JavaEE：response响应和request请求

Web服务器接收到客户端的http请求，会针对每一次请求，分别创建一个用于代表请求的request对象、和代表响应的response对象。
request和response对象既然代表请求和响应，那么我们要获取客户机提交过来的数据，只需要找request对象，就行了。要向客户机输出数据，只需要找response对象就行了。

HttpServletRequest封装客户端相关信息，服务器Servlet程序可以通过request对象操作客户端信息
HttpServletResponse封装服务器向客户端发送响应数据信息，Servlet程序通过response对象向客户端发送响应

response
1.response常用API
setStatus：设置响应行当中的状态码
setHeader：设置响应头信息
getOutputStream：获得字节流 --- 输出响应体内容
getWriter：获得字符流 --- 输出响应体内容
2.HttpServletResponse继承ServletResponse接口，ServletResponse并没有提供与HTTP协议相关API，HttpServletResponse添加了与协议相关API
JavaEE API 中并没有提供HttpServletResponse实现类---实现类由tomcat服务器提供的
3.常用状态码：200 302 304 404 500
200 请求处理成功
302 客户端重定向
304 客户端访问资源没有被修改，客户端访问本地缓存
404 访问资源不存在
500 服务器内部出错
4.案例一：通过302+Location头信息实现页面重定向

package cn.lsl.response;

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 ResponseServlet1 extends HttpServlet {

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //302客户端重定向 --- 结合Location头信息一起使用
        response.setStatus(302);
        //通知浏览器定向到哪个页面
        response.setHeader("Location", "/Response/welcome.html");
    }

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

}

response.setStatus(302);
response.setHeader("Location", "/Response/welcome.html");    //由客户端定向到服务器，必须添加工程虚拟目录

案例二：登陆重定向
在response API中提供sendRedirect() --- 完成302+Location重定向效果
例如：response.sendRedirect("/day06/welcome.html");

package cn.lsl.response;

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 ResponseServlet2 extends HttpServlet {
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        if("admin".equals(username) && "admin".equals(password)){
//            response.setStatus(302);
//            response.setHeader("Location", "/Response/welcome.html");
            //使用response.sendRedirect完成重定向
            response.sendRedirect("/Response/welcome.html");
        }else{
//            response.setStatus(302);
//            response.setHeader("Location", "/Response/login.html");
            response.sendRedirect("/Response/login.html");
        }

    }

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

}

案例三：自动刷新网页
*登陆成功，5秒后自动跳转XX页面
原理：通过refresh头信息
格式 --- refresh:时间;url=跳转路径
例如：refresh:3;url=http://www.baidu.com  --- 3秒后自动跳转http://www.baidu.com网站

package cn.lsl.response;

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 ResponseServlet3 extends HttpServlet {

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("refresh", "3;url=http://www.baidu.com");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("3秒后跳转到百度");
    }

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

}

在HTML页面中存在一类非常特殊标签<meta>,<meta>起到设置头信息作用
<meta content="3;url=http://www.baidu.com" http-equiv="refresh">  ---- 完成自动跳转

案例四：通过response头信息设置浏览器禁止缓存
原理：和禁止缓存相关头信息（三个）
Cache-Control:no-cache
Expires:-1
Pragma:no-cache

package cn.lsl.response;

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 ResponseServlet4 extends HttpServlet {
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("expires", -1);
        response.getWriter().println("Hello");
    }

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

}

中文乱码问题
通过response生成客户端响应体，通过字节流和字符流两种输出方式
*哪些情况用字节流？哪些情况用字符流？
拷贝文件 --- 字节流
分析文件内容 --- 字符流  （中文操作 字符流）

package cn.lsl.response;

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 ResponseServlet5 extends HttpServlet {

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        //需要通知浏览器查看编码
        response.setContentType("text/html;charset=utf-8");    //设置响应编码与浏览器查看编码
        PrintWriter out = response.getWriter();
        out.println("我很好！");
    }

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

}

setCharacterEncoding 和 setContentType区别？
setCharacterEncoding 设置响应内容编码，无法设置浏览器查看编码
setContentType设置响应内容编码，同时通知浏览器查看编码
*在响应头信息中 Content-Type:text/html;charset=utf-8
结论：setContentType具备setCharacterEncoding编码功能，现实开发中，只需要使用setContentType就可以了

注意：
1）getOutputStream和getWriter不能同时使用
2）必须在getOutputStream喝getWriter之前设置响应编码
3）getOutputStream和getWriter输出内容是HTTP响应体
4）getOutputStream和getWriter存在缓冲区，在service方法结束时，自动关闭流，flush缓冲区内容

