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java上一条代码 java第一条代码
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java if 语句如何返回到上一步操作？
if语句返回到上一步操作可以使用while无限循环java上一条代码，根据if的条件来跳到上一步操作，具体代码如下所示：
import java.util.*;
public class mine {
public static void main(String[] args) {
String name = "";
while (true) {
System.out.println("请输入java上一条代码你的名字：");
Scanner in = new Scanner(System.in);
name = in.nextLine();
System.out.println(name);
if (name.equals("xiaoming")) {
System.out.println("欢迎进入系统");
break;//结束循环
} else {
System.out.println("错误，请重新输入");//继续循环，即跳转到上一步
}
}
}
}
java程序的上一条和下一条的实现
建议你用ajax这种方式，ajax就是在不跳转页面java上一条代码的情况下，偷摸的去访问后台，你可以用ajax这种方式，点击上一条或者下一条的时候，偷摸去访问后台，当然java上一条代码了，你访问后台的时候要带着当前这条的标识，后台接收到了这次请求，从你参数的那个标识会知道你当前看的是哪一条，然后去数据库取上一条或者下一条，然后返回给页面，这个时候你要做些事情了，ajax把数据拿到了，你要做的就是用这些数据，把页面上原有的数据替换掉。这样你不跳转页面就可以上一条下一条换数据了。
java数据库操作问题（上一条数据、下一条数据）
给java上一条代码你个思路吧：
lt;%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%gt;
lt;%@ taglib prefix="s" uri="/struts-tags" %gt;
lt;%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%gt;
lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"gt;
lt;htmlgt;
lt;headgt;
lt;base href="lt;%=basePath%gt;"gt;
lt;titlegt;My JSP 'list.jsp' starting pagelt;/titlegt;
lt;meta http-equiv="content-type" content="text/html;charset=utf-8"gt;
lt;meta http-equiv="pragma" content="no-cache"gt;
lt;meta http-equiv="cache-control" content="no-cache"gt;
lt;meta http-equiv="expires" content="0"gt;
lt;meta http-equiv="keywords" content="keyword1,keyword2,keyword3"gt;
lt;meta http-equiv="description" content="This is my page"gt;
lt;!--
lt;link rel="stylesheet" type="text/css" href="styles.css"gt;
--gt;
lt;stylegt;
.row0{
background: #AABBFF;
}
.row1{
background: #FFAABB;
}
lt;/stylegt;
lt;/headgt;
lt;bodygt;
lt;divgt;lt;span style="color:red;"gt;请用list.action访问该页面lt;/spangt;lt;/divgt;
lt;table width="100%" border="1px solid black" cellpadding="0" cellspacing="0"gt;
lt;captiongt;用户列表及操作lt;/captiongt;
lt;theadgt;
lt;trgt;
lt;th width="20%"gt;IDlt;/thgt;
lt;th width="20%"gt;用户名lt;/thgt;
lt;th width="20%"gt;密码lt;/thgt;
lt;th width="20%"gt;是否可用lt;/thgt;
lt;th width="20%"gt;操作lt;/thgt;
lt;/trgt;
lt;/theadgt;
lt;tbodygt;
lt;s:iterator value="%{users}" status="s"gt;
lt;tr class="row${s.index%2 }"gt;
lt;tdgt;${id }lt;/tdgt;
lt;tdgt;${username }lt;/tdgt;
lt;tdgt;${password }lt;/tdgt;
lt;tdgt;${valid }lt;/tdgt;
lt;tdgt;
lt;a href="delete.action?id=${id }amp;p.page=${p.page }" onclick="return confirm('确定删除？')"gt;删除lt;/agt;
lt;a href="load.action?id=${id }amp;p.page=${p.page }"gt;修改lt;/agt;
lt;/tdgt;
lt;/trgt;
lt;/s:iteratorgt;
lt;/tbodygt;
lt;/tablegt;
lt;divgt;
lt;form action="list.action"gt;
lt;s:if test="%{p.page != 1}"gt;
lt;a href="list.action?p.page=1"gt;首页lt;/agt;
lt;/s:ifgt;
lt;s:elsegt;
lt;a style="color:#ccc;"gt;首页lt;/agt;
lt;/s:elsegt;
lt;s:if test="%{p.page != 1}"gt;
lt;a href="list.action?p.page=${p.page-1 }"gt;上一页lt;/agt;
lt;/s:ifgt;
lt;s:if test="%{p.page != p.totalPage}"gt;
lt;a href="list.action?p.page=${p.page+1 }"gt;下一页lt;/agt;
lt;/s:ifgt;
lt;s:if test="%{p.page != p.totalPage}"gt;
lt;a href="list.action?p.page=${p.totalPage }"gt;末页lt;/agt;
lt;/s:ifgt;
lt;s:elsegt;
lt;a style="color:#ccc;"gt;末页lt;/agt;
lt;/s:elsegt;
lt;spangt;第${p.page }页/共${p.totalPage }页lt;/spangt;
lt;spangt;跳lt;input id="page" name="p.page" style="width:30px;"gt;页lt;/spangt;
lt;input type="submit" value="go"gt;
lt;/formgt;
lt;/divgt;
lt;divgt;
lt;input type="button" value="添加用户" onclick="window.location='add.jsp'"/gt;
lt;/divgt;
lt;/bodygt;
lt;/htmlgt;
package com.action;
import java.util.ArrayList;
import java.util.List;
import com.dao.UserDao;
import com.dao.UserDaoImpl;
import com.opensymphony.xwork2.ActionSupport;
import com.pojo.User;
import com.util.Pagination;
public class UserAction extends ActionSupport{
private UserDao dao = new UserDaoImpl();
private Listlt;Usergt; users = new ArrayListlt;Usergt;();
private User user;
private int id;
private Pagination p = new Pagination();
public String list(){
System.out.println("======================list.action");
