+ q.getCountHQL();
        Query countQuery = session.createQuery(countHQL);
        this.setParamter(countQuery, q.getCountParameters());
        int  totalCount= ((Long)countQuery.list().get(0)).intValue();
        //获取currentPage
        Integer currentPage = q.getCurrentPage();
        //获取pageSize
        Integer pageSize = q.getPageSize();
        //获取list
        String listHQL="select o from "+this.TSimpleName+" o "+q.getListHQL();
        Query listQuery = session.createQuery(listHQL);
        this.setParamter(listQuery, q.getListParameters());
        List<T> list = listQuery.setFirstResult((currentPage-1)*pageSize).setProperties(pageSize).list();

        return new Page<List<T>>(totalCount, currentPage, pageSize, list);
    }

    //循环设置参数
    private void setParamter(Query query,List<Object> list) {
        for (int i=0;i<list.size();i++) {
            query.setParameter(i, list.get(i));

        }
    }
}

此后的DAO实现类只需要
1. **实现**DAO接口
2. 继承泛型DAO实现类
3. 构造器中声明调用父类构造器(将泛型T具体化)

public class EmployeeDAOImpl extends genericDAOImpl<Employee> implements IEmployeeDAO{
 public EmployeeDAOImpl() {
     super();
 }
}