分页技术

1.JdbcUtil（使用c3p0组件）

public class JdbcUtil {
    private static DataSource dataSource;
    static {
        dataSource = new ComboPooledDataSource();
    }
    public static QueryRunner getQueryRunner(){
        return  new QueryRunner(dataSource);
    }
}

2.PageBean

public class PageBean <T>{
    private int currentPage = 1;
    private int pageCount = 4;    //每页的行数
    private int totalCount;       //总记录数
    private int totalPage;        //总页数
    private List<T> pageData;     //分页查到的数据

    public int getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }

    public int getPageCount() {

        return pageCount;
    }

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

    public void setTotalCount(int totalCount) {
        this.totalCount = totalCount;
    }
　　
    public int getTotalPage() {
        if(totalCount % pageCount == 0)
            totalPage = totalCount / pageCount;
        else
            totalPage = totalCount / pageCount + 1;
        return totalPage;
    }

    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }

    public List<T> getPageData() { return pageData;
    }

    public void setPageData(List<T> pageData) {
        this.pageData = pageData;
    }
}

3.Dao

public interface IStudentDao {
    //分页查询数据
    public void getAll(PageBean<Student> pb);
    //查询总记录数
    public int getTotalCount();
}

public class StudentDao implements IStudentDao{
    @Override
    public void getAll(PageBean pb) {
        //获取当前页，计算查询的起始行、返回的行数，作为sql语句的参数
        int currentPage = pb.getCurrentPage();
        int pageCount = pb.getPageCount();
        //查询总记录数，保存到pb中
        int totalCount = this.getTotalCount();
        pb.setTotalCount(totalCount);
        int totalPage = pb.getTotalPage();
        if(currentPage>totalPage){
            currentPage = totalPage;
            pb.setCurrentPage(currentPage);
        }
        if(currentPage<1){
            currentPage =1;
            pb.setCurrentPage(currentPage);
        }
        int start = (currentPage-1)*pageCount;
        //分页查询数据，把查询到的数据设置到pb中
        String sql = "select * from student_info limit ?,?";
        QueryRunner queryRunner = JdbcUtil.getQueryRunner();
        try {
            List<Student> pageData = queryRunner.query(sql, new BeanListHandler<Student>(Student.class), start, pageCount);
            pb.setPageData(pageData);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public int getTotalCount() {
        String sql = "select count(1) from student_info";
        QueryRunner queryRunner = JdbcUtil.getQueryRunner();
        //返回结果的第一行的第一列
        try {
            Long count = (Long)queryRunner.query(sql, new ScalarHandler());
            return count.intValue();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

4.service

public interface IStudentService {
    public void getAll(PageBean<Student> pb);
}

public class StudentService implements IStudentService{
    private IStudentDao studentDao = new StudentDao();
    @Override
    public void getAll(PageBean<Student> pb) {
        studentDao.getAll(pb);
    }
}

5.servlet

public class IndexServlet extends javax.servlet.http.HttpServlet {
    private StudentService studentService = new StudentService();
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException {
        PageBean<Student> studentPageBean = new PageBean<>();
        String currentPage = request.getParameter("currentPage");
        if(currentPage == null || "".equals(currentPage)){
            studentPageBean.setCurrentPage(1);
        }else{
            studentPageBean.setCurrentPage(Integer.parseInt(currentPage));
        }
        studentService.getAll(studentPageBean);

        request.setAttribute("pageBean",studentPageBean);
        request.getRequestDispatcher("/WEB-INF/list_student.jsp").forward(request,response);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException {
        doPost(request,response);
    }
}

6.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>分页数据</title>
</head>
<body>
<table>
    <tr>
        <td>学号</td>
        <td>姓名</td>
        <td>电话</td>
    </tr>
    <c:choose >
        <c:when test="${not empty requestScope.pageBean}">
            <c:forEach items="${requestScope.pageBean.pageData}" var="student">
                <tr>
                    <td>${student.stuID}</td>
                    <td>${student.stuName}</td>
                    <td>${student.telephone}</td>
                </tr>
            </c:forEach>
        </c:when>
        <c:otherwise>
            <tr>
                <td>对不起，没有你要找的数据！</td>
            </tr>
        </c:otherwise>
    </c:choose>
    <tr>
        <td colspan="3">
        当前${requestScope.pageBean.currentPage}/${requestScope.pageBean.totalPage}页
        <a href="${pageContext.request.contextPath}/index.do?currentPage=1">首页</a>
        <a href="${pageContext.request.contextPath}/index.do?currentPage=${requestScope.pageBean.currentPage-1}">上一页</a>
        <a href="${pageContext.request.contextPath}/index.do?currentPage=${requestScope.pageBean.currentPage+1}">下一页</a>
        <a href="${pageContext.request.contextPath}/index.do?currentPage=${requestScope.pageBean.totalPage}">末页</a>
        </td>
    </tr>
</table>
</body>
</html>

7.效果

8.hibernate中的分页

    @Test
    public void test1(){
        Session session = sf.openSession();
        session.beginTransaction();

        Query query = session.createQuery("from Employee");

        ScrollableResults scroll = query.scroll();//得到滚动的结果集
        scroll.last();//滚动到最后一行
        int totalCount = scroll.getRowNumber() + 1;//得到总记录数

        //设置分页参数
        query.setFirstResult(3);
        query.setMaxResults(3);

        session.getTransaction().commit();
        session.close();
    }