request对象常用API 获取请求参数的值 request应用 MVC设计模式

1 request对象常用API
  1)表示web浏览器向web服务端的请求
  2)url表示访问web应用的完整路径:http://localhost:8080/day06/Demo1
    uri表示访问web应用的资源路径:/day06/Demo1
    queryString表示?开头的参数;name=jack
    pathInfo：路径之外的信息，如果没有，返回null

package cn.itcast.web.request;

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

/*
 * http://localhost:8080/day06/Demo1?name=jack回车
 */

public class Demo1 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        /*
        String url = request.getRequestURL().toString();
        String uri = request.getRequestURI();
        String query = request.getQueryString();
        String pathInfo = request.getPathInfo();
        System.out.println("url=" + url);
        System.out.println("uri=" + uri);
        System.out.println("query=" + query);
        System.out.println("pathInfo=" + pathInfo);
        */

        String clientIP = request.getRemoteAddr();
        String clientHOST = request.getRemoteHost();
        int clientPORT = request.getRemotePort();

        String serverIP = request.getLocalAddr();
        String serverHOST = request.getLocalName();
        int serverPORT = request.getLocalPort();

        System.out.println("客户端："+clientIP+":"+clientHOST+":"+clientPORT);
        System.out.println("服务端："+serverIP+":"+serverHOST+":"+serverPORT);
    }
}

获得客户机信息

•getRequestURL方法返回客户端发出请求时的完整URL。

•getRequestURI方法返回请求行中的资源名部分。

•getQueryString 方法返回请求行中的参数部分。

•getPathInfo方法返回请求URL中的额外路径信息。额外路径信息是请求URL中的位于Servlet的路径之后和查询参数之前的内容，它以“/”开头。

•getRemoteAddr方法返回发出请求的客户机的IP地址。

•getRemoteHost方法返回发出请求的客户机的完整主机名。

•getRemotePort方法返回客户机所使用的网络端口号。

•getLocalAddr方法返回WEB服务器的IP地址。

•getLocalName方法返回WEB服务器的主机名。

获得客户机请求头

•getHeader(string name)方法:String

•getHeaders(String name)方法:Enumeration

•getHeaderNames()方法

获得客户机请求参数(客户端提交的数据)

•getParameter(String)方法

•getParameterValues（String name）方法

•getParameterNames方法+BeanUtils框架
取得请求头相关的信息

*a)request.getHeader(String):String

b)request.getHeaders(String):Enumeration

c)getHeaderNames():Enumeration

*2 获取请求参数的值

2）取得请求体相关的信息

a)request.getParameter(String):String

b)request.getParameterValues(String):String[]

注意：在GET请求方式下，如果参数不一致，返回null，可能出现空指针异常

c)BeanUtils框架能够自动将String参数设置到JavaBean对象中

1)无需理会参数的类型，个数，但是参数名一定要和JavaBean中的字段一致

2)String->8种基本类型自动转换，非8种基本类型可以注册转换器

3)String或String[]类型的参数自动感知装配

package cn.itcast.web.request;

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

public class Demo1 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        //一次性取得所有的请求头信息
        Enumeration<String> enums = request.getHeaderNames();
        while(enums.hasMoreElements()){
            //key表示请求头
            String key = enums.nextElement();
            Enumeration<String> enums2 = request.getHeaders(key);
            while(enums2.hasMoreElements()){
                String value = enums2.nextElement();
                response.getWriter().write(key+"<->"+value+"<br/>");
            }
        }

        /*
        String acceptLanguage = request.getHeader("Accept-Language");
        String userAgent = request.getHeader("User-Agent");
        String host = request.getHeader("Host");
        response.getWriter().write("Accept-Language=" + acceptLanguage + "<br/>");
        response.getWriter().write("User-Agent=" + userAgent + "<br/>");
        response.getWriter().write("Host=" + host + "<br/>");
        */
    }
}

package cn.itcast.web.request;

import java.io.IOException;
import java.io.PrintWriter;
import java.lang.reflect.InvocationTargetException;
import java.util.Enumeration;

