茶饮月通过本文主要向大家介绍了jsp的通用规则,jsp mvc框架,jsp框架,jsp iframe布局框架,jsp框架模板等相关知识,希望对您有所帮助,也希望大家支持linkedu.com www.linkedu.com
写一个通用的分页框架，这样在项目里面如果想实现分页功能，只需要稍加改动参数就可以实现分页处理了。这样写了会节省很多时间。
一.分页类
既然要分页那么我们就要考虑建一个通用的分页类,里面需要的参数一般有:
总页数 totalPage
总共记录数 totalRecord
每页显示数 pageSize
当前页pageIndex
承载当前页数据的集合 List datas
完整代码:Page.java
import java.util.List;
public class Pager<E> {
/**
* 总共页数
*/
private int totalPages;
/**
* 总共记录数
*/
private int totalRecords;
/**
* 每页显示数量
*/
private int pageSize;
/**
* 当前页
*/
private int pageIndex;
/**
* 当前页数据集合
*/
private List<E> datas;
public void setTotalPages(int totalPages) {
this.totalPages = totalPages;
}
public void setTotalRecords(int totalRecords) {
this.totalRecords = totalRecords;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public void setPageIndex(int pageIndex) {
this.pageIndex = pageIndex;
}
public void setDatas(List<E> datas) {
this.datas = datas;
}
public int getTotalPages() {
return totalPages;
}
public int getTotalRecords() {
return totalRecords;
}
public int getPageSize() {
return pageSize;
}
public int getPageIndex() {
return pageIndex;
}
public List<E> getDatas() {
return datas;
}
}
</div>
二.用户类
这里以查询用户来做分页为例,所以就需要一个用户类
用户号 userId
用户姓名 username
用户密码 password
注册时间 regdate
完整代码
import java.sql.Timestamp;
public class User {
private int userId;//用户id
private String username;//用户名
private String password;//密码
private Timestamp regdate;//注册时间
public int getUserId() {
return userId;
}
public void setUserId(int userId) {
this.userId = userId;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Timestamp getRegdate() {
return regdate;
}
public void setRegdate(Timestamp regdate) {
this.regdate = regdate;
}
}
</div>
三.threadLocal提取公用参数
先说如果不提取公共参数,比如pagesize,pageindex,那么我们的查询方法应该是这样子:
public void GetUsers(String name,int pagesize,int pageIndex)</div>
如果以后再增加参数,无疑这里的参数会变的很多,所以我们利用threadLocal把pagesize和pageindex提取出来.
先写这个类
public class SystemContext {
//页大小
private static ThreadLocal<Integer> pageSize = new ThreadLocal<>();
//当前页
private static ThreadLocal<Integer> pageIndex = new ThreadLocal<>();
public static Integer getPageSize() {
return pageSize.get();
}
public static void removePageSize(){
pageSize.remove();
}
public static void setPageSize(int _pageSize) {
pageSize.set(_pageSize);
}
public Integer getPageIndex() {
return pageIndex.get();
}
public void setPageIndex(int _pageIndex) {
pageIndex.set(_pageIndex);
}
public static void removePageIndex(){
pageIndex.remove();
}
}
</div>
对于threadLocal,这个变量会在线程中一直存在,那么我们就可以在向服务器发送请求的时候添加参数,服务器返回数据的时候移除参数,一来一回的话,自然而然可以用过滤器
那么过滤器如下:
import com.dao.SystemContext;
import javax.servlet.*;
import java.io.IOException;
public class SystemFilter implements Filter{
int pageSize;
int pageIndex = 1;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
try {
pageSize = Integer.parseInt(filterConfig.getInitParameter("pagesize"));
} catch (NumberFormatException e) {
pageSize = 15;
}
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
try {
pageIndex = Integer.parseInt(servletRequest.getParameter("pageindex"));
}catch (NumberFormatException e){
//什么也不做,pageindex=1
}
try {
//开始请求的时候配置参数
SystemContext.setPageSize(pageSize);
SystemContext.setPageIndex(pageIndex);
filterChain.doFilter(servletRequest,servletResponse);
}finally {
//请求返回的时候移除参数
SystemContext.removePageIndex();
SystemContext.removePageSize();
}
}
@Override
public void destroy() {
}
}
</div>
用了过滤器,自然要在web.xml中配置过滤器
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> <filter> <filter-name>SystemFilter</filter-name> <filter-class>com.filter.SystemFilter</filter-class> <!--配置没页大小--> <init-param> <param-name>pagesize</param-name> <param-value>15</param-value> </init-param> </filter> <filter-mapping> <filter-name>SystemFilter</filter-name> <!--这里配置需要分页的页面--> <url-pattern>/index.jsp</url-pattern> </filter-mapping> </web-app></div>
这样的好处不言而喻,结构清晰,修改方便.接下来是分页代码
四.分页代码
分页代码应该写一个接口和实现类的,这里演示项目就写在了一起
import com.util.Pager;
import com.util.User;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
public class UserDAO {
private Connection conn = null;
private ResultSet rs = null;
private PreparedStatement ps = null;
// public static void main(String[] args) {
// UserDAO dao = new UserDAO();
// dao.GetUsers("",15,1);
// dao.close();
// }
public UserDAO() {
String driverName = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/fenyedemo";
String user = "root";String password = "123456";
try {
Class.forName(driverName);
conn = DriverManager.getConnection(url,user,password);
} catch (ClassNotFoundException e) {
System.out.println("没有发现驱动");
e.printStackTrace();
} catch (SQLException e) {
System.out.println("获取连接失败");
e.printStackTrace();
}
}
/**
* 具体分页实现代码
* @param name 查询条件
* @return
*/
public Pager GetUsers(String name){
//获取分页参数
int pagesize = SystemContext.getPageSize();
int pageIndex = SystemContext.getPageIndex();
//分页具体sql语句
String sql = "select * from user ";
String sqlCount = "select count(*) from user ";
if (name!=null && !name.trim().equals("")){
sql += "where username LIKE %"+name+"%";
sqlCount += "where username LIKE %"+name+"%";
}
sql += " LIMIT ?,?";
//存放当前页的集合
List<User> datas = new ArrayList<>();
//存放当前分页的集合
Pager<User> pages = new Pager<>();
User userTemp = null;
try {
ps = conn.prepareStatement(sql);
if(pageIndex<=0) pageIndex=1;
//设置参数
ps.setInt(1,(pageIndex-1)*pagesize);
ps.setInt(2,pagesize);
rs = ps.executeQuery();
//循环取出,添加到datas中
while (rs.next()){
userTemp = new User();
userTemp.setUserId(rs.getString("id"));
userTemp.setUsername(rs.getString("username