我爱Java系列---【分页查询】

一、需求

查询每个分类下的商品详情

二、实现步骤

  • 菜单页面拼接超链接,传递商品分类主键
  • 分类商品页面接收分类主键数据,向服务器发送AJAX请求
  • Servlet接收客户端分类主键的数据
  • 调用业务层方法组装PageBean数据
  • 业务层调用持久层方法,分页查询数据表
  • Servlet接收业务层返回的PageBean数据,转成JSON响应客户端

三、代码如下

用到的jquery工具，用的时候封装成jquery-heima-0.0.1.js，并引入当前页面，可以直接HM.ajax(url,data,function(vo){})

$.ajaxSetup({
    type:"post",
    /*xhrFields: {
          withCredentials: true
    },*/
    error:function (xhr, textStatus, errorThrown) {
    	if(xhr.status==0){
    		console.log("亲,请检查后台服务器是否启动...手动滑稽")
    	}
    	if(xhr.status==404){
    		console.log("亲,请检查请求地址是否正确...手动滑稽")
    	}
    	if(xhr.status==405){
    		console.log("亲,请检查你是否实现了doPost方法...手动滑稽")
    	}
        
    }

})

var HM=
	{
		CTX:"http://api.itheima349.com",
		getParameter:function(name){
			var pvalues=this.getParameterValues(name);
	    	return pvalues==null?null:pvalues[0];
		},
		getParameterValues:function(name){
			return this.getParameterMap()[name];
		},
		getParameterMap:function(){
			var url = location.search;  
		    var HMRequest = new Object();  
		    if (url.indexOf("?") != -1) {  
		      var str = url.substr(1);  
		      strs = str.split("&");  
		      for(var i = 0; i < strs.length; i ++) {  
		      	 var pname=strs[i].split("=")[0];
		      	 var pvalue=unescape(strs[i].split("=")[1]);
		      	  var pvalues=null;
		      	 if(HMRequest[pname]==null){
		      	 	HMRequest[pname]=new Array(pvalue)
		      	 }else{
		      	 	HMRequest[pname].push(pvalue);
		      	 }
		      }  
		   }  
		   return HMRequest;
		},
		isLogin:function(){
			return this.cookie("JSESSIONID")==null?false:true;
		},
		cookie:function (name) {
			return this.cookies()[name];
        },
		cookieValue:function(name){
			var cookie=this.cookie(name);
			if(cookie==null){
				return null;
			}else{
				return cookie.value;
			}

		},
		cookies:function () {
            var cookiesStr = document.cookie ? document.cookie.split('; ') : [];
			var cookies={};
            for (var i = 0; i < cookiesStr.length; i++) {
                var parts = cookiesStr[i].split('=');
                var cookie = {
                	"name":parts[0],
					"value":decodeURIComponent(parts[1])
				};
                cookies[parts[0]]=cookie;
            }
            return cookies;
        },
		ajax:function(url,parameter,fn){
			
			$.ajax({
		        url:this.CTX+url,
		        type:"post",
		        dataType:"json",
		        data:parameter,
		        xhrFields: {
						//允许接受从服务器端返回的cookie信息 ,默认值为false 也就是说如果必须设置为true的时候 才可以接受cookie 并且请求带上
					    withCredentials: true
				},
		        success:function (vo,status,xhr) {
		        	/*if(vo.code==2){
		        		console.log("请检查请求方法是否存在");
		        		return;
		        	}
		        	if(vo.code==3){
		        		console.log("请检查您的服务端控制错误日志");
		        		return;
		        	}*/
		        	
		        	
		            //处理登录的filter
		            if(true){
		                fn(vo,status,xhr);
		            }
		        }
		    })
		},
		ajaxFile:function(url,formId,fn){
			var formData = new FormData($("#"+formId)[0]);
			$.ajax({
	        type: 'post',
	        url:this.CTX+url,
	        dataType:'text',
	        data:formData,
	        contentType:false,
	        processData:false, 
	        success:function(data,status,xhr){
		            //处理登录的filter
		            if(true){
		                fn(data,status,xhr);
		            }
		        }
			})
		},
		page:function(pb,url){
			
			if(url.indexOf("?") != -1){
				//带参数
				
			}else{
				//不带参数
				url+="?_t="+new Date().getTime();
			}
			var pageHTML="";
			if(pb.pageNumber==1){
				pageHTML+="<li class="disabled"><a href="javascript:;" aria-label="Previous"><span aria-hidden="true">«</span></a></li>
";
			}else{
				pageHTML+="<li ><a href=""+url+"&pageNumber="+(pb.pageNumber-1)+"" aria-label="Previous"><span aria-hidden="true">«</span></a></li>
";
			}
			for(var i=pb.start;i<=pb.end;i++){
				if(i==pb.pageNumber){
					pageHTML+="<li class='active'><a href='javascript:;' >"+i+"</a></li>"
				}else{
					pageHTML+="<li ><a  href='"+url+"&pageNumber="+i+"'>"+i+"</a></li>"
				}
				
