JavaWeb之会话技术

文章目录

1.会话技术
2.cookie
- 2.1.概念
- 2.2.快速入门
- 2.3.实现原理
- 2.4.cookie的细节
- 2.5.cookie的特点和作用
- 2.6.案例：记住上一次访问时间
3.JSP：入门学习
- 3.1.概念
- 3.2.原理
- 3.3.JSP的脚本
- 3.4.JSP的内置对象
- 3.5.案例:改造cookie案例
4.Session
- 4.1.概念
- 4.2.快速入门
- 4.3.原理
- 4.4.细节
- 4.5.session的特点
- 4.6.案例：验证码

1.会话技术

会话：一次会话中包含多次请求和响应。
- 一次会话：浏览器第一次给服务器资源发送请求，会话建立，直到有一方断开为止
功能：在一次会话的范围内的多次请求间，共享数据
方式：
- 客户端会话技术：cookie
- 服务器端会话技术：Session

2.cookie 2.1.概念

客户端会话技术，将数据保存到客户端

2.2.快速入门

使用步骤：
- 创建cookie对象，绑定数据，new cookie(String name, String value)
- 发送cookie对象，response.addcookie(cookie cookie)
- 获取cookie，拿到数据，cookie[] request.getcookies()

cookieDemo1

package com.weeks.cookie_;

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

@WebServlet("/cookieDemo1")
public class cookieDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建cookie对象，绑定数据
        cookie cookie = new cookie("msg", "hello");
        //2.发送cookie对象
        response.addcookie(cookie);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

cookieDemo2.java

package com.weeks.cookie_;

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

@WebServlet("/cookieDemo2")
public class cookieDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //3.获取cookie，拿到数据
        cookie[] cookies = request.getcookies();
        //遍历cookies
        if(cookies != null){
            for (cookie cookie : cookies){
                String name = cookie.getName();
                String value = cookie.getValue();
                System.out.println(name + ":" + value);
            }
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

2.3.实现原理

基于响应头set-cookie和请求头cookie实现

2.4.cookie的细节

一次可不可以发送多个cookie?
- 一次可以发送多个cookie
- 可以创建多个cookie对象，使用response调用多次addcookie方法发送cookie即可。

cookieDemo3

package com.weeks.cookie_;

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

@WebServlet("/cookieDemo3")
public class cookieDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建多个cookie对象，绑定数据
        cookie cookie1 = new cookie("msg", "hello");
        cookie cookie2 = new cookie("name", "zhansan");
        //2.发送多个cookie对象
        response.addcookie(cookie1);
        response.addcookie(cookie2);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

cookie在浏览器中保存多长时间？
- 默认情况下，当浏览器关闭后，cookie数据被销毁
- 持久化存储：setMaxAge(int seconds)
  - 正数：将cookie数据写到硬盘的文件中。持久化存储。并指定cookie存活时间，时间到后，cookie文件自动失效
  - 负数：默认值
  - 零：删除cookie信息

cookieDemo4.java

package com.weeks.cookie_;

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

@WebServlet("/cookieDemo4")
public class cookieDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建多个cookie对象，绑定数据
        cookie cookie1 = new cookie("msg", "setMaxAge");
        //设置cookie对象的最大存活时间
        cookie1.setMaxAge(30);//将cookie1持久化存储在文件中，存活时间为30秒，后自动删除
        //2.发送多个cookie对象
        response.addcookie(cookie1);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

cookie能不能存中文？
- 在tomcat 8 之前 cookie中不能直接存储中文数据。需要将中文数据转码—一般采用URL编码(%E3)
- 在tomcat 8 之后，cookie支持中文数据。特殊字符还是不支持，建议使用URL编码存储，URL解码解析

cookieDemo5.java

package com.weeks.cookie_;

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

@WebServlet("/cookieDemo5")
public class cookieDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建多个cookie对象，绑定数据
        cookie cookie1 = new cookie("msg", "你好");

        //2.发送多个cookie对象
        response.addcookie(cookie1);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

cookie共享问题？
- 假设在一个tomcat服务器中，部署了多个web项目，那么在这些web项目中cookie能不能共享？
  - 默认情况下cookie不能共享
  - setPath(String path):设置cookie的获取范围。默认情况下，设置当前的虚拟目录
    - 如果要共享，则可以将path设置为"/"
- 不同的tomcat服务器间cookie共享问题？
  - setDomain(String path):如果设置一级域名相同，那么多个服务器之间cookie可以共享
    - 例如： setDomain(".baidu.com"),那么tieba.baidu.com和news.baidu.com中cookie可以共享

