JavaBean封装

让我们先回顾一下上一篇博客讲的内容

存储：

服务器：session 会话级存储（个人）

客户端：cookie

1.客户端发起请求的时候会把cookie JSESSIONID 自动携带到后端

2.后端获取JSESSIONID，根据id找到对应的session（重新给你session）

3.获取对应的session的数据

今日内容：

application 应用级存储（共享的）

1.统计人数

在登录的方法界面的判断结果里面计算当前人数并且需要进行判断

//计算当前人数(不是存在你的卡里，而是存在整个银行)
Object obj=application.getAttribute("count");
if(obj==null){
    obj=0;
}

进行强转和人数加一

Integer count=(Integer)obj;
count++;//人数加一

重新存入

application.setAttribute("count", count);

然后显示到界面中去

 <ul class="nav navbar-nav navbar-right">
     <li>在线人数<a><%=application.getAttribute("count") %></a></li>
     <li><a><%=application.getAttribute("username") %></a></li>
     <li><a href="${pageContext.request.contextPath }">历史记录</a></li>
     <li><a href="doExit.jsp">退出<span class="glyphicon glyphicon-off"></span></a></li>
</ul>

注：同时在不同的浏览器上登录人数会相应的增加

封装JavaBean

什么是JavaBean？

Java豆荚，Bean豆子，泛指Java对象，就是每一个Java类

连接数据库的步骤

package com.zking.util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import oracle.jdbc.driver.OracleDriver;

public class DBHelper {
	
	//加载驱动
	static {
		//OracleDriver
		try {
			Class.forName("oracle.jdbc.driver.OracleDriver");
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	//定义连接字符串
	private static final String URL="jdbc:oracle:this:@localhost:1521:orcl";
	
	//获得连接
	public static Connection getCon() {
		try {
			return DriverManager.getConnection(URL,"scott","123");
		} 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) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

然后将界面中连接数据库的方法进行修改

Connection con = DBHelper.getCon();

资源关闭

DBHelper.close(con, ps, rs);

注意：建议重启一下服务器

pojo包（设置与数据库相同的数值）

package com.zking.pojo;

import java.io.Serializable;

public class News implements Serializable{
	
	private int newId;
	private String newsTitle;
	private String newsTopic;
	private String newsAuthor;
	private String newsPublisher;
	private String newsContent;
	private int newsCount;
	private int newsMarker;
	
	//get/set方法
	public int getNewId() {
		return newId;
	}
	public void setNewId(int newId) {
		this.newId = newId;
	}
	public String getNewsTitle() {
		return newsTitle;
	}
	public void setNewsTitle(String newsTitle) {
		this.newsTitle = newsTitle;
	}
	public String getNewsTopic() {
		return newsTopic;
	}
	public void setNewsTopic(String 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 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 [newId=" + newId + ", newsTitle=" + newsTitle + ", newsTopic=" + newsTopic + ", newsAuthor="
				+ newsAuthor + ", newsPublisher=" + newsPublisher + ", newsContent=" + newsContent + ", newsCount="
				+ newsCount + ", newsMarker=" + newsMarker + "]";
	}
	
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + newId;
		result = prime * result + ((newsAuthor == null) ? 0 : newsAuthor.hashCode());
		result = prime * result + ((newsContent == null) ? 0 : newsContent.hashCode());
		result = prime * result + newsCount;
		result = prime * result + newsMarker;
		result = prime * result + ((newsPublisher == null) ? 0 : newsPublisher.hashCode());
		result = prime * result + ((newsTitle == null) ? 0 : newsTitle.hashCode());
		result = prime * result + ((newsTopic == null) ? 0 : newsTopic.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		News other = (News) obj;
		if (newId != other.newId)
			return false;
		if (newsAuthor == null) {
			if (other.newsAuthor != null)
				return false;
		} else if (!newsAuthor.equals(other.newsAuthor))
			return false;
		if (newsContent == null) {
			if (other.newsContent != null)
				return false;
		} else if (!newsContent.equals(other.newsContent))
			return false;
		if (newsCount != other.newsCount)
			return false;
		if (newsMarker != other.newsMarker)
			return false;
		if (newsPublisher == null) {
			if (other.newsPublisher != null)
				return false;
		} else if (!newsPublisher.equals(other.newsPublisher))
			return false;
		if (newsTitle == null) {
			if (other.newsTitle != null)
				return false;
		} else if (!newsTitle.equals(other.newsTitle))
			return false;
		if (newsTopic == null) {
			if (other.newsTopic != null)
				return false;
		} else if (!newsTopic.equals(other.newsTopic))
			return false;
		return true;
	}
	
	//无参有参
	public News() {
		super();
		// TODO Auto-generated constructor stub
	}
	public News(int newId, String newsTitle, String newsTopic, String newsAuthor, String newsPublisher,
			String newsContent, int newsCount, int newsMarker) {
		super();
		this.newId = newId;
		this.newsTitle = newsTitle;
		this.newsTopic = newsTopic;
		this.newsAuthor = newsAuthor;
		this.newsPublisher = newsPublisher;
		this.newsContent = newsContent;
		this.newsCount = newsCount;
		this.newsMarker = newsMarker;
	}
	
	
}

实现类（首页的封装）

package com.zking.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
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+"%");
            //得到结果集
            ResultSet rs = ps.executeQuery();
            while(rs.next()) {
            	News news=new News();
            	//给新闻对象属性赋值
            	news.setNewId(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.setNewsCount(rs.getInt(7));
            	news.setNewsMarker(rs.getInt(8));
            	//将新闻对象添加到集合中
            	list.add(news);
            }
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			DBHelper.close(con, ps, rs);
		}
		return list;
	}

}

首页

<%
        	//点击了表单之后 跳转的是当前这个页面 同时携带一个newName过来（查询的关键字）
        	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.getNewId()%>" data-placement="bottom" data-toggle="tooltip" href="" title="<%=news.getNewsTitle()%>">
                    <%=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>
        <%
            }
            
        %>

界面重复代码简化

建一个新的jsp文件，把重复的代码放入

<%
	//怎么判断一个用户有没有登录
	Object username=session.getAttribute("username");
	if(username==null){
		response.sendRedirect("/web08/login.jsp");
	}
%>
<nav class="navbar navbar-default hidden-sm hidden-xs">
    <div class="container-fluid">
        <div class="navbar-header">
            <a class="navbar-brand" href="${pageContext.request.contextPath}/news/index.jsp"
               style="font-size: 25px;">🐖</a>
        </div>
        <ul class="nav navbar-nav">
            <li class="dropdown">
                <a class="dropdown-toggle" data-toggle="dropdown"> 新闻管理
                    <span class="caret"></span>
                </a>
                <ul class="dropdown-menu">
                    <li><a href="${pageContext.request.contextPath}/news/add.jsp">新闻发布</a></li>
                    <li class="divider"></li>
                    <li><a href="#">类别管理</a></li>
                </ul>
            </li>
        </ul>
        <ul class="nav navbar-nav navbar-right">
        	<li>在线人数<a><%=application.getAttribute("count") %></a></li>
            <li><a><%=session.getAttribute("username") %></a></li>
            <li><a href="${pageContext.request.contextPath }">历史记录</a></li>
            <li><a href="doExit.jsp">退出<span class="glyphicon glyphicon-off"></span></a></li>
        </ul>
    </div>
</nav>

然后在需要的界面中进行调用

<%--include 包含 --%>
<%@include file="top.jsp" %>

点击退出后在线人数需要减一

//人在线人数减一
Object obj=application.getAttribute("count");
Integer count=(Integer)obj;
count--;
application.setAttribute("countt", count);

下次见咯