通用分页一

1 pageBean
分页三要素
page` 页码 视图层传递过来
rows 页大小 视图层传递过来
total 总记录数 后台查出来
pagination 是否分页 视图层传递过来
start 查询数据集的起始下表
offset 查询展示在当前页的记录

首先导入jia包

连接数据库

private static String driver;
	private static String url;
	private static String user;
	private static String password;

	static {//  静态块执行一次，加载 驱动一次
		try {
			InputStream is = DBAccess.class
					.getResourceAsStream("config.properties");

			Properties properties = new Properties();
			properties.load(is);

			driver = properties.getProperty("driver");
			url = properties.getProperty("url");
			user = properties.getProperty("user");
			password = properties.getProperty("pwd");

			Class.forName(driver);
		} catch (Exception e) {
			e.printStackTrace();
			throw new RuntimeException(e);
		}
	}

	/**
	 * 获得数据连接对象
	 * 
	 * @return
	 */
	public static Connection getConnection() {
		try {
			Connection conn = DriverManager.getConnection(url, user, password);
			return conn;
		} catch (SQLException e) {
			e.printStackTrace();
			throw new RuntimeException(e);
		}
	}

	public static void close(ResultSet rs) {
		if (null != rs) {
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
				throw new RuntimeException(e);
			}
		}
	}

	public static void close(Statement stmt) {
		if (null != stmt) {
			try {
				stmt.close();
			} catch (SQLException e) {
				e.printStackTrace();
				throw new RuntimeException(e);
			}
		}
	}

	public static void close(Connection conn) {
		if (null != conn) {
			try {
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
				throw new RuntimeException(e);
			}
		}
	}

	public static void close(Connection conn, Statement stmt, ResultSet rs) {
		close(rs);
		close(stmt);
		close(conn);
	}

	public static boolean isOracle() {
		return "oracle.jdbc.driver.OracleDriver".equals(driver);
	}

	public static boolean isSQLServer() {
		return "com.microsoft.sqlserver.jdbc.SQLServerDriver".equals(driver);
	}
	
	public static boolean isMysql() {
		return "com.mysql.jdbc.Driver".equals(driver);
	}

	public static void main(String[] args) {
		Connection conn = DBAccess.getConnection();
		DBAccess.close(conn);
		System.out.println("isOracle：" + isOracle());
		System.out.println("isSQLServer：" + isSQLServer());
		System.out.println("isMysql：" + isMysql());
		System.out.println("数据库连接(关闭)成功");
	}

封装一个工具类

public class PageBean {

	private int page = 1;// 页码

	private int rows = 10;// 页大小

	private int total = 0;// 总记录数

	private boolean pagination = true;// 是否分页

	public PageBean() {
		super();
	}

	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 void setTotal(String total) {
		this.total = Integer.parseInt(total);
	}

	public boolean isPagination() {
		return pagination;
	}

	public void setPagination(boolean pagination) {
		this.pagination = pagination;
	}

	/**
	 * 获得起始记录的下标
	 * 
	 * @return
	 */
	public int getStartIndex() {
		return (this.page - 1) * this.rows;
	}

	@Override
	public String toString() {
		return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";
	}

}

在这里插入代码片

然后是实体类

public class Book {
	private int bid;
	private String bname;
	private float price;

	@Override
	public String toString() {
		return "Book [bid=" + bid + ", bname=" + bname + ", price=" + price + "]";
	}

	public int getBid() {
		return bid;
	}

	public void setBid(int bid) {
		this.bid = bid;
	}

	public String getBname() {
		return bname;
	}

	public void setBname(String bname) {
		this.bname = bname;
	}

	public float getPrice() {
		return price;
	}

	public void setPrice(float price) {
		this.price = price;
	}

}

在这里插入代码片

现在先用之前学的完成一个查询方法

public List<Book> list(Book book,PageBean pageBean) throws SQLException{
		String sql="select * from t_mvc_book where true";
		String bname=book.getBname();
		if(StringUtils.isNotBlank(bname)) {
			sql+=" and bname like '%"+bname+"%'";
		}
		Connection con = DBAccess.getConnection();
		PreparedStatement ps=con.prepareStatement(sql);
		ResultSet rs = ps.executeQuery();
		List<Book> list=new ArrayList<>();
		while(rs.next()) {
			list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
		}
		DBAccess.close(con, ps, rs);
		return list;
		
	}
 

	public static void main(String[] args) throws SQLException {
		BookDao bookDao=new BookDao();
		Book book=new Book();
		book.setBname("不死不灭");
		PageBean bean=new PageBean();
		bean.setPage(2);
		bean.setRows(8);
		bean.setPagination(true);
		try {
			List<Book> list = bookDao.list(book,bean);
			for (Book b : list) {
				System.out.println(b);
			}
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}

}
在这里插入代码片

2、将原有的查询方法进行反射优化，转变成一个可以被所有实体类dao层所继承的通用查询方法

package util;

import java.lang.reflect.Field;
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 entity.Book;

