1.分页
1、通过分页,我们不用一次性将所有的数据查出来,只需先查出来一部分,可以减少数据库的IO数据量的传输,降低数据库读写压力,从而提高数据库响应速度
2、页面也不用一次性显示所有的数据,可以减少浏览器和服务器之间大量数据的IO传输,从而提高服务器的响应速度
3、我们可能值需要很多信息中少数的几条,那么传输其他多余的数据就是无形之中对于资源的浪费,分页可以减少资源的浪费
1.2分页的步骤
首先先建一个类,写上需要的属性，再写一个起始的下标
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 + "]"; }
/** * 带分类的模糊查询 * @param sql * @param clz * @param pageBean * @return * @throws Exception */ public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws Exception{ List<T> list = new ArrayList<T>(); Connection conn = null; PreparedStatement pst = null; ResultSet rs = null; if(pageBean != null && pageBean.isPagination()) { String countSQL = getCountSQL(sql); conn = DBAccess.getConnection(); pst = conn.prepareStatement(countSQL); rs = pst.executeQuery(); if(rs.next()) { pageBean.setTotal(rs.getObject("n").toString()); } String pageSQL = getPageSQL(sql,pageBean); conn = DBAccess.getConnection(); pst = conn.prepareStatement(pageSQL); rs = pst.executeQuery(); }else { conn = DBAccess.getConnection(); pst = conn.prepareStatement(sql); rs = pst.executeQuery(); } while(rs.next()) { T t = (T) clz.newInstance(); // 拿到clz对应的所有属性对象 Field[] fields = clz.getDeclaredFields(); for (Field f : fields) { f.setAccessible(true); // System.out.println(f.getName()); f.set(t, rs.getObject(f.getName())); } list.add(t); } return list; }
2.解析BaseDao
2.1先定义它的属性：
2.2再进行判断
3.案列及效果
package com.xuyahui.Dao; 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 com.xuyahui.entity.Book; import com.xuyahui.util.BaseDao; import com.xuyahui.util.DBAccess; import com.xuyahui.util.PageBean; import com.xuyahui.util.StringUtils; /** * BookDao: 操作的是书籍表 * @author 86155 * */ public class BookDao extends BaseDao<Book>{ public List<Book> list1(Book book,PageBean pageBean) throws Exception{ List<Book> list = new ArrayList<Book>(); Connection conn = DBAccess.getConnection(); String sql = "select * from t_mvc_book"; String bname = book.getBname(); if(StringUtils.isNotBlank(bname)) { sql += " and bname like '%"+bname+"%'"; } PreparedStatement pst = conn.prepareStatement(sql); ResultSet rs = pst.executeQuery(); while(rs.next()) { Book b = new Book(); b.setBid(rs.getInt("bid")); b.setBname(rs.getString("bname")); b.setPrice(rs.getFloat("price")); list.add(b); } return list; } public List<Book> list2(Book book,PageBean pageBean) throws Exception{ String sql = "select * from t_mvc_book 1=1"; String bname = book.getBname(); if(StringUtils.isNotBlank(bname)) { sql += " and bname like '%"+bname+"%'"; } return super.executeQuery(sql, Book.class, pageBean); } @Test public void test1() throws Exception { System.out.println("test1..."); BookDao bookDao = new BookDao(); Book book = new Book(); book.setBname("圣墟"); PageBean pageBean = new PageBean(); List<Book> list = bookDao.list1(book, pageBean); for (Book b : list) { System.out.println(b); } }
效果
