MVC通用分页功能(PageBean)🎀
文章目录
1. 总体思路
- 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
- 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
2. 分页信息实体（PageBean）
🎇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
参考实现：
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;
}
}
3 .后台分页数据查询
3.1 处理流程
- 查询满足条件的总记录数
- 查询满足条件的当前页的数据
- 上两个步骤的查询条件要一致
流程图：
3.2 实现
为简化数据库操作，需要一个DBUtil工具类
public final class DBUtil {
private static String DRIVER_NAME = "com.mysql.jdbc.Driver";
private static String DB_URL = "jdbc:mysql://localhost:3306/t234?useUnicode=true&characterEncoding=utf-8&useSSL=false";
private static String DB_USER = "root";
private static String DB_PASSWORD = "123456";
private DBUtil() {
}
static {
try {
Class.forName(DRIVER_NAME);
} catch (ClassNotFoundException e) {
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();
}
}
}
分页查询
public class StudentDao {
public List<Student> getStudents(String sname, PageBean pageBean) {
String sql = "select * from t_student t ";
if (!Objects.isNull(sname) && sname.length() > 0) {
sql += " where t.sname like ?";
}
List<Student> students = new ArrayList<>();
Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;
/*
* 如果不需要分页，则直接查询查询，并返回查询结果。
*/
if (pageBean == null || !pageBean.isPagination()) {
//3.
try {
con = DBUtil.getConection();
ps = con.prepareStatement(sql);
//设置查询参数
if(sname != null) {
ps.setObject(1, sname+"%");
}
rs = ps.executeQuery();
//1. 差异化部分
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);
}
} catch (Exception e) {
e.printStackTrace();
//2.
} finally {
DBUtil.closeDB(rs, ps, con);
}
return students;
} else {
/*
* 如果需要分页，则分两步操作：
* 1. 查询总记录数
* 2. 查询当前页记录
*/
//1. 生成统计总记录数的SQL， 查询总记录数
try {
String countSql = "select count(*) from (" + sql + ") tmp";
con = DBUtil.getConection();
ps = con.prepareStatement(countSql);
//设置查询参数
if(sname != null) {
ps.setObject(1, sname+"%");
}
rs = ps.executeQuery();
while(rs.next()) {
pageBean.setTotal(rs.getInt(1));
}
/*
* 如果统计的总记录数为0，则表示没有符合条件的记录，直接返回一个空结果集即可。
*/
if(pageBean.getTotal() == 0) {
return students;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
DBUtil.closeDB(rs, ps);
}
/*
* 生成分页sql，查询当前页的数据
*/
try {
String pagingSql = sql + " limit " + pageBean.getStartRow() + ", " + pageBean.getRows();
ps = con.prepareStatement(pagingSql);
//设置查询参数
if(sname != null) {
ps.setObject(1, sname+"%");
}
rs = ps.executeQuery();
//差异化
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);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
DBUtil.closeDB(rs, ps, con);
}
return students;
}
}
public static void main(String[] args) {
StudentDao dao = new StudentDao();
List<Student> students = dao.getStudents("张", new PageBean());
students.forEach(s -> System.out.println(s));
}
}
Student实体，及对应的数据库表可自行准备。
3.3 重构-提取公用方法
1.为了进行公共方法的抽取，需要找出上面实习中的可通用部分，和差异化部分。
- 只要是分页，就会统计总记录数，而总记录数的统计是在业务sql外封装了一个select count(*)是有规律可循的，可以通用
- 只要是分页，则封装分页sql也是有规律可循的（在业务sql后加limit子句即可），可以通用
- 因为每个查询对应的业务实体（即模型）不同，所以ORM映射部分不能通用
2.公用方法封装思路
- 将可通用的部分封装到模板中
- 差异化部分（即不可通用部分），可以定义一个处理接口，以便于通过参数传入个性化的实现部分
- 具体实现
通用分页查询模板类：
public final class DBTemplate {
private DBTemplate() {
}
public static interface IORMConvert<T> {