			}
			if(pb.pageNumber==pb.totalPage){
				pageHTML+="<li class="disabled" ><a href="javascript:;" aria-label="Next"><span aria-hidden="true">»</span></a></li>"
			}else{
				pageHTML+="<li><a href='"+url+"&pageNumber="+(pb.pageNumber+1)+"' aria-label="Next"><span aria-hidden="true">»</span></a></li>"
			}
			return pageHTML;	
			
		},
		time2str:function(t){
			var date=new Date(t);
			return ""+date.getFullYear()+"-"+(date.getMonth()+1)+"-"+date.getDate()+" "+date.getHours()+":"+date.getMinutes()+":"+date.getSeconds();
		}
}

 JAVA中用到的PageBean类

package com.itheima.domain;

import java.util.List;

public class PageBean<T> {
    private List<T> data;
    private int total;
    private int pageSize;
    private int totalPage;
    private int pageNumber;
    private int start;
    private int end;
    private int showNum=10;

    public int getShowNum() {
        return showNum;
    }

    public void setShowNum(int showNum) {
        this.showNum = showNum;
    }

    public List<T> getData() {
        return data;
    }

    public void setData(List<T> data) {
        this.data = data;
    }

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    public int getTotalPage() {
        return (int) Math.ceil(total*1.0/pageSize);
    }


    public int getPageNumber() {
        return pageNumber;
    }

    public void setPageNumber(int pageNumber) {
        this.pageNumber = pageNumber;
    }

    public int getStart() {
        return getRange()[0];
    }

    public int getEnd() {
        return getRange()[1];
    }
    private int[] getRange(){
        totalPage=getTotalPage();

        //开始计算前后可以留几个
        //如果为奇数 7 3-3
        //如果为偶数 8 4-3

        int pre=showNum%2==0?showNum/2:showNum/2;
        int suf=showNum%2==0?showNum/2-1:showNum/2;

        //计算前后的满足情况
        //前后的个数已定
        //前后都满足的情况
        if(totalPage-pageNumber>=suf&&pageNumber-1>=pre){
            start=pageNumber-pre;
            end=pageNumber+suf;
            return new int[]{start,end};
        }
        //前面不满足的情况
        if(pageNumber-1<pre&&totalPage-pageNumber>=suf){
            start=1;
            //前面缺失的个数
            int preNum=pre-pageNumber+1;
            end=pageNumber+suf+preNum>totalPage?totalPage:pageNumber+suf+preNum;
            return new int[]{start,end};
        }
        //后面的不满足
        if(totalPage-pageNumber<suf&&pageNumber-1>=pre){
            end=totalPage;
            //后面缺失的个数
            int sufNum=pageNumber+suf-totalPage;
            start=pageNumber-pre-sufNum<1?1:pageNumber-pre-sufNum;
            return new int[]{start,end};
        }
        //都不满足
        if(totalPage-pageNumber<suf&&pageNumber-1<pre){
            return new int[]{1,totalPage};
        }
        return new int[]{1,1};
    }

}

  header页面添加连接

HM.ajax("/category?method=findAll","",function(data){
var str = ""
var cateData = data.obj;
$(cateData).each(function(i,element){
str= "<li><a href="http://www.itheima326.com:8020/web/view/product/list.html?
cid=" +element.cid+"">" +element.cname+"</a></li>"
$("#cate_list").append(str);
});

