Javaweb中分页功能的实现

刺骨的言语ヽ痛彻心扉 2022-02-15 10:57 346阅读 0赞

# 一 完成后端分页类的封装 #

## 1. 后端分页功能的基本算法思想： ##

**参数准备：**

public class Pager<T> {
    	private int page = 1;// 当前页号
    	private int limit = 10;// 每页显示的记录数
    	private int totalRecord = 0;// 存放总共有多少条记录要显示-sql计算出来
    	private int totalPage;// 总的页数
    	private List<T> list;// 取得当前待显示页的数据集合
    }

假如有19条商品记录，每一页显示6条记录，总共有4页19/6+1=4 （公式）

1\[0 5\] 2\[6 11\] 3\[12 17\] 4\[18 末尾\]

首页page=1 limit=6

上一页 page-1 limit=6

下一页 page+1 limit=6

尾页 page=4 limit=6（limit|totalRecord%limit）

对应的查询语句：

1\[0 5\] 2\[6 11\] 3\[12 17\] 4\[18 末尾\]

If(如果当前处于首页，不应该有上一页和首页)

首页SELECT \* FROM tb\_product LIMIT 0,limit

如果超过一页，第二个参数=limit，否则=记录数

页号在\[1 totalPage\]

上一页page=page-1 limit=6

Select \* from … limit (页号-1)\*limit,limit

下一页 page+1 limit=6

尾页 SELECT \* FROM tb\_product LIMIT (page-1)\*limit, totalRecord%limit

18=（4-1）\*6 19%6

**完整代码：**

public Pager(int page, int limit, int totalRecord) {
    		this.limit = limit;
    		this.totalRecord = totalRecord;
    		this.totalPage = totalRecord % limit == 0 ? totalRecord / limit : totalRecord / limit + 1;
    
    		// 判断page合法性
    		if (page < 1) // 已经是第一页了，上一页
    			this.page = 1; // 不允许page变化，定在第一页
    		if (page > totalPage) // 已经是最后一页了，没有下一页
    			this.page = totalPage; // 定在最后一页，不允许往下加一页
    		else
    			this.page = page;
    	}
    
    	public Pager(int page, int totalRecord) {
    		this.totalRecord = totalRecord;
    		this.totalPage = totalRecord % limit == 0 ? totalRecord / limit : totalRecord / limit + 1;
    		
    		// 判断page合法
    		if (page < 1)
    			this.page = 1;
    		if (page > totalPage)
    			this.page = totalPage;
    		else
    			this.page = page;
    	}

### 2 实体类Product： ###

package cn.domain;
    
    import java.util.Date;
    
    public class ProductDomain {
    	private int id;
    	private int categoryMainId;
    	private int categorBranchId;
    	private String name;
    	private String producingArea;
    	private String description;
    	private Date createTime;
    	private double marketPrice;
    	private double sellPrice;
    	private int salesVolume;
    	private String picture;
    	private int discount;
    	private int stock;
    
    	public int getId() {
    		return id;
    	}
    
    	public void setId(int id) {
    		this.id = id;
    	}
    
    	public int getCategoryMainId() {
    		return categoryMainId;
    	}
    
    	public void setCategoryMainId(int categoryMainId) {
    		this.categoryMainId = categoryMainId;
    	}
    
    	public int getCategorBranchId() {
    		return categorBranchId;
    	}
    
    	public void setCategorBranchId(int categorBranchId) {
    		this.categorBranchId = categorBranchId;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public String getProducingArea() {
    		return producingArea;
    	}
    
    	public void setProducingArea(String producingArea) {
    		this.producingArea = producingArea;
    	}
    
    	public String getDescription() {
    		return description;
    	}
    
    	public void setDescription(String description) {
    		this.description = description;
    	}
    
    	public Date getCreateTime() {
    		return createTime;
    	}
    
    	public void setCreateTime(Date createTime) {
    		this.createTime = createTime;
    	}
    
    	public double getMarketPrice() {
    		return marketPrice;
    	}
    
    	public void setMarketPrice(double marketPrice) {
    		this.marketPrice = marketPrice;
    	}
    
    	public double getSellPrice() {
    		return sellPrice;
    	}
    
    	public void setSellPrice(double sellPrice) {
    		this.sellPrice = sellPrice;
    	}
    
    	public int getSalesVolume() {
    		return salesVolume;
    	}
    
    	public void setSalesVolume(int salesVolume) {
    		this.salesVolume = salesVolume;
    	}
    
    	public String getPicture() {
    		return picture;
    	}
    
    	public void setPicture(String picture) {
    		this.picture = picture;
    	}
    
    	public int getDiscount() {
    		return discount;
    	}
    
    	public void setDiscount(int discount) {
    		this.discount = discount;
    	}
    
    	public int getStock() {
    		return stock;
    	}
    
    	public void setStock(int stock) {
    		this.stock = stock;
    	}
    
    	@Override
    	public String toString() {
    		return "ProductDomain [id=" + id + ", categoryMainId=" + categoryMainId + ", categorBranchId=" + categorBranchId
    				+ ", name=" + name + ", producingArea=" + producingArea + ", description=" + description
    				+ ", createTime=" + createTime + ", marketPrice=" + marketPrice + ", sellPrice=" + sellPrice
    				+ ", salesVolume=" + salesVolume + ", picture=" + picture + ", discount=" + discount + ", stock="
    				+ stock + "]";
    	}
    