List<T> convert(ResultSet rs) throws SQLException;
}
public static <T> List<T> query(String sql,
Object[] params,
PageBean pageBean,
IORMConvert<T> convert) {
List<T> datas = new ArrayList<>();
Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;
//不需要分页
if (pageBean == null || !pageBean.isPagination()) {
try {
con = DBUtil.getConection();
ps = con.prepareStatement(sql);
setParam(params, ps);
rs = ps.executeQuery();
datas = convert.convert(rs);
return datas;
} catch(Exception e) {
e.printStackTrace();
} finally {
DBUtil.closeDB(rs, ps, con);
}
} else {
//1. 查询总记录数
//2. 查询当前页数据
//1. 生成统计总记录数的SQL， 查询总记录数
try {
String countSql = "select count(*) from (" + sql + ") tmp";
con = DBUtil.getConection();
ps = con.prepareStatement(countSql);
setParam(params, ps);
rs = ps.executeQuery();
while(rs.next()) {
pageBean.setTotal(rs.getInt(1));
}
/*
* 如果统计的总记录数为0，则表示没有符合条件的记录，直接返回一个空结果集即可。
*/
if(pageBean.getTotal() == 0) {
return datas;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if(pageBean.getTotal() == 0) {
DBUtil.closeDB(rs, ps, con);
}
DBUtil.closeDB(rs, ps);
}
//查询当前页数据
try {
String pagingSql = sql
+ " limit "
+ pageBean.getStartRow()
+ ", "
+ pageBean.getRows();
ps = con.prepareStatement(pagingSql);
setParam(params, ps);
rs = ps.executeQuery();
datas = convert.convert(rs);
} catch (SQLException e) {
e.printStackTrace();
} finally {
DBUtil.closeDB(rs, ps, con);
}
}
return datas;
}
private static void setParam(Object[] params, PreparedStatement ps) throws SQLException {
if (params != null) {
int i = 1;
for (Object param : params) {
ps.setObject(i, param);
i++;
}
}
}
}
使用示例：
public class StudentDao2 {
public List<Student> getStudents(String sname, PageBean pageBean) {
String sql = "select * from t_student where sname like ?";
return DaoTemplate.query(sql, new Object[] {sname}, pageBean, new IORMConvert<Student>() {
@Override
public List<Student> convert(ResultSet rs) throws SQLException {
List<Student> stus = new ArrayList<>();
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"));
stus.add(stu);
}
return stus;
}
});
}
public static void main(String[] args) {
StudentDao2 dao = new StudentDao2();
PageBean pageBean = new PageBean();
pageBean.setPage(3);
List<Student> students = dao.getStudents("张%", pageBean);
students.forEach(s -> System.out.println(s));
}
}
3.4 分页标签
4.1 准备一个Servlet
准备一个servlet用于处理请求，获取数据库中的数据，并转发到结果显示页面。
@WebServlet(value = "/students")
public class StudentAction extends HttpServlet {
private static final long serialVersionUID = 3152900867611381148L;
private StudentDao2 studentDao = new StudentDao2();
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
PageBean pageBean = new PageBean();
pageBean.setRequest(request);
request.setAttribute("pageBean", pageBean);
String sname = request.getParameter("sname");
List<Student> students = studentDao.getStudents(sname+"%", pageBean);
request.setAttribute("students", students);
System.out.println("dopost .......... ");
request.getRequestDispatcher("/students/stuList.jsp").forward(request, response);
}
}
4.2 结果展示页面
创建一个页面，该页面用于显示结果， 使用jstl的c标签来展示结果，为正常使用c标签，需要引入jstl-1.2.jar和standard-1.1.2.jar。
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@taglib prefix="z" uri="/zking" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<h1>学生信息</h1>