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

import org.apache.commons.beanutils.BeanUtils;

import cn.itcast.web.domain.User;

/*
 * http://localhost:8080/day07/Demo2?username=jack&age=30&salary=5000&likes=dance&likes=sing回车
 */

public class Demo2 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        //分别取得客户端提交的信息
        //String strUsername = request.getParameter("username");
        //String strAge = request.getParameter("age");
        //String strSalary = request.getParameter("salary");
        //String[] strLikes = request.getParameterValues("likes");

        BeanUtils bu = new BeanUtils();
        User user = new User();
        Enumeration<String> enums = request.getParameterNames();
        while(enums.hasMoreElements()){
            String key = enums.nextElement();
            String[] values = request.getParameterValues(key);
            try {
                bu.setProperty(user,key,values);
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter pw = response.getWriter();
        pw.write("用户名：" + user.getUsername() + "<br/>");
        pw.write("年龄：" + user.getAge() + "<br/>");
        pw.write("期望薪水：" + user.getSalary() + "<br/>");
        pw.write("爱好个数：" + user.getLikes().length + "<br/>");
        pw.flush();
        pw.close();
    }
}

*3 request应用
   1)防盗链

判段某个页面来自于何方，即referer请求头

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>index.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      <a href="/day07/DownServlet">下载</a>
  </body>
</html>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>index.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      这是广告页面
  </body>
</html>

package cn.itcast.web.request;

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

public class Demo4 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        //取得浏览器来自于何方
        String referer = request.getHeader("referer");

        //判段
        if(referer!=null && referer.equals("http://localhost:8080/day07/index.html")){
            //转发到download.html页面
            this
                .getServletContext()
                .getRequestDispatcher("/download.html")
                .forward(request,response);
        }else{
            //转发到ad.html页面
            this
            .getServletContext()
            .getRequestDispatcher("/ad.html")
            .forward(request,response);
        }
    }
}

2)收集表单数据
     a)项目中，用户请求的参数，最好做null或空串的二次判段

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>index.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      <form action="/day07/Demo5" method="post">
          <table border="1" align="center">
              <caption>用户注册</caption>
              <tr>
                  <th>用户名</th>
                  <td><input type="text" name="username"/></td>
              </tr>
              <tr>
                  <th>密码</th>
                  <td><input type="password" name="password"/></td>
              </tr>
              <tr>
                  <th>性别</th>
                  <td>
                      <input checked type="radio" name="gender" value="male"/>男
                      <input type="radio" name="gender" value="female"/>女
                  </td>
              </tr>
              <tr>
                  <th>爱好</th>
                  <td>
                      <input type="checkbox" name="likes" value="sing"/>唱歌
                      <input type="checkbox" name="likes" value="dance"/>跳舞
                      <input type="checkbox" name="likes" value="play"/>打球
                      <input type="checkbox" name="likes" value="net"/>上网
                  </td>
              </tr>
              <tr>
                  <th>上传文件</th>
                  <td><input type="file" name="upfile"/></td>
              </tr>
              <tr>
                  <th>城市</th>
                  <td>
                      <select name="city">
                          <option value="bj">北京</option>
                          <option value="sh">上海</option>
                          <option value="gz" selected>广州</option>
                          <option value="cq">重庆</option>
                      </select>
                  </td>
              </tr>
              <tr>
                  <th>留言</th>
                  <td>
                      <textarea name="message" rows="5" cols="20"></textarea>
                  </td>
              </tr>
              <tr>
                  <td>
                      <input type="hidden" name="id" value="20111008"/>
                  </td>
              </tr>
              <tr>
                  <td colspan="2" align="center">
                      <input type="submit" value="提交"/>
                          &nbsp;&nbsp;&nbsp;&nbsp;
                      <input type="reset" value="重填"/>
                  </td>
              </tr>
          </table>
      </form>
  </body>
</html>

package cn.itcast.web.request;

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

public class Demo5 extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        //将[请求体]的中文以UTF-8方式重新编码
        request.setCharacterEncoding("UTF-8");

