Java学习三十九——分页工具类

分页的需求：
select from ssm_goods limit 0,3
首页
上一页
下一页
尾页
起始索引位置 = （当前页-1）分页单位
分页单位
当前页页码值

技巧：当有多个参数需要传到持久层时，可以创建集合，将参数封装到集合，将集合传过去。

分页逻辑：

//接收当前页的页码值
        if (currentPage == null || currentPage.equals("")){
            currentPage = "1";
        }else {
            System.out.println("当前页的页码值为 "+currentPage);
        }
        //计算上一页的页码值
        Integer prevPage = 0;
        if (currentPage.equals("1")){
            prevPage = 1;
        }else {
            prevPage = Integer.parseInt(currentPage) - 1;
        }
        //计算尾页的值
        Integer lastPage = 0;
        //获取商品的总记录条数
        Integer count = goodsService.getCount();
        System.out.println("总记录条数为 "+count);
        //指定分页单位
        Integer pageSize = 2;
        if (count % pageSize == 0){
            lastPage = count / pageSize;
        }else{
            lastPage = (count / pageSize) + 1;
        }
        //计算下一页的值
        Integer nextPage = 0;
        if (currentPage.equals(lastPage+"")){
            nextPage = lastPage;
        }else {
            nextPage = Integer.parseInt(currentPage) + 1;
        }
        //计算起始索引位置
        Integer startIndex = (Integer.parseInt(currentPage) - 1) *  pageSize;
        //将分页所需要的条件传到集合里
        hashMap.put("startIndex",startIndex);
        hashMap.put("pageSize",pageSize);

分页工具类：

package com.ssm.shop.utils;
import org.springframework.stereotype.Component;
@Component
public class PageUtils {
    //当前页
    private String currentPage;
    //上一页
    private Integer prevPage;
    //下一页
    private Integer nextPage;
    //尾页(也可以表示总页数)
    private Integer lastPage;
    //总记录条数
    private Integer count;
    //起始索引位置
    private Integer startIndex;
    //分页单位
    private Integer pageSize;
    public String getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(String currentPage) {
        this.currentPage = currentPage;
    }
    public Integer getPrevPage() {
        return prevPage;
    }
    public void setPrevPage(Integer prevPage) {
        this.prevPage = prevPage;
    }
    public Integer getNextPage() {
        return nextPage;
    }
    public void setNextPage(Integer nextPage) {
        this.nextPage = nextPage;
    }
    public Integer getLastPage() {
        return lastPage;
    }
    public void setLastPage(Integer lastPage) {
        this.lastPage = lastPage;
    }
    public Integer getCount() {
        return count;
    }
    public void setCount(Integer count) {
        this.count = count;
    }
    public Integer getStartIndex() {
        return startIndex;
    }
    public void setStartIndex(Integer startIndex) {
        this.startIndex = startIndex;
    }
    public Integer getPageSize() {
        return pageSize;
    }
    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }
    //计算上一页的值
    public void initPrevPage(){
        prevPage = currentPage.equals("1") ? 1 : Integer.parseInt(currentPage) - 1;
    }
    //计算尾页的值
    public void initLastPage(){
        lastPage = count % pageSize == 0 ? count / pageSize : (count / pageSize) + 1;
    }
    //计算下一页的值
    public void initNextPage(){
        nextPage = currentPage.equals(lastPage+"") ? lastPage : Integer.parseInt(currentPage) + 1;
    }
    //计算起始索引位置
    public void initStartIndex(){
        startIndex = (Integer.parseInt(currentPage) - 1) * pageSize;
    }
    //初始化的方法
    public void init(String currentPage,Integer pageSize,Integer count){
        if (currentPage == null || currentPage.equals("")){
            currentPage = "1";
        }
        this.currentPage = currentPage;
        this.pageSize = pageSize;
        this.count = count;
    }
    //调用的方法
    public void initPage(String currentPage,Integer pageSize,Integer count){
        init(currentPage,pageSize,count);
        initStartIndex();
        initPrevPage();
        initLastPage();
        initNextPage();
    }
}