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Java application&&JavaBean封装

莞尔小迷糊 2022-04-07 阅读 55
javahtml

一、JSP内置对象application

application类似于系统的“全局变量”，用于实现用户之间的数据共享。application对象用于保存应用程序的公用数据，服务器启动并自动创建application对象后，只要没有关闭服务器，application对象就一直存在，所有用户共享application对象。

application对象的常用方法：

 application创建以后 在一个应用服务器范围内有效，当应用服务启动后即创建该对象，并向所有用户所共享

案例：显示在线人数 

<%@page language="java" contentType="text/html; charset=UTF-8"%>
<%
//怎么判断一个用户有没有登录
Object username = session.getAttribute("username");
if (username == null) {
	response.sendRedirect("/web04/login.jsp");
}
%>
	<nav class="navbar navbar-default hidden-sm hidden-xs">
		<div class="container-fluid">
			<div class="navbar-header">
				<a class="navbar-brand" href="index.jsp" style="font-size: 25px;">点我</a>
			</div>
			<ul class="nav navbar-nav">
				<li class="dropdown"><a class="dropdown-toggle"
					data-toggle="dropdown"> 新闻管理 <span class="caret"></span>
				</a>
					<ul class="dropdown-menu">
						<li><a href="/web04/news/add.jsp">新闻发布</a></li>
						<li class="divider"></li>
						<li><a href="/web04/news/show.jsp">类别管理</a></li>
					</ul></li>
			</ul>
			<ul class="nav navbar-nav navbar-right">
			<li><a>在线人数:<%=application.getAttribute("count")%></a></li>
				<li><a><%=session.getAttribute("username")%></a></li>
				<li><a
					href="${pageContext.request.contextPath}/news/history.jsp">历史记录</a></li>
				<li><a href="${pageContext.request.contextPath}/news/doExit.jsp">退出<span
						class="glyphicon glyphicon-off"></span></a></li>
			</ul>
		</div>
	</nav>

 处理登录界面

<%@page import="com.zking.util.DBHelper"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.PreparedStatement"%>
<%@page import="java.sql.Connection"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="oracle.jdbc.driver.OracleDriver"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%
 
   request.setCharacterEncoding("utf-8");
   String yh=request.getParameter("yh");
   String mm=request.getParameter("mm");
  //获得连接
  Connection con=DBHelper.getCon();
  //获得执行对象
  PreparedStatement ps=con.prepareStatement("select * from tb_user where user_name=? and user_pwd=?");
  ps.setString(1, yh);
  ps.setString(2,mm);
  //获得结果集
  ResultSet rs=ps.executeQuery();
  //判断结果
  if(rs.next()){
     //调用用户存入到服务器的session中
     session.setAttribute("username", yh);
     //计算当前人数（不是存在卡里面，而是整个银行）
     Object obj=application.getAttribute("count");
     if(obj==null){
    	 obj=0;
     }
     Integer count=(Integer)obj;
     count++;//人数+1
     application.setAttribute("count",count);
     
     //cookie每次发送请求会被自动带上
     //cookie默认是在你当前服务器打开的过程中生效的
     Cookie cookie1=new Cookie("yh",yh);
     
     //设置存活时间 s
     //-1是在你当前浏览器打开的过程中生效
     Cookie cookie2=new Cookie("mm",mm);
     cookie1.setMaxAge(60*60*24*7);//设置用户名的时间
     cookie2.setMaxAge(60*60*24*7);//设置密码的时间
	//存到前台
	 response.addCookie(cookie1);
	 response.addCookie(cookie2);
     response.sendRedirect("news/index.jsp");
     // request.getRequestDispatcher("/news/index.jsp").forward(request,response);
  }else{
	  //重定向 客户端
	  /**
	  (localhost:8080/web04/)跳转的时候：
	    a.jsp 跳转到当前(同级)路径下的a.jsp (localhost:8080/web04/a.jsp)
	    ../a.jsp  跳转到上一级路径下的a.jsp (localhost:8080/a.jsp)
	    /a.jsp 根目录的a.jsp（localhost:8080/a.jsp）
	   **/
	  response.sendRedirect("login.jsp");
  }
  
  //资源关闭
  DBHelper.close(con, ps, rs);
%>

 退出登录代码

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%
    //session的存储时间
    //session.setMaxInactiveInterval(60);
 
    //怎么删除session
    session.invalidate();
    
    //调回登录页面
    response.sendRedirect("/web04/login.jsp");
 
    //让在线人数减1
    Object obj=application.getAttribute("count");
 
    Integer count=(Integer)obj;
    count--;
    application.setAttribute("count", count); 
%>