        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String gender = request.getParameter("gender");
        String[] likes = request.getParameterValues("likes");
        String upfile = request.getParameter("upfile");
        String city = request.getParameter("city");
        String message = request.getParameter("message");
        String id = request.getParameter("id");

        System.out.println("username="+username);
        System.out.println("password="+password);
        System.out.println("gender="+gender);
        System.out.println("likes="+likes.length);
        System.out.println("upfile="+upfile);
        System.out.println("city="+city);
        System.out.println("message="+message);
        System.out.println("id="+id);
    }
}

3)中文乱码
     a)POST方式下乱码产生的原因：浏览器发送的编码方式与Request对象的编码方式不一致

解决方案：request.setCharacterEncoding("UTF-8)，该方法只能解析请求体中的乱码方式，除此之外，无力解决

b)如果用户是post方式提交，在转发情况下，依然是post请求，但重定向情况下，是get请求

c)如果用户是get方式提交，在转发和重定向情况下，都是get请求

d)405：本身请求是get请求，但未在servlet内提供对应的doGet()方法, post也是类似

针对请求头编码：

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page import="java.net.*" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>My JSP 'get.jsp' starting page</title>
  </head>
  <body>
      <%-- 对中文编码 --%>
    <a href="/day07/Demo7?username=<%=URLEncoder.encode("小王","UTF-8")%>">
        get方式传中文
    </a>
  </body>
</html>

package cn.itcast.web.request;

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

public class Demo7 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        String username = request.getParameter("username");

        //中文解码
        byte[] buf = username.getBytes("ISO8859-1");
        username = new String(buf,"UTF-8");

        if(username!=null || username.trim().length()>0){
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("用户名" + username);
        }
    }
}

//练习获取ip地址和所属地

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>用户登录</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      <form action="/day07/LoginServlet" method="post">
          <table border="1" align="center">
              <caption>用户登录</caption>
              <tr>
                  <th>用户名</th>
                  <td><input type="text" name="username"/></td>
              </tr>
              <tr>
                  <td colspan="2" align="center">
                      <input type="submit" value="提交"/>
                          &nbsp;&nbsp;&nbsp;&nbsp;
                      <input type="reset" value="重填"/>
                  </td>
              </tr>
          </table>
      </form>
  </body>
</html>

package cn.itcast.web.request;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

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

import cn.itcast.web.domain.IpCheckBean;

public class LoginServlet extends HttpServlet {
    //key为IP,value为归属地
    private Map<String,String> map = new HashMap<String,String>();
    public void init() throws ServletException {
        //在用户第一次访问前加载IP和归属地，不存在多线程安全问题
        map.put("192.168.2.222","北京");
        map.put("192.168.10.122","上海");
        map.put("192.168.10.50","深圳");
        map.put("192.168.10.33","佛山");
        map.put("192.168.10.44","珠海");
        map.put("127.0.0.1","广州");
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        //IP
        String ip = request.getRemoteAddr();
        IpCheckBean ipCheckBean = new IpCheckBean();
        //归属地
        String address = ipCheckBean.check(ip,map);
        //用户名
        String username = request.getParameter("username");
        //将信息绑定到ServletContext对象中
        ServletContext context = this.getServletContext();
        context.setAttribute("username",username);
        context.setAttribute("ip",ip);
        context.setAttribute("address",address);
        /*转发到ShowServlet
        context
            .getRequestDispatcher("/ShowServlet")
            .forward(request,response);
        */
        //重定向到ShowServlet
        response.sendRedirect("/day07/ShowServlet");
    }
}

package cn.itcast.web.request;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletExceppackage cn.itcast.web.request;

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

public class ShowServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter pw = response.getWriter();
        pw.write("欢迎："+context.getAttribute("username")+"光临<br/>");
        pw.write("你的IP是："+context.getAttribute("ip")+"<br/>");
        pw.write("归属地："+context.getAttribute("address")+"<br/>");
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        this.doPost(request,response);
    }
}

lrequest对象实现请求转发：请求转发指一个web资源收到客户端请求后，通知服务器去调用另外一个web资源进行处理。请求转发的应用场景：MVC设计模式

*4 再谈MVC设计模式
   1)如果严格按照MVC思想的话，浏览器首页访问的是控制器，然后再由控制器转发到视图

2)位于WEB-INF/目录下的资源，客户端无法直接访问，只能通过服务端转发进入

3)request对象也可用于资源的转发

request

.getRequestDispatcher("/WEB-INF/success.html")

