java web--jsp(4)

          1. JSP 指令: JSP指令（directive）是为JSP引擎而设计的,
                            它们并不直接产生任何可见输出, 而只是告诉引擎如何处理JSP页面中的其余部分。

            2. 在目前的JSP 2.0中，定义了page、include 和 taglib这三种指令

            3. page 指令:

                           1). page指令用于定义JSP页面的各种属性, 无论page指令出现在JSP页面中的什么地方,
                               它作用的都是整个JSP页面, 为了保持程序的可读性和遵循良好的编程习惯, page指令最好是放在整个JSP页面的起始位置。

                          2). page 指令常用的属性:

                               ①. import 属性: 指定当前 JSP 页面对应的 Servlet 需要导入的类.
                                                             <%@page import="java.text.DateFormat"%>

                               ②. session 属性: 取值为 true 或 false, 指定当前页面的 session 隐藏变量是否可用, 也可以说访问当前页面时是否一定要生成 HttpSession
                                                           对象.   <%@ page session="false" %>
                               ③. errorPage 和 isErrorPage:  

                                                           > errorPage 指定若当前页面出现错误的实际响应页面时什么. 其中 / 表示的是当前 WEB 应用的根目录.
                                                          <%@ page errorPage="/error.jsp" %>

                                                          > 在响应 error.jsp 时, JSP 引擎使用的请求转发的方式.
                                                          > isErrorPage 指定当前页面是否为错误处理页面, 可以说明当前页面是否可以使用 exception 隐藏变量. 需要注意的是: 若指定
                                                             isErrorPage="true", 并使用 exception 的方法了, 一般不建议能够直接访问该页面.
                                                          > 如何使客户不能直接访问某一个页面呢 ? 对于 Tomcat 服务器而言, WEB-INF 下的文件是不能通过在浏览器中直接输入地址的方式
                                                             来访问的. 但通过请求的转发是可以的!

                                                          > 还可以在 web.xml 文件中配置错误页面:
                                                                         <error-page>
                                                                               <!-- 指定出错的代码: 404 没有指定的资源, 500 内部错误. -->
                                                                                  <error-code>404</error-code>
                                                                              <!-- 指定响应页面的位置 -->
                                                                                  <location>/WEB-INF/error.jsp</location>
                                                                         </error-page>

                                                                          <error-page>
                                                                                <!-- 指定异常的类型 -->
                                                                                       <exception-type>java.lang.ArithmeticException</exception-type>
                                                                                       <location>/WEB-INF/error.jsp</location>
                                                                         </error-page>

                                   ④. contentType: 指定当前 JSP 页面的响应类型. 实际调用的是 response.setContentType("text/html; charset=UTF-8");
                                                通常情况下, 对于 JSP 页面而言其取值均为 text/html; charset=UTF-8. charset 指定返回的页面的字符编码是什么. 通常取值为 UTF-8

                                   ⑤. pageEncoding: 指定当前 JSP 页面的字符编码. 通常情况下该值和 contentType 中的 charset 一致.

                                   ⑥. isELIgnored: 指定当前 JSP 页面是否可以使用 EL 表达式. 通常取值为 false.

                 4. include 指令: <%@ include file="b.jsp" %>

                                  1). include 指令用于通知 JSP 引擎在翻译当前 JSP 页面时将其他文件中的内容合并进当前 JSP 页面转换成的 Servlet 源文件中,
                                      这种在源文件级别进行引入的方式称之为静态引入, 当前JSP页面与静态引入的页面紧密结合为一个Servlet。

                                  2). file属性的设置值必须使用相对路径

                                  3). 如果以 / 开头，表示相对于当前WEB应用程序的根目录（注意不是站点根目录），否则，表示相对于当前文件。

                 5. jsp:incluce 标签:

                                   1). <jsp:include page="b.jsp"></jsp:include>

                                   2). 动态引入: 并不是像 include 指令生成一个 Servlet 源文件, 而是生成两个 Servlet 源文件, 然后通过一个方法的方式把目标页面包含
                                                  进来.  org.apache.jasper.runtime.JspRuntimeLibrary.include(request, response, "b.jsp", out, false);                                                           

               6. jsp:forward:

                                   1).  <jsp:forward page="/include/b.jsp"></jsp:forward>

                                         相当于.
                                               <%   request.getRequestDispatcher("/include/b.jsp").forward(request, response);  %>

                                   2). 但使用 jsp:forward 可以使用 jsp:param 子标签向 b.jsp 传入一些参数. 同样 jsp:include 也可以使用 jsp:param 子标签.

