Hibernate实现limit语句效果

Hibernate

hibernate实现limit效果

• 由于hql语句内无法直接书写limit语法，所以需要通过别的方式来达成这个效果
• limit效果一般需要有两个参数：开始位置start和查询数量num。两个参数都是final int型
• 实现代码如下：

try {
            //首先新建一个final型的hql语句
            final String hql="from xxb where xx="+xx+" order by xx asc ";
            //hibernate执行查找，参数为请求返回方法
            List<xx> xxList=getHibernateTemplate().executeFind(new HibernateCallback() {
                public Object doInHibernate(Session session){
                    //创建查找对象 ，设置起始位置以及查询数量
                    Query query=session.createQuery(hql);
                    query.setFirstResult(start);
                    query.setMaxResults(num);
                    //转换为list形式
                    return query.list();
                }
            });
            return xxList;
        }catch (RuntimeException e){
            throw  e;
        }

• 对于实现过程中的两个相关方法，截取其源码贴在下方，也可以自行查看。
  • executeFind方法实现如下：

public List executeFind(HibernateCallback<?> action) throws DataAccessException {
        Object result = this.doExecute(action, false, false);
        if (result != null && !(result instanceof List)) {
            throw new InvalidDataAccessApiUsageException("Result object returned from HibernateCallback isn't a List: [" + result + "]");
        } else {
            return (List)result;
        }
    }

• doInHibernate方法实现如下：

    public List<T> doInHibernate(Session session) throws HibernateException, SQLException {
        Query query = session.createQuery(this.hql).setFirstResult(this.pageModel.getBeginIndex()).setMaxResults(this.pageModel.getPageSize());
        if (!CollectionUtil.listIsNull(this.params)) {
            for(int i = 0; i < this.params.size(); ++i) {
                Object obj = this.params.get(i);
                if (obj instanceof String) {
                    query.setString(i, (String)obj);
                } else if (obj instanceof Integer) {
                    query.setInteger(i, (Integer)obj);
                } else if (obj instanceof Date) {
                    query.setDate(i, (Date)obj);
                }
            }
        }

        List<T> list = query.list();
        String counthql = "select count(*) " + this.hql;
        Query countQuery = session.createQuery(counthql);
        if (!CollectionUtil.listIsNull(this.params)) {
            for(int i = 0; i < this.params.size(); ++i) {
                Object obj = this.params.get(i);
                if (obj instanceof String) {
                    countQuery.setString(i, (String)obj);
                } else if (obj instanceof Integer) {
                    countQuery.setInteger(i, (Integer)obj);
                } else if (obj instanceof Date) {
                    countQuery.setDate(i, (Date)obj);
                }
            }
        }

        List<Object> countList = countQuery.list();
        if (CollectionUtil.listIsNull(countList)) {
            this.pageModel.setTotalCount(0L);
        } else {
            this.pageModel.setTotalCount((Long)countList.get(0));
        }

        return list;
    }