案例六：文件下载
第一种：通过超链接完成文件下载
*如果浏览器可以识别该文件格式，直接打开，只有链接文件浏览器不识别文件格式，才会实现下载
第二种：通过Servlet程序实现下载
原理：通过Servlet读取目标程序，将资源返回客户端
通过程序下载文件，设置两个头信息Content-Type Content-Disposition

response.setContentType(getServletContext().getMimeType(filename));     ----设置文件类型
response.setHeader("Content-Disposition","attachment;filename="+filename); ----设置文件以附件形式下载（对于浏览器识别格式文件）

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>download.html</title>
  </head>
  
  <body>
    <h1>通过超链接实现文件下载</h1>
    <a href="/Response/download/xpp3.zip">zip压缩包下载</a>
    <a href="/Response/download/mm.jpg">jpg图片下载</a>
    <!-- 通过?在url地址里拼接参数 get方式提交 -->
    <h1>通过程序实现下载</h1>
    <a href="/Response/response6?filename=xpp3.zip">zip压缩包下载</a>
    <a href="/Response/response6?filename=mm.jpg">jpg图片下载</a>
  </body>
</html>

package cn.lsl.response;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

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

public class ResponseServlet6 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获得文件名
        String filename = request.getParameter("filename");
        response.setContentType(getServletContext().getMimeType(filename));    //设置MIME类型
        response.setHeader("Content-Disposition", "attachment;filename=" + filename);
        
        //绝对磁盘路径
        String fullFilename = getServletContext().getRealPath("/download/" + filename);
        InputStream in = new FileInputStream(fullFilename);
        OutputStream out = response.getOutputStream();
        int b;
        while((b=in.read())!=-1){
            out.write(b);
        }
        in.close();
        out.close();
    }

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

}

案例七：验证码输出案例
Java图形API生成验证码图片
为什么需要验证码？防止有人通过程序恶意攻击网站

package cn.lsl.response;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
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;

public class ResponseServlet7 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int width = 120;
        int height = 30;
        //创建一张内存中缓冲图片
        BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        //背景色
        Graphics graphics = bufferedImage.getGraphics();    //通过graphics对象绘制图片
        graphics.setColor(Color.YELLOW);
        graphics.fillRect(0, 0, width, height);
        
        //边框
        graphics.setColor(Color.BLUE);
        graphics.drawRect(0, 0, width-1, height-1);
        
        //写验证内容
        Graphics2D graphics2d = (Graphics2D)bufferedImage.getGraphics();
        graphics2d.setColor(Color.RED);
        graphics2d.setFont(new Font("宋体",Font.BOLD,18));
        