二、JavaBean

JavaBean是特殊的Java类,使用Java语言书写，并且遵守JavaBean API规范。 

JavaBean的优势 

 JavaBean及其分类

符合规范的Java类都是JavaBean

JavaBean的分类

封装数据

  1. 按照OO原则，属性与数据库表字段相对应
  2. 属性私有
  3. 具有public的set/get方法

 封装业务

  1. 具有实现特定功能的方法和方法实现
  2. 通常与一个封装数据的JavaBean对应

 

 案例：使用JavaBean对新闻发布系统数据进行封装

 DBHelper.java代码如下： 

package com.zking.util;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
 
public class DBHelper {
	// 加载驱动
	static {
 
		try {
			Class.forName("oracle.jdbc.driver.OracleDriver");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
 
	// 定义连接字符串
  private static final String URL="jdbc:oracle:thin:@localhost:1521:orcl";
   //获得连接
  public static Connection getCon(){
	 try {
		return DriverManager.getConnection(URL,"SCOTT","123123");
	} catch (Exception e) {
		e.printStackTrace();
	}
	return null;
	  
  }
  
  /**
   * 关闭资源
   */
  public static void close(Connection con,PreparedStatement ps,ResultSet rs) {
	 try {
	  if(!con.isClosed()) {
		  con.close();
	  }
	  ps.close();
	  rs.close();
  }catch(Exception e) {
	  e.printStackTrace();
  }
  }
  
}

 News.java代码如下：

package com.zking.pojo;
 
import java.io.Serializable;
 
public class News implements Serializable{
private int newsId;
private String newsTitle;
private int newsTopic;
private String newsAuthor;
private String newsPublisher;
private String newsContent;
private String newsCover;
private int newsCount;
private int newsMarker;
public int getNewsId() {
	return newsId;
}
public void setNewsId(int newsId) {
	this.newsId = newsId;
}
public String getNewsTitle() {
	return newsTitle;
}
public void setNewsTitle(String newsTitle) {
	this.newsTitle = newsTitle;
}
public int getNewsTopic() {
	return newsTopic;
}
public void setNewsTopic(int newsTopic) {
	this.newsTopic = newsTopic;
}
public String getNewsAuthor() {
	return newsAuthor;
}
public void setNewsAuthor(String newsAuthor) {
	this.newsAuthor = newsAuthor;
}
public String getNewsPublisher() {
	return newsPublisher;
}
public void setNewsPublisher(String newsPublisher) {
	this.newsPublisher = newsPublisher;
}
public String getNewsContent() {
	return newsContent;
}
public void setNewsContent(String newsContent) {
	this.newsContent = newsContent;
}
public String getNewsCover() {
	return newsCover;
}
public void setNewsCover(String newsCover) {
	this.newsCover = newsCover;
}
public int getNewsCount() {
	return newsCount;
}
public void setNewsCount(int newsCount) {
	this.newsCount = newsCount;
}
public int getNewsMarker() {
	return newsMarker;
}
public void setNewsMarker(int newsMarker) {
	this.newsMarker = newsMarker;
}
@Override
public String toString() {
	return "News [newsId=" + newsId + ", newsTitle=" + newsTitle + ", newsTopic=" + newsTopic + ", newsAuthor="
			+ newsAuthor + ", newsPublisher=" + newsPublisher + ", newsContent=" + newsContent + ", newsCover="
			+ newsCover + ", newsCount=" + newsCount + ", newsMarker=" + newsMarker + "]";
}
public News(int newsId, String newsTitle, int newsTopic, String newsAuthor, String newsPublisher, String newsContent,
		String newsCover, int newsCount, int newsMarker) {
	super();
	this.newsId = newsId;
	this.newsTitle = newsTitle;
	this.newsTopic = newsTopic;
	this.newsAuthor = newsAuthor;
	this.newsPublisher = newsPublisher;
	this.newsContent = newsContent;
	this.newsCover = newsCover;
	this.newsCount = newsCount;
	this.newsMarker = newsMarker;
}
public News() {
	super();
}
 
 
 
 
 
}

 NewsDao.java代码如下：

package com.zking.dao;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
 
import com.zking.pojo.News;
import com.zking.util.DBHelper;
 
public class NewsDao {
	private Connection con;
	private PreparedStatement ps;
	private ResultSet rs;
	
   public List<News> queryByName(String newName) {
	 List<News>list=new ArrayList<News>();
	   try {
		con=DBHelper.getCon();
		ps=con.prepareStatement("select * from t_news where news_title like ?");
	    ps.setString(1, "%"+newName+"%");
	    rs=ps.executeQuery();
	    while(rs.next()){
	    	News news=new News();
//	    	給新聞对象赋值
	    	news.setNewsId(rs.getInt(1));
	    	news.setNewsTitle(rs.getString(2));
	    	news.setNewsTopic(rs.getInt(3));
	    	news.setNewsAuthor(rs.getString(4));
	    	news.setNewsPublisher(rs.getString(5));
	    	news.setNewsContent(rs.getString(6));
	    	news.setNewsCover(rs.getString(7));
	    	news.setNewsCount(rs.getInt(8));
	    	news.setNewsMarker(rs.getInt(9));
//	    	将新闻对象添加到集合中
	    	list.add(news);
	    }
	   } catch (Exception e) {
		e.printStackTrace();
	}finally {
		DBHelper.close(con, ps, rs);
	}
	   return list;
   }
   