                                                      <jsp:forward page="/include/b.jsp">
                                                          <jsp:param value="abcd" name="username"/>
                                                      </jsp:forward>

                                                OR

                                                       <jsp:include page="/include/b.jsp">
                                                           <jsp:param value="abcd" name="username"/>
                                                       </jsp:include>

                                          在 b.jsp 页面可以通过 request.getParameter("username") 获取到传入的请求参数.

                    7. 关于中文乱码:

                                     1). 在 JSP 页面上输入中文, 请求页面后不出现乱码: 保证 contentType="text/html; charset=UTF-8",
                                            pageEncoding="UTF-8" charset 和 pageEncoding 的编码一致, 且都支持中文. 通常建议取值为UTF-8
                                            还需保证浏览器的显示的字符编码也和请求的 JSP 页面的编码一致.  
                                     2). 获取中文参数值: 默认参数在传输过程中使用的编码为 ISO-8859-1

                                          ①. 对于 POST 请求: 只要在获取请求信息之前(在调用 request.getParameter 或者是 request.getReader 等),
                                                调用 request.setCharacterEncoding("UTF-8") 即可.

                                          ②. 对于 GET 请求: 前面的方式对于 GET 无效. 可以通过修改 Tomcat 的 server.xml 文件的方式.

                                                      参照 http://localhost:8989/docs/config/index.html 文档的 useBodyEncodingForURI 属性.
                                                           为 Connector 节点添加 useBodyEncodingForURI="true" 属性即可.

                                                        <Connector connectionTimeout="20000" port="8989" protocol="HTTP/1.1" redirectPort="8443" useBodyEncodingForURI="true"/>

             8.代码区

package com.atguigu.javaweb.mvc;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class DeleteStudentServlet
 */
public class DeleteStudentServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String flowId = request.getParameter("flowId");
        
        StudentDao studentDao = new StudentDao();
        studentDao.deleteByFlowId(Integer.parseInt(flowId));
        
        request.getRequestDispatcher("/success.jsp").forward(request, response); 
    }

}

package com.atguigu.javaweb.mvc;

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ListAllStudentsServlet extends HttpServlet {
    
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        StudentDao studentDao = new StudentDao();
        List<Student> students = studentDao.getAll();
        
        request.setAttribute("students", students);
        
        request.getRequestDispatcher("/students.jsp").forward(request, response);
    }

}

package com.atguigu.javaweb.mvc;

public class Student {

    private Integer flowId;
    
    private int type;
    
    private String idCard;
    
    private String examCard;
    
    private String studentName;
    
    private String location;
    
    private int grade;

    public Integer getFlowId() {
        return flowId;
    }

    public void setFlowId(Integer flowId) {
        this.flowId = flowId;
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public String getIdCard() {
        return idCard;
    }

    public void setIdCard(String idCard) {
        this.idCard = idCard;
    }

    public String getExamCard() {
        return examCard;
    }

    public void setExamCard(String examCard) {
        this.examCard = examCard;
    }

    public String getStudentName() {
        return studentName;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public int getGrade() {
        return grade;
    }

    public void setGrade(int grade) {
        this.grade = grade;
    }

    public Student(Integer flowId, int type, String idCard, String examCard,
            String studentName, String location, int grade) {
        super();
        this.flowId = flowId;
        this.type = type;
        this.idCard = idCard;
        this.examCard = examCard;
        this.studentName = studentName;
        this.location = location;
        this.grade = grade;
    }
    
    public Student() {
        // TODO Auto-generated constructor stub
    }

}

package com.atguigu.javaweb.mvc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class StudentDao {

    public void deleteByFlowId(Integer flowId){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        
        try {
            String driverClass = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql:///atguigu";
            String user = "root";
            String password = "1230";
            
