JavaWeb学习笔记（十九）—— 分页

一、MySQL中的分页

格式：select * from 表 limit ?,?;
    参数1:开始索引start,默认值:0。必须是正数
    参数2:每页显示个数 pageSize

例如:
 select * from products limit 0,5; #第一页,每页显示5条
 select * from products limit 5,5; #第二页,每页显示5条
 select * from products limet 10,5; #第三页.每页显示5条
 select * from products limit ?,5; #第currentPage页,每页显示5条

    start = (currentPage-1)*pageSize;

二、PageBean的设计

public class PageBean {
    // 当前页数(浏览器传递)
    private Integer currentPage;
    // 每页显示条数(固定值,也可以是浏览器传递)
    private Integer pageSize;
    // 总记录数(数据库查询)
    private Integer totalCount;
    // 总页数
    private Integer totalPage;
    // 分页列表数据(数据库查询)
    private List list;

    public PageBean(Integer currentPage,Integer totalCount,Integer pageSize){
        this.totalCount=totalCount;
        this.pageSize=pageSize;
        this.currentPage=currentPage;
        if(this.currentPage==null){
            // 如果页面没有指定显示哪一页,显示第一页
            this.currentPage=1;
        }
        if(this.pageSize==null){
            // 如果页面没有指定显示条数,显示3条
            this.pageSize=3;
        }

        // 计算总页数
        this.totalPage=(this.totalCount+this.pageSize-1)/this.pageSize;

        // 判断当前页数是否超出范围
        // 不能小于1
        if(this.currentPage<1){
            this.currentPage=1;
        }

        // 不能大于总页数
        if(this.currentPage>this.totalPage){
            this.currentPage=this.totalPage;
        }
    }

    // 计算起始索引
    public int getStart(){
        return (this.currentPage-1)*this.pageSize;
    }

    public Integer getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(Integer currentPage) {
        this.currentPage = currentPage;
    }
    public Integer getPageSize() {
        return pageSize;
    }
    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }
    public Integer getTotalCount() {
        return totalCount;
    }
    public void setTotalCount(Integer totalCount) {
        this.totalCount = totalCount;
    }
    public Integer getTotalPage() {
        return totalPage;
    }
    public void setTotalPage(Integer totalPage) {
        this.totalPage = totalPage;
    }
    public List getList() {
        return list;
    }
    public void setList(List list) {
        this.list = list;
    }
    @Override
    public String toString() {
        return "PageBean [currentPage=" + currentPage + ", pageSize=" + pageSize + ", totalCount=" + totalCount
                + ", totalPage=" + totalPage + ", list=" + list + "]";
    }

}