        //String content = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
        String content = "u7684u4e00u4e86u662fu6211u4e0du5728u4ebau4eecu6709u6765u4ed6u8fd9u4e0a" +
                "u7740u4e2au5730u5230u5927u91ccu8bf4u5c31u53bbu5b50u5f97u4e5fu548cu90a3u8981u4e0b" +
                "u770bu5929u65f6u8fc7u51fau5c0fu4e48u8d77u4f60u90fdu628au597du8fd8u591au6ca1u4e3a" +
                "u53c8u53efu5bb6u5b66u53eau4ee5u4e3bu4f1au6837u5e74u60f3u751fu540cu8001u4e2du5341" +
                "u4eceu81eau9762u524du5934u9053u5b83u540eu7136u8d70u5f88u50cfu89c1u4e24u7528u5979" +
                "u56fdu52a8u8fdbu6210u56deu4ec0u8fb9u4f5cu5bf9u5f00u800cu5df1u4e9bu73b0u5c71u6c11" +
                "u5019u7ecfu53d1u5de5u5411u4e8bu547du7ed9u957fu6c34u51e0u4e49u4e09u58f0u4e8eu9ad8" +
                "u624bu77e5u7406u773cu5fd7u70b9u5fc3u6218u4e8cu95eeu4f46u8eabu65b9u5b9eu5403u505a" +
                "u53ebu5f53u4f4fu542cu9769u6253u5462u771fu5168u624du56dbu5df2u6240u654cu4e4bu6700" +
                "u5149u4ea7u60c5u8defu5206u603bu6761u767du8bddu4e1cu5e2du6b21u4eb2u5982u88abu82b1" +
                "u53e3u653eu513fu5e38u6c14u4e94u7b2cu4f7fu5199u519bu5427u6587u8fd0u518du679cu600e" +
                "u5b9au8bb8u5febu660eu884cu56e0u522bu98deu5916u6811u7269u6d3bu90e8u95e8u65e0u5f80" +
                "u8239u671bu65b0u5e26u961fu5148u529bu5b8cu5374u7ad9u4ee3u5458u673au66f4u4e5du60a8" +
                "u6bcfu98ceu7ea7u8ddfu7b11u554au5b69u4e07u5c11u76f4u610fu591cu6bd4u9636u8fdeu8f66" +
                "u91cdu4fbfu6597u9a6cu54eau5316u592au6307u53d8u793eu4f3cu58ebu8005u5e72u77f3u6ee1" +
                "u65e5u51b3u767eu539fu62ffu7fa4u7a76u5404u516du672cu601du89e3u7acbu6cb3u6751u516b" +
                "u96beu65e9u8bbau5417u6839u5171u8ba9u76f8u7814u4ecau5176u4e66u5750u63a5u5e94u5173" +
                "u4fe1u89c9u6b65u53cdu5904u8bb0u5c06u5343u627eu4e89u9886u6216u5e08u7ed3u5757u8dd1" +
                "u8c01u8349u8d8au5b57u52a0u811au7d27u7231u7b49u4e60u9635u6015u6708u9752u534au706b" +
                "u6cd5u9898u5efau8d76u4f4du5531u6d77u4e03u5973u4efbu4ef6u611fu51c6u5f20u56e2u5c4b" +
                "u79bbu8272u8138u7247u79d1u5012u775bu5229u4e16u521au4e14u7531u9001u5207u661fu5bfc" +
                "u665au8868u591fu6574u8ba4u54cdu96eau6d41u672au573au8be5u5e76u5e95u6df1u523bu5e73" +
                "u4f1fu5fd9u63d0u786eu8fd1u4eaeu8f7bu8bb2u519cu53e4u9ed1u544au754cu62c9u540du5440" +
                "u571fu6e05u9633u7167u529eu53f2u6539u5386u8f6cu753bu9020u5634u6b64u6cbbu5317u5fc5" +
                "u670du96e8u7a7fu5185u8bc6u9a8cu4f20u4e1au83dcu722cu7761u5174u5f62u91cfu54b1u89c2" +
                "u82e6u4f53u4f17u901au51b2u5408u7834u53cbu5ea6u672fu996du516cu65c1u623fu6781u5357" +
                "u67aau8bfbu6c99u5c81u7ebfu91ceu575au7a7au6536u7b97u81f3u653fu57ceu52b3u843du94b1" +
                "u7279u56f4u5f1fu80dcu6559u70edu5c55u5305u6b4cu7c7bu6e10u5f3au6570u4e61u547cu6027" +
                "u97f3u7b54u54e5u9645u65e7u795eu5ea7u7ae0u5e2eu5566u53d7u7cfbu4ee4u8df3u975eu4f55" +
                "u725bu53d6u5165u5cb8u6562u6389u5ffdu79cdu88c5u9876u6025u6797u505cu606fu53e5u533a" +
                "u8863u822cu62a5u53f6u538bu6162u53d4u80ccu7ec6";
        
        //内容四个字 -- 随机从content中抽取四个字
        Random random = new Random();
        int x=10;
        int y=20;
        for(int i=0; i<4; i++){
            //为字生成旋转角度 -30 -- 30
            double jiaodu = random.nextInt(60) - 30;
            //将旋转角度换算弧度
            double theta = jiaodu/180*Math.PI;
            System.out.println(theta);
            
            int index = random.nextInt(content.length());
            char letter = content.charAt(index);
            graphics2d.rotate(theta, x, y);
            graphics2d.drawString(letter+"", x, y);
            //将角度还原
            graphics2d.rotate(-theta, x, y);
            x += 30;
        }
        
        //绘制随机干扰线
        int x1;
        int x2;
        int y1;
        int y2;
        graphics.setColor(Color.LIGHT_GRAY);
        for(int i=0; i<10; i++){
            x1 = random.nextInt(width);
            x2 = random.nextInt(width);
            y1 = random.nextInt(height);
            y2 = random.nextInt(height);
            //根据两点  绘制直线
            graphics.drawLine(x1, y1, x2, y2);
        }
        
        
        //内存中资源释放
        graphics.dispose();
        
        
        //将图片输出到浏览器 ImageIO
        //将内存的图片通过浏览器输出流写成jpg格式图片
        ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
    }

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

}

分析：
验证码旋转效果
rotate(double theta, double x, double y)  ----- 参数 theta 旋转弧度
2PI 弧度 = 360 角度