<form action="<%=request.getContextPath()%>/students" method="post">
<input type="text" name="sname">
<input type="submit" value="查询">
</form>
<table border="1" style="width: 98%;">
<tr>
<td>学号</td>
<td>姓名</td>
<td>年龄</td>
<td>备注</td>
</tr>
<c:forEach items="${students}" var="student">
<tr>
<td>${student.sid}</td>
<td>${student.sname}</td>
<td>${student.age}</td>
<td>${student.remark}</td>
</tr>
</c:forEach>
</table>
</body>
</html>
4.3 过滤器解决中文乱码问题
/**
* 中文乱码处理
*/
@WebFilter("/*")
public class EncodingFiter implements Filter {
private String encoding = "UTF-8";// 默认字符集
public EncodingFiter() {
super();
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
// 中文处理必须放到 chain.doFilter(request, response)方法前面
res.setContentType("text/html;charset=" + this.encoding);
if (req.getMethod().equalsIgnoreCase("post")) {
req.setCharacterEncoding(this.encoding);
} else {
Map map = req.getParameterMap();// 保存所有参数名=参数值(数组)的Map集合
Set set = map.keySet();// 取出所有参数名
Iterator it = set.iterator();
while (it.hasNext()) {
String name = (String) it.next();
String[] values = (String[]) map.get(name);// 取出参数值[注：参数值为一个数组]
for (int i = 0; i < values.length; i++) {
values[i] = new String(values[i].getBytes("ISO-8859-1"),
this.encoding);
}
}
}
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
String s = filterConfig.getInitParameter("encoding");// 读取web.xml文件中配置的字符集
if (null != s && !s.trim().equals("")) {
this.encoding = s.trim();
}
}
}
4.3 加入分页功能
- 先不考虑功能性在页面上的table标签下，加入及分页工具条
<div style="text-align: right; width:98%;">
第1页
共100条记录
<a>首页</a>
<a>上页</a>
<a>下页</a>
<a>尾页</a>
第<input type="text" size="2" />
<a href="#">GO</a>
</div>
不考虑通过的分页如下实现，先在结果页面中实现分页功能。
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@taglib prefix="z" uri="/zking" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<h1>学生信息</h1>
<form action="<%=request.getContextPath()%>/students" method="post">
<input type="text" name="sname"/>
<input type="submit" value="查询">
</form>
<table border="1" style="width: 98%;">
<tr>
<td>学号</td>
<td>姓名</td>
<td>年龄</td>
<td>备注</td>
</tr>
<c:forEach items="${students}" var="student">
<tr>
<td>${student.sid}</td>
<td>${student.sname}</td>
<td>${student.age}</td>
<td>${student.remark}</td>
</tr>
</c:forEach>
</table>
<!-- 分页页面元素 -->
<div style="text-align: right; width:98%;">
第${pageBean.page}页
共${pageBean.total}条记录
<a href="javascript: goPage(1);">首页</a>
<a href="javascript: goPage('${pageBean.previousPage}');">上页</a>
<a href="javascript: goPage('${pageBean.nextPage}');">下页</a>
<a href="javascript: goPage('${pageBean.totalPage}')">尾页</a>
第<input type="text" id="pagingPageNum" size="2" onkeypress="goSpecifiedPage(event,this.value);"/>
<a href="javascript: goPage(document.getElementById('pagingPageNum').value)">GO</a>
</div>
<!-- 用于分页的隐藏表单 -->
<form action="${pageBean.url}" id="pagingForm" method="post">
<input type="hidden" name="page" value="${pageBean.page}"/>
<!-- 先只考虑本功能的查询参数，没有考虑公用性（不同功能的参数不同） -->
<input type="hidden" name="sname" value="<%=request.getParameter("sname")%>"/>
</form>
<!-- 用于分页的js代码 -->
<script>
function goPage(pageNum) {
