SSH分页查询问题？？？

Java初学者，学习ssh框架的时候，遇到分页问题，控制台提示
空指针，DepartmentServiceImpl实现类中提示24行有错误，我觉得是当前页数
无法获取，求大神解决一下。
错误信息

DepartmentServiceImpl实现类的代码为
package com.ssh.employee.service.impl;

import java.util.List;

import com.ssh.employee.dao.DepartmentDao;
import com.ssh.employee.entity.Department;
import com.ssh.employee.entity.PageBean;
import com.ssh.employee.service.DepartmentService;

public class DepartmentServiceImpl implements DepartmentService{

//注入Dao层的类
private DepartmentDao departmentDao;
public void setDepartmentDao(DepartmentDao departmentDao) {
    this.departmentDao = departmentDao;
}
@Override
public PageBean<Department> findByPage(Integer currPage) {
    // TODO Auto-generated method stub
    PageBean<Department> pageBean = new PageBean<Department>();
    //封装当前页数
    System.out.println("service 执行了");
    pageBean.setCurrPage(currPage);
    //封装每页显示记录数
    int pageSize= 3;
    pageBean.setPageSize(pageSize);
    //封装总记录数
    int totalCount = departmentDao.findCount();
    pageBean.setTotalCount(totalCount);
    System.out.println(pageBean.getTotalCount());//这个可以显示
    //封装总页数
    double tc = totalCount;
    Double num = Math.ceil(tc/pageSize);
    pageBean.setTotalPage(num.intValue());
    //封装每页显示的数据
    int begin = (currPage - 1) * pageSize;
    List<Department> list =  departmentDao.findByPage(begin,pageSize);
    System.out.println("service 执行了");
    pageBean.setList(list);
    return pageBean;
}

}