try {
System.out.println("list:"+p.getPage()+p.getPageSize());
dao.getMaxPage(p);
users = dao.list(p);
return "success";
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "failed";
}
public String add(){
System.out.println("======================add.action");
try {
dao.add(user);
return "success";
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "failed";
}
public String delete(){
System.out.println("======================delete.action");
try {
dao.delete(id);
return "success";
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "failed";
}
public String load(){
System.out.println("======================load.action");
try {
user = dao.findUserById(id);
return "success";
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "failed";
}
public String modify(){
System.out.println("======================modify.action");
try {
user.setId(id);//设置user的id为所要修改的id
dao.update(user);
return "success";
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "failed";
}
public Listlt;Usergt; getUsers() {
return users;
}
public void setUsers(Listlt;Usergt; users) {
this.users = users;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public Pagination getP() {
return p;
}
public void setP(Pagination p) {
this.p = p;
}
}
package com.util;
/**
* 分页
* @author yun
*
*/
public class Pagination {
private int pageSize = 3;//每页显示几条数据
private int totalPage = Integer.MAX_VALUE;//共多少页
private int page = 1;//第几页
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
if(pageSize lt;= 0){
pageSize = 3;
}
this.pageSize = pageSize;
}
public int getTotalPage() {
return totalPage;
}
public void setTotalPage(int totalPage) {
if(totalPage lt;=0){
totalPage = 1;
}
this.totalPage = totalPage;
//下面的setPage(page)一定要有，因为totalPage是查询出来的，这会影响page的值。
//如：原来有12页数据，现在查询出来的只有2页，那么page大于2的页应该就不存在java上一条代码了
setPage(page);
}
public int getPage() {
return page;
}
public void setPage(int page) {
System.out.println("=========totalPage:"+totalPage);
if(page lt;= 0){
page = 1;
}
if(page gt; totalPage){
page = totalPage;
}
this.page = page;
}
}
package com.dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import com.pojo.User;
import com.util.DBUtil;
import com.util.Pagination;
public class UserDaoImpl implements UserDao {
public void add(User u) throws Exception {
int id = searchMaxId();//获得id值，相当于id = seq.nextval()
System.out.println("获得id值=============="+id);
u.setId(id);
String sql = "insert into s_user(id,username,password,valid) " +
" values(?,?,?,?)";
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, u.getId());
pstmt.setString(2, u.getUsername());
pstmt.setString(3, u.getPassword());
pstmt.setString(4, u.getValid());
System.out.println("打印sql："+sql+"\t参数:["+u.getId()+","+u.getUsername()+","+u.getPassword()+","+u.getValid()+"]");
pstmt.executeUpdate();
DBUtil.close(pstmt);
DBUtil.close(conn);
}
/**
* 查询记录中最大的id，如果没有就默认为1，有就+1返回
* @return
*/
private int searchMaxId() {
int id = 1;
String sql = "select max(id) mid from s_user";
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = DBUtil.getConnection();
stmt = conn.createStatement();
System.out.println("打印sql："+sql);
rs = stmt.executeQuery(sql);
if(rs.next()){
id = rs.getInt("mid")+1;//有结果，就+1
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
rs.close();
stmt.close();
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
return id;
}
public void delete(int id) throws Exception {
String sql = "delete from s_user where id = ?";
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, id);
System.out.println("打印sql："+sql+"\t参数：["+id+"]");
pstmt.executeUpdate();
DBUtil.close(pstmt);
DBUtil.close(conn);
}
public User findUserById(int id) throws Exception {
User u = null;
String sql = "select * from s_user where id = ?";
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, id);
System.out.println("打印sql："+sql+"\t参数：["+id+"]");
ResultSet rs = pstmt.executeQuery();
if(rs.next()){
u = new User();
u.setId(rs.getInt("id"));
u.setUsername(rs.getString("username"));
u.setPassword(rs.getString("password"));