}

 这些写完后 然后就可以对之前写的代码进行简化  首页代码简化后的代码如下：

<%@page import="com.zking.pojo.News"%>
<%@page import="com.zking.dao.NewsDao"%>
<%@page import="java.nio.charset.StandardCharsets"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.PreparedStatement"%>
<%@page import="java.sql.Connection"%>
<%@page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>bootstrap</title>
<meta content="width=device-width, initial-scale=1" name="viewport">
<link
	href="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/css/bootstrap.css"
	rel="stylesheet">
<script
	src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/jquery-3.5.1.js"></script>
<script
	src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/bootstrap.js"></script>
<style>
* {
	outline: none !important;
}
 
body, html {
	background: #7f8d90;
}
 
nav, .breadcrumb {
	border-radius: 0px !important;
	margin-bottom: 0px !important;
}
 
.breadcrumb {
	margin-bottom: 20px !important;
	background: #36485c;
	color: white;
}
 
li h4 {
	width: 300px;
	overflow: hidden;
	text-overflow: ellipsis;
	white-space: nowrap;
}
 
.breadcrumb .active {
	color: yellow;
}
</style>
</head>
 
<body>
 
<%@include file="top.jsp" %>
 
	<ol class="breadcrumb">
		<li>您当前的位置是</li>
		<li>新闻发布系统</li>
		<li class="active">首页</li>
	</ol>
 
	<form action="${pageContext.request.contextPath}/news/index.jsp"
		class="form-inline" style="margin: 0px auto 20px;">
		<div class="form-group" style="display: block; text-align: center;">
			<div class="input-group">
				<div class="input-group-addon">新闻标题</div>
				<input name="newName" class="form-control" placeholder="请在此输入搜索的关键字"
					type="text"> <span class="input-group-btn">
					<button class="btn btn-primary" type="submit">搜索🔍</button>
				</span>
			</div>
		</div>
	</form>
 
	<div class="container">
		<ul class="list-group">
			<%
			//点击了表单之后 跳转的是当前这个页面 同时携带一个newName（查询的关键字）过来
			String newName = request.getParameter("newName");
			if (newName == null) {
				newName = "";//查询所有
			}
			//破碎重组
			//newName=new String(newName.getBytes(StandardCharsets.ISO_8859_1),StandardCharsets.UTF_8);
		for(News news:new NewsDao().queryByName(newName)){
			%>
 
			<li class="list-group-item">
				<h4 class="list-group-item-heading">
					<a
						href="${pageContext.request.contextPath}/news/read.jsp?newId=<%=news.getNewsId()%>"
						data-placement="bottom" data-toggle="tooltip" href=""
						title="国家卫健委：昨日新增确诊病例29例，其中本土病例2例"> <%=news.getNewsTitle()%>
					</a>
				</h4>
				<p class="list-group-item-text text-right">
					<span class="glyphicon glyphicon-user"><code><%=news.getNewsAuthor()%></code></span>
					<span class="glyphicon glyphicon-eye-open"><code><%=news.getNewsCount()%></code></span>
					<span class="glyphicon glyphicon-tag"><code><%=news.getNewsMarker()%></code></span>
					<span class="glyphicon glyphicon-time"><code><%=news.getNewsPublisher()%></code></span>
				</p>
			</li>
 
			<%
			}
			 
			%>
		</ul>
	</div>
	<div class="container text-center">
		<ul class="pagination" style="margin: 20px auto;">
			<li><a href="#"><span>&laquo;</span></a></li>
			<li><a href="#">1</a></li>
			<li><a href="#">2</a></li>
			<li><a href="#">3</a></li>
			<li><a href="#">4</a></li>
			<li><a href="#">5</a></li>
			<li><a href="#"><span>&raquo;</span></a></li>
		</ul>
	</div>
	<script>
		$(function() {
			$('[data-toggle="tooltip"]').tooltip({
				trigger : "hover"
			})
		})
	</script>
</body>
</html>

今天的分享就到这里结束啦！！✌

以上就是Java application&&JavaBean封装的一些内容！！📖

 感 谢 阅 读 ……

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