分页查询
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2022-06-21 15:08:38
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网页中显示表中所有数据,当数据过多时,采用分页查询,一页只显示少量数据。可以跳转到首页或末页,可以直接跳转到某一页。
实体类
/**
* 查询列表分页显示
*/
public class Page {
private Integer pageNum; //当前第几页
private Integer pageSize; //每页几条
private Integer totalCount; //总共几条
private Integer totalPages; // 总共几页
private Integer startRows; //从第几行开始
public Page() {
}
public Page(Integer pageNum, Integer pageSize) {
this.setPageNum(pageNum);
this.setPagesize(pageSize);
this.startRows = (this.pageNum - 1) * this.pageSize;
}
public Integer getPageNum() {
return pageNum;
}
public void setPageNum(Integer pageNum) {
if(pageNum == null || pageNum < 0){
pageNum = 1;
}
this.pageNum = pageNum;
}
public Integer getPageSize() {
return pageSize;
}
public void setPagesize(Integer pageSize) {
//当pageSize过大过小时,默认为2
if(pageSize == null || pageSize < 0 || pageSize > 5){
pageSize = 2;
}
this.pageSize = pageSize;
}
public Integer getTotalCount() {
return totalCount;
}
public void setTotalCount(Integer totalCount) {
this.totalCount = totalCount;
//计算总页数
if(this.totalCount % this.pageSize == 0){
this.totalPages = this.totalCount / this.pageSize;
}else {
this.totalPages = this.totalCount / this.pageSize + 1;
}
}
public Integer getTotalPages() {
return totalPages;
}
public void setTotalPages(Integer totalPages) {
this.totalPages = totalPages;
}
public Integer getStartRows() {
return startRows;
}
public void setStartRows(Integer startRows) {
this.startRows = startRows;
}
}
Dao层,操作数据库
/**
* 查询所有书籍,并分页显示
* @param offset 从第几行开始
* @param pageSize 每页几条
* @return
*/
public List<Book> getBookList(Integer offset,Integer pageSize){
String sql = "select id,name,author,publish,publish_date publishDate,borrower from book limit ?,?";
try {
return queryRunner.query(sql,new BeanListHandler<Book>(Book.class),offset,pageSize);
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
/**
* 查找共有多少条数据
* @return
*/
public long selectCount(){
String sql = "select count(*) from book";
try {
return queryRunner.query(sql,new ScalarHandler<>());
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
service层
/**
* 查询所有数据
* @param page
* @return
*/
public List<Book> getBookList(Page page){
BookDao bookDao = new BookDao();
long count = bookDao.selectCount();
page.setTotalCount((int) count);
return bookDao.getBookList(page.getStartRows(),page.getPageSize());
}
contrallor层
import entity.Book;
import entity.Page;
import service.BookService;
import util.ParameterUtil;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
@WebServlet(name = "BookListServlet", urlPatterns = "/booklist")
public class BookListServlet extends HttpServlet {
BookService bookService = new BookService();
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Integer pageNum = ParameterUtil.getInteger(request,"pn");//页码
Integer pageSize = ParameterUtil.getInteger(request,"ps");//每页几条
Page page = new Page(pageNum,pageSize);
List<Book> bookList = bookService.getBookList(page);
request.setAttribute("booklist",bookList);
request.setAttribute("page",page);
request.getRequestDispatcher("booklist.jsp").forward(request,response);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
}
前端JSP页面
<!--数据列表代码省略-->
<a href="booklist?pn=1">首页</a>
<%--第1页没有上一页--%>
<c:if test="${requestScope.page.pageNum gt 1}">
<a href="booklist?pn=${requestScope.page.pageNum-1}">上一页</a>
</c:if>
<c:forEach begin="1" end="${requestScope.page.totalPages}" varStatus="i">
<a href="booklist?pn=${i.count}">第${i.count}页</a>
</c:forEach>
<%--最后一页没有下一页--%>
<c:if test="${requestScope.page.pageNum lt requestScope.page.totalPages}">
<a href="booklist?pn=${requestScope.page.pageNum+1}">下一页</a>
</c:if>
<a href="booklist?pn=${requestScope.page.totalPages}">末页</a>
总共${requestScope.page.totalCount}条 / 共${requestScope.page.totalPages}页<br/>
当前第${requestScope.page.pageNum}页 / 每页${requestScope.page.pageSize}条
效果
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