内置对象实例

  1 1.网页访问量计数
  2 <%@page import="java.math.BigInteger"%>
  3 <%@page import="java.io.*"%>
  4 <%@page import="java.util.*"%>
  5 <%@ page language="java" contentType="text/html"
  6     pageEncoding="utf-8"%>
  7 <!DOCTYPE html>
  8 <html>
  9 <head>
 10 <title>网页访问量计数</title>
 11 </head>
 12 <body>
 13     <%!
 14         //定义全局变量
 15         BigInteger count = null;
 16     %>
 17     <%!  //读入文件读取方法
 18         public BigInteger load(File f){
 19             BigInteger count = null;
 20             try{
 21                 if(f.exists()){//判断文件存不存在
 22                     Scanner sc = new Scanner(new FileInputStream(f));
 23                     if(sc.hasNext()){
 24                         count = new BigInteger(sc.next());
 25                     }
 26                     sc.close();
 27                 }else{
 28                     //文件不存在,即还没有访客进行访问
 29                     count = new BigInteger("0");
 30                     //保存到文件中
 31                     save(f,count);            
 32                 }
 33             }catch(Exception e){
 34                 System.out.println(e);
 35             }    
 36             return count;
 37         }
 38     //写出文件保存方法
 39      public void save(File f,BigInteger count){
 40          try{
 41              PrintStream ps= null;
 42              ps = new PrintStream(new FileOutputStream(f));
 43              ps.println(count);
 44              ps.close();
 45          }catch(Exception e){
 46              System.out.println(e);
 47          }
 48      }    
 49     %>
 50     <%   
 51         String name = this.getServletContext().getRealPath("/")+"count.txt";
 52         System.out.print(name);
 53         File f = new File(name);
 54         if(session.isNew()){
 55             synchronized(this){
 56                 //读取数据以及保存
 57                 count = load(f);
 58                 //做自增操作
 59                 count = count.add(new BigInteger("1"));
 60                 //保存数据
 61                 save(f,count);
 62             }
 63         }
 64     %>
 65     <h2>您是第<%=count==null?0:count %>位访客</h2>
 66 </body>
 67 </html>
 68 2.获取真实路径
 69 <%@ page language="java" contentType="text/html"
 70     pageEncoding="GBK"%>
 71 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 72 <html>
 73 <head>
 74 <title>Insert title here</title>
 75 </head>
 76 <body>
 77     <%
 78         String path = this.getServletContext().getRealPath("/");
 79     %>
 80     真实路径：<%=path%>
 81 </body>
 82 </html>
 83 3.获取属性名称及属性
 84 <%@page import="java.util.Enumeration"%>
 85 <%@ page language="java" contentType="text/html"
 86     pageEncoding="GBK"%>
 87 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 88 <html>
 89 <head>
 90 <title>Insert title here</title>
 91 </head>
 92 <body>
 93     <%
 94         Enumeration en = this.getServletContext().getAttributeNames();
 95         while(en.hasMoreElements()){
 96             String name = (String)en.nextElement();
 97     %>
 98         <h1><%=name %>----<%=this.getServletContext().getAttribute(name) %></h1>
 99     <%    
100         }
101     %>
102 </body>
103 </html>
104 4.缓冲区大小
105 <%@page import="java.util.Enumeration"%>
106 <%@ page language="java" contentType="text/html"
107     pageEncoding="GBK"%>
108 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
109 <html>
110 <head>
111 <title>Insert title here</title>
112 </head>
113 <body>
114     <%
115         int buffer = out.getBufferSize();//全部缓冲区大小
116         int unuse = out.getRemaining();//未使用缓冲区大小
117         int use = buffer-unuse;
118     %>
119     <h3>缓冲区大小<%=buffer %></h3>
120     <h3>未使用缓冲区大小<%=unuse %></h3>
121     <h3>已使用缓冲区大小<%=use %></h3>
122 </body>
123 </html>
124 5.表单内容写入、写出文件
125 <!DOCTYPE html>
126 <html>
127 <head>
128 <meta charset="GBK">
129 <title>Insert title here</title>
130 </head>
131 <body>
132     <form action="input_context.jsp" method="post">
133         文件名：<input type="text" name="filename"><br>
134         文件内容<textarea rows="10" cols="30" name="context"></textarea><br>
135         <input type="submit" value="保存">
136     </form>
137 </body>
138 </html>
139 
140 <%@ page language="java" contentType="text/html"
141     pageEncoding="GBK"%>
142 <%@ page import="java.io.*" %>
143 <%@ page import="java.util.*" %>
144 <%@ page import="java.lang.*" %>
145 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
146 <html>
147     <head>
148         <title>Insert title here</title>
149     </head>
150     <body>
151         <%
152             //设置统一编码
153             request.setCharacterEncoding("GBK");
154             //获取到文件名称 文件内容
155             String filename = request.getParameter("filename");
156             String content = request.getParameter("context");
157             //拼凑path  内容保存于 当前路径下新建的note文件夹中，
158             String path = this.getServletContext().getRealPath("/")+"note"+File.separator+filename;
159             //判断父文件夹是否存在
160             File f = new File(path);
161             if(!f.getParentFile().exists()){
162                 f.getParentFile().mkdir();//创建文件夹
163             }
164             PrintStream ps = null;
165             ps = new PrintStream(new FileOutputStream(f));
166             ps.println(content);
167             ps.close();
168             System.out.println("输出成功");
169         %>
170         <%
171             Scanner sc = new Scanner(new FileInputStream(f));
172             sc.useDelimiter("
");//按换行符扫描
173             StringBuffer sbu = new StringBuffer();
174             while(sc.hasNext()){
175                 sbu.append(sc.next()).append("<br>");//显示文件内容
176             }
177         
178         %>
179             <%=sbu %>
180     </body>
181 </html>