u.setValid(rs.getString("valid"));
}
DBUtil.close(rs);
DBUtil.close(pstmt);
DBUtil.close(conn);
return u;
}
public Listlt;Usergt; list() throws Exception {
Listlt;Usergt; list = new ArrayListlt;Usergt;();
String sql = "select id,username,password,valid from s_user order by id";
Connection conn = DBUtil.getConnection();
Statement stmt = conn.createStatement();
System.out.println("打印sql："+sql);
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()){
int id = rs.getInt("id");
String username = rs.getString("username");
String password = rs.getString("password");
String valid = rs.getString("valid");
User u = new User();
u.setId(id);
u.setUsername(username);
u.setPassword(password);
u.setValid(valid);
list.add(u);
}
DBUtil.close(rs);
DBUtil.close(stmt);
DBUtil.close(conn);
return list;
}
public Listlt;Usergt; list(Pagination p) throws Exception {
Listlt;Usergt; list = new ArrayListlt;Usergt;();
String sql = "select * from (select ini.*,rownum rn from " +
"(select id,username,password,valid from s_user order by id) ini " +
"where rownum lt;= ?) where rn gt;= ? ";
int begin = p.getPageSize()*(p.getPage()-1)+1;//10*(3-1)+1=21 1-10 11-20 21-30
int end = p.getPageSize()*p.getPage();//10*3=30
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, end);
pstmt.setInt(2, begin);
System.out.println("打印sql："+sql+"\t参数：["+end+","+begin+"]");
ResultSet rs = pstmt.executeQuery();
while(rs.next()){
int id = rs.getInt("id");
String username = rs.getString("username");
String password = rs.getString("password");
String valid = rs.getString("valid");
User u = new User();
u.setId(id);
u.setUsername(username);
u.setPassword(password);
u.setValid(valid);
list.add(u);
}
DBUtil.close(rs);
DBUtil.close(pstmt);
DBUtil.close(conn);
return list;
}
public void update(User u) throws Exception {
String sql = "update s_user set username=?,password=?,valid=? where id=?";
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setString(1, u.getUsername());
pstmt.setString(2, u.getPassword());
pstmt.setString(3, u.getValid());
pstmt.setInt(4, u.getId());
System.out.println("打印sql："+sql+"\t参数:["+u.getUsername()+","+u.getPassword()+","+u.getValid()+","+u.getId()+"]");
pstmt.executeUpdate();
DBUtil.close(pstmt);
DBUtil.close(conn);
}
/**
* 设置最大页
* @param p
* @throws SQLException
*/
public void getMaxPage(Pagination p) throws SQLException{
String sql = "select count(*) from s_user";
Connection conn = DBUtil.getConnection();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sql);
if(rs.next()){
int s = rs.getInt(1);//一共有多少条数据
int n = p.getPageSize();//每页大小
int t = (s+n-1)/n;
p.setTotalPage(t);//共有多少页
}
DBUtil.close(rs);
DBUtil.close(stmt);
DBUtil.close(conn);
}
/**
* 测试UserDaoImpl
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
UserDaoImpl impl = new UserDaoImpl();
int size = impl.list().size();
System.out.println("size======"+size);//size======0
}
}
总体来说，这是一个翻页查询问题。
上一条，下一条如果是两个按钮的话，就要写javascript去异步发送请求了，请求时来带上参数，参数为当前的页数减一（上一条），或加一（下一条）。然后就是写查询语句了。
如：
public ListUser list(Pagination p) throws Exception {
ListUser list = new ArrayListUser();
String sql = "select * from (select ini.*,rownum rn from " +
"(select id,username,password,valid from s_user order by id) ini " +
"where rownum = ?) where rn = ? ";
int begin = p.getPageSize()*(p.getPage()-1)+1;//10*(3-1)+1=21 1-10 11-20 21-30
int end = p.getPageSize()*p.getPage();//10*3=30
Connection conn = DBUtil.getConnection();
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, end);
pstmt.setInt(2, begin);
System.out.println("打印sql："+sql+"\t参数：["+end+","+begin+"]");
ResultSet rs = pstmt.executeQuery();
while(rs.next()){
int id = rs.getInt("id");
String username = rs.getString("username");
String password = rs.getString("password");
String valid = rs.getString("valid");
User u = new User();
u.setId(id);
u.setUsername(username);
u.setPassword(password);
u.setValid(valid);
list.add(u);
}
DBUtil.close(rs);
DBUtil.close(pstmt);
DBUtil.close(conn);
return list;
}
同理，还是要去查询，然后得到两条记录，还是要传参数的。
java上一条代码的介绍就聊到这里吧，感谢你花时间阅读本站内容，更多关于java第一条代码、java上一条代码的信息别忘了在本站进行查找喔。
