分页查询步骤

最新推荐文章于 2025-10-19 20:18:08 发布

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本文介绍了数据库分页查询的常见方法，首先通过SQL查询所有记录的数量，然后使用LIMIT关键字获取指定页码的数据，实现高效的数据分页展示。

dao层

1.先查询所有的记录数量（select count(*) from）

2.再查询每页的数据（select * from 表 limit ?,? ）

public class CustomerAction extends ActionSupport implements ModelDriven<Customer> {

	private static final long serialVersionUID = 3744982332278861955L;

	@Autowired
	private CustomerService customerService;

	private Customer customer = new Customer();

	public Customer getModel() {
		return customer;
	}

	public String add() {
		System.out.println("web层：保存客户...");
		customerService.save(customer);
		return NONE;
	}

	// 属性驱动的方式
	// 当前页，默认值1
	private Integer pageCode = 1;

	public void setPageCode(Integer pageCode) {
		if (pageCode == null) {
			pageCode = 1;
		}
		this.pageCode = pageCode;
	}

	// 每页显示的数据的条数
	private Integer pageSize = 2;

	public void setPageSize(Integer pageSize) {
		this.pageSize = pageSize;
	}

	public String findByPage() {
		DetachedCriteria criteria = DetachedCriteria.forClass(Customer.class);
		PageBean<Customer> page = customerService.findByPage(pageCode, pageSize, criteria);
		return NONE;
	}
}

@Transactional
@Service
public class CustomerServiceImpl implements CustomerService {

	@Autowired
	private CustomerDao customerDao;

	public void setCustomerDao(CustomerDao customerDao) {
		this.customerDao = customerDao;
	}

	@Override
	public void save(Customer customer) {
		System.out.println("业务层：保存客户...");
		customerDao.save(customer);
	}

	@Override
	public PageBean<Customer> findByPage(Integer pageCode, Integer pageSize, DetachedCriteria criteria) {
		return customerDao.findByPage(pageCode, pageSize, criteria);
	}
}

public class CustomerDaoImpl extends HibernateDaoSupport implements CustomerDao {

	@Override
	public void save(Customer customer) {
		System.out.println("持久层：save...");
		this.getHibernateTemplate().save(customer);
	}

	@Override
	public PageBean<Customer> findByPage(Integer pageCode, Integer pageSize, DetachedCriteria criteria) {

		PageBean<Customer> page = new PageBean<>();
		page.setPageCode(pageCode);
		page.setPageSize(pageSize);

		// 先查询总记录数
		criteria.setProjection(Projections.rowCount());
		List<Number> list = (List<Number>) this.getHibernateTemplate().findByCriteria(criteria);
		if (list != null && list.size() > 0) {
			int totalCount = list.get(0).intValue();
			// 总的记录数
			page.setTotalCount(totalCount);
		}

		// 强调：把select count(*)先清空。变成select * ...
		criteria.setProjection(null);

		List<Customer> beanList = (List<Customer>) this.getHibernateTemplate().findByCriteria(criteria,
				(pageCode - 1) * pageSize, pageSize);

		// 分页查询数据，每页显示的数据，使用limit
		page.setBeanList(beanList);
		return page;
	}
}