2.5.cookie的特点和作用

特点
- cookie存储数据在客户端浏览器
- 浏览器对于单个cookie 的大小有限制(4kb) 以及对同一个域名下的总cookie数量也有限制(20个)
作用
- cookie一般用于存出少量的不太敏感的数据
- 在不登录的情况下，完成服务器对客户端的身份识别

在设置中查看浏览器中的cookie

2.6.案例：记住上一次访问时间

需求：
- 访问一个Servlet，如果是第一次访问，则提示：您好，欢迎您首次访问。
- 如果不是第一次访问，则提示：欢迎回来，您上次访问时间为:显示时间字符串
分析：
- 可以采用cookie来完成
- 在服务器中的Servlet判断是否有一个名为lastTime的cookie
  - 有：不是第一次访问
    - 响应数据：欢迎回来，您上次访问时间为:2018年6月10日11:50:20
    - 写回cookie：lastTime=2018年6月10日11:50:01
  - 没有：是第一次访问
    - 响应数据：您好，欢迎您首次访问
    - 写回cookie：lastTime=2018年6月10日11:50:01

package com.weeks.cookie_;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet("/cookieTest")
public class cookieTest extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置响应的消息体的数据格式以及编码
        response.setContentType("text/html;charset=utf-8");
        //1.获取所有cookie
        cookie[] cookies = request.getcookies();
        boolean flag = false;//设置标记有没有cookie为lastTime
        //2.遍历cookie数组
        if(cookies != null && cookies.length > 0){
            for(cookie cookie : cookies){
                //3.获取cookie的名称
                String name = cookie.getName();
                //4.判断名称是否是：lastTime
                if("lastTime".equals(name)){
                    //有该cookie，则说明不是第一次访问
                    flag = true;//有lastTime的cookie
                    //设置cookie的value
                    //获取当前时间的字符串，重新设置cookie的值，重新发送cookie
                    Date date = new Date();
                    //含有 空格 需要重新编码浏览器才能解析，否则会出错
                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

                    String str_date = sdf.format(date);
                    System.out.println("编码前：" + str_date);
                    //URL编码
                    str_date = URLEncoder.encode(str_date, "utf-8");
                    System.out.println("编码后：" + str_date);
                    cookie.setValue(str_date);
                    //设置cookie的存活时间
                    cookie.setMaxAge(60 * 60 * 24 * 30);//一个月
                    //响应数据
                    response.addcookie(cookie);
                    //获取cookie的value，时间
                    String value = cookie.getValue();
                    System.out.println("解码前：" + value);
                    //URL解码：
                    value = URLDecoder.decode(value, "utf-8");
                    System.out.println("解码后：" + value);
                    response.getWriter().write("欢迎回来，您上次访问时间为:"+value+"");
                    break;
                }
            }
        }
        if(cookies == null || cookies.length == 0 || flag == false){
            //没有，说明是第一次访问
            //设置cookie的value
            //获取当前时间的字符串，重新设置cookie的值，重新发送cookie
            Date date = new Date();
            //含有 空格 需要重新编码浏览器才能解析，否则会出错
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

            String str_date = sdf.format(date);
            System.out.println("编码前：" + str_date);
            //URL编码
            str_date = URLEncoder.encode(str_date, "utf-8");
            System.out.println("编码后：" + str_date);
            cookie cookie = new cookie("lastTime", str_date);
            //设置cookie的存活时间
            cookie.setMaxAge(60 * 60 * 24 * 30);//一个月
            //响应数据
            response.addcookie(cookie);

            response.getWriter().write("您好，欢迎您首次访问");
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

3.JSP：入门学习 3.1.概念

Java Server Pages（JSP）： java服务器端页面
- 可以理解为：一个特殊的页面，其中既可以指定定义html标签，又可以定义java代码
- 用于简化java代码的书写

index.jsp

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>



    JSP - Hello World



    <%
        //java代码
        System.out.println("Hello jsp");
    %>
    
    Hi~ JSP

3.2.原理

JSP本质上就是一个Servlet

在项目路径下可以找到index.jsp转换为java的代码：
Using CATALINA_base: "C:UsersWeeksAppDataLocalJetBrainsIntelliJIdea2020.3tomcat7d5d4983-5def-48dd-8235-57e06a3e0416"
C:UsersWeeksAppDataLocalJetBrainsIntelliJIdea2020.3tomcat7d5d4983-5def-48dd-8235-57e06a3e0416workCatalinalocalhostday16_war_explodedorgapachejsp