/**
 * 用来处理所以表的通用的增删改查的基类
 * @author 陌陌
 *
 * @param <T>
 */
public class BaseDao<T> {
	/**
	 * 
	 * @param sql    可能不同的表，那么意味着sql是变化的，那么它是从子类处理好再传递到夫类
	 * @param clz    需要返回不同的对象集合  Book.class/Order.class
	 * @param pageBean   可能要分页
	 * @return
	 * @throws SQLException
	 * @throws IllegalAccessException 
	 * @throws InstantiationException 
	 */
	public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
		List<T> list=new ArrayList<>();
		Connection con = DBAccess.getConnection();
		PreparedStatement ps=con.prepareStatement(sql);
		ResultSet rs = ps.executeQuery();
		T t=null;
		while(rs.next()) {
//			list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
			/**
			 * 1.实例化一个book对象   null
			 * 2.通过book对象的属性名去游标中取出属性值
			 * 2.1.获取到类对象中的属性
			 * 2.2.给属性赋值
			 * 3.已经赋值好的book实例对象，放入list集合中
			 */
			t=(T) clz.newInstance();
			Field[] fields=clz.getDeclaredFields();
			for (Field f : fields) {
				f.setAccessible(true);
				f.set(t, rs.getObject(f.getName()));
			}
			list.add(t);
		}
		
		return list;
		
	}
}

在这里插入代码片

ublic List<Book> list(Book book,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
		String sql="select * from t_mvc_book where true";
		String bname=book.getBname();
		if(StringUtils.isNotBlank(bname)) {
			sql+=" and bname like '%"+bname+"%'";
		}
		return super.executeQuery(sql, Book.class, pageBean);
		
	}
 
	public static void main(String[] args) throws SQLException {
		BookDao bookDao=new BookDao();
		Book book=new Book();
//		book.setBname("不死不灭");
		try {
			List<Book> list = bookDao.list(book,null);
			for (Book b : list) {
				System.out.println(b);
			}
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}
在这里插入代码片

3、考虑该方法可以进行分页

public class BaseDao<T> {
	/**
	 * 
	 * @param sql    可能不同的表，那么意味着sql是变化的，那么它是从子类处理好再传递到夫类
	 * @param clz    需要返回不同的对象集合  Book.class/Order.class
	 * @param pageBean   可能要分页
	 * @return
	 * @throws SQLException
	 * @throws IllegalAccessException 
	 * @throws InstantiationException 
	 */
	public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
		List<T> list=new ArrayList<>();
		Connection con = DBAccess.getConnection();
		PreparedStatement pst=null;
		ResultSet rs =null;
		if(pageBean !=null && pageBean.isPagination()) {
//			分页代码
			/**
			 * 1.分页是与pagebean中total，意味着需要查询数据库得到total赋值给pagebean
			 * 2.查询出符合条件的某一页的数据
			 */
//			select count(*) from (select * from t_mvc_book where bname like '%%') t;
			String countSql=getCountSql(sql);
			pst=con.prepareStatement(countSql);
			rs =pst.executeQuery();
			if(rs.next()) {
				pageBean.setTotal(rs.getObject(1).toString());
			}
//			select * from t_mvc_book where bname like '%圣墟%' limit 0,10;
			String pageSql=getCountSql(sql,pageBean);
			pst=con.prepareStatement(pageSql);
			rs =pst.executeQuery();
		}else {
//		不分页代码	
			pst=con.prepareStatement(sql);
			rs =pst.executeQuery();
		}
		T t=null;
		while(rs.next()) {
//			list.add(new Book(rs.getInt("bid"),rs.getString("bname"),rs.getFloat("price")));
			t=(T) clz.newInstance();
			Field[] fields=clz.getDeclaredFields();
			for (Field f : fields) {
				f.setAccessible(true);
				f.set(t, rs.getObject(f.getName()));
			}
			list.add(t);
		}
		
		return list;
		
	}

	private String getCountSql(String sql, PageBean pageBean) {
		return sql + "limit"+pageBean.getStartIndex()+","+pageBean.getRows();
	}

	private String getCountSql(String sql) {
		return "select count(1) from (+sql+) t";
	}
在这里插入代码片

	public List<Book> list(Book book,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{
		String sql="select * from t_mvc_book where true";
		String bname=book.getBname();
		if(StringUtils.isNotBlank(bname)) {
			sql+=" and bname like '%"+bname+"%'";
		}
		return super.executeQuery(sql, Book.class, pageBean);
		
	}
 
	public static void main(String[] args) throws SQLException {
		BookDao bookDao=new BookDao();
		Book book=new Book();
		PageBean pageBean=new PageBean();
	//	pageBean.setPage(2);
		book.setBname("圣墟");
		try {
			List<Book> list = bookDao.list(book,pageBean);
			for (Book b : list) {
				System.out.println(b);
			}
			System.out.println(pageBean);
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}
在这里插入代码片