Servlet 工具类的使用 和分页功能

@WebServlet("/UserServlet/*")
public class UserServlet extends DispatcherServlet {




    public String login(String username, String password, String code, HttpServletRequest request, HttpServletResponse response) {
        String sessioCode = request.getSession().getAttribute("code").toString();


        if(sessioCode.equalsIgnoreCase(code)){


            if("admin".equals(username) && "123".equals(password)){


                request.getSession().setAttribute("username",username);


                return ConstUtils.REDIRECT + ":EmpServlet?action=listEmp";


            }else{
                try {
                    response.getWriter().write("用户名或密码错，<a href='index.jsp'>登录</a>");
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }


        }else{
            try {
                response.getWriter().write("验证码有误，重新<a href='index.jsp'>登录</a>");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }


    public String logout(HttpServletRequest request) {
        request.getSession().invalidate();
        return ConstUtils.REDIRECT + ":index.jsp";
    }


}

// 登陆
<form method="post" action="UserServlet/login">
    用户名:<input type="text" name="username" value="admin"> <br>
    密码:<input type="text" name="password" value="123"> <br>
    验证码:<input type="text" name="code"> <img src="CodeServlet?action=getCode"><br>
    <input type="submit" value="登陆">
  </form>


// 登出
<a href="UserServlet/logout">登出</a>

// 实体类
@Data
public class Page {


    private Integer page = 1;
    private Integer pageSize = 10;


    private Integer totalNum;
    private Integer totalPage;


    private List data;


}

// DaoUtils 工具类
// 查询数据个数
    public static int commonQueryTotal(String sql) {


        Connection connection = DBUtils.getConnection();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        int total = 0;
        try {
            preparedStatement = connection.prepareStatement(sql);


            resultSet = preparedStatement.executeQuery();


            if (resultSet.next()) {
                total = resultSet.getInt(1);
            }


        } catch (SQLException e) {
            e.printStackTrace();
        }




        return total;
    }

// dao 类
//class EmpDaoImpl implements IEmpDao


// 查询每页数据
  @Override
    public List<Emp> getEmpListPage(Integer pageStart, Integer pageSize) {
        String sql = "select * from t_user limit ?,?";
        return DaoUtils.commonQueryPage(sql, Emp.class, pageStart, pageSize);
    }


// 查询数据总数
    @Override
    public int getEmpTotal() {


        String sql = "select count(1) from t_user";


        return DaoUtils.commonQueryTotal(sql);
    }

// 业务类
// class EmpServiceImpl implements IEmpService


 @Override
    public List<Emp> getEmpListPage(Page page) {


        return empDao.getEmpListPage((page.getPage() -1) * page.getPageSize(), page.getPageSize());


    }


    @Override
    public int getEmpTotalNum() {
        return empDao.getEmpTotal();
    }


  // 计算总页数
    @Override
    public int getEmpTotalPage(Page page) {
        int num = getEmpTotalNum();
        if (num % page.getPageSize() == 0) {
            return num / page.getPageSize();
        } else {
            return num / page.getPageSize() + 1;
        }
    }

//class EmpServlet extends HttpServlet


  if ("listEmp".equals(action)) {
            // 查询


            int iPage = 1;
            // 在 链接中获取页码
            String sPage = request.getParameter("page");
            if (sPage != null && sPage.length() > 0) {
                iPage = Integer.parseInt(sPage);
            }




            Page page = new Page();
            page.setPage(iPage);
            page.setPageSize(5);
            page.setTotalNum(empService.getEmpTotalNum());
            page.setTotalPage(empService.getEmpTotalPage(page));
            page.setData(empService.getEmpListPage(page));


      // 在域中存储 page
            request.setAttribute("page", page);


            request.getRequestDispatcher("selectListUser.jsp").forward(request, response);


        }

// 页面逻辑


<body>


    欢迎【${sessionScope.username}】登陆<br>
    <a href="UserServlet/logout">登出</a>
    <a href="addUser.jsp?action=addEmp">添加用户</a>


    <table border="1">
        <tr>
            <th>id</th>
            <th>用户名</th>
            <th>密码</th>
            <th>年龄</th>
            <th>性别</th>
            <th>邮箱</th>
            <th>生日</th>
            <th>编辑</th>
        </tr>


        <c:forEach items="${page.data}" var="emp">
            <tr>
                <td>${emp.id}</td>
                <td>${emp.username}</td>
                <td>${emp.password}</td>
                <td>${emp.age}</td>
                <td>${emp.sex == 1 ? "男" : "女"}</td>
                <td>${emp.email}</td>
                <td>${emp.birthday}</td>
                <td>
                    <a href="addUser.jsp?action=updateEmp&id=${emp.id}">修改</a>
                    <a href="EmpServlet?action=deleteEmp&id=${emp.id}&page=${page.page}">删除</a>
                </td>
            </tr>
        </c:forEach>
    </table>


    <span>总页数:${page.totalPage}</span><br>
    <span>总个数:${page.totalNum}</span><br>
    <span>当前页</span>:${page.page}</span><br>
    <a href="/EmpServlet?action=listEmp&page=1">首页</a>


    <c:if test="${page.page > 1}">
        <a href="/EmpServlet?action=listEmp&page=${page.page - 1}">上一页</a>
    </c:if>
    <c:if test="${page.page < page.totalPage - 1}">
        <a href="/EmpServlet?action=listEmp&page=${page.page + 1}">下一页</a>
    </c:if>


    <a href="/EmpServlet?action=listEmp&page=${page.totalPage}">尾页</a>


</body>