            Class.forName(driverClass);
            connection = DriverManager.getConnection(url, user, password);
            
            String sql = "DELETE FROM examstudent WHERE flow_id = ?";
            preparedStatement = connection.prepareStatement(sql);
            
            preparedStatement.setInt(1, flowId);
            
            preparedStatement.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            
            try {
                if(preparedStatement != null){
                    preparedStatement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            
            try {
                if(connection != null){
                    connection.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    
    public List<Student> getAll(){
        
        List<Student> students = new ArrayList<>();
        
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        
        try {
            String driverClass = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql:///atguigu";
            String user = "root";
            String password = "1230";
            
            Class.forName(driverClass);
            connection = DriverManager.getConnection(url, user, password);
            
            String sql = "SELECT flow_id, type, id_card, exam_card, student_name, location, grade " +
                    "FROM examstudent";
            preparedStatement = connection.prepareStatement(sql);
            
            resultSet = preparedStatement.executeQuery();
            while(resultSet.next()){
                int flowId = resultSet.getInt(1);
                int type = resultSet.getInt(2);
                String idCard = resultSet.getString(3);
                String examCard = resultSet.getString(4);
                String studentName = resultSet.getString(5);
                String location = resultSet.getString(6);
                int grade = resultSet.getInt(7);
                
                Student student = new Student(flowId, type, idCard, examCard, 
                        studentName, location, grade);
                students.add(student);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            try {
                if(resultSet != null){
                    resultSet.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            
            try {
                if(preparedStatement != null){
                    preparedStatement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            
            try {
                if(connection != null){
                    connection.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        
        return students;
    }

}

/*
 * $Id: TokenProcessor.java 471754 2006-11-06 14:55:09Z husted $
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package com.atguigu.javaweb.mvc;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class TokenProcessor {
    
    private long previous;

    public synchronized String generateToken(String id) {
        try {
            long current = System.currentTimeMillis();

            if (current == previous) {
                current++;
            }

            previous = current;

            byte[] now = new Long(current).toString().getBytes();
            MessageDigest md = MessageDigest.getInstance("MD5");

            md.update(id.getBytes());
            md.update(now);

            return toHex(md.digest());
        } catch (NoSuchAlgorithmException e) {
            return null;
        }
    }

    private String toHex(byte[] buffer) {
        StringBuffer sb = new StringBuffer(buffer.length * 2);

        for (int i = 0; i < buffer.length; i++) {
            sb.append(Character.forDigit((buffer[i] & 0xf0) >> 4, 16));
            sb.append(Character.forDigit(buffer[i] & 0x0f, 16));
        }

        return sb.toString();
    }
    
    public static void main(String[] args) {
        TokenProcessor tokenProcessor = new TokenProcessor();
        String id = tokenProcessor.generateToken("尚硅谷");
        System.out.println(id); 
    }
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <% 
        //判断用户是否登录, 只有登录的用户才会得到响应. 
        //登录方式有两种: 
            //1. 从 login.jsp 页面提交表单
            //2. 从含有登录名的 Cookie 中登录
            
        String name = request.getParameter("name");
    
        if(name == null){
            Cookie [] cookies = request.getCookies();
            
            if(cookies != null){
                for(Cookie cookie: cookies){
                    if("loginName".equals(cookie.getName())){  
                        name = cookie.getValue();
                    }
                }
            }
        }
        //把 loginName 保存在 Cookie 中, 并回传给浏览器
        else{
            Cookie cookie = new Cookie("loginName", name);
            cookie.setMaxAge(45);
            
            response.addCookie(cookie);
        }
        
        if(name == null){
            response.sendRedirect("login.jsp");
        }else{
            out.print("Hello: " + name);
        }
    %>

</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <form action="index.jsp" method="post">
        
        name: <input type="text" name="name"/>
        
        <input type="submit" value="Submit"/>
    
    </form>

</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.util.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>Book Detail Page</h4>
    
    Book: <%= request.getParameter("book") %>
    
    <br><br>
    
    <a href="books.jsp">Return</a>
    
    <% 
        String book = request.getParameter("book");
        Cookie tempCookie = null;
        
        //只显示最近浏览过的 3 件商品. 
        