.forward(request,response);

4)通过正则表达式验证中文：[\u4E00-\uFA29]+

5)对于重定向而言，前后的二个Request域对象不同，如果取值不到，返回"null"，不会报错

6)request对象提供了一个getRequestDispatcher方法，该方法返回一个RequestDispatcher对象，调用这个对象的forward方法可以实现请求转发。

7)request对象同时也是一个域对象，开发人员通过request对象在实现转发时，把数据通过request对象带给其它web资源处理。

•setAttribute方法

•getAttribute方法

•removeAttribute方法

•getAttributeNames方法

package cn.itcast.web.request;

import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.itcast.web.domain.ModelBean;

public class Demo8 extends HttpServlet {
    //NO1
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        //转发到view.html页面
        RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/view.html");
        rd.forward(request,response);
    }
    //NO2
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        String username = request.getParameter("username");
        ModelBean mb = new ModelBean();
        boolean flag = mb.validate(username);
        if(flag){
            //将用户名绑定到Request域对象中
            request.setAttribute("USERNAME",username);

            /*转发到ListServlet.java
            request
                .getRequestDispatcher("/ListServlet")
                .forward(request,response);
            */    

            //重定向到ListServlet.java
            response.sendRedirect("/day07/ListServlet");

        }else{
            request
            .getRequestDispatcher("/WEB-INF/fail.html")
            .forward(request,response);
        }
    }
}

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>用户登录</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      <form action="/day07/Demo8" method="post">
          <table border="1" align="center">
              <caption>用户登录</caption>
              <tr>
                  <th>用户名</th>
                  <td><input type="text" name="username"/></td>
              </tr>
              <tr>
                  <td colspan="2" align="center">
                      <input type="submit" value="提交"/>
                          &nbsp;&nbsp;&nbsp;&nbsp;
                      <input type="reset" value="重填"/>
                  </td>
              </tr>
          </table>
      </form>
  </body>
</html>

package cn.itcast.web.request;

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

public class ListServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        String username = (String) request.getAttribute("USERNAME");
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().write("欢迎"+username+"光临");
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        String username = (String) request.getAttribute("USERNAME");
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().write("欢迎"+username+"光临");
    }
}

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>用户登录</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
    登录失败
  </body>
</html>

package cn.itcast.web.domain;

public class ModelBean {
    public boolean validate(String username){
        boolean flag = false;
        if(username!=null && username.matches("[\u4E00-\uFA29]+")){
            flag = true;
        }
        return flag;
    }
}

5 request的细节

1)转发是通过RequestDispatcher对象的forward(request,response)方法完成的

2)forward()方法之前的输出，如果是输出到缓冲区，再转发到其他Servlet，那么原缓冲区的数据忽略不计

3)forward()方法之前的输出，如果真正输出到浏览器，再转发到其他Servlet，再转发到其他Servlet代码忽略不计

4)forward()方法之前的输出，如果是对响应头的设置，会保留到转发的其他Servlet中

请求转发的细节

•forward方法用于将请求转发到RequestDispatcher对象封装的资源。

•如果在调用forward方法之前，在Servlet程序中写入的部分内容已经被真正地传送到了客户端，forward方法将抛出IllegalStateException异常。

•如果在调用forward方法之前向Servlet引擎的缓冲区(response)中写入了内容，只要写入到缓冲区中的内容还没有被真正输出到客户端，forward方法就可以被正常执

•行，原来写入到输出缓冲区中的内容将被清空，但是，已写入到HttpServletResponse对象中的响应头字段信息保持有效

package cn.itcast.web.request;