var form = document.getElementById("pagingForm");
form.page.value = pageNum;
form.submit();
}
function goSpecifiedPage(event) {
if(event.keyCode == 13) {
var pageNum = document.getElementById("pagingPageNum").value;
var form = document.getElementById("pagingForm");
form.page.value = pageNum;
form.submit();
}
}
</script>
</body>
</html>
目前为止，分页功能已经实现了。
4.4 封装分页标签
为了方便代码的复用，及可维护性，我们将分页功能封装了一个自定义标签（其实就是将原来写在页面中的代码，通过移入到自定义标签中去实现），开发自定义标签分成三步：
- 编写助手类
- 编写标签描述文件
- 在页面上引入标签库，并使用
- 编写助手类
public class PagingTag extends BodyTagSupport {
private PageBean pageBean;
public PageBean getPageBean() {
return pageBean;
}
public void setPageBean(PageBean pageBean) {
this.pageBean = pageBean;
}
@Override
public int doStartTag() throws JspException {
JspWriter out = this.pageContext.getOut();
try {
out.println(buildHtml());
return SKIP_BODY;
} catch (IOException e) {
throw new JspException("分页标签异常", e);
}
}
//生成Html内容
private String buildHtml() {
//构建分页页面元素
String pagingElement = "<div style=\"text-align: right; width:98%;\">\r\n" +
" 第" + pageBean.getPage() + "页 \r\n" +
" 共" + pageBean.getTotal() + "条记录 \r\n" +
" <a href=\"javascript: goPage(1);\">首页</a> \r\n" +
" <a href=\"javascript: goPage('" + pageBean.getPreviousPage() + "');\">上页</a> \r\n" +
" <a href=\"javascript: goPage('" + pageBean.getNextPage() + "');\">下页</a> \r\n" +
" <a href=\"javascript: goPage('" + pageBean.getTotalPage() + "')\">尾页</a> \r\n" +
" 第<input type=\"text\" id=\"pagingPageNum\" size=\"2\" value='"+pageBean.getPage()+"' οnkeypress=\"goSpecifiedPage(event,this.value);\"/> \r\n" +
" <a href=\"javascript: goPage(document.getElementById('pagingPageNum').value)\">GO</a>\r\n" +
" </div>";
//构建隐藏表单，用于在分页时传递分页参数
String hiddenForm = "<form action='" + pageBean.getUrl() + "' id=\"pagingForm\" method=\"post\">"
+ "<input type=\"hidden\" name=\"page\" />";
Map<String, String[]> parameterMap = pageBean.getParameterMap();
for(Map.Entry<String, String[]> param: parameterMap.entrySet()) {
String paramName = param.getKey();
if("page".equals(paramName)) continue;
String[] values = param.getValue();
for(String val: values) {
hiddenForm += "<input type='hidden' name='" + paramName + "' value='" + val + "'>";
}
}
hiddenForm += "</form>";
//构建分页功能需要的js代码块
String script = "<script>\r\n" +
" function goPage(pageNum) {\r\n" +
" var form = document.getElementById(\"pagingForm\");\r\n" +
" form.page.value = pageNum;\r\n" +
" form.submit();\r\n" +
" }\r\n" +
" \r\n" +
" function goSpecifiedPage(event) {\r\n" +
" if(event.keyCode == 13) {\r\n" +
" var pageNum = document.getElementById(\"pagingPageNum\").value;\r\n" +
" var form = document.getElementById(\"pagingForm\");\r\n" +
" form.page.value = pageNum;\r\n" +
" form.submit();\r\n" +
" }\r\n" +
" }\r\n" +
" </script>";
return pagingElement + hiddenForm + script;
}
}
标签库描述文件中添加paging标签
<tag>
<name>paging</name>
<tag-class>com.zking.mvc.tag.PagingTag</tag-class>
<body-content>empty</body-content>
<attribute>
<name>pageBean</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
使用分页标签
首先在页面中引入标签
<%@taglib prefix="z" uri="/zking" %>
将原来的分页功能，替换为标签即可
<z:paging pageBean="${pageBean}"/>
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