3.3.JSP的脚本

JSP的脚本：JSP定义Java代码的方式
- <% 代码 %>：定义的java代码，在service方法中。service方法中可以定义什么，该脚本中就可以定义什么。
- <%! 代码 %>：定义的java代码，在jsp转换后的java类的成员位置。
- <%= 代码 %>：定义的java代码，会输出到页面上。输出语句中可以定义什么，该脚本中就可以定义什么。
  index.jsp

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>



    JSP - Hello World



    <%
        //java代码
        System.out.println("Hello jsp");
        int i = 5;
    %>
    <%! int i = 3; %>
    <%= i %>
    
    Hi~ JSP

index_jsp.java

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class index_jsp extends org.apache.jasper.runtime.HttpJspbase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceimports {

 int i = 3; 
  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map _jspx_dependants;

  private static final java.util.Set _jspx_imports_packages;

  private static final java.util.Set _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("javax.servlet");
    _jspx_imports_packages.add("javax.servlet.http");
    _jspx_imports_packages.add("javax.servlet.jsp");
    _jspx_imports_classes = null;
  }

  private volatile javax.el.expressionFactory _el_expressionfactory;
  private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set getPackageimports() {
    return _jspx_imports_packages;
  }

  public java.util.Set getClassimports() {
    return _jspx_imports_classes;
  }

  public javax.el.expressionFactory _jsp_getexpressionFactory() {
    if (_el_expressionfactory == null) {
      synchronized (this) {
        if (_el_expressionfactory == null) {
          _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getexpressionFactory();
        }
      }
    }
    return _el_expressionfactory;
  }

  public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
    if (_jsp_instancemanager == null) {
      synchronized (this) {
        if (_jsp_instancemanager == null) {
          _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
        }
      }
    }
    return _jsp_instancemanager;
  }

  public void _jspInit() {
  }

  public void _jspDestroy() {
  }

  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
      throws java.io.IOException, javax.servlet.ServletException {

    final java.lang.String _jspx_method = request.getMethod();
    if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD");
      return;
    }

    final javax.servlet.jsp.PageContext pageContext;
    javax.servlet.http.HttpSession session = null;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    javax.servlet.jsp.JspWriter _jspx_out = null;
    javax.servlet.jsp.PageContext _jspx_page_context = null;


    try {
      response.setContentType("text/html; charset=UTF-8");
      pageContext = _jspxFactory.getPageContext(this, request, response,
      			null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("n");
      out.write("n");
      out.write("n");
      out.write("n");
      out.write("    JSP - Hello Worldn");
      out.write("n");
      out.write("n");
      out.write("n");
      out.write("    ");

        //java代码
        System.out.println("Hello jsp");
        int i = 5;
    
      out.write("n");
      out.write("    ");
      out.write("n");
      out.write("    ");
      out.print( i );
      out.write("n");
      out.write("    n");
      out.write("    Hi~ JSPn");
      out.write("n");
      out.write("");
    } catch (java.lang.Throwable t) {
      if (!(t instanceof javax.servlet.jsp.SkipPageException)){
        out = _jspx_out;
        if (out != null && out.getBufferSize() != 0)
          try {
            if (response.isCommitted()) {
              out.flush();
            } else {
              out.clearBuffer();
            }
          } catch (java.io.IOException e) {}
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
        else throw new ServletException(t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

3.4.JSP的内置对象

JSP的内置对象：在jsp页面中不需要获取和创建，可以直接使用的对象
jsp一共有9个内置对象。现在先了解3个
- request
- response
- out：字符输出流对象。可以将数据输出到页面上。和response.getWriter()类似
  - response.getWriter()和out.write()的区别：
    - tomcat服务器真正给客户端做出响应之前，会先找response缓冲区数据，再找out缓冲区数据。
    - response.getWriter()数据输出永远在out.write()之前

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>



    JSP - Hello World



    <%
        //java代码
        System.out.println("Hello jsp");
        int i = 5;

        String contextPath = request.getContextPath();
        out.print(contextPath);
    %>
    <%! int i = 3; %>
    <%= i %>
    