        //1. 获取所有满足条件的 Cookie
        List<Cookie> books = new ArrayList<Cookie>();
        
        Cookie [] cookies = request.getCookies();
    
        if(cookies != null && cookies.length > 0){
            
            
            for(Cookie cookie: cookies){
                String cookieName = cookie.getName();
                
                if(cookieName.startsWith("book_")){ 
                    books.add(cookie);
                    
                    String cookieVal = cookie.getValue();
                    if(cookieVal.equals(book)){ 
                        tempCookie = cookie;
                    }
                }
            }
            
        }
        
        if(books.size() == 5){
            if(tempCookie == null){
                tempCookie = books.get(0);
            }
            
            tempCookie.setMaxAge(0);
            response.addCookie(tempCookie);
        }
        
        //2. 在数组 length == 3 的情况下, 把最早的那个(即数组的第 1 个元素-下标是 0 的那个元素)删除 
        Cookie cookie = new Cookie("book_" + book, book);
        response.addCookie(cookie);
    %>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.util.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <!--  
        
        利用 Cookie 实现 "您浏览过的图书有: x, y, z", 只显示最近浏览的 3 本图书的信息
        且支持 Cookie 的持久化. 其余的 Cookie 被删除: 调用其 setMaxAge() 方法, 传入
        0 即可。 
        
    -->
    
    <h4>Books Page</h4>
    
    <a href="book.jsp?book=JavaWeb">Java Web</a><br><br>
    <a href="book.jsp?book=Java">Java</a><br><br>
    <a href="book.jsp?book=Oracle">Oracle</a><br><br>
    <a href="book.jsp?book=Ajax">Ajax</a><br><br>
    <a href="book.jsp?book=JavaScript">JavaScript</a><br><br>
    <a href="book.jsp?book=Android">Android</a><br><br>
    <a href="book.jsp?book=Jbpm">Jbpm</a><br><br>
    <a href="book.jsp?book=Struts">Struts</a><br><br>
    <a href="book.jsp?book=Hibernate">Hibernate</a><br><br>
    <a href="book.jsp?book=Spring">Spring</a><br><br>
    
    <br><br>
    
    
    
    <% 
        StringBuilder books = new StringBuilder("");
    
        Cookie [] cookies = request.getCookies();
    
        if(cookies != null && cookies.length > 0){
            
            
            for(Cookie cookie: cookies){
                String cookieName = cookie.getName();
                String cookieVal = cookie.getValue();
                
                if(cookieName.startsWith("book_")){ 
                    books.append(cookieVal + "&nbsp;&nbsp;");
                }
            }
            
        }
        
        if(!books.toString().equals("")){
            out.print("您浏览过的商品有: " + books.toString()); 
        }
    
    %>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
   
   <h3>AAA PAGE</h3>
   
   <% 
           String str = "abcde";
           
   %>
   
   <!-- 在 a.jsp 中包含 b.jsp -->
   <%--  
   <%@ include file="b.jsp" %>
   --%>
   
   <jsp:include page="/include/b.jsp">
        <jsp:param value="abcd" name="username"/>
   </jsp:include>

    
    <%-- 
    <jsp:forward page="/include/b.jsp">
        <jsp:param value="abcd" name="username"/>
    </jsp:forward>       
        request.getRequestDispatcher("/include/b.jsp").forward(request, response);
    --%>
   
