java原生代码实现分页

1、 创建分页类

public class PageBean<T> {
    
    private int pageNum; 
    private int pageSize; 
    private int totalRecord;  
    private int totalPage;  
    private List<T> list;
    private int start;
    private int end;
    private int fromIndex;
    private int toIndex;
 
    public PageBean(int pageNum, int pageSize, int totalRecord) {
        this.pageNum = pageNum;
        this.pageSize = pageSize;
        this.totalRecord = totalRecord;
        fromIndex=(pageNum-1)*pageSize;
        toIndex=pageNum*pageSize>totalRecord?totalRecord:pageNum*pageSize;
 
        if (totalRecord % pageSize == 0) {
            this.totalPage = totalRecord / pageSize;
        } else {
            this.totalPage = totalRecord / pageSize + 1;
        }
        start = 1;
        end = 5;
        if (totalPage <= 5) {
            end = this.totalPage;
        } else {
            start = pageNum - 2;
            end = pageNum + 2;
 
            if (start < 1) {
                start = 1;
                end = 5;
            }
            if (end > this.totalPage) {
                end = totalPage;
                start = end - 5;
            }
        }
    }
 
    public int getPageNum() {
        return pageNum;
    }
 
    public void setPageNum(int pageNum) {
        this.pageNum = pageNum;
    }
 
    public int getPageSize() {
        return pageSize;
    }
 
    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }
 
    public int getTotalRecord() {
        return totalRecord;
    }
 
    public int getFromIndex() {
        return fromIndex;
    }
 
    public void setFromIndex(int fromIndex) {
        this.fromIndex = fromIndex;
    }
 
    public int getToIndex() {
        return toIndex;
    }
 
    public void setToIndex(int toIndex) {
        this.toIndex = toIndex;
    }
 
    public void setTotalRecord(int totalRecord) {
        this.totalRecord = totalRecord;
    }
 
    public int getTotalPage() {
        return totalPage;
    }
 
    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }
 
    public List<T> getList() {
        return list;
    }
 
    public void setList(List<T> list) {
        this.list = list.subList(fromIndex, toIndex);
    }
 
    public int getStart() {
        return start;
    }
 
    public void setStart(int start) {
        this.start = start;
    }

public int getEnd() {
return end;
    }

public void setEnd(int end) {
this.end = end;
    }

}

2、 service层

@WebServlet("/main")
public class Servlets extends HttpServlet {
 
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String page = request.getParameter("pageNum");
        int pageNum = Integer.parseInt((page == null ? "1" : page));
        int pageSize = 5;
        Service s = new Service();
        PageBean<User> pb = s.findAll(pageNum, pageSize);
        request.setAttribute("pageBean", pb);
        request.getRequestDispatcher("/main.jsp").forward(request, response);
    }
}

3、 dao层

public class Service {
    public PageBean<User> findAll(int pageNum, int pageSize) {
        UserDao userDao = new UserDao();
        List<User> users = userDao.findAll();
        int totalRecord = users.size();
        PageBean<User> pb = new PageBean<>(pageNum, pageSize, totalRecord);
        pb.setList(users);
        return pb;
    }
}