-30 ---- 30 角度

Request
HttpServletRequest相比ServletRequest添加与协议相关的API
HttpServletRequest对象代表客户端的请求，当客户端通过HTTP协议访问服务器时，HTTP请求中的所有信息都封装在这个对象中，可通过这个对象的方法，获取客户这些信息。
HttpServletRequest分为四个部分
1.获取客户机信息
1）几个方法：
getRequestURL方法返回客户端发出请求完整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
getRemoteAddr方法返回发出请求的客户机的IP地址
getMethod得到客户机请求方式
getContextPath获得工程虚拟目录名称

package cn.lsl.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 RequestServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("url:" + request.getRequestURL());
        System.out.println("uri:" + request.getRequestURI());
        
        //通过getQueryString可以获得get方式提交查询串url中？后面部分
        System.out.println("querystring:" + request.getQueryString());
        
        //获得客户端ip
        System.out.println("ip:" + request.getRemoteAddr());
        
        //通过getContextPath获得工程虚拟目录名称
        System.out.println(request.getContextPath());
        
        //通过getMethod获取请求方式
        System.out.println("请求方式:" + request.getMethod());
        
        
        //获得当前访问资源路径  --- /request1
        System.out.println("当前访问资源路径:" + request.getRequestURI().substring(request.getContextPath().length()));
    }

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

}

URI和URL区别
url:http://localhost:8080/Request/request1  （完整）
uri:/Request/request1  （部分）

URI包含URL的
http://localhost:8080/Request/request1 是一个URL，同时也是URI
./hello  /day06/request1 都是URI，不是URL

2.获取请求头信息
getHeader获得头信息的值，转换一个字符串
getHeaders获得头信息值，返回Enumeration
getHeaderNames获得所有头信息名称，返回Enumeration

package cn.lsl.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 RequestServlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String value = request.getHeader("Accept-Encoding");
        System.out.println(value);
        System.out.println("--------------");
        Enumeration<String> enumeration = request.getHeaderNames();
        while(enumeration.hasMoreElements()){
            String name = enumeration.nextElement();
            System.out.println(name + ":" + request.getHeader(name));
        }
    }

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

}

案例：
编写防盗链程序，存在合法referer不是盗链，否则控制目标资源无法访问！

package cn.lsl.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 RequestServlet3 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String referer = request.getHeader("referer");
        response.setContentType("text/html;charset=utf-8");
        if(referer == null || !referer.startsWith("http://localhost")){
            response.getWriter().println("是盗链");
        }else{
            response.getWriter().println("不是盗链");
        }
    }

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

3.获取请求参数
什么是请求参数？
用户用过请求提交服务器一些数据

四个常用API
getParameter
getParameterValues
getParameterNames
getParameterMap

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>request.html</title>
  </head>
  
  <body>
    <h1>分别以get和post方式提交数据</h1>
    <h1>第一种 通过超链接提交数据 以？方式</h1>
    <a href="/Request/request4?name=zhangsan&&city=beijing"">超链接提交数据</a>
    <h1>第二种 通过form的post方式提交数据</h1>
    <form action="/Request/request4" method="post">
        请输入姓名<input type="text" name="name" /><br/>
        请输入城市<input type="text" name="city" /><br/>
        <input type="submit" value="提交" />
    </form>
  </body>
</html>

package cn.lsl.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 RequestServlet4 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //通过getParameter获得请求数据
        String name = request.getParameter("name");
        System.out.println(name);
        String city = request.getParameter("city");
        System.out.println(city);
    }


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

}

乱码问题
post --- request.setCharacterEncoding("客户端编码集");

get乱码手动解决：
username = URLEncoder.encode(username, "ISO-8859-1");// 用ISO编码
username = URLDecoder.decode(username, "utf-8"); // 用utf-8解码
简化上面写法 ： username = new String(username.getBytes("ISO-8859-1"), "utf-8")

get乱码 配置tomcat默认解码字符集
在tomcat/conf/server.xml
Connector中 添加一个属性 URIEncoding="utf-8"

结论：开发时，尽量不要修改tomcat默认解码集，提交请求尽量使用post，如果非要使用get，手动编码

问题：http://localhost/day06/servlet?username=zhangsan+lisi
在服务器端 通过 request.getParameter("username") 结果是 ？？？ ----- zhangsan lisi