    Hi~ JSP
    <% response.getWriter().write("response...");%>

3.5.案例:改造cookie案例

直接将cookieTest.java中的代码拷贝到home.jsp中就能直接使用

<%@ page import="java.util.Date" %>
<%@ page import="java.text.SimpleDateFormat" %>
<%@ page import="java.net.URLEncoder" %>
<%@ page import="java.net.URLDecoder" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    Title


    <%
        //1.获取所有cookie
        cookie[] cookies = request.getcookies();
        boolean flag = false;//设置标记有没有cookie为lastTime
        //2.遍历cookie数组
        if(cookies != null && cookies.length > 0){
            for(cookie cookie : cookies){
                //3.获取cookie的名称
                String name = cookie.getName();
                //4.判断名称是否是：lastTime
                if("lastTime".equals(name)){
                    //有该cookie，则说明不是第一次访问
                    flag = true;//有lastTime的cookie
                    //设置cookie的value
                    //获取当前时间的字符串，重新设置cookie的值，重新发送cookie
                    Date date = new Date();
                    //含有 空格 需要重新编码浏览器才能解析，否则会出错
                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

                    String str_date = sdf.format(date);
                    System.out.println("编码前：" + str_date);
                    //URL编码
                    str_date = URLEncoder.encode(str_date, "utf-8");
                    System.out.println("编码后：" + str_date);
                    cookie.setValue(str_date);
                    //设置cookie的存活时间
                    cookie.setMaxAge(60 * 60 * 24 * 30);//一个月
                    //响应数据
                    response.addcookie(cookie);
                    //获取cookie的value，时间
                    String value = cookie.getValue();
                    System.out.println("解码前：" + value);
                    //URL解码：
                    value = URLDecoder.decode(value, "utf-8");
                    System.out.println("解码后：" + value);
                    response.getWriter().write("欢迎回来，您上次访问时间为:"+value+"");
                    break;
                }
            }
        }
        if(cookies == null || cookies.length == 0 || flag == false){
            //没有，说明是第一次访问
            //设置cookie的value
            //获取当前时间的字符串，重新设置cookie的值，重新发送cookie
            Date date = new Date();
            //含有 空格 需要重新编码浏览器才能解析，否则会出错
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

            String str_date = sdf.format(date);
            System.out.println("编码前：" + str_date);
            //URL编码
            str_date = URLEncoder.encode(str_date, "utf-8");
            System.out.println("编码后：" + str_date);
            cookie cookie = new cookie("lastTime", str_date);
            //设置cookie的存活时间
            cookie.setMaxAge(60 * 60 * 24 * 30);//一个月
            //响应数据
            response.addcookie(cookie);

            response.getWriter().write("您好，欢迎您首次访问");
        }
    %>

4.Session 4.1.概念

服务器端会话技术，在一次会话的多次请求间共享数据，将数据保存在服务器端的对象中。HttpSession

4.2.快速入门

获取HttpSession对象：HttpSession session = request.getSession();
使用HttpSession对象：
- Object getAttribute(String name)
- void setAttribute(String name, Object value)
- void removeAttribute(String name)

SessionDemo1.java

package com.weeks.session_;

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

@WebServlet("/sessionDemo1")
public class SessionDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取HttpSession对象
        HttpSession session = request.getSession();
        //2.设置HttpSession对象
        session.setAttribute("msg", "hello session");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

SesionDemo2.java

package com.weeks.session_;

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

@WebServlet("/sessionDemo2")
public class SessionDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取HttpSession对象
        HttpSession session = request.getSession();
        //2.获取HttpSession对象的内容
        Object msg = session.getAttribute("msg");
        System.out.println(msg);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

4.3.原理

Session的实现是依赖于cookie的。

4.4.细节

细节1：当客户端关闭后，服务器不关闭，两次获取session是否为同一个？
- 默认情况下。不是。
- 如果需要相同，则可以创建cookie,键为JSESSIONID，设置最大存活时间，让cookie持久化保存。
```
cookie c = new cookie("JSESSIONID",session.getId());
         c.setMaxAge(60*60);
         response.addcookie(c);
```

SessionDemo3

package com.weeks.session_;

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

@WebServlet("/sessionDemo3")
public class SessionDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取HttpSession对象
        HttpSession session = request.getSession();
        //打印一下session对象
        System.out.println(session);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

package com.weeks.session_;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

@WebServlet("/sessionDemo3")
public class SessionDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取HttpSession对象
        HttpSession session = request.getSession();
        //为了关闭客户端后想再次访问同一个session，需要创建cookie对象实现持久化
        cookie cookie = new cookie("JSESSIONID", session.getId());
        cookie.setMaxAge(60 * 60);//一个小时
        response.addcookie(cookie);
        //打印一下session对象
        System.out.println(session);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