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

public class Demo91 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        //response.setContentType("text/html;charset=UTF-8");
        //PrintWriter pw = response.getWriter();
        //pw.write("Demo91");
        //pw.flush();
        //pw.close();
        //request.getRequestDispatcher("/Demo92").forward(request,response);
        response.sendRedirect("/day06/success.html");
    }
}

package cn.itcast.web.request;

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

public class Demo92 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        response.getWriter().write("哈哈");
    }
}

*6 重定向和转发区别

•一个web资源收到客户端请求后，通知服务器去调用另外一个web资源进行处理，称之为请求转发/307。

•一个web资源收到客户端请求后，通知浏览器去访问另外一个web资源进行处理，称之为请求重定向/302。
   1)转发只能相对于当前web应用而言，不能转发到其它web应用

重定向可以在当前web应用之外的其它web应用重写向资源

2)转发/表示当前web应用

重定向/表示web服务器的根目录，即webapps目录

3)转发时，浏览器地址栏不变

重定向时，浏览器地址栏改变

4)转发是服务端的内部行为，浏览器不知

重定向是浏览器和服务端的共同行为，浏览器必知

5)转发时二个Servlet共享request域对象

重定向时二个Servlet独享request域对象

6)request具有二义性：

a)请求对象

b)域对   
7 include包含

1)需要使用Servlet包含相同的页面输出时，类似于函数调用

•RequestDispatcher.include方法用于将RequestDispatcher对象封装的资源内容作为当前响应内容的一部分包含进来，从而实现可编程的服务器端包含功能。

•被包含的Servlet程序不能改变响应消息的状态码和响应头，如果它里面存在这样的语句，这些语句的执行结果将被忽略

package cn.itcast.web.request;

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

public class Demo10 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

        //取得客户端请求的类型
        String method = request.getMethod();
        System.out.println("method="+method);

        //包含head.html(类似于函数调用)
        request
            .getRequestDispatcher("/common/head.html")
            .include(request,response);
        response.getOutputStream().write("<hr/>".getBytes());

        //动态生成
        response.getOutputStream().write("login.html".getBytes());
        response.getOutputStream().write("<hr/>".getBytes());

        //包含foot.html
        request
            .getRequestDispatcher("/common/foot.html")
            .include(request,response);
        response.getOutputStream().write("<hr/>".getBytes());
    }
}

会话
   1)用户输出URL地址，有效访问某个网站，在该网站上的一系列有效操作，随后关闭浏览器的整个过程，叫一次会话

2)会话主要解决服务端如何保存每个客户端对应的私有信息。

3)会话主要有二种：

a)Cookie技术[客户端技术]

b)Session技术 
  
Cookie

1)Cookie是客户端的技术

2)每次发送请求时，客户端都会带上各自已的不同Cookie到服务端，服务端一解析Cookie，就知道是哪个客户端发送过来的信息

3)一个Cookie只能存储一种类型的信息

4)更新某个名的Cookie，即向浏览器写一个相同名的Cookie

5)Cookie一定要设置一个有效时间，如果不设置的话，默认该请求访问结束后，该Cookie自动销毁，用专业名词来讲，

Cookie的默认有效期时一个有效会话结束

package cn.itcast.web.cookie;

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

public class Demo1 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        /*
        //服务端产生Cookie
        Cookie cookie = new Cookie("username","haha");
        //设置Cookie存活时间
        cookie.setMaxAge(1*24*60*60);
        //服务端将Cookie写到客户端暂存
        response.addCookie(cookie);
        */

        //取得客户端所有的Cookie
        Cookie[] cookies = request.getCookies();
        Cookie usernameCookie = null;
        if(cookies!=null){
            for(Cookie c : cookies){
                if(c.getName().equals("username")){
                    usernameCookie = c;
                    break;
                }
            }
            //如果找到了Cookie
            if(usernameCookie!=null){
                System.out.println("Cookie的名字：" + usernameCookie.getName());
                System.out.println("Cookie的值：" + usernameCookie.getValue());
                System.out.println("Cookie的生命：" + usernameCookie.getMaxAge());
                System.out.println("Cookie的路径：" + usernameCookie.getPath());
            }
        }
    }
}

package cn.itcast.web.cookie;

