Mybatis第七讲 原始分页实现 PageHelper的分页

分页插件-PageHelper

原始分页实现
显示所有的页码数

​ 1、总的数据条数 total

​ 2、每页要显示的数据数量是多少 count

​ 3、总页码数 total%count==0?total/count:(total/count+1)

每页要显示的数据来源

​ 1、起始位置

​ 2、固定的排序方式(查询的条件一致)

起始下标和页码数之间的关系

public class PageInfo {

	/**
	 * 总数据条数
	 */
	private int totals;
	
	/**
	 * 每页要显示的数据条数
	 */
	private int pageCount;
	
	/**
	 * 总页数
	 */
	private int pageTotals;
	
	/**
	 * 起始下标
	 */
	private int startIndex;
	
	/**
	 * 当前的页码数
	 */
	private int pageIndex;

	public int getTotals() {
		return totals;
	}

	public void setTotals(int totals) {
		this.totals = totals;
		if(totals%pageCount==0) {
			setPageTotals(totals/pageCount);
		}else {
			setPageTotals(totals/pageCount+1);
		}
	}

	public int getPageCount() {
		return pageCount;
	}

	public void setPageCount(int pageCount) {
		this.pageCount = pageCount;
	}

	public int getPageTotals() {
		return pageTotals;
	}

	public void setPageTotals(int pageTotals) {
		this.pageTotals = pageTotals;
	}

	public int getStartIndex() {
		return startIndex;
	}

	public void setStartIndex(int startIndex) {
		this.startIndex = startIndex;
	}

	public int getPageIndex() {
		return pageIndex;
	}
	//通过前台传递过来的页码数设置对应的起始下标
	public void setPageIndex(int pageIndex) {
		this.pageIndex = pageIndex;
		setStartIndex((pageIndex-1)*pageCount);
	}

	@Override
	public String toString() {
		return "PageInfo [totals=" + totals + ", pageCount=" + pageCount + ", pageTotals=" + pageTotals
				+ ", startIndex=" + startIndex + ", pageIndex=" + pageIndex + "]";
	}
	
}

<select id="queryUsersLimit" parameterType="pageInfo" resultType="user">
    select <include refid="baseUser"/> from t_user users
    limit #{startIndex},#{pageCount}
select>

@Test
public void testQueryUsersLimit() {
    IUserDao userDao = sqlSession.getMapper(IUserDao.class);
    //当前页的页码数
    int pageIndex = 3;
    //每页要显示的条数
    int pageCount = 5;
    PageInfo info = new PageInfo();
    info.setPageCount(pageCount);
    info.setStartIndex((pageIndex-1)*pageCount);
    List<User> userList = userDao.queryUsersLimit(info);
    System.out.println(userList);
}

/**
	 * 分页查询
	 * @param req
	 * @param userDao
	 * @param out
	 */
public void queryUsersLimit(HttpServletRequest req,IUserDao userDao,PrintWriter out) {
    String infoJson = req.getParameter("info");
    PageInfo info = JSON.parseObject(infoJson, PageInfo.class);
    List<User> userList = userDao.queryUsersLimit(info);
    String jsonData = JSON.toJSONString(userList);
    out.write(jsonData);
}

PageHelper的分页

导入相关的jar

​ pageHelper.jar jsqlparser.jar

配置拦截器(拦截通过Mybatis发送的请求)

<plugins>
 
 <plugin interceptor="com.github.pagehelper.PageInterceptor">plugin>
plugins>

代码中的使用

@Test
public void testQueryUsers() {
 IUserDao userDao = sqlSession.getMapper(IUserDao.class);
 PageHelper.startPage(1, 5);
 List<User> userList = userDao.queryUsers();
 System.out.println(userList);
}

注意：分页插件只能对紧邻的第一个查询语句生效
使用postman测试