    	public ProductDomain(int id, int categoryMainId, int categorBranchId, String name, String producingArea,
    			String description, Date createTime, double marketPrice, double sellPrice, int salesVolume, String picture,
    			int discount, int stock) {
    		super();
    		this.id = id;
    		this.categoryMainId = categoryMainId;
    		this.categorBranchId = categorBranchId;
    		this.name = name;
    		this.producingArea = producingArea;
    		this.description = description;
    		this.createTime = createTime;
    		this.marketPrice = marketPrice;
    		this.sellPrice = sellPrice;
    		this.salesVolume = salesVolume;
    		this.picture = picture;
    		this.discount = discount;
    		this.stock = stock;
    	}
    
    	public ProductDomain() {
    		super();
    	}
    
    }

### 3ProductDao和ProductImp: ###

package cn.dal;
    
    import cn.util.Pager;
    
    public interface ProductDao {
    	Pager find(int page);// 初始值为limit=10
    
    	Pager find(int page, int limit);
    
    	int getTotalRecord();// 获得总记录个数
    }

package cn.dal;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.List;
    
    import org.junit.Test;
    
    import cn.domain.ProductDomain;
    import cn.util.DBConnection;
    import cn.util.Pager;
    
    public class ProductDaoImp implements ProductDao {
    	private Connection connection = DBConnection.getConnection();
    
    	public Pager find(int page) {
    		PreparedStatement preparedStatement = null;
    		ResultSet resultSet = null;
    		List<ProductDomain> list = new ArrayList<ProductDomain>();
    		Pager pager = new Pager(page, getTotalRecord());
    		String sql = "select * from tb_product limit ?,?";
    		try {
    			preparedStatement = connection.prepareStatement(sql);
    			preparedStatement.setInt(1, (page - 1) * pager.getLimit());
    			int tempLimit = 0;
    			if (page > pager.getTotalRecord() / pager.getLimit())
    				tempLimit = pager.getTotalRecord() % pager.getLimit();
    			else
    				tempLimit = pager.getLimit();
    			preparedStatement.setInt(2, tempLimit);
    			resultSet = preparedStatement.executeQuery();
    			ProductDomain product = null;
    			while (resultSet.next()) {
    				product = new ProductDomain(resultSet.getInt("id"), resultSet.getInt(2), 
    						resultSet.getInt(3), resultSet.getString(4),
    						resultSet.getString(5), resultSet.getString(6), 
    						resultSet.getDate(7), resultSet.getDouble(8), 
    						resultSet.getDouble(9),resultSet.getInt(10), 
    						resultSet.getString(11), resultSet.getInt(12), 
    						resultSet.getInt(13));
    				list.add(product);
    			}
    			pager.setList(list);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return pager;
    	}
    
    	public Pager find(int page, int limit) {
    		PreparedStatement preparedStatement = null;
    		ResultSet resultSet = null;
    		List<ProductDomain> list=new ArrayList<ProductDomain>();
    		Pager pager=new Pager(page,limit,getTotalRecord());	
    		String sql="select * from tb_product limit ?,?";
    		try {
    			preparedStatement=connection.prepareStatement(sql);
    			preparedStatement.setInt(1, (page-1)*pager.getLimit());
    			int tempLimit=0;
    			if(page>pager.getTotalRecord()/pager.getLimit())
    				tempLimit=pager.getTotalRecord()%pager.getLimit();
    			else tempLimit=pager.getLimit();
    			preparedStatement.setInt(2,tempLimit );
    			resultSet=preparedStatement.executeQuery();	
    			ProductDomain product=null;
    			while(resultSet.next()){
    				product = new ProductDomain(resultSet.getInt("id"), resultSet.getInt(2), 
    						resultSet.getInt(3), resultSet.getString(4),
    						resultSet.getString(5), resultSet.getString(6), 
    						resultSet.getDate(7), resultSet.getDouble(8), 
    						resultSet.getDouble(9),resultSet.getInt(10), 
    						resultSet.getString(11), resultSet.getInt(12), 
    						resultSet.getInt(13));
    				list.add(product);
    			}
    			pager.setList(list);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return pager;
    	}
    
    	public int getTotalRecord() {
    		PreparedStatement preparedStatement = null;
    		ResultSet resultSet = null;
    		int result = 0; // mysql中总的记录数
    		String sql = "SELECT COUNT(*) AS number FROM tb_product"; // 通过mysql语句记录总的记录数
    		try {
    			preparedStatement = connection.prepareStatement(sql);
    			resultSet = preparedStatement.executeQuery();
    			if (resultSet.next())
    				result = resultSet.getInt(1);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    		return result;
    	}
    
    }

### 4 测试类： ###

@Test
    	public void test0() {
    		ProductDao dao = new ProductDaoImp();
    		/*System.out.println(dao.getTotalRecord());*/
    		
    		  Pager pager = dao.find(1, 6); //第一页显示6条记录
    		  List<ProductDomain> list = pager.getList(); //19 
    		  for(int i=0; i<list.size(); i++)
    		  System.out.println(list.get(i).toString());
    		 
    	}

结果：显示第一页的结果（一页按6个显示）

![20190424135245377.png][]

[20190424135245377.png]: /images/20220215/3ad54a4028ed4149b35447bbab2d2d06.png