list 商品分页展示页面

$(function(){
//获取菜单传递的商品分类主键数据集
var cid = HM.getParameter("cid");
//获取当前的页数
var currentNumber = HM.getParameter("currentNumber");
if(currentNumber==null){
//默认第一页
currentNumber=1;
}
var param = "cid="+cid+"&currentNumber="+currentNumber;
HM.ajax("/product?method=findByPage",param,function(data){
//取出返回pagebean的数据
//取出商品数据
var products = data.obj.list;
$.each(products, function(i,element) {
var s = "<div class="col-md-2" style="text-align:center;height:200px;padding:10px
0px;">
" +
"						<a
href="http://www.itheima326.com:8020/web/view/product/info.html?pid="+element.pid+"">
" +
"							<img
src="http://www.itheima326.com:8020/web/"+element.pimage+"" width="130" height="130"
style="display: inline-block;">
" +
"						</a>
" +
"						<p><a
href="http://www.itheima326.com:8020/web/view/product/info.html?pid="+element.pid+""
style='color:#666'>"+element.pname+"</a></p>
" +
"						<p><font color="#E4393C" style="font￾size:16px">¥"+element.shop_price+"</font></p>
" +
"					</div>";
$("#products").append(s);
});
var pb=data.obj;
//拼接分页字符串
ProductServlet
var page = "";
//判断第一页
if(pb.currentNumber==1){
page+="<li class='disabled'><a href='javascript:;' aria-label='Previous'><span ariahidden='true'>«</span></a></li>";
}else{
page+="<li><a href='http://www.itheima326.com:8020/web/view/product/list.html?
cid="+cid+"&currentNumber="+(pb.currentNumber-1)+"' aria-label='Previous'><span ariahidden='true'>«</span></a></li>";
}
//拼接页码
for(var i=1;i<=pb.totalPage;i++){
//判断当前页
if(i==pb.currentNumber){
page+="<li class='active'><a href='javascript:;'>"+i+"</a></li>";
}else{
page+="<li><a href='http://www.itheima326.com:8020/web/view/product/list.html?
cid="+cid+"&currentNumber="+i+"'>"+i+"</a></li>";
}
}
//判断最后一页
if(pb.currentNumber==pb.totalPage){
page+="<li class='disabled'><a href='javascript:;' aria-label='Next'><span ariahidden='true'>»</span></a></li>";
}else{
page+="<li><a href='http://www.itheima326.com:8020/web/view/product/list.html?
cid="+cid+"&currentNumber="+(pb.currentNumber+1)+"' aria-label='Next'><span ariahidden='true'>»</span></a></li>";
}
$("#page").html(page);
});
})

 ProductServlet

/**
* 根据商品分类信息
* 分页查询数据
* 封装PageBean对象
*/
public void findByPage(HttpServletRequest request,HttpServletResponse response)throws
IOException{
//获取分类主键
String cid = request.getParameter("cid");
//获取当前页数
int currentNumber = Integer.parseInt(request.getParameter("currentNumber"));
//定义每页显示条数10
int pageSize = 10;
ProductService
ProductDao
//调用业务层方法,获取PageBean
PageBean<Product> pageBean = service.findByPage(cid, currentNumber, pageSize);
Result re = new Result(pageBean);
response.getWriter().print(JSONObject.fromObject(re));
}

 ProductService

/**
* 接收分类id
* 当前页数和每页条数
* 查询数据表,封装PageBean对象
*/
public PageBean<Product> findByPage(String cid,int currentNumber,int pageSize){
//分页查询数据表,返回集合
List<Product> productList = productDao.findByPage(cid, currentNumber, pageSize);
//查询分类商品总数
int totalCount =(int) productDao.getTotalCount(cid);
//封装PageBean对象
PageBean<Product> pageBean = new PageBean<Product>();
//当前页数
pageBean.setCurrentNumber(currentNumber);
//总条数
pageBean.setTotalCount(totalCount);
//每页个数
pageBean.setPageSize(pageSize);
//计算总页数
int totalPage = (int)Math.ceil(totalCount/pageSize*1.0);
pageBean.setTotalPage(totalPage);
//存储商品数据
pageBean.setList(productList);
return pageBean;
}

 ProductDao

/**
* 查询该分类下的所有商品的总数
* 传递参数,分类id
*/
public long getTotalCount(String cid){
String sql = "select count(*) from product where cid=?";
return template.queryForObject(sql,Long.class,cid);
}
/**
* 分页查询商品数据
* 传递参数,分类id
* 当前页数,每页显示的条数
*/
public List<Product> findByPage(String pid,int currentNumber,int pageSize){
String sql = "select * from product where cid=? limit ?,?";
return template.query(sql,new BeanPropertyRowMapper<Product>(Product.class),
pid,(currentNumber-1)*pageSize,pageSize);
}

 Redis优化菜单查询

菜单对于一个网站系统,基本上变化非常小,每次用户访问都去读取数据库效率很低,也浪费资源.将菜单存储在redis
数据库中,每次用户访问只要从内存数据库中读取菜单即可.

public List<Category> findAll(){
//先查询redis数据库
//如果不存在,查询MySQL数据库,存储到redis中,再返回
Jedis jedis = JedisUtils.getConnection();
String category = jedis.get("category");
if(category==null){
List<Category> categoryList = categoryDao.findAll();
jedis.set("category", JSONArray.fromObject(categoryList).toString());
return categoryList;
}else{
JSONArray jsonObject = JSONArray.fromObject(category);
List<Category> list = JSONArray.toList(jsonObject,Category.class);
return list;
}
}
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原文地址：https://www.cnblogs.com/hujunwei/p/11046544.html