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h3>BBB PAGE</h3>
    
    <%= request.getParameter("username") %>
    
</body>
</html>

<%@page import="java.text.DateFormat"%>
<%@ page language="java" contentType="text/html; charset=UTF-8" %>
<%@ page pageEncoding="UTF-8" import="java.util.Date" %>
<%@ page session="false" isELIgnored="false" %> 
    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <% 
        Date date = new Date();
        DateFormat dateFormat = null;
        
        HttpServletRequest req = null;
        
        //int i = 10 / 0;
    %>
     
    <form action="hello.jsp" method="get"> 
        
        username: <input type="text" name="username"/>
        <input type="submit" value="Submit"/>
    
    </form>
    
        
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="GB2312"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>Hello Page</h4>
    
    学习 Java!
    
    <br><br>
    
    <% 
        request.setCharacterEncoding("UTF-8");
    %>
    
    username: <%= request.getParameter("username") %>
    
    <br><br>

    
    <%-- 
        String val = request.getParameter("username");
        String username = new String(val.getBytes("UTF-8"), "UTF-8");
        out.print(username); 
    --%>
    
</body>
</html>

 

<%@page import="com.atguigu.javaweb.mvc.Student"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <% 
        List<Student> stus = (List<Student>)request.getAttribute("students");
    %>
     
    <table border="1" cellpadding="10" cellspacing="0">
    
        <tr>
            <th>FlowId</th>
            <th>Type</th>
            <th>IdCard</th>
            <th>ExamCard</th>
            <th>StudentName</th>
            <th>Location</th>
            <th>Grade</th>
            <th>Delete</th>
        </tr>
        
        <% 
            for(Student student: stus){
        %>
                <tr>
                    <td><%= student.getFlowId() %></td>
                    <td><%= student.getType() %></td>
                    <td><%= student.getIdCard() %></td>
                    <td><%= student.getExamCard() %></td>
                    <td><%= student.getStudentName() %></td>
                    <td><%= student.getLocation() %></td>
                    <td><%= student.getGrade() %></td>
                    <td><a href="deleteStudent?flowId=<%=student.getFlowId() %>">Delete</a></td>
                </tr>
        <%        
            }
        %>
    
    </table>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    操作成功!
    
    <br><br>
    
    <a href="listAllStudents">List All Students</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    操作成功!
    
    <br><br>
    
    <a href="listAllStudents">List All Students</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.security.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <%!public static String TRANSACTION_TOKEN_KEY = "TRANSACTION_TOKEN_KEY";

    public static String TOKEN_KEY = "TOKEN_KEY";

    private long previous;
    
    public synchronized void resetToken(HttpServletRequest request) {
        HttpSession session = request.getSession(false);

        if (session == null) {
            return;
        }

        session.removeAttribute(TRANSACTION_TOKEN_KEY);
    }

    public synchronized String saveToken(HttpServletRequest request) {
        HttpSession session = request.getSession();
        String token = generateToken(request);

        if (token != null) {
            session.setAttribute(TRANSACTION_TOKEN_KEY, token);
        }

        return token;
    }

    public synchronized String generateToken(HttpServletRequest request) {
        HttpSession session = request.getSession();
        return generateToken(session.getId());
    }

    public synchronized String generateToken(String id) {
        try {
            long current = System.currentTimeMillis();

            if (current == previous) {
                current++;
            }

            previous = current;

            byte[] now = new Long(current).toString().getBytes();
            MessageDigest md = MessageDigest.getInstance("MD5");

            md.update(id.getBytes());
            md.update(now);

            return toHex(md.digest());
        } catch (NoSuchAlgorithmException e) {
            return null;
        }
    }

    private String toHex(byte[] buffer) {
        StringBuffer sb = new StringBuffer(buffer.length * 2);

        for (int i = 0; i < buffer.length; i++) {
            sb.append(Character.forDigit((buffer[i] & 0xf0) >> 4, 16));
            sb.append(Character.forDigit(buffer[i] & 0x0f, 16));
        }

        return sb.toString();
    }%>
    
    <%= generateToken(request) %>

</body>
</html>