通用分页01

1.分页的作用以及好处

1）为了提高查询性能及节约网络流量，每次只查询指定的记录数，而不是全部，在数量比较大时很有用
2）当点击下一页或指定页面的数据时，将带着所有的查询条件，再次执行查询

一、分页信息实体
用于存储和传递分页参数，主要内容如下：

页码，从页面传递过来
每页行数，从也能传递过来
总记录数， 从数据库中统计得到
是否分页， 如果为false，则查询所有记录
查询参数， 点击上一页或下一页时需要及携带用户输入的所有查询参数
另外提供上页，下页，总页数等计算
如下（示例）：
 

import java.util.Map;
 
import javax.servlet.http.HttpServletRequest;
 
import com.mysql.jdbc.StringUtils;
public class PageBean {
	/**
	 * 页码
	 */
	private int page = 1;
 
	/**
	 * 每页显示的记录数
	 */
	private int rows = 10;
 
	/**
	 * 总记录数
	 */
	private int total = 0;
 
	/**
	 * 是否分页
	 */
	private boolean pagination = true;
	
	/**
	 * 记录查询的url，以便于点击分页时再次使用
	 */
	private String url;
	
	/**
	 * 存放请求参数，用于生成隐藏域中的元素
	 */
	private Map<String,String[]> parameterMap;
	
	/**
	 * 根据传入的Request初始化分页对象
	 * @param request
	 */
	public void setRequest(HttpServletRequest request) {
		
		if(!StringUtils.isNullOrEmpty(request.getParameter("page"))) {
			this.page = Integer.valueOf(request.getParameter("page"));
		}
		if(!StringUtils.isNullOrEmpty(request.getParameter("rows"))) {
			this.rows = Integer.valueOf(request.getParameter("rows"));
		}
		if(!StringUtils.isNullOrEmpty(request.getParameter("pagination"))) {
			this.pagination = Boolean.valueOf(request.getParameter("pagination"));
		}
		
		this.url = request.getRequestURI();
		this.parameterMap = request.getParameterMap();
		
		request.setAttribute("pageBean", this);
	}
 
 
	public int getPage() {
		return page;
	}
 
 
	public void setPage(int page) {
		this.page = page;
	}
 
 
	public int getRows() {
		return rows;
	}
 
 
	public void setRows(int rows) {
		this.rows = rows;
	}
 
 
	public int getTotal() {
		return total;
	}
 
 
	public void setTotal(int total) {
		this.total = total;
	}
 
	public boolean isPagination() {
		return pagination;
	}
 
	public void setPagination(boolean pagination) {
		this.pagination = pagination;
	}
	
	public String getUrl() {
		return url;
	}
 
	public void setUrl(String url) {
		this.url = url;
	}
 
	public Map<String, String[]> getParameterMap() {
		return parameterMap;
	}
 
	public void setParameterMap(Map<String, String[]> parameterMap) {
		this.parameterMap = parameterMap;
	}
 
	//计算起始页码
	public int getStartIndex() {
		return (this.page - 1) * this.rows;
	}
	
	//获取总页数
	public int getTotalPage() {
		if (this.getTotal() % this.rows == 0) {
			return this.getTotal() / this.rows;
		} else {
			return this.getTotal() / this.rows + 1;
		}
	}
 
	//上一页
	public int getPreviousPage() {
		return this.page - 1 > 0 ? this.page - 1 : 1;
	}
	
	//下一页
	public int getNextPage() {
		return this.page + 1 > getTotalPage() ? getTotalPage() : this.page + 1;
	}

二、后台分页数据查询

1.处理流程

1） 查询满足条件的总记录数

2） 查询满足条件的当前页的数据

3） 上两个步骤的查询条件要一致

流程图：

 

2.实现

1） 为简化数据库操作，需要一个DBUtil工具类

代码如下（示例）：

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;
 
/**
 * @author Administrator
 * @create 2020-05-0811:43
 */
public class DBUtil {
	private static String DRIVER_NAME;
 
    private static String DB_URL;
 
    private static String DB_USER;
 
    private static String DB_PASSWORD;
 
 
    private DBUtil() {
    }
 
 
    static {
        try {
        	InputStream in = DBUtil.class.getResourceAsStream("/jdbc.properties");
        	Properties properties = new Properties();
			properties.load(in);
			
			DRIVER_NAME = properties.getProperty("driver.name");
			DB_URL = properties.getProperty("db.url");
			DB_USER = properties.getProperty("db.user");
			DB_PASSWORD = properties.getProperty("db.password");
			