数据获取和乱码解决的案例：

<!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>
<!-- 最复杂form表单 -->
<!-- 用户注册 -->
<form action="/Request/request5" method="post">
    <table>
        <!-- 文本输入框 -->
        <tr>
            <td>用户名</td>
            <td><input type="text" name="username"/></td>
        </tr>
        <!-- 密码框 -->
        <tr>
            <td>密码</td>
            <td><input type="password" name="password" /></td>
        </tr>
        <!-- 单选按钮 -->
        <tr>
            <td>性别</td>
            <td>
                <input type="radio" name="gender" value="male" /> 男
                <input type="radio" name="gender" value="female" />女
            </td>
        </tr>
        <!-- 复选框  -->
        <tr>
            <td>爱好</td>
            <td>
                <input type="checkbox" name="hobby" value="sport" /> 体育
                <input type="checkbox" name="hobby" value="music" /> 音乐
                <input type="checkbox" name="hobby" value="game" /> 游戏
            </td>
        </tr>
        <!-- 下拉框 -->
        <tr>
            <td>城市</td>
            <td>
                <select name="city">
                    <option value="beijing">北京</option>
                    <option value="shanghai">上海</option>
                    <option value="shenzhen">深圳</option>
                </select>
            </td>
        </tr>
        <!-- 多行文本框 -->
        <tr>
            <td>个人简介</td>
            <td>
                <textarea rows="5" cols="60" name="introduce"></textarea>
            </td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" value="注册"/></td>
        </tr>
    </table>
</form>
</body>
</html>

package cn.lsl.request;

import java.io.IOException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

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

public class RequestServlet5 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        
        //解决post乱码
        request.setCharacterEncoding("utf-8");
        
        String username = request.getParameter("username");
        System.out.println(username);
        
//        解决get乱码 --- 使用手动编码
//        username = URLEncoder.encode(username, "ISO-8859-1");    //用ISO编码
//        username = URLDecoder.decode(username, "utf-8");    //用utf-8解码
        
        //以下一句等效于上面两句
//        username = new String(username.getBytes("ISO-8859-1"), "UTF-8");
        
        System.out.println(username);
        
        String[] hobbies = request.getParameterValues("hobby");
        System.out.println(Arrays.toString(hobbies));
        
        
        //打印所有请求提交参数
        //方式一：先获得所有参数name，然后通过name获得value
        Enumeration<String> names = request.getParameterNames();
        while(names.hasMoreElements()){
            String name = names.nextElement();    //获得每一参数名称
            System.out.println(name + Arrays.toString(request.getParameterValues(name)));
        }
        
        System.out.println("--------------");
        Map<String, String[]> paramterMap = request.getParameterMap();
        Set<String> keys = paramterMap.keySet();
        for(String key : keys){
            System.out.println(key + ":" + Arrays.toString(paramterMap.get(key)));
        }
        
    }

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

}

4.利用请求域传递对象
HttpServletRequest和ServletContext类似，都是数据域对象，以Map方式保存数据
区分：
ServletContext对象：服务器启动对象创建，服务器停止对象销毁
ServletRequest对象：当产生一次请求时创建，当响应结束后，对象销毁

package cn.lsl.request;

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

public class AServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        //通过request对象传递
        //向request域对象保存一个属性
        request.setAttribute("name", "lsl");
        //传递数据给BServlet必须使用请求转发
        RequestDispatcher dispatcher = request.getRequestDispatcher("/b");
        dispatcher.forward(request, response);
    }

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

}

package cn.lsl.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 BServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println(request.getAttribute("name"));
    }

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

}

注意事项：
1）在使用forward之前，不能将响应内容传输到客户端
情况一：response输出流输出流执行flush，导致内容不能输出
情况二：同一个Servlet不能连续使用forward和redirect
2）在执行forward和redirect时，清除之前写入响应流数据
3）ServletContext进行转发路径必须以/开始，request进行转发路径可以使用相对路径

转发和重定向区别：
1、转发一次请求、一次响应，重定向 两次请求 两次响应
2、转发只能跳转站内程序，重定向定向任何站点
3、转发 URL地址不变 ，重定向URL地址改变
4、转发 对客户端不可见，重定向对客户端可见
5、转发共享同一个Request中数据，重定向两次请求，不同Request对象，不能共享Request数据

* request.setAttribute 必须和 request.getRequestDispatcher().forward 一起使用

RequestDispatcher 的 include 方法 用来做页面布局 ------ <%@include%> <jsp:include>
将页面公共部分抽取出来，通过include 引用到页面中 ---- 更加方便维护

package cn.lsl.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 MainServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.getRequestDispatcher("/logo.html").include(request, response);
        response.getOutputStream().println("<h1>A</h1>");
        request.getRequestDispatcher("/footer.html").include(request, response);
    }

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

}

package cn.lsl.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 MainServlet2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.getRequestDispatcher("/logo.html").include(request, response);
        response.getOutputStream().println("<h1>B</h1>");
        request.getRequestDispatcher("/footer.html").include(request, response);
    }

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

}