细节2：客户端不关闭，服务器关闭后，两次获取的session是同一个吗？
- 不是同一个，但是要确保数据不丢失。tomcat自动完成以下工作
  - session的钝化：在服务器正常关闭之前，将session对象系列化到硬盘上
  - session的活化：在服务器启动后，将session文件转化为内存中的session对象即可。

在IDEA中无法演示session的活化，所以上面过程需要使用tomcat来演示

细节3：session什么时候被销毁？
- 服务器关闭
- session对象调用invalidate() 。
- session默认失效时间 30分钟
  - 选择性配置修改，可以在项目的web.xml文件中配置，也可以在tomcat的web.xml文件中配置

4.5.session的特点

session用于存储一次会话的多次请求的数据，存在服务器端
session可以存储任意类型，任意大小的数据
session与cookie的区别：
- session存储数据在服务器端，cookie在客户端
- session没有数据大小限制，cookie有大小限制
- session数据安全，cookie相对于不够安全

4.6.案例：验证码

案例需求:
- 访问带有验证码的登录页面login.jsp
- 用户输入用户名，密码以及验证码
  - 如果用户名和密码输入有误，跳转登录页面，提示:用户名或密码错误
  - 如果验证码输入有误，跳转登录页面，提示：验证码错误
  - 如果全部输入正确，则跳转到主页success.jsp，显示：用户名,欢迎您
分析：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    login
    
    


    
        
            
                用户名
                
            
            
                密码
                
            
            
                验证码
                
            
            
                
            
            
                
            
        
    
    <%=request.getAttribute("cc_error") == null ? "" : request.getAttribute("cc_error")%>
    <%=request.getAttribute("login_error") == null ? "" : request.getAttribute("login_error")%>

success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    Title


    <%= request.getSession().getAttribute("user")%>，欢迎您！

LoginServlet.java

package com.weeks.servlet_;

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

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置request编码
        request.setCharacterEncoding("utf-8");
        //2.获取参数
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String checkCode = request.getParameter("checkCode");
        //3.先获取生成的验证码
        HttpSession session = request.getSession();
        String checkCode_session = (String) session.getAttribute("checkCode_session");
        //删除session中存储的验证码,保证验证码是一次性的，不会因为后退而造成重复使用
        session.removeAttribute("checkCode_session");
        //3.先判断验证码是否正确
        if(checkCode_session != null && checkCode_session.equalsIgnoreCase(checkCode)){//checkCode_session != null 防止抛出空指针异常
            //忽略大小写比较
            //验证码正确
            //判断用户名和密码是否一致
            if("zhangsan".equals(username) && "123".equals(password)){//需要调用UserDao查询数据库
                //登录成功
                //存储信息，用户信息
                session.setAttribute("user", username);
                //重定向到success.jsp
                response.sendRedirect(request.getContextPath() + "/success.jsp");
            }else{
                //登录失败
                //存储提示信息到request
                request.setAttribute("login_error", "用户名或密码错误");
                //转发到登录页面
                request.getRequestDispatcher("/login.jsp").forward(request, response);
            }
        }else{
            //验证码不一致
            //存储提示信息到request
            request.setAttribute("cc_error", "验证码错误");
            //转发到登录页面
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

CheckCodeServlet.java

package com.weeks.servlet_;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        int width = 100;
        int height = 50;

        //1.创建一对象，在内存中图片(验证码图片对象)
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);


        //2.美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.PINK);//设置画笔颜色
        g.fillRect(0,0,width,height);

        //2.2画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width - 1,height - 1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random ran = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);//随机字符
            sb.append(ch);

            //2.3写验证码
            g.drawString(ch+"",width/5*i,height/2);
        }
        String checkCode_session = sb.toString();
        //将验证码存入session
        request.getSession().setAttribute("checkCode_session",checkCode_session);

        //2.4画干扰线
        g.setColor(Color.GREEN);

        //随机生成坐标点

        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }


        //3.将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

JavaWeb之会话技术

Hi~ JSP

Hi~ JSP

Hi~ JSP

欢迎回来，您上次访问时间为:"+value+"

您好，欢迎您首次访问

<%= request.getSession().getAttribute("user")%>，欢迎您！

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