            Class.forName(DRIVER_NAME);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }  catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }
 
 
    public static Connection getConection() throws SQLException {
        Connection connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
        return connection;
    }
 
 
    public static void closeDB(ResultSet rs, Statement ps, Connection con) {
 
        try {
            if (rs != null && !rs.isClosed()) {
                rs.close();
            }
 
            if (ps != null && !ps.isClosed()) {
                ps.close();
            }
 
            if(con != null && !con.isClosed()) {
                con.close();
            }
 
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    
    public static void closeDB(ResultSet rs, Statement ps) {
 
        try {
            if (rs != null && !rs.isClosed()) {
                rs.close();
            }
 
            if (ps != null && !ps.isClosed()) {
                ps.close();
            }
 
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    
    
    public static void main(String[] args) throws SQLException {
    	Connection conection = DBUtil.getConection();
    	DBUtil.closeDB(null, null, conection);
    	System.out.println("------- 成功 -------------");
    }

2） 分页查询

代码如下（示例）：

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 com.zking.mymvc.model.Student;
import com.zking.mymvc.util.DBUtil;
import com.zking.mymvc.util.PageBean;
import org.junit.Test;
public class StudentDao {
public List<Student> getStudents(String sname, PageBean pageBean) {
		
		String sql = "select * from t_student t ";
		
		if(sname != null && !"".equals(sname)) {
			sql += " where t.sname like ?";
		}
		
		//查询之前的准备
		List<Student> students = new ArrayList<>();
		Connection con = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		
		//如果不需要分页，直接查询
		if(pageBean == null || !pageBean.isPagination()) {
			try {
				con = DBUtil.getConection();
				ps = con.prepareStatement(sql);
				
				if(sname != null && !"".equals(sname)) {
					ps.setObject(1, sname+"%");
				}
				
				rs = ps.executeQuery();
				
				while(rs.next()) {
					Student stu = new Student();
					stu.setSid(rs.getInt("sid"));
					stu.setSname(rs.getString("sname"));
					stu.setAge(rs.getInt("age"));
					stu.setRemark(rs.getString("remark"));
					students.add(stu);
				}
				
				return students;
				
			} catch(SQLException e) {
				e.printStackTrace();
			} finally {
				DBUtil.closeDB(rs, ps, con);
			}
			
		} else {
			//如果需要分页
			
			//1. 总记录数
			String countSql = "select COUNT(*) from ("+sql+") t";
			
			try {
				con = DBUtil.getConection();
				ps = con.prepareStatement(countSql);
				
				//设置查询参数
				if(sname != null) {
					ps.setObject(1, sname+"%");
				}
				
				rs = ps.executeQuery();
				
				//为总记录数赋值
				while(rs.next()) {
					pageBean.setTotal(rs.getInt(1));
				}
				
				//如果总记录为0， 则直接返回一个空的结果集
				if(pageBean.getTotal() == 0) {
					return students;
				}
				
				//查询当前页数据的sql
				String pagingSql = sql + " limit " + pageBean.getStartIndex() + ", " + pageBean.getRows();
				ps = con.prepareStatement(pagingSql);
				
				//设置查询参数
				if(sname != null) {
					ps.setObject(1, sname+"%");
				}
				
				rs = ps.executeQuery();
				
				while(rs.next()) {
					Student stu = new Student();
					stu.setSid(rs.getInt("sid"));
					stu.setSname(rs.getString("sname"));
					stu.setAge(rs.getInt("age"));
					stu.setRemark(rs.getString("remark"));
					students.add(stu);
				}
				
				return students;
				
			} catch(SQLException e) {
				e.printStackTrace();
			} finally {
				DBUtil.closeDB(rs, ps, con);
			}
			
		}
		
		return students;
		
	}
}
Student实体，及对应的数据库表可自行准备。

public class Student {
private Integer sid;
	
	private String sname;
	
	private Integer age;
	
	private String remark;
 
	public Integer getSid() {
		return sid;
	}
 
	public void setSid(Integer sid) {
		this.sid = sid;
	}
 
	public String getSname() {
		return sname;
	}
 
	public void setSname(String sname) {
		this.sname = sname;
	}
 
	public Integer getAge() {
		return age;
	}
 
	public void setAge(Integer age) {
		this.age = age;
	}
 
	public String getRemark() {
		return remark;
	}
 
	public void setRemark(String remark) {
		this.remark = remark;
	}
 
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", age=" + age + ", remark=" + remark + "]";
	}