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

/*
 * http://localhost:8080/day07/Demo2?name=jack回车
 */
public class Demo2 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        String name = request.getParameter("name");
        if(name==null){
            name="default";
        }

        //取得客户端的所有Cookie的值
        Cookie[] cookies = request.getCookies();
        if(cookies==null){
            Cookie cookie = new Cookie("name_"+name,System.currentTimeMillis()+"");
            cookie.setMaxAge(1*24*60*60);
            response.addCookie(cookie);
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("欢迎"+name+"首次光临,访问时间：" + new Date().toLocaleString());
        }else{
            //查找名为name的Cookie
            Cookie nameCookie = null;
            for(Cookie c : cookies){
                if(c.getName().equals("name_"+name)){
                    nameCookie = c;
                    break;
                }
            }
            //找到了
            if(nameCookie!=null){
                String strTime = nameCookie.getValue();
                response.setContentType("text/html;charset=UTF-8");
                long lastTime = Long.parseLong(strTime);
                response.getWriter().write("欢迎"+name+"再次光临,你上次访问时间：" + new Date(lastTime).toLocaleString());
                //更新时间
                Cookie cookie = new Cookie("name_"+name,System.currentTimeMillis()+"");
                cookie.setMaxAge(1*24*60*60);
                response.addCookie(cookie);
            }
        }
    }
}

*0 带用验证码功能的用户登录
  1)验证码使用一个CheckCodeSerlvet产生，通过<img src=""/>发送请求，将验证码绑定到HttpSession中

2)产生的验证码一定要在输出到浏览器之前绑定到HttpSession中

3)设置验证码禁止缓存要在输出到浏览器之前 
  4)所有响应头的设置放置在最先

package cn.itcast.web.session;

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

public class CheckCodeServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        response.setHeader("expires","-1");
        response.setHeader("cache-control","no-cache");
        response.setHeader("pragma","no-cache");
        String token = Token.getNum();
        //将验证码绑定到域对象
        HttpSession session = request.getSession();
        session.setAttribute("checkCodeServer",token);
        BufferedImage image = new BufferedImage(50,25,BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        g.drawString(token,15,15);
        //加干扰线
        for(int i=0;i<10;i++){
            Random r = new Random();
            int x1 = r.nextInt(50);
            int y1 = r.nextInt(25);
            g.drawLine(x1, y1, x1+4,y1+4);
        }
        ImageIO.write(image,"JPG",response.getOutputStream());
    }
}
class Token{
    public static String getNum(){
        Random r = new Random();
        int num = r.nextInt(10000);
        return num + "";
    }
}

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>login.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
      <form action="/day09/LoginServlet" method="post">
          <table border="1" align="center">
              <tr>
                  <th>用户名</th>
                  <td><input type="text" name="username"/></td>
              </tr>
              <tr>
                  <th>密码</th>
                  <td><input type="password" name="password"/></td>
              </tr>
              <tr>
                  <th>验证码</th>
                  <td>
                      <input type="text" name="checkCodeClient"/>
                  </td>
                  <td>
                      <img src="/day09/CheckCodeServlet"/>
                  </td>
              </tr>
              <tr>
                  <td colspan="2" align="center">
                      <input type="submit" value="提交"/>
                  </td>
              </tr>
          </table>
      </form>
  </body>
</html>

package cn.itcast.web.session;

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

public class LoginServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        //收集客户端填入的验证码
        String checkCodeClient = request.getParameter("checkCodeClient");
        //取得服务端填入的验证码
        String checkCodeServer = (String) request.getSession().getAttribute("checkCodeServer");
        //判段
        response.setContentType("text/html;charset=UTF-8");
        if(checkCodeClient!=null && checkCodeClient.trim().length()>0 && checkCodeServer!=null && checkCodeServer.equals(checkCodeClient)){
            response.getWriter().write("验证码正确");
        }else{
            response.getWriter().write("验证码出错");
        }
    }
}